Thread created automatically to discuss a document in the White Papers.
Nothing But Dewalts by Joe P
Great! Thanks Joe and Joe. I’m disappointed to see that its a bit more work than I had thought, but after the additional testing that OCCRA gave it, I think we can be assured that its up to the job.
I thought Joe Johnson had said that he had interfaced the drill motors with it, too. Is this true?
Finally, what exactly does Lou Odin provide in this kit of his? The aluminum and plastic plates for the Chiaphua, neccesary bolts, and the modification of the sun gear? What kind of lead time can we expect during build?
Again, thanks for the great work.
MAx,
The kit id Drawing 1,2, 3, and 5. You have to send him the carrier gear to be modified.
Yes you can interface the drill motors however we didn’t do it in this paper because they may not be in this years kit.
Great paper - thanks so much for those details. Have any of you done any testing to determine the motor “curves” (torque/speed/current data) for the various motor/transmission assemblies at different reduction settings (1st, 2nd, 3rd gear)?
Is there any reason that the Globe and Fisher Price versions are shown without a shifter?
This is Very Cool. Thanks joe for the whitepaper. even though this maybe be time consuming, its definitely worth it. and its not even that much money only 65 dollard. Again, Thanks Joe. 
No reason
I did it on the Chiaphua and didn’t want to repeat it over again in the paper.
It is because the shifter is on the transmission side and therefore can be coupled with any of the motor transmission combinations relatively easily. Last year we drove with the motor transmission described without a single issue or repair of the motor transmission set.
There is one mistake in the paper that I want everyone to know about.
Page 17 - Step 3. for the Fisher Price - The distance from the top of the pinion gear to the front of the motor case should be 0.72 inches. not .072 inches. Had a bad day with decimal points.
STU,
We just got a prototype chassis running with the CIM Dewalts. We haven’t had time to think about this yet. Maybe someone on Team 47 has done some work on this, I don’t know?
Why did you decide to throw out the first stage of the DeWalt for the CIM interface? Did you find a problem with using an input pinion as in the other arrangements?
So these modules were attached to the robot only by the aluminum clamp? Did you ever have problems with slippage?
Thanks for sharing this paper. I had been looking to discard the yellow clamshell, but I’m impressed by your use of it.
I’m not sure what their reason to discard the first stage for the CIM was, but there is a very good reason I can think of. The gearbox is surely designed for a very high rpm, low torque motor (like the drills from our kit of parts) and the CIM probably has 2 or 3 times the torque of the motor it was designed for. A mas produced gearbox like this is most likely engineered down pretty close to the specs its needed for. It wouldn’t take 2 or 3 times the torque.
My notes say the advertised output torque for the 18V XRP drill is 500 inch-pounds = 56Nm. The stall torque of the CIM (at 107A) is 2.2Nm. So the CIM put through the 46:1 reduction of first gear represents a 101Nm output, or just about twice the number DeWalt puts on the box.
I know someone out there was building CIM-Bosch-DeWalt combos in the off season, and I’m under the impression that the DeWalts survived that fine. Does anyone know if they were using the full reduction?
Just a note, the CIM assembly involves dropping the first stage of the transmission, so the gear reductions on the CIM assembly are 3:1, 4:1, 12:1. The CIM puts out .79Nm at 40A (which was the amp limit last year) so after the 12:1 gear reduction, the whole assembly puts out about 9.5Nm (assuming I did math right of course!).
Great paper Joe, thanks for posting it. Hopefully more teams can have shifters with this method, since it is so much easier and cheaper than building one from scratch.
Edit: Jim, I believe that Andy Brockway and Team 716 were the people trying out the XRP transmission with the FP and Bosch motors linked.
Thanks Ryan. I was responding to Max’s suggestion that retaining all three reduction stages (not what Joe P recommends) might lead to a gearbox failure. Personally, I think that the XRP can probably handle twice its rated torque-- but thats just a gut feeling.
Although I am aware that the CIM outputs only .79Nm at 40A, it must be remembered that our 40A breakers can actually sustain upwards of 80A for short durations. Using the 40A number, even with all three stages we remain well under rated torque for the transmission. In my calculation I used the stall current to be conservative. I am curious what the real maximum momentary load from a CIM motor is, once you factor in our breakers and our non-ideal voltage source.
I too am confident the Dewalts can take 2X the published numbers.
As to the 40A fuse letting much more than 40A through for short periods, this is a certaintly. “Short periods” are essentially infinite time for the gear teeth in that once they are broken, they are broken. Beyond this, there is the problem of static vs. dynamic loading.
BUT… …I really question the need for a 47:1 ratio with the Chiaphua motor. 47:1 with 3 planetary stages will provide effectively 34:1 which would give you 70+ N-m With a 12mm (.5") radius sprocket you’d get 6000N (1400 lbs). That is a lot of force!
Beyond this, the sprocket woud be turning at a mere 2 Rev/Sec. Not very speedy.
This is a thing easily done. The planetary gearboxes should be pretty close to the “published” efficiencies of 85-90% for each planetary stage (with these low ratios per stage – higher ratios like 10:1 in one stage can be VERY inefficient).
This would mean that in 2nd & 3rd, the gearbox should be 70-80% effecient and in 1st, the gearbox should be 60-70% efficient.
Note well that effeciencies apply to TORQUE not speed. The speeds are simply divided by the ratio while the torques are multiplied by the (ratio X eff).
Given this data, it is a simple matter to go into DrJoesMotorCalc spreadsheet and get any speed-torque curve your heart desires.
Joe J.
Yes, I agree with Mike A. The shifter can be applied to any gearbox easily. The WHY is an open question, but I can think of reasons to apply the shifter to other gearboxes.
It is possilbe that future FIRST games will involve balls. One of the things about ball handling is that it is nice to have FAST rollers but with fast rollers that JAM come high current and (perhaps) toasted motors. One may decide to put a shifter on the ball roller transmission to allow for jams to be cleared in a low gear while normal operation involves the higher gears.
Also perhaps you want to drive with the Fisher Price AND a Chiaphua, you may just put 2 Dewalts on each side rather than going to the bother of designing a 2 motor input to one Dewalt. In this case, a shifter on both a F-P and a Chiaphua will be nice.*
Joe J.
*Note that FIRST will have to open up the rules on servos to make this legal because only 2 per robot were allowed in past years.
Joe J.
The Bosch drill motor is perhaps the easiest to motor to make work with the Dewalts: Buy a Dewalt motor, press off the pinion gear, press it on the the Bosch motor, Bore out the motor adapter for the Dewalt to hold the Bosch, Install the motor.
But… …FIRST had a fire sale on the Bosch motors so I suppose they are not in the kit.
The seat motor is very very easy to use too, but, I have a suspicion (not inside knowledge, but a suspicion) that Keyang is in the same (lousy) position the rest of the auto industry is in and therefore, I think perhaps they are not going to come up with $20K of motors for free for FIRST.
Given my suspicions and my lack of a “spare” to send Joe P for him to reverse engineer, the details of how to implement the Keyang modifications is left for an exercise for the reader. (Lou Oudin will make you the square hole sun if you want – FYI)
Joe J.
We don’t know what we are going to do with them but we are sure we will need them.
ASAP we’ll be kickoffing off
4 Chiaphua (CIM) transmissions,
3 Fisher-Price transmissions (the extra Mabuchi is the same form factor as the F-P, according to Paul Copioli, it may be the same performance too), and
2 Globe transmissions…
…9 more yellow power packs for CD10. NBD baby… NBD!
Joe J.