TondeuseRC Arduino RC Lawnmower

http://www.instructables.com/id/Arduino-RC-Lawnmower/

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Arduino R/C Lawnmower (painted)by johndavid400 on May 19, 2009

Table of Contents

Arduino R/C Lawnmower (painted) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Intro: Arduino R/C Lawnmower (painted) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Step 1: Setting up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Step 2: The Motor Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Step 3: The Wheels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Step 4: The Frame part A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Step 5: The Frame part B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Step 6: Mounting the motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Step 7: Mounting the mower deck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Step 8: Select and Install the batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Step 9: Mount the electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Step 10: The Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

File Downloads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Step 11: More Videos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26


Author:johndavid400 author's websiteI have always been one to take things apart to figure out how they work, so most of what I own has been dismantled. If it can't be taken apart or hacked, i'drather not have it. And I like to do things the cheapest way possible, because I like to do a lot of things and I don't have a lot of money.

Intro: Arduino R/C Lawnmower (painted)What this is:

This instructable will show you how to make your Arduino into an R/C interface that you can use for just about anything requiring remote control. I will also show you howI built an R/C lawnmower using my Arduino, a cheap R/C transmitter and receiver pair, and a couple of electric-wheelchair motors from Ebay. I have used this interfaceto control anything from basic LED's to Bipolar stepper motors, mini-robots, lifeless R/C cars from the thrift store, and even a 100lb lawnmower (all with appropriate motorcontrollers). It is very flexible and easy to change and very simple to set up.Check it out in MAKE magazine in the April 2010 issue (#22) or here:http://www.make-digital.com/make/vol22#pg1

UPDATE 3-24-10

New wheel-barrow bucket mounted on top with hinges so it can dump its contents.

UPDATE 3-10-10: NEW CODE

And new video of the Lawnbot400 moving a bunch of dirt from my truck to the flower beds across the yard, also I updated the code again.

.

I added some new code to the project that is safer, including a manual kill-switch and a Failsafe switch.To implement the Failsafe, I used another Atmega168 (or an Arduino), to control a normally-open 60amp power relay. The relay disconnects the power to the motor-controller unless receiving a "good" signal from the 2nd microcontroller. This signal is updated 2 times every second and is either ON or OFF. If the bot gets out of range,it loses power to the motors. If I flip the kill-switch on the Transmitter, it loses power to the motors. This is also a handy way to disable it remotely if anything were to gonear it that wasn't supposed to. The updated code for both microcontrollers is on the CODE page.

In addition to the failsafe, I changed the way the code reads the PPM signals to make it more reliable. Also, I realized that I was only able to run the bot at 80% speedwith the old code, so now it is quite a bit faster and has more power (it can carry me across the yard @ 155lb).Check out this new video of me riding the Lawnbot400, my wife driving it over a bunch of branches, then me making do some wheelies. Don't worry, the mower wasturned off this time since the grass didn't need cutting, we were just having fun.

Disclaimer:DANGER!!! This is a VERY dangerous piece of equipment if not handled appropriately. Since all the electronics have been home-built and the Arduino code is new, youMUST be very careful while operating anything heavy with this code. I have had 1 or 2 times during testing - and before adding a secondary failsafe - that the mainArduino jammed up and I temporarily lost control of the mower for a few seconds!!!! Though I have added several filters to discard unwanted signals and I rarely haveany issues, an un-manned lawnmower IS STILL A POTENTIAL DEATH TRAP and I assume no responsibility for anything that happens as a result of your use of thiscode or this tutorial. This is meant as a guide for people who not only have the ability to build such a contraption, but the responsibiltity to operate it safely as well. Anysuggestions or ideas on how to make this a safer project is always gladly accepted. Having said that, it's also awesome.


Background:

Most R/C equipment comes packaged for a single specific use, which makes it easy to use but is very limited in what you can do with it. So using the Arduino as aninterpreter between the R/C system and the motor driver, I can use any motor controller that I want (depending on the size of the motor and power required),reprogramming the Arduino to supply the required signals.

What I ended up with:

After successfully hacking a few R/C cars from the thrift store, I got bored driving them around the driveway and I was having a hard time convincing my wife that therewas any usefulness in the revived toy car. So I decided it was time to make my biggest chore at home, a whole lot easier and actually put my Arduino to work, and thatshow I ended up building an R/C lawnmower.

While designing the lawnmower, I thought it would be cool to learn about the electronics that made it move, so I designed and built my own motor speed controller (or H-bridge) to power the lawnmower. I looked around at every H-bridge design I could find before deciding to go with a Mosfet h-bridge that uses both N-channel and P-channel Mosfets.

I built several different motor driver boards for this project, the first two were on Radio-Shack perf-board and the next 4 were designed using EagleCad and etched to apiece of copper-clad PCB, using the toner-transfer method. The most recent board is the one I use to mow the lawn as it has the ability to stay cool even while operatingfor long periods of time (30-40 mins straight) at 10-20amps and 24vdc. FWIW, I had to burn up a lot of Mosfets to find this out. If you want to see any of my other motorcontrollers, go to www.rediculouslygoodlooking.com and check out the Mosfet shield.

Here is what I bought already assembled:FM R/C transmitter and receiver pair from ebay = $40Arduino = $30I already had a used push-mower = $60Here is what I bought and assembled into the Lawnbot400 (as I call it):(2) electric-wheelchair motors from ebay = $40 ea(2) 12v marine deep cycle batteries - Walmart - $60 ea new (used batteries might work)36" pieces of 2" angle-iron (2) and 1" square-tubing (2) from Home Depot = $8 ea36" pieces of 1" angle-iron (2) and 1" flat steel bar (2) from Home Depot = $5 ea(a lot) of nuts, bolts, washers, lock washers 3/8" or 1/2" with drill bit = $20(2) caster wheels from Harbor Freight Tools = $14 ea(2) drive wheels from Harbor Freight Tools = $8 ea(36") 5/8" threaded rod with several 5/8" nuts and washers from Home Depot = $8(2) sprockets from Allelectronics = $5 ea#25 roller chain and a few universal links from Allelectronics = $10 for 3'sprockets from Electronics Goldmine = $1.50 ea(24) mosfets from Digikey = $1 ea(there were quite a few small parts for building the H-bridge, they are listed later on)


Image Notes1. the front left mower deck hanger2. the rear left mower deck hanger


Image Notes1. the Triple8 motor controller with 24 mosfets, each set of 3 is bolted togetherand each mosfet is heatsinked. It has 3x as many Mosfets as it's little brother,but essentially the same circuit.2. the predecessor to the Triple8, only 8 mosfets total (just enough to completea dual h-bridge). Though it would run the Lawnbot400 around for about 10minutes, it would end up getting hot after some use.

Image Notes1. the 2 neutral indicator LED's (1 red and 1 yellow) hard-wired to digital pins 12and 13. Anytime I center one of the control sticks on the lawnbot400, one ofthese lights turns on.2. the female headers used to plug my R/C receiver directly onto (they usestandard .1" spacing like perfboard you can buy at Radio Shack)3. these are the breakout screw-terminals used to route the R/C receiver signalsto the Atmega168. I am only using 2 of the 6 R/C channels right now, so theother 4 can be used for extra servo's or whatever else.4. digital pins 2 and 3 of the Atmega168, used for the External Interrupts onthose pins to capture the R/C signals from the receiver.5. These are the screw-terminals for the signal wires leading to the H-bridgemotor controller. I only need 4 wires to run my motor controller, but there are 3extra digital pins that are unused by the current code.... Any ideas for their use?6. all 6 analog pins are unused! I might add some sensors to automate theLawnbot400 one day.7. the Atmega168, it's reset button, and a kind-of hidden 16mHz crystal oscillator(together make a bare-bones Arduino).8. 5-35v power terminal and onboard 5v regulator for powering the Atmega andR/C receiver. Plus a bunch of capacitors and a reverse polarity protection diode.


