Attaching Wheels Never attach wheels directly onto the motor.  Use gears instead.  Attaching wheels directly onto the motor risks damaging it.  If the motor axle becomes slightly bent from being overloaded your robot will not e able to travel in a straight line.

Make it strong and avoid friction Use beams to lock down your motors firmly, otherwise they are likely to work themselves loose.  Take time to make your robots sturdy and strong.  Make sure all your bricks are stuck firmly together and all your gears run smoothly. Friction is your biggest enemy.  Minimize the number of gears. The more gears, the more friction. Make sure that every gear you use is needed. Keep axles as short as possible. The more beams an axle passes through, the more friction and the greater the power loss. Long axles can get bent, resulting in higher friction and power loss. Use bushings and short bushings to lock gears and axles in place. One on each side of a gear, where possible, will keep the gear from slipping along the axle. Bushings and short bushings can also be used to keep an entire axle from sliding in and out, if placed just next to (but not touching) the beams they pass through.

Gears

The Lego motor has high speed with very little torque (turning strength).  By using gears you can turn it into a motor that turns something very slowly but with great strength. You need to find a good compromise between speed and torque. Your robot needs to move with some speed, but it also needs to be able to transport itself and a heavy load of batteries and rcx.

Gears work together to transfer movement from one place to another.  You can use gears to make something spin faster or slower.  You measure gears by counting their teeth. The gear that is turning the other is called the driver and the other gear is called the follower. 

If you turn a small gear by using a large driver, you can make the small gear turn much faster.  This is called 'gearing up'.  Gearing up gives you high speed, but little strength.

If you turn a large gear by using a small driver, you make the large gear turn slower.  This is called 'gearing down'.  Gearing down gives you lower speed, but high strength.

Gear Trains

By mounting a series of gears you can get different effects

	In this gear train we have an 8 tooth, a 24 tooth and a 40 tooth gear. It will take 3 turns of the 8 tooth gear to turn the 24 tooth gear once. It will take 5 turns of the 8 tooth gear to turn the 40 tooth gear once. If the 8 tooth gear rotates clockwise, which way do the 24 tooth and 40 tooth gears rotate?
	In this gear train there are two 8 tooth gears and two 24 tooth gears. By putting 2 gears on the one shaft as in this picture, you can increase the gearing effect dramatically. If the right hand axle turns once, how many times will the centre axle turn? Then how many times will the left hand axle turn?
	Spur gears are used for gears in a straight line.  Crown and bevel gears are used for motion at right angles.

A Differential

A differential is very useful for a turning vehicle.  It allows one wheel to turn faster than the other which saves tyre wear.  It takes some of the speed from one wheel and transfers it to the other.  The Lego differential is limited in strength, so is likely to fall apart in a high torque situation.

Here is one way to build a differential (Design and photos by Odys Zawalski)

The Learning Federation has a number of very useful Learning Objects relating to gears.  A search using Scootle will find them.
 

This page has been produced by Margaret Meijers.  Questions or feedback may be directed by email to mmeijers at ictmindtools.net

 
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 License.
Attribution should include the statement: "This has been adapted from a resource originally created by Margaret Meijers at http://ictmindtools.net"