Re: 3-motor transmissions
 

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.

Re: 3-motor transmissions
 

Funny, I'm wearing a Cheesy Poof sweatshirt right now...Would a PTO take more customization of a gearbox, as I imagine you would need to shift to a different axle instead rather than the axle the wheels are on?

Re: 3-motor transmissions
 

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.

Re: 3-motor transmissions
 

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.

Re: 3-motor transmissions
 

I was just looking at 973's 2010 robot on FRC-designs.com last night and they have a power take off system.

http://frc-designs.com/CAD2010.html#frc973

Re: 3-motor transmissions
 

I'll check the CAD tomorrow and open a new thread if need be to stop hijacking this one

Re: 3-motor transmissions
 

Not 100% sure but I believe they used a 3 position piston for the main drive shaft. They had 2 speeds and neutral. They shifted to neutral and activated the second piston to engage a gear on to the main drive shaft. All the power was routed to the second drive shaft via the engaged gear.

Boy was that cool to see.

Re: 3-motor transmissions
 

Even more fun to help design ;) But most of the credit on that lies with others.

Re: 3-motor transmissions
 

Anyone know what 3 position piston they used in these setups?

Re: 3-motor transmissions
 

Allen,

I'm unsure what the exact p/n 254 used. But similar to what we'd use:

FOP-040.25/0.25-L

Its a Flat Multiple Position Cylinder from Bimba.

http://www.bimba.com/Products-and-Ca...iple-Position/

You can order them here:

https://secure-102.portline.com/e-bimba/item.cfm

-RC

Re: 3-motor transmissions
 

188 had this capability in:

• 2002: Old Bosch Drill, Johnson F-P & Old CIM (single-speed)
• 2003: Bosch/Scintilla Drill, Mabuchi F-P & CIM (single-speed; never did get the radial-engagement shifter to stay engaged)
• 2004: Bosch/Scintilla Drill, Mabuchi F-P & CIM (two-speed pneumatic dog clutch)
• 2006: gearbox was designed to be adaptable for combinations of up to 5 motors (F-P with planetary, big CIM, 2 small CIM, and even a Globe if you really wanted to), but only built with 2 small CIM (three-speed servo-shifted DeWalt XRP¹; in retrospect, the shifter was pointless for that game, and the servo too slow to actuate the mechanism)

(I have to admit it's been a few years since I dealt with these robots, so where this differs from previous information, assume this list is inaccurate.)

¹ That was a crazy design that combined all these motors into a single XRP gearbox—which actually worked surprisingly well, apart from the manufacturing errors, and the tendency to break shafts. (The interface shaft between the XRP gearbox and the motor gearbox was too difficult to make on our lathes as a single piece of steel; it had a joint that wasn't initially robust enough. Also, the output shaft was AISI 12L14, replacing the hardened steel output shaft that comes with the DeWalt gearbox; we found out that after about an hour of running, they would fail in a ductile manner, in torsion. We should have picked a better material, preferably something easily hardenable like AISI O1.)

Re: 3-motor transmissions
 

Incidentally, I also built some bolt-on adapters that add F-Ps to a pair of SuperShifters, with only reversible modifications to retain COTS status. That's another way to do more motors quite cheaply and easily.

(Andy, you should sell those....)

Re: 3-motor transmissions
 

He does sell those, they are called AM planetaries.

Re: 3-motor transmissions
 

I think he means adding the FP as the third motor in the super shifter, not replacing a CIM.