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Electric Longboard Build & Clever CIM Motor Drivetrainby all1by on August 25, 2010

Table of Contents

Electric Longboard Build & Clever CIM Motor Drivetrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Intro:   Electric Longboard Build & Clever CIM Motor Drivetrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 1:   Parts and Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 2:   Defining Problems and Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 3:   Turning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 4:   Losing Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Step 5:   CIM Motor Drive Part1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Step 6:   CIM Motor Drive Part2 - Application to the longboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Step 7:   Flexibility and Shock Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Step 8:   Miscellaneous Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Step 9:   Cost and Feasibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Step 10:   Performance and Pictures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

Author:all1byMIT Undergraduate

Intro:  Electric Longboard Build & Clever CIM Motor DrivetrainThis Instructable documents the improving of a Proline 600 Altered Electric Longboard. It also serves as a useful resource for anyone attempting their own electricskateboard/longboard build. It ALSO serves as documentation for a mini-build: a new drive-train for the ever-so-popular CIM motors, which are often used in FIRSTrobotics competitions.

Altered/Exkate electric skateboards/longboards are not known for their turning radius (it’s HUGE), their weight (the one we used was 48 pounds stock!), nor theirperformance (1, yes ONE, wheel drive). In fact, about the only thing they are known for is being one of the first companies to produce electric skateboards/longboards.So we decided to make it better. The further we went, the more we realized we could have started with a deck and built up; thus, I will endeavor to make this Instructableuseful to both types of builders.

CIM motors have been without a cheap, easy, and compact gear-reduction drive-train since their beginning. Now the wait is over. Read on!

The team was part of MIT’s Edgerton Center Summer 2010 Engineering and Design Class, a month-long class where high school students learn and apply real-worldengineering skills to various projects.

Note: I'll apologize in advance for any bad quality photos.

Also Note: I am in no way affiliated with any of the companies mentioned in this Instructable.

Image Notes1. Stock Altered Pro-line 6002. Transmitter3. Lead Acid charger

Image Notes1. CIM motor2. The compact gear reduction drive3. Aluminum lip-lick extension that keeps the belt from contacting the deck duringturns.

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Step 1: Parts and ToolsNote: All parts listed are for/from the Proline 600 model. Other models’ parts may be able to be used with modifications.

Parts:Option A: Rebuild an Exkate.1) Proline 600 Exkate (It’s not worth buying one for $600. Go to option B if you don’t already have one)2) Two CIM motors3) Two of these planetary gearboxes .4) Some ¼” aluminum plate. At least 12” x 12”.5) Some 2” Aluminum round. At least 2” in length.6) Two timing belt gears. A good source for these is: http://www.sdp-si.com/7) Two timing belts .  (We used 400-5M)8) Two ball bearings that have OD’s small enough to fit inside the timing belt gear hubs and have a 5/16” ID. McMaster has cheap ones.9) Two MBS mountain-board trucks .10) Four ¼” rubber shock absorption (soft) risers11) Nine lithium polymer batteries. We used these wired in 3S3P for a total of 9S3P (~36V and 6600mAh). Read up on safety information before using LiPo’s!!! They canexplode if used improperly!12) Nine electronic project boxes (used as battery boxes). Preferably plastic and as close to the size of your batteries as possible.13) About 6 feet of 14+AWG wire.14) PTC fuses~1Amp. At least 2415) Deans connectors or other low resistance battery connector. 1 pair16) Three of these charger s or equivalent. (why you need three will become clear)17) Three of these power supplies or equivalent.18) Low voltage detectors or equivalent.19) electrical tape/ assorted heat shrink tubing20) Blue RTV silicon sealant or equivalent.21) LED strips. We used two 12V 16” Red strips and one 12V 8” white strip.22) Lots of various machine screws.23) LoctiteOptional: 3 balloons (for waterproofing LVD’s), some extra hard bushings (rider’s preference, but due to the extra long trucks, harder seems to be better), a small switchfor the LED circuit

         Option B: Build from ground up.All of Option A minus the Exkate and plus the following:1) A deck2) An Altered electronics modul e.3) Exkate Wheels: Two regular (http://www.alteredexkate.com/servlet/Detail?no=104 ) and two with drive gears (http://www.alteredexkate.com/servlet/Detail?no=103 )

Tools:Soldering IronBand SawBelt sanderDrill pressDrillDremel with cut off, sanding, grinding bitsHot glue gunHex keys, screw drivers, wrenches etc.Tap and die setFiles (various)Optional: Metal Lathe (very helpful), Cold saw

Step 2: Defining Problems and GoalsNote: if you are building an electric board from scratch, you can skip this step.

Problems and goals:The Altered longboard presented an interesting challenge. On one hand, it sorta kinda worked. It ran, accelerated reasonably fast, and had a reasonably fast top speed.You could get from point A to point B. On the other hand, it had some major flaws:

1. Turning radius.The minimum turning radius was measured to be about 10 feet. This is simply unacceptable for a longboard. It wasn’t error on our part either. When the turning radiuswas measured, we were leaning so far out that the motor contacted the deck and the outside wheels started coming off the ground; it really was the most the board couldbe turned. But why is 10 feet too large for a turning radius? If you were riding on a sidewalk and needed to go around a corner, 10 feet would put you in the street. Thismeans that you had to stop, pick up the board, turn it, and then keep going in order to make turns. Now that’s a pain, but it was compounded by the 2nd major flaw: theweight.

2. Weight.The board weighed approximately 48 pounds stock. That is ridiculous. The lead acid batteries were the major contributor. The next was the 10 pound motor. The weightmade it hard to pick up and carry (say at stairs or when turning).

3. One wheel drive.Only one wheel (rear left) was powered. This meant that whenever you turned right, the drive wheel would lose downward force, thus losing traction. It would often comeoff the ground completely, and you would just stop moving.

