Ball Shifter Ratchet Noises
 

All season we have been using the 60:24 3rd stage gear set (8.4 fps actual) on 2 CIM VEXpro ball shifters and decided to speed it up in the off season. We had no turning or stopping issues, it was just extremely slow. A few months ago we were planning to testing the 54:30 set but they were out of stock. We ended up ordering the 50:34 kit just to try out even though we knew it would be too fast for 2 CIMs. Low gear was fine, but in high gear we couldn't turn while moving forward or do a hard stop without hearing a loud ratcheting noise. We didn't have the time to find the cause before our off season events so we switched back to the 60:24 set. Tonight we swapped in the 30:54 gear set to give us 12.6 free speed. While not nearly as bad, the ratcheting was still occurring. We could at least turn while moving but we still couldn't do a hard stop and reverse. I found a way around this by shifting into low right before coming to a hard stop, then shifting back into high to accelerate in the opposite direction. We thought that the shifting plunger might not be engaging but I taped my phone to the robot and saw that it was fully in gear when making the noise. What exactly is this noise? Is this normal? Do 4 CIMs simply not have enough power to turn and stop at these ratios?

Robot specs:
134 pounds
AM14U with 2 CIM VEXpro ball shifters
4 inch HiGrip wheels

Here is a video of our testing

Re: Ball Shifter High Gear Issues
 

12.6fps free speed for high gear is nowhere near the max speed for a 4 cim setup. We ran 15fps on 4 cims easily last year, and bumped it up to 17fps later with no problems (at least not on the gearbox side).
Are your c-c distances correct on the gears? The situations you describe are high-torque situations, and the ratcheting sound might be gears slipping. Get out some calipers and measure the c-c distance. Also, try running it without load and see if the issue persists.

Re: Ball Shifter High Gear Issues
 

That's what I figured. It would really be nice to have a solid 14ish fps high option. I have not measured it but it is a COTS gearbox so unless something is seriously wrong I don't think it would be the c-c. With no load there is no noise. Thank you for the suggestions.

Re: Ball Shifter High Gear Issues
 

We had ratcheting noise on our 14U last season, found some pulleys were cracked. Doesn't explain all your symptoms though.

Re: Ball Shifter High Gear Issues
 

I can almost guarantee that you are experiencing a worn out shifting shaft/plunger.

When you were geared so low all season, I assume that you usually used high gear, which means that the shaft was consistently exposed to large compressing forces that deformed it. You probably didn't notice the damage because not a lot of input torque was required to drive around with such a slow gear ratio. After all, you had low gear for the heavy stuff.
When you switched to the taller ratio, there was an increase in load that made the ratcheting start. The part I am referring to is made out of aluminum, and vex may be changing it to steel for future years.

There is a possibility that i got this wrong though. You can confirm my theory by disassembling the gearbox, but that's a pain...

Re: Ball Shifter High Gear Issues
 

Thanks for the suggestion. We recently disassembled them since we suspected the issue to be wear on the plunger or gears but that was not the case. Also, I believe the majority of the force is put on the ball carrier, which is why it's steel.

Re: Ball Shifter High Gear Issues
 

I would suggest checking the distance that the shifter is pulled toward the cylinder to get to the correct part of the plunger. If it is on the edge if the hump in it it is prying the cylinder out of gear. We had this issue several times from the coupler coming loss through the season.

Re: Ball Shifter High Gear Issues
 

Are you saying that you found the problem but it was not where expected?

Or are you saying that you found no evidence of damage or wear on any of the parts? Did you inspect them with strong light and adequate magnification?

Re: Ball Shifter Ratchet Noises
 

Mike,

Every time I have had a customer contact me regarding this issue, it has been due to an incorrectly assembled piston coupler. Please check the nut location on the piston set screw and confirm it is flush with the end, also that the set screw is completely bottomed out in the piston rod.
Having this incorrectly set results in the shifting plunger not being in the correct location, which results in the balls not being on the round OD of the plunger, and rather the ramp edge, enough to "ratchet" as you're seeing.

Feel free to email me at prosupport.

-Aren

Re: Ball Shifter Ratchet Noises
 

We found no evidence of wear under strong light. We did not use magnification.

That makes sense, we will check that. Thank you.

Re: Ball Shifter Ratchet Noises
 

It was in fact the piston coupler. It looks like someone tightened it way too much and the piston end started to open up. I put a new one on and the robot stops and turns great now. Thank you for the help.

Re: Ball Shifter Ratchet Noises
 

Mike,

When the two halves do not mate flush together it is not because of overtightening, instead it is because the nut was not oriented correctly to seat in its pocket and the plastic was stopped from mating correctly. This means it does not properly grab the piston flats either.

From your video I would assume the nut was almost off the end of the screw, glad to hear you've got it working.

-Aren