Image Notes1. this is the 2nd H-bridge, notice that the motor screw-terminals for each motorwill be on opposite sides of the board.2. This is the 1st H-bridge

Step 1: Setting up1. Get R/C transmitter and receiver (I have tested FM and AM systems and they both work)2. Upload code to Arduino (it is on the last page)3. Make sure you are getting a good signal

You will need an R/C radio transmitter(Tx) and receiver(Rx) pair, which is the most expensive part of the project, but can be used for every future project you might haveinvolving R/C. I went with a 6-channel FM system, but I have tested a 27mHz AM transmitter/receiver and it works just as well. The beauty of the Arduino is that if youwant to adjust the deadband or the motor-speed at turn-on, (unlike commercial ESC's) it is all easy changed in the Arduino IDE.Once you have your radio, all you need to do is upload the code to your Arduino, plug in the 2 channels that you want to use from your radio receiver into Digital pins 2and 3 of the Arduino (these are the 2 external interrupt pins on the Arduino) and you are ready to control whatever you want. If you don't have a batter pack for thereceiver, you can run jumper wires from the Arduino +5v and GND to the R/C receiever for power, you only need to supply a single channel with GND and +5v (it is notnecessary to power every channel).Upload the code using the Aruino IDE (I am using version 0016 on Ubuntu).I started by controlling 3 LED's with 1 channel on a breadboard. I wired a red LED to be Forward (digital pin 9), a yellow LED for Reverse(digital pin 5), and a green LEDfor Neutral (digital pin 12). This allows you to adjust the code to fit the needs of your radio system. You will have smooth 0-100% PWM control of both LED's and theneutral light will turn on when the control stick is centered. If needed, you can widen the deadband for Neutral, but doing so will increase the speed at turn-on (whichstarts at 0%, so that would likely be desirable). See pictures.----------------------------------------

The code has 4 PWM outputs for motor control:

channel 1 Forward = Arduino digital pin 9channel 1 Reverse = Arduino digital pin 5channel 2 Forward = Arduino digital pin 10channel 2 Reverse = Arduino digital pin 6


2 outputs for Neutral indicator lights:

channel 1 = digital pin 12channel 2 = digital pin 13

The 2 INPUTS from the R/C receiver should go to:

channel 1 = digital pin 2channel 2 = digital pin 3

---------------------------------------

If you are interested to see your readings, turn on your Serial Monitor in the Arduino IDE (set to 9600bps) and you can see the actual real-time pulse readings for eachchannel, they should read:

full forward = 2000 (2 milliseconds)center = 1500 (1.5 ms)full reverse = 1000 (1 ms)These readings reflect the number of microseconds that the pulse signal from the R/C receiver stays HIGH (or at 5v). The typical Servo signal that comes from an R/Creceiver is a pulse whose length varies from approximately 1 ms to 2 ms with 1.5 ms being Neutral (which should also be the position that the control stick returns towhen you let it go). The transmitter reads the position of the control stick and sends that pulse length about once every 20milliseconds. So it is constantly updating forprecise control (for more info, look up PPM on wikipedia). If you push the transmitter control stick forward, the reading should go up to 2000, if you push it backward itshould go down to 1000. You can also use a voltage meter at this point to see that Digital Pins 5, 6, 9, & 10 will be changing from 0-5v depending on the position of thecontrol sticks on the R/C transmitter.

If you care to know, the code uses the Arduino's 2 external interrupts to capture when the Rx signal pin changes states (goes from HIGH to LOW or vice versa), when itdoes at the beginning of each signal, it calls the interrupt function which reads the digital state of the pin and if HIGH, it records the microseconds value on the Arduinosystem timer0. It then returns to the loop until the pin goes LOW, at which point it subtracts the previously recorded microsecond value from the new current microsecondvalue to determine how long the pulse stayed HIGH (which tells us the position of the Transmitter control stick). It then does that over and over really fast.I have the values constrained from 600-2400 in the Arduino code to keep things simple. Once it receives the signal and constrains it, it maps that value to beproportionally between 0 and 511, where 255 will be Neutral. The code then determines when the value changes and uses a function to determine the appropriate 0-255PWM value in the appropriate direction and each direction has it's own PWM output pin to control the H-bridge.

On a side note:

To make things easier, I built an Arduino-based breakout board using Radio-Shack perf-board, a 28pin DIP socket, a 16mhz oscillator, and a bit of wire. I also added aset of female-headers in such a way that I can plug my R/C receiver directly onto the breakout board. For secure connections while mowing grass, I added screw-terminals on each Output pin and each of the 6 channels from the receiver. It also has a built in 5v regulator to power both the Atmega168 from the Arduino and the R/Creceiver (which gets power when you plug it onto the breakout board). So you just route jumper wires from the channels you want to use on the receiver, to the Atmegadigital pins 2 and 3. I also added 2 LED lights that are hard wired to the digital pins 12 and 13 for the Neutral lights for each channel so I can easily see when I am inneutral.

Since this bot is a Tank steer setup with 1 drive motor on each wheel, the coding is very straightforward where the left stick controls the left motor and the right stickcontrols the right motor. Both sticks forward means lawnmower goes straight forward, both backward and it goes in reverse. If you push the left forward and the rightbackward, it does a zero-turn circle. As you can imagine, mowing the grass is really fun now.

Image Notes1. this is my receiver plugged into a breakout board I made for it using perfboard.2. the Arduino receiving R/C servo signals and translating them intoforward/reverse PWM values.3. each set of LED's is controlled by it's own channel from the R/C receiver.Forward will turn on the green light, reverse the Red light, and neutral will light upthe Yellow light. This is the easiest way to test the setup.

Image Notes1. this is a typical R/C transmitter with 4 channels, the one I got is a knockoff ofthis one, but looks very similar.2. this is a typical R/C receiver. Mine has it's connector pins on the end of theunit instead of the top, enabling me to plug my receiver directly onto the controlboard.3. these are typical servo motors. They can be controlled directly by the R/Creceiver and are useful for many things.


Image Notes1. the Atmega168 from my Arduino (I bought a few extras to use for projects likethis). I remove it when I need to re-program it in the Arduino.2. my R/C receiver plugged into the control board. Notice the green antennacoming out.

Step 2: The Motor DriverI built several motor drivers before finding a design that worked for my needs. For what it's worth, there are several nice products already out there that are fullyassembled and require a lot less work if you are not interested in building your own electronics. The Open Source Motor Controller is an open source design that hasbeen under constant community improvement for several years now and can handle up to 160amps at 36vdc! But they are over $100 and only control 1 motor. TheSabertooth 2x25amp motor controller is nice and controls 2 motors, but it is $125.So I thought I would just make an extremely simple dual h-bridge that could handle at least 25 amps at 24vdc continuous and handle surges of up to 100amps for a fewseconds. Once I found out that you can parallel Mosfets and multiply their current carrying capacity accordingly, I thought I would come up with a simple design andslightly complicate it by adding more mosfets until I had enough to handle the current that I needed. Digikey has a good selection of Mosfets to choose from and goodfilters to narrow it down by what you need, so I spent a lot of time looking for Mosfets that were rated for around 50amp and could handle over 30 volts. Also, they have tobe cheap because my plan is to use a bunch of them. I decided on the FQP47P06 p-channel and the FQP50N06L n-channel Mosfets from Fairchild Semiconductor,which I bought from Digikey.

If you are wondering what an H-bridge is, find out here: en.wikipedia.org/wiki/H-bridge and this will all make more sense to you.

The design is simple: 2 P-channel mosfets control the high-side switches and 2 N-channel mosfets for the low-side switches. But instead of using 1 mosfet for eachswitch, lets use 3. Now we have 12 mosfets per H-bridge (3 mosfets x 4 switches) and theoretically the ability to carry 150 amps (that is not accurate though). The boardis as small as I could make it with nothing touching. Each set of 3 mosfets have heatsinks and are bolted together to help dissipate heat. Also, there is an 80mm coolingfan mounted directly above mosfets to further keep them cool. The mosfets are very good at handling sudden changes in direction and speed changes.

