Are there any known problems with respect to the standard andymark chassis gearboxes specifically regarding the gears binding in such a way that the wheels have problems turning with ease. We have greased the gears and disassembled and reassembled it multiple times in order to check each gear. We have also replaced both motors one at a time with new motors but the problem hasn’t been solved.
Did you try running one motor at a time with the other disconnected?
The motors might be fighting each other and canceling each other out.
Also be sure not to over tighten the gearbox mounting screws…
Make sure you get the gears in the proper way. There’s a raised lip on each gear that should face outwards so it interacts with the inner race of the bearing. I’ve seen problems when one or more gears are put in backwards.
Also check that the gears aren’t in upside down. No, not a joke. The gears have small bosses (bumps) around the central hole designed to keep the gears from rubbing against the edges of the bearings. These bosses should point towards the adjacent bearing (away from each other on the cluster shaft). [sniped on this one]
AndyMark also recommends running the gearbox with no grease and no load for a while in order to work down any imperfections on the gears. If you did not do this and other things don’t fix it, you may want to de-grease the gears, do break in, then apply new grease.
Apart from these, the only issue like this we had was when there was some flashing left in the well for the drive bearing shaft on the plastic housing that caused the bearing to ride high, which pushed the shaft up, which caused it to rub against the motor plate. Once identified, we fixed it in seconds with a small knife. Check around for any excess flashing or pieces which do not fully go into place.
Edit: Oh, yes, one more! We have had motors for which the front plate and shaft weren’t perfectly square with each other. Sometimes the binding goes away by removing the motor mount screws, rotating the motor 180 degrees around the axis, and re-mounting.
During our Rookie KoP workshop, we had multiple problems with transmissions binding up in one direction. In some, I was able to correct by rotating the CIM 180 degrees and reinstalling. Had one that no matter what I did made a difference. It was at the end of the workshop, so I was unable to swap parts from one to the other. I advised to contact AndyMark for further assistance.
I second the advice to double check the gear orientation - we’ve experienced that several times when they are put in upside down. The raised part should be on the bearing. Also check the bearings. I’ve seen students put them in with the flange on the wrong side. It causes it to slip and the gears bind. When my team doesn’t mess up those two things, the toughbox mini has been very dependable.
I’ll fourth the suggestion on gears faces. No matter how many times I remind my students of this they end up doing one gear wrong each season.
After that make sure bearings are completely seated in the gearbox, check for the E-clip on the output shaft (seen that not fully seated once), make sure the flanges are right on the frame bearings, and lastly make sure the washers on the CIM motors weren’t forgotten (this throws off the gear height and can lead to issues with the retaining clip).
Can you spin the gearbox freely in both directions using a 1/2" wrench on the output shaft? If not the issue is mechanical in your gearbox, if it seems good check that your motors are not being powered opposite directions.
Hope this helps!
I agree with Donut - Besides the gear orientation, be sure that all the washers and bearings are seated properly (in all the way in). If not seated all the way, the gear sets may rub/bind/pinch due to excessive stack up height. The housing fasteners are strong enough to pinch gears if the items are not seated to be proper depth.
Turn with ease, is a relative term - I test each assembly after stacking gears inside but before installing onto frame or installing motors. Spinning the output shaft does take a little effort while applying the red grease. They won’t spin like a top without some resistance though. If they spin during this step, they should turn once installed onto the frame and after installing the motors.
Mike
I also second the gear orientation check (been there, done that).
I also recommend that when you get the AndyMark gearboxes that your always carefully check the bearings for damage. I have gotten multiple gear boxes from them with cracked bearings.
I will second all the comments above, and also add:
- Are you using 2 CIM motors in each gearbox? The Andymark chassis tends to be very underpowered if you only have 1 CIM in each gearbox.
- What size wheels are you using? Increasing wheel diameter reduces effective torque and can make it harder to turn. Andymark KOP gearboxes are optimized for 4in wheels.
- Is your center wheel lower than the the other two on each side? Using a “Drop-Center” configuration ensures the best possible turning on an AM chassis (the belts the kit comes with are also designed with this spacing in mind and will be over/under tensioned if you use a different set of holes). If you aren’t using a drop-center, you might consider replacing the outer wheels with “omni wheels” which will improve turning at the cost of some traction.
Hi there,
The AM14U3 chassis’ Toughbox Mini gearbox ratios were chosen for 6" wheels - they’re 10.71:1 for an approximate 10 ft/s drive chassis speed.
Here are some of troubleshooting steps I recommend for these issues:
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Ensure that the round bosses on the gears are facing the bearings. The flat sides of the two cluster gears should be up against each other, and the flat on the output gear should be against the E-Clip on the 1/2" Hex Output Shaft.
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Ensure the four #10-32 screws securing the ToughBox Mini housing to the AM14U3 Inside Plate are not over-tightened.
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Ensure the R6ZZ bearings are fully seated in the ToughBox Mini housing.
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Ensure that the CIM Motor mounting screws are not overtightened
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Check to make sure that the two bronze washers were installed between pinion gears and the Motor Housings.
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You can slightly adjust the gear spacing on the CIM motors to the first cluster gear. You may resolve the binding by slightly loosening the CIM motors, spinning the gearbox by hand and then re-tightening the motors.
Sincerely,
-Nick
The motors need to be clocked. Should be marks on them as an orientation guide
This is huge! Unfortunately there seems to be a fairly wide tolerance stackup in these gearboxes. Some are fabulous… smooth and quiet right out of the box, some are horrible… loud, very uneven with both tight and loose spots.
First check is to assemble dry (very important) and see how they spin. If reasonable, proceed to break in. If something seems off, disassemble and verify. Biggest mistake, as called out many times, in putting gears in upside down.
Next is to break in: Officially you assemble, install in drive base, load to full weight, and drive around, varying both speed and load. This is a large time suck. You can make this easier, and almost as effective (?) by raising the drive base off the ground securely (if you want to direct connect a battery to the motors, you want it secure) and run it at high speeds for 30+ minutes.
This will wear in the gear interfaces, and make a massive difference to both the smoothness and noise level of the transmission.
Disassemble, clean out metal dust, grease, reassemble.
For example, last year we built 4 kit transmissions. 3 were fine from the start. One was nasty. Multiple tight spots, binding, and loud. At the end of 30 minutes of break in I actually had a visible amount of metal dust under the robot. After disassembly, cleanup and greasing it was difficult to pick out the “bad” one.
If you try and do the break in after greasing you have two issues; firstly it takes way longer with the grease, and secondly you have all the debris that is worn away left in the grease, degrading its lubricating properties. With “bad” transmissions this is a non trivial amount of crud.
I seem to recall that the team I was mentoring last season over-tightened some of the bolts acting as dead axles making difficult for the wheels to turn. This was on an older kit chassis they were building up as a practice robot. I am not mentoring a team so I don’t know the current kit chassis has a similar vulnerability.