3-motor transmissions

[Nuttyman54]

Originally Posted by CalTran

Is there anywhere one can find some in depth information about how an FRC power take off would work? I know there are teams who have used them, IE 1114 in 2010, but I've never been able to find a paper or an explanation or a CAD of how they work.

If 254's 2010 robot had it, you can find good pictures here:
http://www.chiefdelphi.com/media/photos/35993
http://www.chiefdelphi.com/media/photos/35997

If their build log is public somewhere from 2010, that might have some good info on their designs, but they might not be accessible after they rearranged their website.

[MichaelBick]

Originally Posted by CalTran

Is there anywhere one can find some in depth information about how an FRC power take off would work? I know there are teams who have used them, IE 1114 in 2010, but I've never been able to find a paper or an explanation or a CAD of how they work.

254/968 and 973 also had them off the top of my mind. 973 has their CAD posted so check that out if you want to see more in depth of how it works. Basically, there is an extra shifting stage on a different axle. It it's simplest form, this stage can either be in neutral or driving the PTO. Both 254/968 and 973 also incorporated anti-backdriving and PTO lock into their PTOs too(kidn of hard to explain, best to look at the 973 CAD). Both 254/968 and 973 had shifting gearboxes, so they also had a 3 position actuator on the drive shift so that they could place the shifting dog in the middle of the two shifting gears so that their wheels wouldn't turn when they were lifting.

254 build blogs are back in place: http://team254.com/resources/. It's under FRC build.

[MichaelBick]

The three teams that I know of that used 3 motor gearboxes were 33 2012, 973 2011, and 254 2012(I'm sure there are a lot more, these are just the ones I know of off the top of my head).

1) I know 973 ran into problems with their 3rd motor because it was a 775(case short problem). I've heard that if they were to do it again they would use a 550 instead. Not quite sure if 254 or 33 ran into problems. I know 254 and 973 ran theirs off their WCD shifting gearbox. IIRC 33 ran theirs off an AM shifter. One of the things that I noticed was that 254 was able to gear higher this year because they used a 3rd motor. According to their website, they geared over 20 FPS with a full weight robot, something that would have been unable to do otherwise(very slow acceleration).

2)Never heard of burning out motors. I'm pretty sure 254 and 33 ran a 550. I know 973 used a 775 later and regretted it after due to the case short problem.

3) 254 ran their normal wheels. Not sure about 33. 973 ran wider (2" wheels), though they ran these same wheels once they took the extra motor off. I know it allowed them to push most people, even with only 4 motors(they pushed 469). I don't know if they used 2" wide wheels specifically because they were running 3 motors per gearbox.

That's a brief overview of what I know about 3 motor gearboxes. I've never actually made/run a 3 motor gearbox, so take this all with a grain of salt.

[Ravage457]

Does anyone have an Autocad drawing or pictures of this type of setup? Im curious to see it

[Gregor]

Originally Posted by Ravage457

Does anyone have an Autocad drawing or pictures of this type of setup? Im curious to see it

Check out team 254's website.

[ttldomination]

Originally Posted by Gregor

Check out team 254's website.

I think 254 rebuilt their website. Their image gallery has been unavailable for a while.

- Sunny G.

[Ravage457]

Originally Posted by ttldomination

I think 254 rebuilt their website. Their image gallery has been unavailable for a while.

- Sunny G.

Actually it back up, just saw it right now, thanks gregor

[MichaelBick]

254 has rebuilt their website, so their gallery is empty. However they do have renders of their 2012 gearbox posted. In addition you can look through Patrick Fairbank's 254 Build album.

[apalrd]

Originally Posted by MICHAELABICK

33

We designed our 2011 and 2012 gearboxes to accept more motors.

Our 2011 robot was CAD'd to accept a FP/550 through 2-stage Banebot planetary (driving the 28-tooth high gear on the intermediate cluster shaft via a larger spur gear), we later found (no surprise) we didn't have the weight. We later designed a lighter system with 775 motors (before the case short issue was well-known) into CIM-u-lators, where the extra motor would be directly across the gearbox from an existing CIM. We would have welded two CIM pinions together into a pinion/coupler for the two motors, but we didn't feel like we needed the extra power by CMP, we didn't have the weight before CMP. We had very little choice in gear ratios since we were running super shifters direct drive to 6" wheels, any gear changing would require us to machine gears, something we cannot do well.

Our 2012 robot was designed to hold a CIM-u-lator on an intermediate plate in the gearbox, we CAD'ed it with clearance for two 550's (making 8 drive motors in CAD). We assembled the gearboxes with a single 550 (plus the two CIMs), and removed the extra 550's due to weight concerns. We were able to re-gear the robot appropriately since we used a chain final drive, although we still didn't gear low enough.

We do not have definitive data showing anything about the third motor. The math says it should be good, we've been going purely on that.



As for a power take-off, your goal is essentially to have two or more clutches: One engages the motor to each load. A single dog from Andymark acts as two clutches - In one position one gear is engaged and the other is not, in the other the reverse happens (it exists in neutral with neither engaged for a short time during a shift, if you play with it you can get it there manually).

In the case of 254's 2010 robot, they had two dogs which could engage two separate outputs in three different ways each, plus a one-way ratchet. The lower dog engaged the drive into either motors via low gear, motors via high gear, or neutral. The upper dog engaged the arm into either the motors, neutral, or locked (a fixed plate with dog-face). Something like that would likely be the simplest way to design a PTO in FIRST. I would have to look at their design again to tell you anything else about it.