4. Flexibility.The giant plastic battery box underneath the deck really hurt board flex. This made for a very bumpy, uncomfortable ride.

Goals:

1. Decrease turning radius by at least half (5ft).2. Decrease weight to something more carry-able.3. Make it 2 wheel drive.4. Increase board flex.

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4. Increase board flex and shock absorption.

Step 3: TurningThe first step was to understand why the turning radius was so bad. Part of the problem was that giant motor attached to the rear truck; its can would contact the deck,limiting how far the rear truck could turn. Trying to relocate the big motor was pointless, since the one large motor was going to be replaced with two smaller onesanyways. However, this wasn’t the major problem. Exkate/Altered (same company fyi) trucks are custom- they have a unique footprint and use torsion bushings insteadof compression bushings. They try to make their new type of truck sound awesome on their website, but the fact is they don’t work as well as regular compressiontrucks. The front truck on our board would only turn so far before stopping. So we took it apart and found that it was stopping due to an irreparable metal design feature(it’s complicated, and the only way to fully explain it is in person with one taken apart). The rubber torsion bushing is held in place by three metal pins and showed someserious strain at those points. In summary, we didn’t think it was a very good design, and our opinion is backed up by the poor performance of the board with respect toturning.

So we replaced the trucks. Regular longboard trucks weren’t long enough for the giant wheels (even 180mm trucks). More specifically, the length of the axle wasn’t longenough for the super wide wheels. Mountainboard trucks are designed to accept very wide pneumatic wheels, so we went with those. We chose to use the bushing-styletrucks to save money, but shock absorber mountain board trucks would probably be fine. The MBS trucks came with small metal brackets (used to mount brakes) on bothsides. The drive gears on the wheels would interfere with these brackets, so both brackets were cut/ground/sanded off of one of the trucks (making it the rear truck). Thefront truck was unmodified. Oh, and it turned out that the axle diameters were so similar that new bearings didn't need to be purchased (it was 9.5mm for the new onesvs. 3/8").We found that using an extra hard bushing in the back and a hard one in the front gave the best ride, but it’s of course up to the riders taste.

These trucks cut the turning radius from 10ft down to our goal of 5ft!

Image Notes1. Extra wide wheels2. Rubber torsion bushing3. Non-standard bolt pattern.

Image Notes1. Way over-built = heavy

Image Notes1. The metal stop thing that prevented the trucks from turning far enough.2. Metal pins that held the bushing in place.

Image Notes1. The rear truck with motor attached.2. Giant 10lb motor3. Extra long axles4. Timing belt drive

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Image Notes1. MBS mountainboard truck2. Standard bolt pattern3. Compression bushing4. Brake brackets5. Extra long axles6. Riser

Image Notes1. Bracket partially cut off

Step 4: Losing Weight48 pounds is heavy. Our main strategy here was to replace the 20 pounds of stock lead acid batteries with lighter lithium polymer batteries, while maintaining or improvingspeed, acceleration, and range characteristics.

The original batteries were three 12V lead acid batteries wired in series. We chose to use nine 11.1V, 2200mAh LiPo packs for various reasons. 9 was a nice number forwiring 3 sets of 3 packs in series and then wiring those sets in parallel. This gave us a total of approximately 36V (37.8V at full charge and 27V dead) and 6600mAh. Wedidn’t want to go too far over 36V because the Exkate speed controller was designed for 36V, and we didn’t want to increase capacity much because the stock rangewas fine and increased capacitance meant unnecessary battery weight and expense. LiPo’s were chosen for their high energy density and (now) relatively low expensethanks to Chinese exporters like HobbyKing. It also turned out that 9 would fit under the deck nicely. We could have gone with six or even three higher capacity packs,but having larger packs would have decreased board flex (larger, stiff battery boxes) and modularity.

Modularity was important. Lipo’s are infamous for their violent explosions when handled improperly or punctured. Individual, waterproof, hard-plastic boxes(actuallyelectronic project boxes-these come in almost any size fyi) were used so that if one pack failed, it wouldn’t take out the other packs with it. The one issue with the boxeswas that if a pack failed violently, the tight enclosure would pressurize and go off like a bomb. This necessitated the intentional weakening of a side of the boxes (aka.taking a dremel to a side and grinding down a thin spot) for a controlled blow-out point.

The batteries were also wired such that if one failed, it wouldn't cause any others to short across it. Battery connectors were not used between packs; they were all hardwired together. However, not every pack was directly connected to every other. Wiring 3 packs in a series set, and then wiring those sets in parallel at the end meant thatif one of the batteries shorted, the series set would just cut out. See circuit picture below. If the packs were wired in parallel sets (and those sets wired later in series), anda pack shorted, the rest of the parallel set would short across it and likely blow up, too.

The packs were then wired in parallel sets. Yes, I just contradicted myself, but let me explain. The charging/balancing taps between corresponding packs in the seriessets were wired in parallel (3S3P) to allow for easier charging. This way, there were only 3 balancing taps instead of 9. The main power leads were not wired in parallelbetween sets (they were wired in parallel at the end). However, we didn’t want large amounts of current flowing in the small gauge tap wires (which would happen in thecase of, for example, a shorted pack). Thus, small 1.2A PTC fuses were placed inline with the tap wires between the packs. PTC fuses act like little circuit breakers, andwere small enough for our application. See picture for how the taps were physically wired.

