3 CIM Ballshifter help

Technical Technical Discussion
#1

I don’t know how many teams use the VEXpro 3 Cim ballshifters but ours has been having issues we need resolved. While driving around our shop we unintentionally ran into a wall when we heard what sounded like the gears inside the transmission. He had this problem once before but solved the issue by increasing the pressure to the shifters but only had the issue while in high gear. Now the this grinding noise happens in low gear as well as high and seems to happen on both transmissions. Something to note is the robot will drive normally until we add to much load on the motors and does occasionally happen when shifting from low to high while moving. By best guess is ball shifter has either carved a path into the gear itself or worn away the balls on the shifter causing it to spin under too much load.

Any help would be great

#2

Have you opened it up to take a look yet? Sounds like stripped teeth and/or center distances messing up.

#3

We did take it apart when it first started doing it, and after and hour of carefully looking at it we saw nothing like that. The white lithium grease we used had darkened so we thought it could have been flexing and rubbing in the plastic so we added more support to the tops of the gear boxes.

#4

IMO, I prefer Red Tacky Grease as it seems to hold up longer and stick to the gears better. It is certainly possible that if enough grease has rubbed off the gears the gearbox will operate more loudly.

Other things to check:

  • Look for loose debris in the gearbox (especially screws or locknuts)
  • Check that the gears don’t rub against the sides or support structures of the gearbox case
  • Make sure all of the spacers inside the gearbox are correctly installed
  • Make sure the motors are mounted flush to the gearbox and are engaging the larger gear correctly (not at an angle)
  • Run each motor individually, see if the issue only happens with certain motors (it’s possible, though unlikely, that something broke internally on a motor)
#5

Make sure you’re giving the ball shifter proper pressure. It sounds like you’re giving even pressure to both sides of the cylinder so the only pressure difference is caused by the rod diameter. This causes it to shift with very little force and may allow it to pop out of gear if hit hard (like ramming into a wall) To root cause this put a pressure gauge in line with each side of your cylinder and shift. Make sure pressure reads 0 on one gauge and 60 on the other.

Also check that you have V2 shifter shafts. The easy way to tell is that the shifter shaft that attached to the cylinder is a grey shade (steel) and not black (anodized aluminum). The V1 shafts can get pitted and wear out.

#6

Okay next time we’re there that’s something we will try, we were running our pressure at 30psi so we didnt use too much air and we could keep our pressure up longer but if it should be ran at 60 then we can make that adjustment

#7

This is almost certainly your issue. They need to be run well above 30psi to hold position properly. It’s generally easy to just add tanks so that you don’t have to worry about running out of pressure.

Those were the exact symptoms we would see whenever the gearboxes were not staying in gear. Causes ranged from improper installation at the start to wireing on our compressor flaking out (leading to low pressure being applied).

The sound is a little different than true teeth grinding though. If piston engagement does turn out to be the issue, try to remember that sound so that you can recognize it :slight_smile:

#8

Yeah, bare minimum you should be using 40PSI; in fact, most FRC-legal solenoids won’t even actuate under 40PSI.

#9

Your shifter coupler is not correctly positioned (the plastic coupler between the cylinder and the shifting rod)

Be sure the 10-32 set screw is fully tightened into the cylinder, and the nut is flush with the end per the instructions.

The shifter plunger has an even diameter on it, that when properly set sits under the balls and no amount of load should kick it out. Raising the pressure will raise the torque at which the popping happens, but that’s fixing a symptom, not the issue itself.

-Aren

#10

Maybe the common FRC solenoids (i.e. the ones sold by AndyMark/Vex) won’t actuate below 40PSI, but there are plenty of FRC legal solenoids that do. In 2015 we used our solenoids at 15 PSI (their minimum) to lift the totes. We never had a problem with the solenoids not actuating. They were solenoids we had in storage so I don’t remember where we got them from, but they definitely exist and aren’t particularly expensive.

#11

We bought a solenoid (Single Action, Festo IIRC) off of Andymark, specifically for our gear mechanism. We used the gear mechanism at around 18 PSI. While this is just one example I feel like it’s a pretty common solenoid.

We also used a VexPro 2-cim ball shifter at the same pressure (18PSI) on our climber. No issues with grinding or changing gear unexpectedly. Granted it was always shifted into in low gear (piston extended).