Since there are 24 mosfets in total (8 groups of 3) I dubbed it the Triple-8. It is running at the Arduino default PWM frequency of 1kHz (I plan on playing with that to getthe frequency higher). The board has 4 inputs, 2 for each bridge. If you bring an input HIGH, that side of the bridge goes HIGH, but opposite corners of the H-bridge areturned on together, so you can "Brake" or stop the motor by bringing both inputs HIGH, but you can't create a shoot-through condition (as long as it's connect it properly)which is good.

Ideally, you would control the board by holding 1 input LOW and applying a PWM signal to the other input. This allows for easy speed control. I have written into the codethat if you bring digital pin 7 HIGH, the code switches to Relay mode and either turns the mosfets all the way ON or all the way OFF. This is far more difficult to control,but is useful sometimes.

If you are interested in building your own H-bridge you can download the eagle file to etch a pcb and the schematic to show where everything goes. You can geteverything to make this dual h-bridge at Radio-shack (including the copper clad), except the Mosfets and a special resistor network I used to save space. I bought most ofthe parts from Digikey though because it was cheaper and arrives to my house in 2 days.

Here are the parts needed for this motor driver:

(12) FQP47P06 - P-channel mosfet 47a 60v - Digikey - $1.73 ea(12) FQP50N06L - Logic level N-channel mosfet 52a 60v - Digikey - $1.04 ea(4) 2n7000 - Logic level N-channel mosfet 200ma 60v - Digikey - $0.26 ea(8) 4606X-1-470LF-ND - 47ohm bussed resistor network - Digikey - $0.25 ea(6) ED1609-ND - 2 position screw terminal - Digikey or Radio Shack- $0.46 ea(24) CF1/84.7KJRCT-ND - 4.7k 1/8w resistor - Digikey or Radio Shack - $1.78 (for 50pk)(1) PC9-ND - 3"x4.5" 1-sided copper-clad .064" 2oz copper - Digikey or Radio Shack- $4.66(4) P5575-ND - 1000uf Capacitor or similar - Digikey - $1.19 ea(1) 330ohm - 1kohm resistor 1/4w - for power LED, doesn't have to be exact(1) power LED any color you like, I use the 3mm size to save spaceMaybe something smaller?

If you are going to use this for something smaller than a 100lb lawnmower, you can look up one of the many H-bridge circuits and build your own smaller motor controllerwith as few as 4 mosfets (or BJT transistors) or even use a packaged IC H-bridge like the l293d (dual 1 amp) or the l298n (dual 2 amp).Or if anyone is interested, I will post a schematic and Eagle .brd file for a smaller version of this H-bridge that only requires 8 mosfets total (everything else is the same),and it can handle about 10amps at 24vdc.

Etching:


I am not going to go into all the details of PCB etching, because there are already many excellent instructables on that topic. So once you download my .BRD file of mymotor controller, all you need to do is print the .brd file onto some magazine paper using a laser printer, and iron that onto a piece of clean copper-clad. Then etch it withyour favorite etchant solution (I use 2 parts Hydrogen Peroxide to 1 part Muriatic Acid and it works perfectly). And remove the toner with Acetone when done etching.For ease of assembly I designed this board to be Single-sided and to use only through-hole components, no surface-mount stuff to mess with! Yay for you.

You can get the .brd files for the various h-bridges at www.rediculouslygoodlooking.com

Image Notes1. this is the 2nd H-bridge, notice that the motor screw-terminals for each motorwill be on opposite sides of the board.2. This is the 1st H-bridge

Image Notes1. bussed resistor networks 47ohm. They have 1 input and 5 outputs, thisboard only uses 3 of the outputs.2. pull up/down resistors 4.7k ohm, these keep the Mosfets turned off when notbeing used.3. capacitors, I used (4) 680uF 50v, but you can substitute others that fit.4. screw terminal connectors for motor terminals and power


Image Notes1. this is 1 complete h-bridge to control 1 DC motor. The 2 smaller mosfetstoward the bottom are used as signal-inverters to control the High-side p-channel mosfets.2. each h-bridge has it's own set of direction lights to determine the direction ofthe current.

Image Notes1. the Triple8 motor controller with 24 mosfets, each set of 3 is bolted togetherand each mosfet is heatsinked. It has 3x as many Mosfets as it's little brother, butessentially the same circuit.2. the predecessor to the Triple8, only 8 mosfets total (just enough to complete adual h-bridge). Though it would run the Lawnbot400 around for about 10 minutes,it would end up getting hot after some use.

Image Notes1. R/C receiver plugged into Arduino breakout board2. cooling fan for motor controller (h-bridge)


Image Notes1. Atmega168 microcontroller programmed in the Arduino, then transferred to thishome-made breakout board for permanent use.2. The R/C receiver is plugged directly onto my home-made breakout boardwhich supplies the +5v and GND needed for power as well as a breakout screw-terminal for each channel. This receives the signals from the remote-control (R/Ctransmitter) and sends them into the Atmega168 for processing.

Step 3: The WheelsFirst you need to mount the drive sprockets to the wheels.

The EASY way:If you are smart and have more money, you can find a set of wheelchair motors that have the wheels mounted to them.

The CHEAP way:I could not find any in my price range, so I went with just the motors, then bought wheels, then sprockets. Believing it would not be strong enough to mount the wheelsdirectly to the motors, I opted to mount the drive wheels on an axle, then the motors to the frame, and use chain to transmit the power. A picture is worth 1000 words, solook at them carefully.

Mount the sprockets to the wheels:

I had to place the sprocket on the center of the wheel and drill 3 holes through the sprocket and then through the wheel itself. Once the sprocket is lined up and properlycentered, I placed the 3 bolts through the sprocket and wheel and tightened them up as much as possible. I then welded the sprocket to the wheel hub to keep itcentered.

The wheels from Harbor Freight Tools have built in bearings for a 5/8" shaft, hence the 5/8" threaded-rod we are going to use as an axle.

Repeat this process for both wheels.

There is more detailed info tagged in the pictures.


Image Notes1. The bolts coming from around the axle are the 3 bolts that hold the sprocketonto the other side.

Image Notes1. The drive sprockets are about 6.5" in diameter and had no holes to mountthem. I had to drill 3 holes and mount bolts through the sprocket into the wheel. Ithen added a small bead of weld to keep it centered around the axle.

Image Notes1. save a bolt on each side by using the same one that you used to bolt theframe riser brace into the frame.


Step 4: The Frame part AThis is the difficult part to explain. You will likely have to have some mechanical ability and a good set of tools to build a large metal frame from scratch. And since thiswas a prototype, the dimensions are not all perfect, but luckily they don't need to be.

The frame will be custom measured for your particular lawnmower, so I won't be giving you exact measurements.

Tools needed to build a frame:measuring tapeangle-grinderratchet setcrescent-wrencha levelelectric drillbolts, nuts, washers, and lock washers of either 3/8" or 1/2" diameter and 3/4"- 2" longdrill bits the size of the bolts you are using1" and 2" angle-iron (36" long pieces) you'll need both1" square tubing (36" pieces, steel)1" flat steel bar (36" long pieces)the 4 wheels you got from Harbor Freight Tools (2 drive wheels and 2 caster wheels)5/8" threaded rod (36" long) and several 5/8" nuts/washersFirst you need to plan out the frame of your bot. Since I was attaching a lawnmower, I started by measuring the height that the lawnmower stood off the ground and tooksome basic measurements to see how big the frame needed to be. My frame turned out to be about 24" wide (this distance must match the width from the center of therear lawnmower wheels) and 48" long (long enough for the front caster wheels to swing 360 degrees without hitting the front of the mower deck) and about 18" tall. Sincewe want the height of the mower-deck to be adjustable, we are going to attach the mower to the frame by removing the lawnmower wheels and using angle-iron tosuspend the mower-deck from the frame of the bot.

1. I started out by using 2 of the 36" pieces of angle-iron (2" wide) for the main part of the frame running long-ways.2. Cut the rear-piece of angle-iron the width of the rear of the mower (this measurement will be from the center of the left-rear wheel to the center of the right-rear wheel).3. Drill holes in the ends of the angle-iron and bolt the rear-piece to the adjacent pieces from step 1, making sure they are straight.4. Cut two front-pieces using 1" square steel tubing, the same length as the rear. We need 2 in the front to bolt the caster wheels to.5. Drill holes and bolt these 2 pieces to the front of the angle-iron from step 1. You have to measure the holes from the 2 front caster wheel's mounting plates and drill thepattern into the front square tubing bars. Then bolt the wheels through those holes onto the front of the frame.