There’s one more problem that needs addressing. If three chargers are used in tandem, and the chargers are relatively cheap (like the ones listed in the parts list), thenyou will need three separate power supplies for them all, even if the power supply can handle the wattage. The problem with using a single power supply isn’t related topower or the supply at all, but to the charging circuitry. Refer to the third battery diagram. Cheap chargers likely have the negative balancing tap lead output (the blackone) connected directly to the ground (black/negative) input. This means that if all the chargers are wired in parallel to a single power supply, all of the chargers will be atthe same potential and not allowed to “float” up to the higher voltages, e.g. 33.3V and 22.2V, necessary for charging the upper parallel stacks. If a separate powersupply is used for every charger, the chargers will be able to float up to the necessary voltages. When in doubt, use separate power supplies for chargers. Alternatively,you could wire your batteries with connectors at all the series connections and disconnect them for charging.

It turns out that we also saved weight by changing motors. Each of the smaller CIM motors we used weighs about 3 pounds. By using two of them instead of the onelarger 10lb motor, we saved about 4 pounds. Switching trucks also saved us a few pounds.

This battery scheme, or some variation, would work great for anyone building their own electric longboard from scratch.

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Image Notes1. Lead Acid Batteries

Image Notes1. 3 packs in series2. Wired in parallel at the ends

Image Notes1. Fuses2. 1 of 3 balancing taps. Wiring the packs like this got rid of 6 balancing taps andallowed us to charge 3 packs at a time.

Image Notes1. These smaller wires represent the parallel balancing tap connections betweenpacks. There wasn't enough space to draw all four and the fuses.2. Trace the black wires. One goes to 22.2, another to 11.1, and another to 0V.This is bad. Three separate power supplies are needed.3. Cheap chargers connect the ground input to ground output. More expensivechargers may have more sophisticated circuitry that alleviates this problem.4. Thin wires represent balancing tap leads. Not enough room to draw all fourwires.

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Image Notes1. The battery boxes were bolted to the deck with small machine screws.

Image Notes1. One of three balancing/charging taps.2. Fuses are here (covered by electrical tape).3. The four tap leads. Each pack has 4 tap wires. They hook directly to eachindividual cell inside the packs.4. power leads

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Image Notes1. Controlled blow-out point. The side packs have blow-out points on the sidesfacing out.2. Blue RTV Silicon for waterproofing3. These three are wired in parallel via the balancing taps and fuses.4. These three are wired in series via the power leads5. The three sets of series packs are finally wired in parallel here (hiddenunder the white tap).6. One of the electronic project boxes with a LiPo in it.

Image Notes1. having lots of batteries, and thus, lots of gaps, allowed for lots of board flex

Image Notes1. rubber spacers were used to cut down on pack vibration

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Step 5: CIM Motor Drive Part1The first step is figuring out how/where you are going to mount the motor. After figuring that out, you can cut (band saw) the aluminum plate into the proper bracketshape. For example, we were mounting the motor parallel to the truck, so our mounting brackets were shaped as in the pictures below. There is a small raised ring nearthe shaft of the motor that is approximately 1/8” high and 1” in diameter (see: http://www2.usfirst.org/2005comp/Specs/CIM.pdf ) . A large (~1”) hole has to be drilled inthe bracket to allow it to sit flush against the motor face. The next step is to drill the two clearance holes for 10-32 screws that will secure the bracket to the face of themotor. Then countersink the holes so that 10-32 flat head screws may sit flush with the face of the plate.

The next step is securing the planetary. The great thing about this particular planetary is that it is built for a 5/16”, which happens to be the shaft size of the motor. All thatyou have to do is grind/file a flat spot on the shaft so that it can fit in the D-slot planetary hole. The next step is actually securing the planetary to the motor/bracketassembly. This is done by carefully transferring the 8 hole locations of the outer ring of the planetary to the bracket. Then those holes need to be drilled and tapped for#8-32s. The outer ring of the planetary cannot be drilled out or threaded due to the very brittle steel used in its construction (it WILL crack if this is attempted). The #8screws will be a pretty loose fit, but this is ok and actually good because it is VERY hard to get the 8 hole locations exact with a drill press (if you have access to a mill,that might make it better); having the loose fit builds in error protection.

The next step is to locate the four shallow holes on one side of the planetary’s inner disk (see pics). Drill out and tap (using a *bottoming* 10-32 tap) these holes; makesure you don’t drill the holes any deeper because you run the risk of drilling into the planetary gears. These holes will be the ones holding the timing belt gear. The bestmethod we found for transferring these hole locations to the gear was cutting the heads off of some 10-32 screws, grinding them down to points, screwing them into thetapped planetary holes with the points facing out, and simply pressing the gear onto these points. Doing this would leave marks for clearance hole locations in the gear. Ifthe gear you are using has support struts, then you will likely need to cut out (probably with a dremel) some of them.

The next step is to modify the gear (this step can be done before the others). The hub of the gear needs to accept a bearing that has a 5/16” ID. The OD will bedependent on your gear. For example, if you are using a small-ish gear, you might need a smaller bearing. The whole point of having the bearing is to transfer forces(from the belt) from the gear to the shaft of the motor. The gear cannot be directly attached to the motor shaft because the shaft will be spinning at a different rpm thanthe gear (because the gear is attached to the planetary). Thus, a bearing is needed. I tried to draw a cut-away of the assembly showing the force transfer (see pics).Anyways, the best way to do this is on a lathe because bearings require very precise mounting surfaces. I first bored out the hole in the gear to a clearance diameter of3/8” so that the motor shaft wouldn’t contact the gear hub. You can see in one of the pics that the gears we used had a hub that extend past the front and rear planes ofthe gear. I cut this extension off. Then using a boring bar, a recess was cut in the hub to accept a raised portion of the planetary, allowing the gear to sit flush against theinner disk of the planetary. Then, again using the boring bar, the bearing surface was cut into the hub. I didn’t put the recess and the bearing surface right next to eachother; afterwards, I wish I had- see the pics for why, but basically, the motor shaft wasn’t long enough to reach the bearing, so we had to flip the gear over, meaning thatit was no longer flush with the planetary’s inner disk.

