Quote:
Originally Posted by Joe Johnson
If possible, help us with as much data as you can give us- approximate weight of the robot
- the type of wheels you have (size and surface type)
- the ratio from 56mm shaft to the wheels,
- the number of CIMs (1 or 2),
- the ratio of the Banebots Transmission (12:1 or 16:1)
- tell us if you are using support on the output shaft or if not, how far from the bearing plate is the sprocket
- if possilbe the angular backlash at your wheels before and after testing/driving.
- If the backlash increases signficantly from start to finish, give us a picture of the carrier plate
- if possible, give us pictures of your robot chassis so we can judge your traction etc.
- tell us what kind of driving you were doing (climbing stairs, crashing down brick walls, starting and stopping, pushing around old robots, etc).
I know that Banebots is committed to a addressing this issue regardless of whether it is a real or theoretical problem. Even so, I would like to know that the money they are spending is going for more than just public relations.
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Thanks again to everyone for recognizing this problem quickly and dealing with it. While I haven't counted the number of forward/backward transistions, I have posted earlier reporting one of our DD joints was bowtied after less than 30 minutes of testing. We have since driven around for another 90-120 minutes, some of it quite aggressively. The transmissions have not failed... yet... but the backlash is increasing. Here is some data that I hope will help:
1) Approximate weight: 75 pounds (plus 15 for battery)... bumpers, body and actuators yet to be added.
2) Wheels: Andy Mark Mecanum. Testing conducted mostly on carpet (similar to FRC carpet) and some on linoleum.
3) Ratio from tranny to wheel: 1:1 (wheel mounted directly to shaft)
4) #Cims: One CIM and one BB tranny per wheel
5) BB Tranny Ratio: 12:1
6) Outboard end of shaft IS supported. See
http://www.chiefdelphi.com/forums/sh...highlight=1346 for pictures and a link to an older video.
7) I measure the backlash one one transmission to be between 15 and 20 degrees and on the other three to be roughly 22-27 degrees. It may be that the one tranny with the low backlash was the one on which we destroyed the encoder (see below) and it was not "worked" as hard while the programmers had the drive base up on blocks adjusting their PID code.
I do not have "initial backlash" readings, other than to say they were "pretty tight when new". I am surprised (and pleased) that the trannies have held out as long as they have after my earlier posting reporting a bow tie... but the metal around the double D is definitely "mushing". Perhaps work hardening is ocurring in the deformed area. If I get a chance to take one apart and snap a picture, I will share it here (wish I had taken a picture when I had one apart last night)... but we are a bit behind in the rest of our build at the moment.
As for the destroyed encoder, one of our trannies had sufficient end play that the banebots encoder disc would rub against the optical sensors. While we were able to solve this problem by putting a thin spacer between the two tranny shaft bearings, the encoder on this wheel had already ceased to function. We have since had to add a spacer to another transmission as it developed end play and are monitoring the other transmissions. This is off-topic, perhaps, for this thread and may be a unique problem to mecanum drives using the banebots encoders, but it needs to be noted somewhere and perhaps dealt with in any revisions of the 56mm gearbox -- a gearbox which I quite like, despite the teething pains we're experiencing with it this year.
I hope this information is helpful in producing a solution. We need our transmissions to be reliable not just for drive testing, but for two regionals as well as a couple years of demonstrations and experimentation afterwards.
Jason