I later added another set of 2" angle-iron bars to the front caster wheel assembly to make the length of the bot adjustable at the front (see pics)Now we should have a rectangular frame with the front wheels attached.

Image Notes1. the front 1" steel square tubing that the front caster wheels attach to.


Image Notes1. Motor controller and Arduino2. push mower3. (2) 12v batteries (deep cycle marine is the best)4. electric wheel-chair motors

Image Notes1. you need 1 nut on the inside of the frame riser bar to, and 1 on the outside tohold it securely to the axle.2. I bolted the support bar in with the rear lawnmower-deck hangers to save abolt on each side.

Image Notes1. the rear bar should be the same width as the center of the rear wheels on yourpush-mower (must be measured before you remove the wheels).2. the main frame bars.3. the support brace


Image Notes1. one of the main frame bars from step 1, which is 2" angle-iron.2. the other main frame bar from step 1


Step 5: The Frame part BWe now need to see how far down to mount the drive axle to make the frame level. So raise the rear of the frame up until the top of the frame is level with the ground(use your level). Now measure the distance from the top-rear of the frame to the ground, this is the frame height.Now we need to take into account the height that the wheels will raise the axle off the ground. So measure the distance from the center of the rear drive wheel to theground (the wheel's radius). Subtract the wheel radius from the frame height and we will have the correct distance from the top of the frame to the drive axle, which wewill call the frame-riser height (we need to cut these pieces next). They are going to connect the rear of the frame down to the axle which the wheels will be mounted on.6. We are going to add 2" to the frame-riser measurement (so we have a little to work with) and cut the 2 frame risers (mine were about 10-12" long).7. Now drill (2) 5/8" holes, 1 at the bottom of each frame riser (about 1" from the bottom), this is where the drive axle will go through.8. Drill 2 holes at the top and bolt the frame risers to the rear of the main-rectangular frame with the frame-risers pointed down.9. Now feed the threaded-rod through the bottom holes of the frame risers and use 4 nuts to secure the frame risers to the drive axle (1 nut on each side of each frameriser, tightened down).10. put the rear wheels on the axle and use 1 more nut on each wheel to secure them to the axle (these wheels have built in bearings). The sprockets should face inwardtoward the frame.

Now we should have a frame that stands on it's own with 4 wheels. However, the rear axle is not completely secure yet. We will need to add 2 braces from the bottom ofthe frame risers (near the axle) to the main part of the frame in order to keep the frame risers positioned properly. These braces can be flat steel and do not need to bevery thick, they are just keeping the frame risers from moving.Measure about 2" above each axle and drill a hole, then measure how far down that hole is from the top-rear of the frame and measure the same distance from the rearof the frame toward the front. Drill another hole on each side at this measurement. The support braces will need to be measured to be bolted in through these holes oneach side (see pictures). The placement of the support braces is less important, meaning you can bolt them in wherever is convenient, as long as they are present.

Image Notes1. the rear bar should be the same width as the center of the rear wheels onyour push-mower (must be measured before you remove the wheels).2. the main frame bars.3. the support brace

Image Notes1. The drive sprockets are about 6.5" in diameter and had no holes to mountthem. I had to drill 3 holes and mount bolts through the sprocket into the wheel. Ithen added a small bead of weld to keep it centered around the axle.


Image Notes1. The bolts coming from around the axle are the 3 bolts that hold the sprocketonto the other side.

Image Notes1. one of the main frame bars from step 1, which is 2" angle-iron.2. the other main frame bar from step 1

Image Notes1. you need 1 nut on the inside of the frame riser bar to, and 1 on the outside tohold it securely to the axle.2. I bolted the support bar in with the rear lawnmower-deck hangers to save abolt on each side.

Step 6: Mounting the motorsThis was the most difficult part to plan out on the frame. We need the motors to be adjustable so we can adjust the tension of the chain, however they just have 4 holes inthe bottom of each motor and nobody makes a mounting plate that I could find.

The simplest way I could come up with was to mount the motors to an 8" long piece of 2" angle-iron, and then mount that piece of angle iron to the frame through somespecially cut holes that allow the motor mount to travel forward and backward (but not side to side) along the frame.Make the motor mount plate:

Cut an 8-10" section of 2" angle-iron, depending on how much room your motors need to mount. Mine only needed about 4", so I made it 8" to have plenty of room for themounting bolts. Drill a hole about 1.5" from each end of the top of this bar, this is where the mounting bolts will go through the frame.

Mount the motor to the motor mounting plate:

Now you have to find the center of your motor mount plate (the 8" long piece of 2" angle iron) and measure the mounting holes on your DC motors. Use a sharpie markerto plot the hole pattern from the motor, centered onto the motor mount plate. My motors have (4) 1/4" diameter tapped holes in a rectangular pattern on the bottom of thegear box.

Drilling and cutting the adjustment holes on the frame:Next you need to drill and cut the holes in the frame to let the motor mounting plate become adjustable. I cut these holes using a dremel tool and a cutoff wheel. You haveto line up the motor mounting plate (with motor mounted preferrably) onto the frame rail and use a sharpie marker to mark where the holes will need to be on the framerails. Start as far back as you can (without hitting any other bolts underneath the frame), and mark the center of each hole. Then move the motors forward 2" and markthe holes again. You want to cut the holes out of the frame so that the motor mount plate (with bolts going through the frame), can move forward or backward about 2".The holes in the frame are the width of the bolt and about 2" long. I drilled 1 hole at each end and used the dremel to cut out the rest.


The holes drilled in the motor mount plate are just single holes for the bolt to fit through, the holes through the frame were cut with a Dremel tool with a cutoff wheel tomake channels for the motor mount bolts to travel forward/backward through. You want the 2" angle-iron motor mount bracket to set as much on top of the main framerails as possible, the bolts (which you can't see with the motors mounted) that hold the motors to the motor mount plates will keep the motor mount plate from laying flatagainst the frame bars. Go ahead and mount the motors loosely to the frame using 2 bolts on each.

Cutting and connecting the chain:

Now get your 10' of #25 chain and wrap it around the main drive sprocket on the wheel. With the motors pushed all the way toward the back of the frame (closest to thedrive wheel sprockets), wrap the chain around the motor drive sprocket and mark where they overlap. You need 2 of the universal chain links from to connect the 2 looseends. Cut the 2 pieces of chain and connect them to each side with the universal links to connect them.

Tensioning the chain:

Push the motor mounts forward until there is good tension with the chain, and tighten up the bolts that hold the motor mount plates to the main frame.

Now you can generate electricity. Connect a voltage meter to 1 set of motor terminals and push the bot around.

Image Notes1. notice the motor is mounted to this piece of 2" angle-iron and that is mounted tothe frame with these bolts. They allow the motor to slide forward/backwards on theframe when loosened.

Image Notes1. notice the gap between the motor mount plate and the main frame bar. This iscaused by the bolts that hold the motor to the motor mount plate.2. These are 2 unfinished holes for a 3rd mounting hole which I later deemedunnecessary.


Image Notes1. This is how to make the motor mount slide holes. Drill 2 holes where you wantthe ends of the track to be. Then use a Dremel with a cutoff wheel to cut a straightline between the tops and bottoms of each hole. They should end up looking likethe ones above with bolts in them.2. Tighten up these bolts when you get proper tension with the chain.

Step 7: Mounting the mower deckNext we need to mount the mower deck to the frame. Remember we made the frame wide enough that the edges of the frame would be centered on the lawnmowerwheel shafts.

All we have to do is cut 4 pieces of 1" angle-iron equal lengths so that the mower deck hangs evenly from the frame.