After machining the bearing surface, the whole thing can be assembled. First, screw the bracket to the motor. Next, slide the planetary on, making sure that the holes formounting the gear face out. You’ll need to find at least 3 out of 8 good holes to bolt the planetary onto the bracket with. “Good” here is defined as putting the leastamount of stress on the planetary and making the planetary as concentric with the motor shaft as possible. If the planetary is off-center, the gears will grind and make alot of noise. The inner disk/motor shaft should be somewhat easy to spin by hand. If it is not, or if it locks up, then you’ll probably need to find another set of holes. Thereis no good method for doing this…just try lots of combinations until one seems to work best. The planetary will likely need to be spaced out from the bracket slightly toprevent rubbing. We found that #8 nuts with the threads drilled out and small washers worked best for spacers between the planetary and bracket. Another thing thathelped was not tightening the screws down all the way; this lets the planetary find the spot it likes. Next, slide the gear on and screw it to the planetary. Now undo all thescrews one by one, put Loctite on them, and screw them back in. Loctite will keep them from vibrating off. Finally, mount this assembly on yourrobot/longboard/invention/etc, put on the timing belt, and your good to go!

Mounting the planetary in this fashion gives a 1:4.5 gear reduction (not including your timing belt gear ratio, of course). If you mount the planetary in a different way, Ibelieve you can also achieve a 1:4 reduction. You can get some pretty serious final gear ratios if you use the right timing belt gears. Another great thing about this drive isthat multiple planetaries can be stacked to achieve multi-stage gear reduction for a lot of torque. For example, instead of attaching a gear to the 4 inner disk holes, youcould attach an aluminum disk that would also bolt to the 8 outer holes of another planetary. Then the timing gear would be attached to this second planetary.

One flaw with this method is that you have to use a relatively large timing belt gear (for the gear attached to the planetary) because the 4 mounting holes are pretty farout. Another flaw is that getting the 8 holes in the bracket drilled precisely enough is very very hard; that being said, we did it twice without having to re-do anything.

Image Notes1. CIM motors

Image Notes1. The planetary2. 5/16" D-slot3. 8 outer ring holes that get bolted to the bracket

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Image Notes1. Our bracket2. large hole for clearing the raised ring on motor so that this bracket can sit flushagainst the motor surface3. 8 tapped #8-32 holes for securing planetary4. two clearance holes for the screws holding this plate to the motor. These holesstill needed to be countersunk at this point.5. Threading #8-32

Image Notes1. the hub extension that extended past the plane of the gear. I cut this off witha lathe

Image Notes1. cutting the bearing surface. I should have put the bearing surface on the otherside with the relief cut for the raised ring on the planetary2. 3/8" clearance hole3. Gear clamped in lathe chuck4. boring bar

Image Notes1. The four holes that needed to be tapped 10-32 in the planetaries.2. pointy for transferring screw locations to gear3. The raised ring on the planetary that required a relief cut in the gear.

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Image Notes1. bearings. again, I should have put them in the other side2. holes not drilled yet for screwing to planetary. parts of these supports had tobe removed for the screw heads.3. 5M pitch timing belt gears.

Image Notes1. First step. Screw bracket to motor. Note that no screw head is protruding.This is due to the countersink.2. you can sorta see the ground down section for the D-slot on the other side ofthe shaft3. Bracket sits flush against motor face thanks to this hole.

Image Notes1. The four tapped holes for screwing on the gear.2. #8-32 screws go in here.3. spacers go between here

Image Notes1. No shaft...oops. The shaft is too short, so we had to flip the gear around sothat the bearing would contact the shaft.2. Nice and flush.

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Image Notes1. The bearing contacts the shaft now, but this relief cut is now useless.2. No longer nice and flush.

Image Notes1. we painted them black2. hole for truck3. mounting bracket to hold motor bracket to truck4. Countersunk

Image Notes1. Trying to find the right combination of holes2. drilled out nuts for spacers3. We didn't tightening the screws down all the way; this lets the planetary findthe spot it likes.

Image Notes1. CIM motor2. The compact gear reduction drive3. Aluminum lip-lick extension that keeps the belt from contacting the deckduring turns.

Image Notes1. no bearing2. forces are transferred to the planetary, which is bad

Image Notes1. with bearing2. force transferred to shaft

Step 6: CIM Motor Drive Part2 - Application to the longboardThe CIM motor drive was originally developed to be compact enough to fit under a longboard deck. We decided that only one bracket was sufficient to hold the motor inposition. We could have fixed other side of motor, too, but they’re so light that ¼” aluminum on one side was fine.

The CIM motor spins at a much higher rpm/V than the stock motor. In order to keep stock torque and top speed characteristics, we needed to gear them down- thus theneed for the planetary gearboxes. The CIM motors @ 18V + the planetary + 1:1 timing belt gear ratio ~= stock motor @36V + 19:44 timing belt gear ratio in terms of rpmand torque. Note: we know that CIM motors are meant to be run on 12V and that we are running them at 18V (2 motors in series on a 36V circuit = 18V per motor). Thisis fine; they handle the higher voltage and rpm without any issues.

The Exkate drive wheels have a 44T gear permanently attached to them. We did the gear ratio calculations and it turned out that a 1:1 timing belt gear ratio was fine, sowe bought 44T gears to attach to the planetaries. If you use a smaller gear, you’ll get more torque (and thus acceleration), but I can tell you from experience that there isPLENTY of torque. A larger gear will give you a higher top speed (but less acceleration).

