Mechanical drive mechanisms

By Robert Wall, Christopher Lockwood, Joe Gregson Lockie

Ball screws

What is a ball screw!!

Chain/ Belt drives

Chain/Belt drives

Chain driveA chain drive is a way of transmitting power from one place to another. There are three main functions which a chain belt can operate:1. Transmitting power2.Conveying materials3.Timing purposes

Advantages• chains don’t slip like belt drives • There is no power loss due to slippage, making them more

efficient• They can operate effectively at high temperaturesDisadvantages • Chains require frequent lubrication • Chains are very noisy and can cause vibration within the

machine• Chain drives cannot be used where the drive must slip

https://www.myodesie.com/index.php/wiki/index/returnEntry/id/3058

Belt driveA belt drive is a method of transferring rotary motion between two shafts. A belt drive includes one pulley on each shaft and one or more continuous belts over the two pulleys.Power transmission belts are available in several types: flat belts, V-belts, synchronous belts, and multi-ribbed belts.When considering belt driven machines you have to take in environmental conditions such as:• Exposure to oil and grease • range of operating temperatures• SunlightAdvantages • Wide range of speeds • No lubrication needed• Single belt drives will accept more misalignment than chain drives Disadvantages • Belts cannot be used where exact timing or speed is required

because slippage does occur• Belts are easily damaged by oil, grease, abrasives, some chemicals• Belts can be noisy; also loose or worn belts can be a major cause

of machinery vibration

http://www.roymech.co.uk/Useful_Tables/Drive/Belt_Drives.html

Reduction Gears in Robots

Understanding Gear Reduction

What is it and why does it work?What are they?– Gears of different sizes connected together.– Used for speed reduction in general whether its used

in traditional gear setups, chain and sprockets, or belts.

– Used in different areas of a robot.

Focus of this information will be mainly on the drive train(The most important part)

Understanding how and why they work

Gear reduction involves using gears/sprockets/pulleys of two or more different size that work together.

Different sizes of wheels have different circumferences, thus, the distance travelled for one full rotation would

be different.

Distance covered by wheel in 1 rotation = Circumference of the wheel

Examples

As you can see in the 2 pictures above, the general rule is shown:

The larger the diameter of the wheel, the larger the distance that’s covered in one full

rotation. Double the diameter of a wheel and you also double the distance covered.

Why they are used

Example:Most DC motors spin at well over 1000 rpm and some even spin at over 50,000 rpm.

If we had a robot motor that spun at 3000 rpm and attached a 6 inch wheel, that wheel would theoretically be able to move the robot at almost 54 Miles Per Hour!This is obviously far too fast!

Speed of a wheel can be found by:Diameter (inches) x RPM

336

This is where reduction gears come into play.We need to reduce the speed so we have more overall control of the robots movements by using 2 or more different sized wheels.

Advantages and Disadvantages

Advantages

• More manageable robot speed

• Less work for the motor• More torque (inversely proportional to the amount of reduction created. Example: 4:1 gear box moves the bot ¼ the speed but has 4x the torque – More pulling/pushing power)

Disadvantages

• Loss of speed (debatable)

• More weight for the gear box