So measure the height of the frame from the top to the ground. Now measure how high the mower sits off the ground from the center of the wheel shafts (when theoriginal wheels are on the lawnmower and all the height adjusters for each wheel are in the middle position). Now subtract the height the mower sits of the ground fromthe frame height, and cut 4 pieces of 1" angle iron to that length.

Now drill 1 hole in the end of each piece of angle-iron, about 1/2" from each end. The holes at the bottom will need to be the diameter of the lawnmower wheel shafts andthe holes at the top will need to be bolted into the frame (hung at equal distances from the top of the frame).Once you have all 4 hangers installed, you can install the mower deck and tighten up the bolts. Make sure you have at least 1/2" of clearance or more between the drivetires and the lawnmower wheel shafts.

You are almost ready to go.



Image Notes1. make sure to keep the old wheel shafts from touching the drive tires (leave1/2" or so)

Image Notes1. save a bolt on each side by using the same one that you used to bolt the frameriser brace into the frame.

Image Notes1. adjustable total length (for different model push mowers)2. caster wheels with 360 degree turning3. leave a gap or the front wheels will hit the mower deck!!!

Image Notes1. by mounting the lawn mower deck-hangers to the old wheel shafts, you can still

Image Notes1. these are the 1" angle-iron lawnmower-deck hangers, they hold the mower-


adjust the mowing height of the mower deck without taking anything apart. deck to the main frame

Image Notes1. make sure the front caster wheels won't hit the mower deck when they swingaround (leave at least 1/2" clearance)

Image Notes1. I only installed 3 of the 4 bolts on each front caster wheel.2. these 2 bolts on each side go through the caster wheel mounting plate ANDthe frame

Step 8: Select and Install the batteriesThis is the simple part. Go BIG. I only bought 1.. which I got at Walmart for $62.I got 2 car batteries (actually 1 marine deep cycle and 1 gel-cell car battery) both 12vdc. They together keep my lawnmower running strong for the duration of my frontand back yard (I have about 1/2 acre of grass to cut and it is somewhat hilly). I slacked while trying to learn about batteries and just went with the biggest ones I could findfor the price (the gel cell is actually used). I initially thought 12vdc would work, but the added weight of the mower deck made it travel so slowly at 12vdc, that it would notquite make it up some larger hills, so 24volts was necessary. The 2 batteries are connected in series with each other.

The microcontroller is also powered by these batteries. I have never had any problems with the electronics not getting enough power, so I didn't see the need to have aseparate power supply.

The batteries (due to their weight) are mounted behind the rear wheels. This GREATLY improves control of the bot because it counters the weight of the mower deck infront. Zero-turns are very easy now.

I needed a place to hold the 2 big batteries that were going to power the lawnbot, so I measured the 2 batteries and welded a small 1" angle-iron frame to hold them. It iswelded to the rear of the frame behind the drive axle to maintain even weight distribution.

You can use bolts and 1" angle-iron to make a battery holding cage that is bolted to the rear of the bot, or you can use smaller batteries and secure them to the top of thebot. 12v 20ah Sealed Lead Acid batteries can be found online for around $35-45 each. Any battery rack that you can whip up will likely be just fine, as long as it cansupport the weight of the batteries it is carrying. I used a welder to speed up the process.


Image Notes1. Motor controller and Arduino2. push mower3. (2) 12v batteries (deep cycle marine is the best)4. electric wheel-chair motors

Step 9: Mount the electronicsConnect the electronics to the motors and batteries. The motor drive board has 1 connector for the main battery power and 1 power connector for the 80mm cooling fanthat I would highly recommend you install directly above the mosfets. There is spacing for some long skinny bolts to hold a cooling fan. I bolted the motor driver above theArduino breakout board to save space.

Also, you might want to use some smaller wire coming from the batteries to power the Arduino board, as the 10ga wire I used for main power and motors is a bit overkillfor the microcontroller.

I installed a 30a 120v toggle switch from Radio Shack to switch the main power ON/OFF, this is my kill-switch. I also found a terminal-block for power distribution at RadioShack for a few bucks. It is the white thing that all the wires go into in the pictures. This makes removing the electronics a whole lot easier.

It is very important that you wire everything up correctly. Otherwise you might blow up the motor controller.

So make sure that you check the code before connecting anything to verify that you haven't mixed any wires up.


Image Notes1. Atmega168 microcontroller programmed in the Arduino, then transferred to thishome-made breakout board for permanent use.2. The R/C receiver is plugged directly onto my home-made breakout board whichsupplies the +5v and GND needed for power as well as a breakout screw-terminalfor each channel. This receives the signals from the remote-control (R/Ctransmitter) and sends them into the Atmega168 for processing.

Image Notes1. R/C receiver plugged into Arduino breakout board2. cooling fan for motor controller (h-bridge)


Step 10: The CodeI changed the code so that the Interrupt Service Routines (ISR) would run more quickly and the sketch would spend less timein the ISR. This means less overhead which means more signals are processed and smoother operation of the bot.

I also added a 2nd sketch for the 2nd microcontroller to process 2 signals (you can add as many more as you want) using thepulseIn method instead of using interrupts. This only processes about 1/5th of the available signals from the R/C Receiver,but also severely decreases the chance of receiving a "BAD" signal. Also, since the power relay is setup to only be ON if thesignal is "GOOD", when you go out of range, it automatically shuts off the power to the motors only.

The 2nd Atmega by default should have digital pin 4 used as the R/C servo signal input from the R/C receiver, digital pin 6should control a 5v relay or N-channel mosfet that is used to switch the 60amp power relay ON/OFF. That is all that isneeded, you can also use an LED on pins 12 and 13 to indicate whether the relay is ON or OFF.

You can also add 2 12v running lights from Walmart for a car... I use an N-channel mosfet directly tied to pin 9 of the 2ndArduino to control the brightness of the lights using a hacked channel on my transmitter. This input from the receiver wouldgo to digital pin 2. Check the code.

Download the .zip file on this page and upload the sketches. If you don't plan on adding the 2nd Atmega with the failsafe andkillswitch, that is fine. You can still update the new code for just the main Atmega and it should run more smoothly.

File Downloads

Lawnbot400_code.zip (152 KB)[NOTE: When saving, if you see .tmp as the file ext, rename it to 'Lawnbot400_code.zip']Step 11: More Videoshere are a few more videos in case anyone wanted to see...

#2

#3


#4

#5


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Comments50 comments Add Comment view all 160 comments

Rakkety Tam says: Feb 22, 2011. 9:15 PM REPLYI'm trying to use your software to get a radio controller much like the one you used to work with an arduino to run a robot, however, I'm running into someproblems. When you say in your code to "adjust these values if your R/C readings are above or below these for channels 1 and 2," what would thesereadings be? I got it working once, with signals sending, but now it seems to be giving me entirely sporadic readings. Help?

johndavid400 says: Feb 23, 2011. 6:27 AM REPLYhey buddy,

give this newer code a try...

ftp://ftp.rediculouslygoodlooking.com/arduino/LawnBot400/Lawnbot400_main_code/Lawnbot400_main_code.pde

regards,JD

Rakkety Tam says: Feb 23, 2011. 3:08 PM REPLYAh, thanks. The code still isn't working for some reason though. The incoming signal stays at 1500 and doesn't change. I'm sure the batteries arecharged and wires are plugged in. Do you know whats up?

johndavid400 says: Feb 24, 2011. 6:00 AM REPLYhmmm, what type of transmitter/receiver are you using?