But why did we go with 2 motors instead of 1 bigger motor with a solid rear axle or differential? (You can buy differentials for tricycle-style bicycles that are small enoughto fit.) One reason is that both would require a complete chop-and-rebuild of the rear truck in order to get them to fit in the proper place; we’d basically have to design our

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

own truck. But besides that, there are other problems with both. A solid rear axle would mean that both rear wheels would be spinning at the same rate. This is bad forturning. When a car turns, the outer wheels have to spin faster than the inner ones. If you have a solid axle on a longboard, the outer wheels have to slip in order to makethe turn. This would seriously hurt the turning radius. A differential would alleviate this problem; however, in the case of longboards, it causes a different problem. Alongboard is turned by leaning in the direction you with to go, causing more force to be on the inner wheels than the outer wheels. This means that the outer wheels haveless traction. With a differential, the side with less resisting force (traction) gets more torque and vice versa. This means that, in very sharp turns where the outer wheelcomes off the ground, the outer wheel will get all of the power and the inner wheel will stop spinning. This is the same problem we had with 1 wheel drive, but now oneither side of the board! In summary, a solid rear axle or differential were not good ideas.

So we used two motors. However, one thing we didn’t foresee until it was too late was that we had created an electronic differential by wiring the motors in series. If onemotor has less load than another, it will steal power from the other motor. Ideally, the two motors should be wired in parallel. However, that can’t be done with CIMmotors because, while 18V is fine, 36V would probably cause them to explode. The second best possible solution is to find two relatively low rpm/V (so that you don’tneed the planetaries), light weight, compact, 36V motors and wire them in parallel…I couldn’t find any such commercial motors. The best possible solution would be tocompletely overhaul the power system by using two motor controllers (one for each motor),  finding motors that match our needs exactly (and don't need the planetaries),and creating a new radio scheme (because the radio receiver is integrated into the current electronics module).

Note: when I say “motor”, I mean brushed motor. We decided to go with brushed motors over brushless because of their simplicity, being cheap, and ability to wire themin series or parallel. Brushless motors are more efficient and more powerful, so if anyone wants to undertake a brushless version of this project, that would be cool! (I’mbuilding one with in-wheel brushless hub motors, check it out here: http://www.mitrocketscience.blogspot.com / ) .

The last thing to mention is how we mounted the brackets to the trucks. A hole was drilled in the bracket plate large enough to fit the truck through. Two small two piececlamps were machined out of 2” aluminum round stock. First, we cut 1/2 inch pieces of the 2” round. Then those had a big hole drilled in the center smaller than thediameter of the trucks at the point we were going to clamp it (if these holes end up being too small, filing can fix them). Then they were notched (see pic) and holes drilled(for a #10-32 tap) perpendicular to those notches. Two clearance holes for 10-32 were drilled through the face of each (to be used to screw the bracket to). Then theywere cut in half (see pics). Then the bottom sections were threaded for 10-32 and the top sections were drilled out for clearance. The end result was two, 2-piece clampsthat would fit snugly onto the trucks when screwed together. After fixing them to the trucks, the two face hole locations were transferred to the brackets and drilled andtapped for 10-32. Then everything was shimmed (to get the motors straight because I can almost guarantee that the clamps won’t sit perfectly straight on the trucks) andbolted (with loctite!) together. Note: a better way to do this than clamps would be to weld the 2” round disks onto the truck.

Image Notes1. figuring out where exactly the brackets should go along the truck

Image Notes1. The custom 2-piece clamps.2. clamping screws3. two clearance holes for 10-32 drilled through the face4. notches5. cut in half6. drilled hole7. filed hole8. After these were clamped onto the trucks, these hole locations weretransferred to the brackets that were then drilled and tapped.

Image Notes1. shims went between here2. shim3. bolted on4. We calculated the exact distance the two gears needed to be apart beforemaking the brackets so that the belts would be under proper tension.

Image Notes1. CIM motor2. The compact gear reduction drive

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

3. Aluminum lip-lick extension that keeps the belt from contacting the deckduring turns.

Image Notes1. New, standard truck bolt holes carefully drilled

Image Notes1. Motor positioned far enough below deck to not interfere with turning.2. 1/2" ground clearance

Image Notes1. Electronic Differential

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

Step 7: Flexibility and Shock AbsorptionThe deck is one of the two things Exkate really got right (the other is the electronics module). It is a VERY nice deck. Each of the 9 layers that make up the plywood deckwas stained prior to assembly. It also flexes like a dream when it doesn’t have a giant battery box screwed to it. Having individual battery boxes really helped flex, andthus, shock absorption.

The other thing that helped shock absorption was a 1/2” of soft rubber risers between the trucks and the deck.

Image Notes1. MBS mountainboard truck2. Standard bolt pattern3. Compression bushing4. Brake brackets5. Extra long axles6. Riser

Step 8: Miscellaneous NotesThe low voltage detectors (LVD) plug into the taps and monitor cell voltage. If any cell drops below 3V (the lower threshold for LiPo’s), then the LED turns red and anannoying alarm sounds. A neat trick: You can put them in balloons and fill the neck of the balloons with hot glue to waterproof them.

Hot glue can also be used to hold wires in place.

While the longboard we built is technically water proof, I wouldn’t run it through anything more than a light drizzle.

Adding LED’s: Three waterproof, 12VDC LED light strips were purchased for the board: two 16” red strips, and one 8” white strip. These were wired together in series(with a switch inline so that they could be turned on and off) directly to the speed controller input power leads. They are held in place with hot glue.

Note: the batteries were not hardwired to the controller. A deans connector is used to connect and disconnect the batteries from the controller.

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

Image Notes1. LED strip

Step 9: Cost and FeasibilityThe following are estimates:

Electronics module: $170Batteries: $150CIM motors: $60Deck: $150Wheels: $55Trucks: $65Chargers/power supplies: $45Other parts (wire, aluminum, hardware, gears, etc): $100Total: ~$795 (not bad and totally worth it)

Proline 600: $600

The extra $200 makes all the difference. It turns something barely rideable into something amazing to ride.

The Altered board we altered was donated by a private party (thanks Stephen!) to the Edgerton Center.

