pic: Modified super shifter gear box


We modified the Supershifter by using Andymark beveled gears. We have gears going directly to the wheels and sprockets for #35 chain so we can add front and rear wheels. We left a space in the top center for an additional motor. With 4 inch wheels the speed is a little higher than the original with six inch wheel direct drive. We will be turning the shifter cylinder 90 degrees to help save space.

Do you by chance have any CAD models of this that you wouldn’t mind sharing? I’m very curious to see how you assembled the internals of it. This is probably one of the narrowest inline gearboxes I’ve ever seen.

I too would like to see something (even a photo) that shows how the bevel gears are set up. Did you use the AM-2621 bevel gear on the motor? If so, how did you adapt the .375 bore to the 8mm motor shaft?

I replaced the original first stage gear with the beveled gear. They both have a hex shaft. I did have to lathe the last stage gear to give clearance for the wheels. I do not have CAD drawings yet. Still waiting on the students. The beveled gears are easy to find on the Andy mark web site.

It would be really cool to see this as a drop module.

This is super cool. I’d love to see more pictures of the bevel gears interface.


Great work! Just wondering, what was the motivation for using bevel gears? Was it to save space for electronics inside the robot, or was there some other reason?

A bevel gear set creates a thrust load on each of the shafts – motor and driven gear. This load is opposed by bearings of some type, causing a component of friction that is not present with the original spur gears.

This extra friction increases current draw and therefore reduces power available at the wheels when current is limited, as it will be by circuit breakers and by motor heating. Current draw with no wheel loading (fully assembled drive train with wheels-up; i.e., chassis on jack stands) is a good indicator of how much friction has been added.

A CIM with nothing attached to its shaft will draw about 2.5 Ampere from a 12V source while spinning “freely” at about 5300 rev/min. A CIM back-driving a second CIM (with its terminals disconnected) will therefore draw about 5 Ampere. A well designed, correctly assembled, and properly lubricated 2-CIM single reduction gearbox adds about 2 Ampere to this “free” current draw. Extra stages add a bit more, but the adder is less because the extra stages are not moving as fast. So, as an initial health check, I like to see free current less than 8 Ampere when testing a new spur-gear drive train.

Do you have free current measurements for this set up?

Thanks for sharing. We recently tested one side of a new drive train and measured about 7.5 amps. At the time I wasn’t sure if this was reasonable. Your 8 amp rule of thumb makes sense!

What kind of drive train? Any bevels or worms in it, or just spurs and sprockets/pulleys?

edit: is it this one?

Yes, that was the drive train I measured the current on. I expect the current draw to go down once it has been driven a while and things loosen up. The chains are pretty tight because we added 0.018 to the center distance.