Rakkety Tam says: Feb 24, 2011. 4:06 PM REPLYThe transmitter is a JR sport S400, while the receiver is a JR sport RS600.

iceman1 says: Feb 8, 2011. 7:46 PM REPLYyou should add a electronic clutch for the blade so when you are mowing you can stop the blade but not the engine

dreiduke says: Feb 4, 2011. 7:52 AM REPLYOk i will use a low cost version of the motor controllerI plan to build a Relais-Mosfet Hybrid H-Bridge.Relais to controll the Current direction.and several Mosfets in parallel and these serial to the relais-h-bridge,to control the speed during PWM from Arduino.it is low cost, an with double contact relais, Fail safe.

everywhere says: Apr 1, 2010. 6:41 PM REPLYwhat brand is your rc transmiter and how much did you pay?

johndavid400 says: Apr 2, 2010. 6:53 AM REPLYI first bought an Esky 6-channel FM system from Ebay for $40 shipped (new), and it works great for most things, but getting near a chain-link fence willcause distubance and it had no failsafe built-in. So I bought the 2.4gHz Spektrum DX5 with the BR6000 bot receiver for $120. It has a failsafe on eachR/C channel so if you turn the remote off or get out of range, it puts each channel back at the set position... so no glitching at all.It works much better than the FM radio. I got it here:http://www.superdroidrobots.com/shop/item.asp?itemid=923


Jedx says: Jan 26, 2011. 1:28 PM REPLYSpektrum to the rescue once again!However, if you really want make somthing even more spectacular you could get a DX6i, it's programmable and not that much more cash is needed.

sifihog says: Sep 5, 2010. 7:56 PM REPLYWould the Turnigy 9X 9Ch work ?http://hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8992&Product_Name=Turnigy_9X_9Ch_Transmitter_w/_Module_&_8ch_Receiver_(Mode_2)_(v2_Firmware)

johndavid400 says: Sep 5, 2010. 8:28 PM REPLYshould work just fine... the only thing is it says PCM, which I am unfamiliar with. But if it outputs Servo signals, you should be able to decode them. Ialmost bought the 6ch tx/rx from that website for $25:http://hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=9041&Product_Name=Hobby_King_2.4Ghz_6Ch_Tx_&_Rx_V2_%28Mode_1%29shipping was too high for me, I bought the 6ch Exceed from here for $44: http://www.hobbypartz.com/exrc62tr.html

everywhere says: May 19, 2010. 6:38 PM REPLY okay I bought that and my arduino is having problems supplying power to my motorcontroler and my reciver any help??

johndavid400 says: May 20, 2010. 8:17 AM REPLYWhat motor controller are you using? Also, are you using a standard Arduino Duemilanove or similar or are you using a smaller version like theArduino nano or a 3.3v version?

everywhere says: May 20, 2010. 5:07 PM REPLY duelmelinove...motor control is L298 motor driver from solarbotics as i dont want to make the tripple8 and is going in a smaller robot more like the isotope 11on your website

tank1357 says: Aug 27, 2010. 9:52 PM REPLYRead the specs on the duelmelinove, you'll notice each pin can't drive very much power. It much easier to set up an independent powersupply using a regulator like the LM7805 and then buffering the outputs from the arduino. Its also good practice, as this provides a layer ofisolation between the arduino and the device. Its easy to replace a buffer system if anything happens, but not so easy to replace a M.C.

everywhere says: Aug 31, 2010. 1:43 PM REPLYi can replace the M.C. in 3 seconds its not that hard take out old chip, put in new chip, program, upload code

everywhere says: Jun 24, 2010. 10:26 AM REPLYnever mind it is both my arduinos pin 6 dosent work

tycobb48 says: Jan 23, 2011. 12:26 PM REPLYI know this post is older, but I wanted to chime in. Now that everyone is having so much fun hacking the new Kinect system, it seems that it would be thenext logical progression for this project. (although I wouldn't test with the kids in the yard!) Any thoughts?PS - great instruct - I've got a dead mower in the back and I think I've found my winter project - thank you!

seabee890 says: Jan 21, 2011. 3:50 AM REPLYI own a self propelled, and was wondering how hard it would be to use the drive belt from the self propell to turn a small alternator that would keep thebatteries charged. then would i only need one battery to save weight . also a spring loaded cuttoff that would act as a deadman if the radio has enoughchannels. the signal is intrupted and the motor controls are disconnected. the other method was a stick above the mower that would disconnect if toppledfrom any direction, but that would require a shepards crook and i don't know any. Amazing device, as soon as i figure out alll of the electroinics involved i willbuild one. I hate mowing the lawn but love r/c. thanks,

johndavid400 says: Jan 21, 2011. 8:43 AM REPLYexactly what I was thinking... last season I began looking for a way to mount a pulley above the mower deck, but below the motor on the output shaft. Ithought about adding metal blocks between the motor and deck, but then saw a self-propelled and realized that it is the same thing already done for you.I would remove the self-propelled drive (use if for another robot) and replace it with (as you said) a 12v alternator, generator, or stator, that charges thebattery.

The lawnbot only works as well as it does because the batteries are marine deep-cycle and provide hours of run time - but this makes it very heavy. Witha generator recharging the batteries and providing much of the motor power during use, you could easily get by with only one battery, or a small set ofmedium sized SLA batteries (12 to 18AH).My next lawnmower is going to be a fully electric - I found a Black and decker 24v cordless mower and plan to build a lightweight "garden-home" versionof the lawnbot.


seabee890 says: Jan 21, 2011. 9:38 AM REPLYA wonderful idea, as far as you have gone so far and with the mechanical skills that i have seen, you should be able to get away with shaving thedeck of the mower and placing the forward tires in the "void "space in the front corners of the mower, this should allow you to get in corners better. Ilook forward to trying out your plans as soon as i return from this deployment. I an curious what the power ratio will be when you operate a electricmower. If you can arrange a generator system, how much longer will it allow the mower to run than without? I can see that the power used to drivethe mower and turn the generator will drain the battery but I am not familiar enough with the formulas to see if you would get a gain. Ialso wonderwhat a 125 or 50 cc motrocycle engine would benifit the system, it already has a power generation system included to run the lights and a very smallbattery to start things. I might try to find a scooter engine to see what i can make so the wife does not give me that look when i do frankenstein withour only mower. wish me luck.

unrealjohn says: Oct 27, 2010. 3:12 PM REPLYAll you have to do now is shrink the kids ........

dreiduke says: Oct 21, 2010. 11:28 AM REPLYi have recoded the program to use a RC Car Pistol Transmitter.one chanel for drive and one for steering.

johndavid400 says: Oct 21, 2010. 1:52 PM REPLYcool, I made some code to do that as well, mixed mode steering. I personally prefer tank steering for control, though sometimes using 1 stick to controlboth steering and direction is desirable, like when also using a pan/tilt camera controlled by the same remote.

dreiduke says: Oct 21, 2010. 3:30 PM REPLYtheory:when i use IGBT`s i havt to change following:

//FWDdigitalWrite(motor1_b, LOW);


http://cgi.ebay.com/Shoprider-Power-Wheelchair-Scooter-Part-Motors-Pihsiang-/180562031210?pt=LH_DefaultDomain_0&hash=item2a0a55f26a

http://cgi.ebay.com/JET-JAZZY-POWER-WHEELCHAIR-24-VDC-MOTOR-SET-/190455553380?pt=LH_DefaultDomain_0&hash=item2c58091d64

http://cgi.ebay.com/ROBOT-PRIDE-JET-3-WHEELCHAIR-MOTORS-TIRES-/160492132451?pt=LH_DefaultDomain_0&hash=item255e139863

http://cgi.ebay.com/Power-wheel-chair-motors-Brand-new-Robot-Battlebot-/330483000510?pt=LH_DefaultDomain_0&hash=item4cf25264be

If you would like to use something cheaper, you can maybe try windshield wiper motors (12v gear motors), or 24v scooter motors geared down with alarge wheel sprocket. These are between $15 and $50. See below for scooter and windshield wiper motors:http://www.robotcombat.com/products/AME-210-1011.html

http://www.robotcombat.com/products/AME-218-1001.html

http://www.allelectronics.com/make-a-store/item/DCM-1250/24-VDC-250W-MOTOR-11-TOOTH-SPROCKET/1.html

http://www.allelectronics.com/make-a-store/item/DCM-130/24-VDC-135W-MOTOR-W/BELT-GEAR/1.html

smartrobot says: Oct 16, 2010. 4:21 AM REPLYThanks!!!!

gjm says: Sep 11, 2010. 10:03 AM REPLYThis is sooo cool; I just hope it doesn't decide that it must destroy mankind.(Too many movies)

tank1357 says: Aug 27, 2010. 10:16 PM REPLYwhat kind of etchant and printing paper did you use to make the 24-FET dual-bridge board?

