pic: Partial PTO Gearbox


There have been numerous PTO gearboxes on CD lately and I was bored today and decided to make one.

Unlike a typical PTO gearbox, this switches only one of the drive motors (or two by moving the center CIM) to allow the robot to continue driving while using the PTO mechanism. This feature would be useful for something like loading a shooter in 2014, where the robot would still need to be able to drive while the PTO is in use. Shifting uses the VexPro Ball Shifter shaft with two 34 tooth gears. The free speed of the drive base portion is around 10 fps. It could be lightened somewhat if I were to pocket the plates more.

Interesting, could be handy for a lot of things.
I don’t quite understand how the PTO shifting works. While in PTO mode, are all three motors engaged in DT and PTO? Do they have to move together or can you configure it so that they are separate?
What is the weight?

You may want to make your tapped standoffs hex so you can get a wrench on them.

Link to the CAD?

In the current configuration, when in PTO mode, two motors are on the drive train and one is on the PTO, but it could be inverted easily. Since the PTO motor is not connected to the drive train when the PTO is engaged, it can be driven separately. When in the full drive train mode, all three motors are on the drive train.

The weight is slightly over 12 lbs with materials set correctly according to Inventor.

Here’s a link to the CAD: https://workbench.grabcad.com/workbench/projects/gchgW5c_EuGOlCDKb7YQJXzExNwh7C05kVFdDPoVBvtR4O#/space/gcJoETXlTi3EXXADsbk0_mrvlWHZPVRfGLc2OPK4aS5nCL I haven’t used GrabCAD partner spaces before, so let me know if it doesn’t work.

A neat idea, but the number of possible failure modes coordinating the shift is troublesome. To minimize both mechanical and electrical transients, I would probably want to put the PTO motor(s) in coast and dead band during the shift, and re-enable the PTO motor controllers after the shift is complete.

I’ve thought of alternate uses of this mechanism:

  • If you used two of these and linked the PTOs together, you could make a drive system that shifted from 2 3-CIM shafts to 3 2-CIM shafts, which might be useful for some articulated drive styles, such as a Nonadrive or a (just thought of this) “TanKiwi”.
  • The concept (though probably not this implementation) could also be used to couple and decouple the forward and rear wheels for an octanum or decanum implementation.

Wow, that’s super handy then. You could use it for shooters or lifting things while still driving, which seems extraordinarily useful.