pic: Planitary Transmission

[Madison]

Out of curiosity, where are you getting the combined spur/ring gear?

[Alex.Norton]

Originally Posted by Jeff Waegelin

I would be cautious about using the long screws in the CIM motors to mount a back plate. Once you take them out, it can be exceedingly hard to get the screws back in, due to all the magnets inside the motor. I've trashed a CIM before doing that, and I know a few other people have done similarly.

First off I haven't even said that this was the intended method of ataching the back plate but it is one that I have been thinking. I would be more cautious of doing this more because I might have a hard time finding just the right bolt.

I have taken a CIM apart on many occasions in the past to do many things to them (turning the shaft down to mate a pinion gear during the off season) and while the turning the shaft down destroyed the motor getting the bolts back in was extremely easy. It also happens that on our robot this year we had a big CIM that could only be taken out by taking the motor apart (it wasn't a bad design, it was my incompitent machining) and that big CIM still works like a dream.

Originally Posted by M. Krass

Out of curiosity, where are you getting the combined spur/ring gear?

I'm not. I would get a normal gear and a ring gear. I would bore out the normal gear so the ring fits inside and drill holes for pins to transfer the torque. The pieces that hold the ring/spur gear are also pins that could transfer the torque. I would have to try this before actually using it during the season cause it seems a little fishy in terms of actually working.

On a similar note if anybody knows where to get a 20DP, 40 tooth ring gear that would help imensly cause mcmaster doesn't seem to have ring gears and stock drive products doesn't have 20DP gears.

Thanks

[chris31]

Originally Posted by Alex.Norton

On a similar note if anybody knows where to get a 20DP, 40 tooth ring gear that would help imensly cause mcmaster doesn't seem to have ring gears and stock drive products doesn't have 20DP gears.

Boston Gear doesn't have them. I am not to sure were else to have you check.

[Paul Copioli]

Alex,

Here are some words of wisdom from someone who has lived through the variable planetary gear train design and implementation cycle.

1. You do not get ANY added output torque from the ring gear motor ... zero, nada, nothing. The ring gear has to react against the input torque of the sun gear and adds nothing to the output torque.

2. The ring gear motor only changes the speed ratio. Designing it to not need motor torque at 0 RPM is a good idea, but the Denso motor worm gear may not be able to handle the load.

3. When sizing the gears, make sure when the ring gear is spinning in the opposite direction of the sun gear that the robot still moves forward. If you do not do this then any amount of force can stop you. However, you can pretty much stop any amount of force pushing you.

4. When designing your gear ratio's, there are three basic areas that the CCT gives you: Ring gear in reverse, ring gear at 0, and ring gear forward. Design your normal operating conditions at ring gear at 0 speed.

5. Read the paper that I attached here: http://www.chiefdelphi.com/media/papers/1361


-Paul

[Alan Anderson]

Originally Posted by Paul Copioli

1. You do not get ANY added output torque from the ring gear motor ... zero, nada, nothing. The ring gear has to react against the input torque of the sun gear and adds nothing to the output torque.
...
4. When designing your gear ratio's, there are three basic areas that the CCT gives you: Ring gear in reverse, ring gear at 0, and ring gear forward. Design your normal operating conditions at ring gear at 0 speed.

It looks like Alex has designed his system "inside out" from the way you expect. If I'm reading the drawing correctly, the dual CIMs drive the ring gear, and the "variable" part is due to rotating the sun gear.

[Paul Copioli]

Either way, the motor sets do not both add to the output torque. The sun motor chain reacts against the ring gear motor chain, or visa versa.

[Gabe]

Originally Posted by Alex.Norton

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Please correct me if I am wrong, but I do not believe this design will work because of the fact that the window motor does not actually spin the central shaft, but rather the worm gear spins centered around the stationary shaft. However, adding a much larger adapter for the spline on the motor will separate the motors, changing the distances between the gears.

And if you are looking for a source of gears, check out what SDP-SI has to offer.