Jorad says: Jul 31, 2010. 1:22 PM REPLYwould this work http://www.robotpower.com/products/scorpion_XL_info.html instead of the h-bridge?

a_k_a__wolfboy says: Jul 27, 2010. 6:10 PM REPLYI have a question It may sound stupid I have a 2 channel rc remote and reciever of 27MHz can I user that to give the arduino commands??

johndavid400 says: Jul 28, 2010. 6:06 AM REPLYsure, any type of radio that ouputs a Servo signal will work - that is, the R/C receiver can directly drive a servo motor. I tried an old 27mHz pair withsuccess, but the radio I was using had poor range. FWIW, the 2.4gHz radios are worth the money if you can afford one - excellent range and nointerference.

Unit042 says: Jul 7, 2010. 2:11 PM REPLYAmazing project... I have a wheechair in my garage that I have been struggling to figure out motor controllers for, but nothing cheap.A wise old friend strongly recommends I just beak down and shell out the cash for something similar to that sabertooth motor controller. Viewing your ible,homebrew hopes are revived, but before I go out and buy... what, 24 power mosfets? (tempting prospect, as I have never seen any mosfets that size for lessthan 5 bucks) I need to know a bit more about the schematic.Does the lack of swamping resistors allow any one of the mosfets from taking the entire load (leaving the others to sit idly by), and failing early?Are these really the cheapest power mosfets you could find (cheapest as in, more current carrying capacity per dollar spent getting it.)?Do you think only two mosfets per switch (eight mosfets per motor H-bridge) would give close to the same performance (same size motors etc.), or does thecurrent version risk burnout enough as-is?

By the way, I absolutely LOVE the idea of making a robot mow the lawn for me, you happened to beat me to doing it... keep up the excellent robot-building! :)

johndavid400 says: Jul 8, 2010. 8:23 AM REPLYThere are Gate resistors connected to each mosfet (both P and N channel) to limit the amount of current allowed to any mosfet. This keeps 1 from usingall the current and leaving the others in the leg closed. I have never had a problem with uneven heating on this design. I searched for days and weeks forany mosfets that I could find. If you are trying to make a P and N channel bridge (easier since it needs no charge pump), you should try to find somewhatsimilar Mosfets to use. Additionally, the voltage from Gate to Source on the P-channel fets must not exceed the Vgs max in the datasheet - which istypically +/- 20v. This means that applying a GND signal to the P-channel fets to turn them On when using a 24v main power supply, will apply a voltagedifference to the P-channel Gates that is above the +/-20v (since the Source voltage is above 20v) which can kill the mosfet. So my search was mainlyfor a good P-channel mosfet that was capable of handling at least 40 amps at 30v, had a Vgs of higher than 24v, and was cheap. The FQP47P06 isaround $2 each, has a 25v Vgs rating, and is rated for 47 amps at 60v. It happens to work wonderfully and I have used this mosfet with the FQP50N06LN-channel equivalent quite extensively on a 24v power supply with no problems (The N-channel is only about $1 each). The number of mosfets you mustuse per leg will depend on the weight of your bot and the efficiency of the bridge. Running this bridge as in the instructable is not the best way to do it -that is, driving the P-channel and opposing N-channel with the same PWM signal, as this causes unnecessary switching losses. A better way to drive thebridge is to use a separate Arduino output pin for each quadrant of the H-bridge, and using the PWM signal only on the lower N-channel fets. Then drivethe P-channel fets with a simple digital On or Off. This nearly eliminates the risk of excessive transient voltages present at the mosfet Gate due to PWMswitching. I have switched to running all of my H-bridges as 4-quadrant, which also allows for electric braking. If you really want to make the bridgeefficient, you will need a mosfet driver chip. The OSMC motor-controller uses an all N-channel design with the hip4081 driver chip that has a built-in


charge pump for the upper N-channel fets. I have designed and built several variants based on the OSMC design, and they are far more efficient than myfirst attempts with the triple8. I have an OSMC bridge using 2 mosfets per leg that stays just as cool as the Triple8 with 3 mosfet per leg. My more recentversions of the triple8 use a mosfet driver (TC4427) for the lower fets which allows them to be driven at ultrasonic PWM frequencies (24kHz +), and avoltage divider for the upper fets to allow use with main power supplies above 24vdc. The wheelchair motors I am using will draw around 15 amps undernormal load, but I have a 200lb bot that often has a load of dirt or rocks in the bucket, so it can easily surpass 25amps fully loaded. I recently bought aSabertooth 2x25 and while it works well for normal use, if I try to run it hard for more than 5 or 10 minutes (going up hills and such), it begins to warm upand disable the outputs until it cools down. Trust me, with a bot as heavy as the Lawnbot400, the triple8 is not overkill - it actually works harder than theSabertooth, but has no overcurrent protection so you must keep an eye on it. Bottom line: the more efficiently you drive the mosfets, the fewer of themyou will need to do the same job.

Unit042 says: Jul 8, 2010. 1:36 PM REPLYThank you for giving me such a comprehensive reply. The info about efficiently driving the mosfets, now that is something I will have to read over afew times.... To make sure I understand, in ordder to efficiently drive a mosfet, I need a large enough voltage difference between the gate and thesource. For the N type on the lower side of the H-bridge, I would simply apply positive 24 volts to turn it on; for the P-type, I would have to... have anegative 24 volt difference? (as in, apply GND, or 0 volts to the gate while the source has +24 volts?) Eliminating the switching transients makessense. The TC4427 datasheet says it is for low side, so that part is taken care of (except for it's max supply voltage of +22v. Does that get in the wayof using it in a 24v system?), but how does that voltage divider work (in terms of creating the proper driving voltage)? Does it simply lower (ie "dividedown") the higher-than-24v-supply down to a usable voltage? That hip4081 looks expensive... The 47 ohm resistors on the gate limits the current? Ithought it had to be a very low value resistor on the source of the mosfet. And... wait-wait-wait... These are 50 amp mosfets here. Sorry for being a bit(a lot) dense, but why not use just one instead of the three on the triple8? Is it because of inefficient switching?

Unit042 says: Jul 7, 2010. 2:28 PM REPLYI just thought of another couple of (relatively important) questions: The P-mosfets cost extra. Would it be advisable to swap them out for cheaper N-mosfets (and making needed schematic changes of course), or were they chosen simply because of the convenience of automatically having the biasresistor, or the high side/low side stuff or whatever work out? About how much current do your wheelchair motors really require (when under load)? I askbecause this project seems a bit overkill for wheelchair motors.... Which leads to question 3 of my previous post.

tank1357 says: Aug 27, 2010. 9:45 PM REPLYPMOSs coast extra because they are harder to manufacture. But trust me, it is well worth the cost to use them. I've built plenty of bridges in my day,and every time i try to design one using only NMOS I always end up banging my head against the wall trying to get the voltages right, especially inbig power projects where the resistors get warm, and when resistors get warm, their values change, negating all that careful math you just did. SO:use the PMOS in conjunction with the NMOSs. You'll thank yourself later.

Unit042 says: Jul 7, 2010. 2:56 PM REPLYYou know what? Looking at the Digikey datasheet for the N-mosfet, it seems to be able to handle 52.4 amps (assuming a good deal of cooling offwith the aid of a fan), AND if more than 10 are ordered, you get a quantity discount on them. So, I wonder if these things would handle 24 volts at 25amps (continuous, but this is worst case scenario), with only four mosfets per motor in the traditional H-bridge arrangement (ie same as yourschematic, but only one mosfet per 'switch'). Hmmm. Additionally, the 2n7000 mosfets might/could be substituted by a signal transistor like the2n4401 (or somesuch), which I already have in my junk bin.... Sorry for triple posting, this project has me thinking. :D

tank1357 says: Aug 27, 2010. 10:23 PM REPLYI don't know if this was mentioned, but if you're unsure if the MOS can handle the power, just place a few of them in parallel. They'll still behaveas one unit, but be able to handle more power. This way you can use the relatively cheap Power MOSs from DigiKey. I think they're rated at 15Amps. As a general rule of thumb, don't exced 80% of what the power specs say the MOS can handle. IE: if the specs say stay under 10 Amps,don't ask it to handle more than 8. The real trouble begins when you're trying to deal with big loads. I had a go-kart system with motors that couldeasily draw more than 40 amps, and as soon as those babies got under load, my PCB tracks burnt up. I had been using 0.15" tracks, which ithought were massive, but now I never drop below 0.3" wide tracks when expecting them to handle some juice.

