Problems with Gearbox

[Jake M]

Has anyone else had problems with the gearboxes being tight and locking up. One of ours hits a load of tension at a certain point during each rotation. On high power, it runs slightly slower than the other side and on low power, it actually stops turning at that point, as if we were sending pulses to the motor, rather than a constant signal. We opened it up to find a small amount of gear dust inside. We've since packed it with lithium grease and it seems to run fine, but it does get quite warm, very quickly.

The other one has a very minute form of this problem. If you put it on low power, you can feel the tension point very slightly, but it doesn't pose any real problem.

Has anyone else encountered this and is there anything worth telling us?

[Joe Ross]

See the following post for some ideas: http://www.chiefdelphi.com/forums/sh...5&postcount=38

[Brian C]

OK

For what it's worth I ran our teams 2 BaneBot trannys with single CIM's mounted on the workbench last night in a no load condition.

Note: this was after machining (ok grinding ) the bushing down to make sure it doesn't bottom out against then planetary. It was ground down to make the pinion even with the end of the CIM shaft.

The units appear to be lubed up nicely from the factory. However with experience being my guide I did add some light grease to the pinion (read: Vaseline) when I re-assembled the unit.

Initially the CIM's drew over 6 amps measured with a DC clamp-on. After running them for approximately 1/2 hour the current dropped to a steady 3.5 amp draw. There was a noticeable change in sound from the units as well during this break-in period. Not so much in volume as in smoothness.

One of the units did seem to have some issues when you flexed the motor/tranny assembly slightly while running. Note that all screws were tight. Once the current draw had settled to the 3.5 amp area I noticed that the slight flexing now had no effect.

After running each CIM for 1/2 hour the outer casing of the motors were each measured at 105 deg F. I was happy with this temp as 1/2 hour is a long run time for these motors. With last years KOP trannys our CIM's never came in after a match any less than 160 deg F.

This is well within what we consider a "safe" area. When drill motors were the main drive motors a few years ago the temp was usually around the "hot enough to boil spit" (The Joe J unit of measure) or pretty much close to leaking out all the smoke range so I'll take under 200 deg F any day.

Conclusions?

I would trim the bushing down and carefully assemble your units, keeping everything clean.

Break-in the transmissions and let them run for a while. This is good practice anyway and lets all the parts get "comfortable" with each other.

When mounting them on your robot I would carefully tighten them down to make sure you don't add any undue stress/flex. Just as suggested in the BaneBots post.

Then drive the snot out of your robot base and see where any weak points may be.


This was our experience and as always your mileage may vary.

Good luck.

[KriegerEhre]

Hi there, yes our team has had somewhat of an experiance with the transmission slipping - it matchs up perfectly bolts together does'nt show any signs of play and then it just slips, grind noises ect. . .

[dtengineering]

Originally Posted by Brian C

OK

Conclusions?

I would trim the bushing down and carefully assemble your units, keeping everything clean.

Break-in the transmissions and let them run for a while. This is good practice anyway and lets all the parts get "comfortable" with each other.

Excellent advice, thank you! We were having the exact same problem, did exactly as posted and had the exact same results. I have e-mailed the advice on to a few teams we work closely with, but everyone should know... BREAK IN THE BANEBOTS.

We started out at 11+ amps and got down to under 3. They run smoother, more quietly, etc... and yes... they did get quite warm, but they seem to have been able to handle it.

If you don't break in your banebots before you mount them in the robot, expect to have serious tracking problems (unless you're running closed-loop feedback... the Banebots encoders seem to work great, by the way) and generally reduced performance.

Thanks again for sharing the info.

Jason

[Brian C]

No problem, glad it was of some help.

[cbpetrovic]

Yes, we have had problems. We followed the instructions posted by Banebots when assembling the CIMs, used a spacer to accomodate what we thought to be motor shafts that were too long. Encoders were installed and calibrated, the things ran well and pushed our proto bot nicely. However, after about 3 hours of running, one of them developed a lot of what was thought to be gear backlash, and so it was pulled apart.


The gears were fine, but what was damaged is the planet gear carrier that affixes to the output shaft. The output shaft has two milled flats that caused the planet carrier to become damaged, allowing almost 90 degrees of wheel rotation before engaging. This drive assembly also trashed an encoder. What happened to the encoder came about as a result of excessive axial end-play, moving the encoder wheel assembly into contact with one of the sensors, effectively grinding away the sensing element. The encoder wheel appears fine. When the encoder wheel was affixed to the shaft and glued thereon (following the packaged assembly instructions) there was no discernable end-play and the wheel was centered in the encoder sensor.

We were able to resurrect the drive plate and reassemble the transmission to find that the spacer that we needed between the motor and its mounting plate was not necessary. Apparently the assembly had about .040” end-play from the factory because of the output shaft not fitting snugly into the planet carrier.

Dr. Joe has a post in a separate thread that talks about this problem. We are investigating ways to improve the lifetime of the planet carrier, maybe it can be hardened. Is welding the shaft and carrier together the only solution?

C. B. Petrovic
Mentor, T166

[Joe Johnson]

I am closing this and several related threads. Please feel free to continue the discussion on the following thread:

Banebots 56mm Gearbox - Double D related

Joe J.