[Veselin Kolev]

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Both the times I have done direct drive to four wheels with 4 motors, I used a very similar setup.

I had a gear bolted to the wheel and the wheels rolled freely on bearings and shafts. The gearing was as follows: small gear on the CIM output mates with a larger gear, which is on the same shaft as a smaller gear. The smaller gear then mates with the larger gear that is bolted to the wheel. EX: CIM speed of 5342 x two 12:40 reductions = 480 rpm = about 12 feet per second on 6" wheels.

The reason for the two reductions being the same was so the first gear (on the CIM, 12 tooth) and the last gear (on the wheel, 40 tooth) could be on the same rotational axis. This proved for a very small drive train, and if you mess around with the shafts and gears, you can pull it off with very few parts, meaning less fabrication.

My reason for using a gear on the wheel itself is so it can act as the final reduction, instead of having extra bearings and shafts to have that reduction inside the transmission, only to run a shaft out to the wheel.

I really like the 4 wheel 4 motor independent direct drive system, it doesnt clutter your robot with drive shafts or chains, it makes everything modular. Also, fabrication is a blast, you're making 4 of the same part for the drive trains, and the gear reductions arent that complex or anything. No CNC required (unless you have interesting cheeseholes) and I would say this is a really reliable system, very low maintainance if done right.

The only way you can go wrong is if you use a face width that is too small for the gears. Then you start snapping teeth. I used .375 on all the gears, it worked quite fine. Also, it is a must to have your wheel on stable bearings and shafts, because if the gear on the wheel and the gear on the transmission misalign, the teeth get worn down or they snap. And the last rule of thumb, use loctite! When direct driving like this, there tends to be more vibrations through the drive train (it is usually dulled by the chain in chained transmissions). These vibrations make set screws and bolts back out and your drive train to misalign.. etc. Keep your drive trains screwed together!