Unit042 says: Dec 12, 2010. 11:15 AM REPLYSo, after rereading what you've wrote, then thinking about it (ie procrastinating), I went back and studied the datasheet for the N-mosfet youused:FQP50N06L Whose datasheet is here: http://www.fairchildsemi.com/ds/FQ/FQP50N06L.pdfI was looking at Figure 10 on page 4.And comparing that chart to the IRFZ48VPBF datasheet here: http://www.irf.com/product-info/datasheets/data/irfz48vpbf.pdfFigure 9 on page 5.Both charts show the case temperature versus the drain current. Since you used 3 FQP's on your triple8, the theoretical max amps would be3 times 52.4 which is 157.2.... and for the IRF, whose advertised rating is 72 amps, it would take two to make 144 amps.

BUT, those numbers are for ideal conditions. Looking at the temperature charts I pointed out, at 100 degrees celsius (which is really hot, sothat's a good worst-case point), the FQP gives about 36 amps and the IRF does 51. 80% of those two numbers gives us:28.8A for the FQP30.8A for the IRFEither way, the numbers keep telling me that one mosfet per leg will do it for an average 25A load. Am I reading the datasheets wrong? Yousaid that you used a driver chip for yours that enabled you to have two mosfets per leg and it ran as cool as the one with 3 per leg. Were thetwo per leg still for extra insurance?

Something must not have sunk in to my cranium, because I am confused as to a good rule of thumb to make sure I am1: Getting enough mosfets to handle the motors under realistic conditions, and2: Not wasting money on extra mosfets, like the triple8 apparently seems to do.....

I would really like to use one mosfet per leg, but I still do not know how to be absolutely sure it will work. Oh, and how does the junctionbetween the mosfet legs and the PCB trace keep from burning up? I would think it's a narrow choke point. (For that matter, how do theymanage to handle that much current in a TO-220 package?)Attached to this post should be a picture of my wheelchair frame, motors, battery, and redneck DPDT switch for testing.


Unit042 says: Dec 12, 2010. 11:20 AM REPLYAlright, the image should be attached to this post....

johndavid400 says: Dec 12, 2010. 12:54 PM REPLYAlso, for a more thorough explanation of heat dissipation, check out this link:

http://www.mcmanis.com/chuck/robotics/projects/esc2/FET-power.htmlHe has built some awesome motor-controllers:

http://www.mcmanis.com/chuck/robotics/projects/esc2/index.html

johndavid400 says: Dec 12, 2010. 12:51 PM REPLYUnit042, you have been doing good research. While the ratings for the mosfets are important, there are really only 2 things that areimportant - the internal resistance of the mosfets (ie. RdsOn rating) and how you drive them. Regardless of what a mosfet says that itcan handle in Amps, check the On state resistance and calculate how many watts will be produced using your predicted current-draw:

FQP50NO6L = RdsOn = 0.026 ohmsPower in watts = resistance x current ^2 (that's current squared)Now lets assume the motors will take 20 Amps continuously (about right for a geared down, 200lb bot running at 24v):Power = 0.026 ohms x (20A x 20A) = 0.026 x 400 = 10.4 wattsWow, 10.4 watts will be dissipated through this mosfet if using only 1. That's not good, as the TO-220 package at best can dissipateabout 2.5W without a heatsink and/or cooling fan, about 5W with both.

To get this 10.4 number down to 2.5 - 5, add more mosfetsL. 2 mosfets in parallel = 5.2watts, and 3 fets in parallel = 3.5watts. This iswhere I landed on 3 fets per leg..... my calculations could be flawed, but the mosfets on the Triple8 never got hot in the least bit.

Let me be the first to say, that the Triple8 is not nearly as efficient as it could be - for instance, it uses the Arduino's 20mA ouptut PWMpin to drive a set of 3 mosfets. While this works just fine at 1kHz PWM, try running the Triple8 at 32kHz pwm, and watch it short outdue to cross-conduction! This is because the mosfets will not get switched fully On and back Off between each cycle at such a highpwm speed without more current. Ideally, you need a mosfet-driver IC, be it a simple signal buffer (push/pull driver), or a full-fledgedH-bridge driver for driving all N-channel fets like the extremely efficient OSMC design (which is what I later used on the Lawnbot).Though the Triple8 is not the best design in terms of pushing each Mosfet to it's full potential, How cheap it is to build (for a dual-motorcontroller of its power capability) is what makes it nice to have around. As I learned more, I saw more flaws in the design - but I am stillamazed at how powerful it is.

The reason for the Triple8 mosfets that I picked out was because they were:1. Logic-level for interfacing directly to Arduino2. Cheap cheap, at only about $1 each when I last bought them,3. they have a +/-25v Gate to Source voltage, higher than normal so we can use the simple pull-up resistor design to turn off the P-channel fets and still use a +24v system voltage.

I later built a few home-made OSMC motor-controllers using their schematic and the HIP4081 driver chip - and this bridge onlyrequired 2 mosfets per leg, never getting hot and just as powerful as the Triple8 (mowing for 3-hour straight periods). This is becausethey are being driven with 2 amps peak signals, have shottkey turn-off diodes for high-speed PWM, and dead-time between cycles toprevent cross-conduction. These bridges cost more to build, but requires less mosfets, as they are driven very efficiently.

I later bought a Sabertooth 2x25 to test out, and while it works well for tame mowing, try powering over a small tree or plowing througha large pile of brush and it usually trips the over-current limiter, making it look like the bot is having a seizure. the Triple8 and OSMC'swould do no such whining, they would power the lawnbot over anything it had enough traction to climb.

I have been working a lot on several new high-powered motor-controllers with Lawnbot sized robots in mind... these are much moreefficient than the Triple8, but not as expensive as the OSMC. I have a book coming out in a month (Arduino Robotics) with plans forthese designs, though they will also be posted on my website at that point for anyone to use.

Cheers,jd

Unit042 says: Dec 12, 2010. 9:33 PM REPLYThank you for posting that link, it has helped me understand the thermal properties of mosfets more. Those datasheets are muchless cryptic now...Also, some info I was looking at:http://homepages.which.net/~paul.hills/SpeedControl/Mosfets.html


I used the mosfet I proposed in following the calculations on the website you posted, and now I have two pages of equations thattell me that if I want my 24v battery to put 30A through it, I will need a heatsink whose resistance to ambient room temperature at40 degrees celsius to be 3.67 deg. celsius per watt, and the article mentioned a typical cheap heatsink was something like 16 to18. Not good.

Looking back at what you told me.... assuming that a TO-220 package ought to dissipate no more than 5W, and that the only otherthing that was important was the internal resistance, I pose a new set of equations.For reference:Watts = resistance of mosfet * (desired amperage squared)So, if we are dissipating 5 watts, and we have 30A for current, we have: 5 = mosfet resistance * (900)5/900=mosfet resistance 5.5556 miliohms = maximum mosfet resistance.

And that is a standard to which I compared digikey mosfets to.here's one that seems inexpensive enough:http://ixdev.ixys.com/DataSheet/99970A.pdfAdvertised resistance is less than 5.4miliohms, but looking at figure 4 on page 3, at 100 degrees celsius, it is 1.6 miliohms.Plugging that with 30A, it disipates 1.44 watts.

So, do you think this will work for one mosfet per leg, or am I missing more info?

TheMONKEY says: Mar 26, 2010. 5:39 PM REPLYJust so you you know this is Rock Awesome Ive always wanted to build one of these and Ive just now started to collect the things to do it. I got many ?about the H-bridge control and how to hook it all up to the remote control Could you do it with a basic stamp????

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