Lego Technic Measuring Gear Backlash

Lego Technic gear backlash, also known as gear slop, gear play or simply gear lash is explained and demonstrated. The idea for this video came from a previous lego Technic design that exhibited problem causing gear backlash.

The angle of lego technic gear backlash depends on the air gap and the number of teeth on the gear. It is measured for 16 tooth gears using a chain of thirty-one gears and measuring the cumulative angle and dividing by the number of gear meshes.

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[doncourter]

Glad I watched until the end. The last 1 minute was the most useful. I like how you showed that a simple design change can greatly affect the amount of backlash in the system.

[eliotlong]

I was making a mechanism out of Lego that would measure the indentation pattern of a flat surface like wood. It need utmost precision since the change was on a very small scale, and backlash became a significant problem. I simply added a weak rubber band on one of the gears, and this pulled the gear to the extent of its backlash, therefore preventing the backlash entirely.

[KlaasDeSmedt]

Interesting video. My 2 cents: backlash is caused by play (between gears and between the axle and the hole) but also based on deflection of the parts. That deflection is based on torque (forces on the gears) and when you line up 30 gears, the input torque will be higher than the output torque (which is zero).
Also, using cantilever shafts will cause the center of the gear to move quit a bit out of alignment, increasing the backlash.

Backlash is also measured from one direction to the other so double what you calculated :)

[SuperAWaC]

You might be able to preload the gear train as well, to eliminate backlash in one direction. To eliminate backlash in the other direction, you could have a duplicate gear train which is preloaded in the other direction. Since you don't need unlimited rotation, you're not as limited in your solutions.

[chrismofer]

Lego parts are suprisingly precise but backlash adds up quick. For long distances I'm fond of the Lego chain or axles and bevels.