Step 10: Performance and PicturesIt is truly an amazing machine. It accelerates smooth, has ridiculous amounts of power, and is fast (I'd say around 15mph top speed). It also has a turning radius of about5ft, which isn't bad for long boards. It weighs a little over 30 pounds, which is significantly better than 50, but still rather heavy to lug around. One flaw with it is that it onlyhas 1/2” of ground clearance, which is fine for sidewalk bumps, but bad for large cracks, pot holes, etc. It’s also somewhat noisy due to the planetary gear chatter.

There is extra, lip-like ¼” aluminum on the bracket extending above the planetary (see pic). During turning, that hits the deck before the belt does, sparing the belt fromdamage. On your deck, make sure the belt doesn’t contact the deck. If it does, you can try cut outs or more aluminum.

Now enjoy some pictures of the longboard that has been affectionately codenamed “eXKate.C.D.”

For more, including links to videos, check out: http://www.mitrocketscience.blogspot.com/ 

Image Notes1. CIM motor2. The compact gear reduction drive

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

3. Aluminum lip-lick extension that keeps the belt from contacting the deck duringturns.

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

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Comments

50 comments Add Comment view all 55 comments

 nuttyjr says:  Mar 28, 2011. 7:43 PM  REPLYFriggin great example of what first robotics kids do after 6 weeks off builld lol

 cschultz-1 says:  Mar 6, 2011. 9:22 PM  REPLYWhat i don't understand, is that your battery system is set up for 36V, but your motors are clearly 12V, and trust me they will burn if you run them at 36??

 all1by says:  Mar 7, 2011. 6:38 PM  REPLYThey are wired in series (36/2=18V), and they can handle 18V without issue.

 motleypixel says:  Dec 30, 2010. 10:01 AM  REPLYOkay this is cool...I have all the tools including a mini metal lathe etc. I want to build from scratch (ground up) and your instructable isn't 100% detailed. Forinstance, could you please update some line items like #2 "Two CIM motors", where, how much, part numbers, etc.? What are the part numbers for every"major" component like in #6 the belt gears, you just give the main site and they have a ton of gears? Thanks!

 all1by says:  Jan 1, 2011. 5:04 PM  REPLYThe CIM motors are the classic FIRST robotics motors. I put links in various places in the instructable to their specs. As for a place to buy them, I justgoogled "first cim motor". Many places sell them. Ex: http://www.trossenrobotics.com/store/p/5142-FIRST-CIM-Motor.aspx

The timing belt gear ratio you use is somewhat dependent on the motor controller(s) you use. If you use the Exkate one like us, then you could try thegear ratio we used. Step 6 mentions the gears we used (44T). https://sdp-si.com/eStore/ , and look under "timing belt pulleys".

Anything else?

Hope that helped.

 all1by says:  Oct 3, 2010. 7:34 AM  REPLYSome updates:

1. Make sure you make the bracket-claps better than we did. They should match the profile of the trucks. If they don't, they are prone to slipping. Also, I'dsuggest using bigger and coarser thread screws for the clamp. Or just braze or weld it.

2. Make sure you use a good bottoming tap with the drive gear - planetary interface because you'll need as much thread engagement as possible to preventthe motor's torque from ripping the screws out. If worst comes to worse, JB Weld the screws in.

 paperclip32 says:  Aug 31, 2010. 2:57 AM  REPLYGreat instructable,but I somewhat disagree with the premise of making an electric longboard.I think longboarding is about the experience,about pushingyourself(literally) to go that extra mile.An electric longboard just takes out the fun of riding a longboard,because you're pretty much capped at the speed ofthe motor,and pushing isn't an option because of the weight. But that's just my opinion.

 denotsKO says:  Sep 2, 2010. 10:14 PM  REPLYIt is ideal for a person like me who has limited control of my left side due to nerve damage. I felt like a schmuck when I could no longer skate, but anelectric drive board put me back on the streets.

 paperclip32 says:  Sep 12, 2010. 12:31 PM  REPLYWoah.What happened?Are you better now?

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

 all1by says:  Aug 31, 2010. 6:21 AM  REPLYHave you ever ridden an electric longboard? It's a lot of fun, and I believe it is actually a progression towards the original goal of longboarding: surfing onland. And this board is even more so. But that is just my opinion. As for the speed (if 15mph, 20mph with gear changes, isn't fast enough), the speed ofthe motor is not the limit- the motor itself is. You are by no means limited to CIM motors. There are hundreds of more powerful (in terms of rpm andtorque) motors out there, including much more efficient and powerful brushless motors....the brushed CIM motors are just the tip of the iceberg. With afew hundred dollars in upgrades, I know I could change its topseed to well over 30. However, you are correct about pushing; while it is possible to pushthis board, it really isn't pleasant.

 paperclip32 says:  Sep 1, 2010. 7:38 AM  REPLYI know a shop by the beach that rents them.Will try them out sometime! As for surfing on land,I'll have to agree with you.That's where the sportstarted,am i right?

 all1by says:  Sep 1, 2010. 4:59 PM  REPLYYep. Just a warning, the boards they rent might not turn well (if the stock exkate we used was any indication).

 paperclip32 says:  Sep 3, 2010. 2:30 AM  REPLYI tried it out today,you were right about it not turning well. It was pretty cool,but the longboard I rented was topped at 5mph since it was abeachside park with tons of people.

 ArNe_ says:  Sep 8, 2010. 1:20 PM  REPLY(No REPLY button??)

No sensorless.Making your own sensored speed controller won't be eazy and will take mutch more time. + a more expensive motor :)I don't think it need to be sensored with that power (can be wrong,, ...will see... ) :)

I measure the current of the motor to adjust the controll signal,, its not really the same as sensored control but better than nothing :)

You need more speed but I need more torque :)

For more speed you need better motors. If you use more motors you will have more torque but still the same speed. (II think you already know that) :)

No problem :) I have the same controller as him to drive my revo (http://www.traxxas.com/products/promo/5605_promo.htm)Massive brushless power!!!! :D Top speed 65mph! :p

 all1by says:  Sep 9, 2010. 1:22 AM  REPLYI'm not sure why the reply button disappeared.

I'm running sensored brushless on mine (not the board in this instructable). Like you said, it takes more time and more expensive motors. The reasonsfor using sensored control are: a. the motors are current (and therefore torque) controlled, allowing for precise acceleration control. b. no coggingbecause the sensors know what state the motor is in. With sensorless, you might find that you have to kick start the board. As for measuring motorcurrent, I don't see how that could help you control the board if you're using sensorless control. Sensorless control is always voltage control, whichmeans control via RPM and not torque. Another way of putting it is that if you slam on the throttle with a voltage controlled system, it will apply infinite(well, as much as the batteries or motor controller can handle) current until that throttle command (RPM) is reached. There is no direct control of current,so you don't have any direct control over acceleration (indirectly, you do control acceleration by slowly applying throttle so you don't burn out). Sensor vs.sensorless brushless control is a subject I strongly suggest reading up on if it interests you.

I feel "better" is the wrong word, especially because I custom engineered (design and fabrication) them. For more speed, I'd need a motor with one ormore of the following: less turns, shorter, weaker magnets, larger diameter tires. However, I felt around 25mph was plenty, so I designed for that.

It is true that if I use more motors, and don't divide the current among the motors, then I will have more torque.

Nice. I used to have a brushless Revo, too. It was an old Gorillamaxx conversion with a Neo 8XL and BK-electronics controller: 1800W. It could hit about55mph. I sold it because I got sick of replacing twisted Ti driveshafts and shreaded hardened steel diff gears, haha.

 ArNe_ says:  Sep 9, 2010. 10:46 AM  REPLYI use pwm control so the motor has always the same voltage,, and the same torqueMuch better than voltage control.

Do you have pictures or videos of your other boards? :)I'm really interested :)

I have steed drive shafts on it now :)I don't have much time for it now...But I see it on the bright side,, no more broken parts :p

 all1by says:  Sep 9, 2010. 11:19 AM  REPLYYeah. There's a link to my blog in the instructable (and from there you can link to other blogs that are amazing sources of knowledge).

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

 ArNe_ says:  Sep 2, 2010. 12:53 PM  REPLYIf you take a total of 9S lipo battery's you have 33.3V and not 36V

 all1by says:  Sep 2, 2010. 6:01 PM  REPLYYou didn't read everything. At full charge, a lipo cell is at 4.2V. At full discharge, it's at about 3V per cell (depending on your LVD or motor controller).Therefore, at max charge, 9S is 4.2*9 = 37.8V. At full discharge, 9S is 3*9 = 27V. Please actually read up on batteries before commenting.

 ArNe_ says:  Sep 3, 2010. 9:03 AM  REPLYThe original batteries are 13,8V when totally charged. 13,8*3 = 41,4V. When using 10S lipo,, at max charge you have 4,2*10= 42V So you do have alittle more power and still 30V when full discharged. I use 6 5SLipo's,, 18,5V 5200mah so you have with 10S3P ~37V and 15,8A (for larger runtimes)Its only a suggestion. Its a nice instructable. Do you have a video of it when driving?

 all1by says:  Sep 3, 2010. 1:19 PM  REPLYWe didn't go with 10S because we were worried about over-volting the electronics module and frying it...but that's a good point about the leadacids. Still, we erred on the side of caution, and there is no noticeable speed loss, probably due to the CIM motors. That's a lot of battery. 6.6Ahis plenty for this boards purposes (getting around campus). The other board I'm building will have a 12S setup with either 10Ah or 15Ah. For vids,see the link in step 10.

 ArNe_ says:  Sep 4, 2010. 12:55 AM  REPLYI'm using 1 big 1KW motor. (35A) So I need the 15Ah :) nice vids You already now the top speed? :)

 all1by says:  Sep 4, 2010. 8:30 PM  REPLYDang, what's you're top speed and acceleration like? Our top speed is around 15mph. The other one I'm building will be using four 500Whub motors and it should have a top speed of just under 30.

 ArNe_ says:  Sep 8, 2010. 5:09 AM  REPLYIts not finished jet :)I'm building my own speed controller for it.And I also use a mountainboard wit air tiresTop speed will be (at least) 40 Km/h (25 mph)

If you go faster it becomes a little dangerous...But it's possible :p

I'll post a video when finished and tested :)

4 500W motors? I think you can reach the 40 mph with that :pSee this link: http://www.hobbycity.com/hobbycity/forum/forum_posts.asp?TID=12064

The board with 4 motors is so awesome!! :p

 all1by says:  Sep 8, 2010. 10:53 AM  REPLYAre you using sensored control?

For my board, I calculated the top speed to be just under 30mph. My wheels are 4" in diameter compared to the 8" for air tires, sofor a given power rating, my top speed will be lower (however, my acceleration can be quicker).

THAT IS AWESOME! Haha, wow. Thanks for sharing the link! He's using sensor-less control, so he gets cogging at start up. I likehis design though. Very simple and relatively easy to implement. My hub motor design takes a lot of machining and wouldn't beable to handle the kind of shock loads a mountainboard experiences.

 all1by says:  Sep 9, 2010. 1:25 AM  REPLYOh, and after reading more of the thread, it turns out he switched to sensored control (by just adding sensors to sensorlessmotors...very easy to do) and his performance improved greatly.

 Rimwulf says:  Sep 5, 2010. 8:37 PM  REPLYI bought one from Exkate when they were still small, and I found out how expensive they were. See I bought it from my local Spencers for about $39because it was their last one in stock and had it for years. So it got cheaper but the battery was existed from sitting so long unused. Then I made the mistakeof returning it it was only after I found how much it was worth. The only thing I didn't (don't) like about it (them) is that it uses a radio transmitter, I'd preferwired because there is no chance of someone being on the same frequency. But one question: Doesn't the belt and reduction wheel look a little to close tothe ground for turning?

 all1by says:  Sep 6, 2010. 6:38 PM  REPLYThe new ones use digital link up, which means it's physically impossible for someone to be on the same frequency...it's very reassuring to know theboard won't randomly fly out from under me.

Nope. They don't interfere with the ground when turning. The motor bracket will scrape sometimes because of the 1/2" ground clearance, but it protectsthe gear and belt.

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

 unbattlebots says:  Sep 3, 2010. 10:23 AM  REPLYlols they are frc cim motors, but hey you can buy them online anyway and with pre mounted planetary gaer reductions too

 all1by says:  Sep 3, 2010. 1:08 PM  REPLYYes, I know you can, I never denied that. But this one is the most compact design I've seen.

 unbattlebots says:  Sep 5, 2010. 7:51 PM  REPLYim sorry if i came off in that manner, i was meerly stating something

 rasta_mon_ya_know says:  Sep 3, 2010. 10:47 PM  REPLYthats rad mannn smoke a duby on dat sunbitch i like it alot

 huston says:  Sep 2, 2010. 6:07 PM  REPLYWith all the materials, what the cost of this project?

 all1by says:  Sep 2, 2010. 7:12 PM  REPLYSee step 9

 kyle brinkerhoff says:  Sep 1, 2010. 4:13 PM  REPLYdude you totally ganked them from an frc kit.....

 all1by says:  Sep 1, 2010. 5:01 PM  REPLYWhich one?

 kyle brinkerhoff says:  Sep 2, 2010. 4:51 PM  REPLYprobably the 2010,2009,or 2008 KOP

 all1by says:  Sep 2, 2010. 6:10 PM  REPLYI've never seen it before. Can you send me links to pics? Regardless, no one has posted an instructable on a similar drive that I can find.

 menahunie says:  Sep 2, 2010. 2:47 PM  REPLYI can not wait for the high speed face plant you will do with this board. NO GROUND CLEARANCE. The minute you hit an unlevel surface the motor; pulley;battery will snag on the ground and "face plant"... The motor should have been mounted in the kicker area - more ground clearance. Battery made using18650 li-ion batteries; longer and thinner; more ground clearance. I have a plug on the rear for a speed controller; trigger type to squeeze on how fast I wantto go.. I machined a custom rear truck with a solid axle that DRIVES BOTH WHEELS..TOTAL WEIGHT ADDED TO THE BOARD ABOUT TEN POUNDS.

 all1by says:  Sep 2, 2010. 6:09 PM  REPLYNo high speed face plants yet. There's 1/2" of ground clearance, which is fine for cracks in sidewalks, minor inclines, and minor pavement holes/cracks.Bigger stuff is easily avoided. The only thing that contacts the ground is the motor bracket, everything else is protected. The motors were mounted ashigh as possible without interfering with the deck during turns. We could have mounted them above the deck (the "kicker area"), but then it wouldn't havebeen very sleek looking. So you used 18650 li-ions? Cool. Our batteries are not the ground clearance limiters in our case, so we went with the moreenergy dense (aka, lighter) Lipos. If you're using a solid axle, do you experience turning issues (such as slip, poor turning radius, etc)? It's cool youmachined your own truck. You should post an instructable about your design.

 gripracer says:  Sep 2, 2010. 10:36 AM  REPLYWhy not use a limited slip differential? Was a second motor cheaper to implement?

 all1by says:  Sep 2, 2010. 12:16 PM  REPLYBecause any sort of differential/axle/driveshaft addition or modification would have required a complete rebuild of the rear truck assembly, which wouldhave meant basically designing our own trucks and machining them. We only had 3 weeks (5 days a week and 4 hours a day) to design and build (andmess up and re-design) everything, so we went with two motors. These motors are only $28 each, so dual motors probably IS cheaper to implement, butI'm not sure. I haven't checked prices on small diffs, nor looked at how much it would cost to build one for ourselves. It would be very cool if someonecould incorporate a limited slip differential into their electric longboard.

http://www.instructables.com/id/Electric-Longboard-Build-Clever-CIM-Motor-Drivet/

 geegn1 says:  Sep 2, 2010. 9:27 AM  REPLYthis is the coolest f***ing thing i have ever seen. god bless MIT

 1up says:  Aug 30, 2010. 11:00 AM  REPLYI have been working on an electric mountain board for a while and have been trying to figure out an efficient way to mount the motor. This is a good idea,thank you!

 all1by says:  Aug 31, 2010. 6:23 AM  REPLYYou're welcome! I'd love to see pics of the mountain board when its done.

 1up says:  Aug 31, 2010. 10:24 PM  REPLYNot a problem! In fact, I will most likely be making an Instructable of it.

 killerjackalope says:  Aug 29, 2010. 4:29 PM  REPLYExcellent Instructable, really great project, I've been wanting to pick up a cheap electric skateboard to work on as a pet project and this gives me a greatbase of ideas to start with. My one criticism would be that the project needs broken in to smaller steps for easier reading...

 all1by says:  Aug 29, 2010. 7:01 PM  REPLYYeah, I probably should have split step 5 up...

 robomaniac says:  Aug 29, 2010. 6:56 PM  REPLYNice insutructables, I like the way you use the 1:4.5 gear reduction with the CIM motors. Really compact.

 TOCO says:  Aug 29, 2010. 12:17 PM  REPLYwhere did you get the strip of red leds?

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