Drive Motor Drop-out

[sgeckler]

Also, does this only happen with wheels on the ground, or does it also happen with wheels off the ground?

Not sure but will check tonight. Thank you for replying.

[sgeckler]

Can you provide the mechanical information on your drive train?

You mentioned our current draw seems high, and it sure seems that way to me too. Perhaps, our drop isn’t enough but we ran this exact same drive style with Tough Boxes last year for >90 matches without zero drivetrain associated problems including this type of electrical bugaboo.

2018 Config:
VEX 2-CIM Ball Shifter transmission
3.66:1
8.33:1
6" Omni’s in the front
6" AM High grip in the middle and back
Versablock bearing supports on 2"x1" aluminum tubing

Thank you for chiming in!

[sgeckler]

GeeTwo’s initial question is key - I’m presuming the actual problem you’re chasing down is “left side of drivetrain occasionally stops turning”, not “logs look weird but robot drives just fine”.

As others have said too, I’d start with watching motor controller lights.

Other experiments to try:
–swap motor controllers from left to right (and vice versa). Does the problem move with the controllers?
–Check connectors. We’ve seen similar things with loose electrical connections from PDP->controller and controller->Motor. That being said, it’s very odd that the connections for both motors would simultaneously become loose.
–Talon SRX’s do retain settings over power cycle. Have you tried doing a factory reset on both and seeing if that resolves the issue?

A few others have mentioned brownout conditions, which don’t appear to be happening here (all motors should shut off simultaneously, and you should see flashing red on the battery voltage on the driver station, and it should be logged).

Does the driver station ever spew errors about CAN messages and the PDP/controllers? What is your current CAN bus load? Do changes in either of the above correlate to the issue you’re seeing?

Would you be willing to post your code as well? Although it seems unlikely, there may be some clues in the software implementation.

There is definitely an observable problem with the drive. The log I posted was taken by driving like heck in our shop and I told them to disable as soon as the “felt” it so we could look at the end of the log and know what we were dealing with. Although it occurred at the beginning of that test too.

We’ll check all the stuff you mentioned. We are a LabView team and would be more than willing to share the project if that made sense, but let us check all this stuff first, including what others have suggested.

Thank you very much for responding. -Sam

[JamesCH95]

You mentioned our current draw seems high, and it sure seems that way to me too. Perhaps, our drop isn’t enough but we ran this exact same drive style with Tough Boxes last year for >90 matches without zero drivetrain associated problems including this type of electrical bugaboo.

2018 Config:
VEX 2-CIM Ball Shifter transmission
3.66:1
8.33:1
6" Omni’s in the front
6" AM High grip in the middle and back
Versablock bearing supports on 2"x1" aluminum tubing

Thank you for chiming in!

That drivetrain is what I would call too fast. Your low gear is nearly 17ft/s free speed, and high gear is around 38ft/s. You’re likely seeing controllers pop breakers because of excess current draw. Unless you have omitted additional power train reduction…

[Ryan_Dognaux]

You mentioned our current draw seems high, and it sure seems that way to me too. Perhaps, our drop isn’t enough but we ran this exact same drive style with Tough Boxes last year for >90 matches without zero drivetrain associated problems including this type of electrical bugaboo.

2018 Config:
VEX 2-CIM Ball Shifter transmission
3.66:1
8.33:1
6" Omni’s in the front
6" AM High grip in the middle and back
Versablock bearing supports on 2"x1" aluminum tubing

Thank you for chiming in!

Ah yep, that would be your issue. Assuming you don’t have any further reduction off your gearbox, you need a 3rd stage of reduction. VEX sells a 3rd stage for the 2 speed ball shifter gearbox.

Plugging into our handy dandy JVN spreadsheet, you get some pretty crazy ft/s and current draw numbers. I’d recommend purchasing the 3rd stage and integrating that into your drive train. The 54:30 ratio on the 3rd stage would be a good choice.

If you ran the Toughbox Mini’s last year with 6" wheels in their out of the box configuration, those gearboxes have a much higher output reduction at 12.75:1. You’d be at around 11 ft/s free speed which is very reasonable for a single speed drive train.

After going back and watching a few of your matches, you can see the slow acceleration of your robot. This is due to being geared way too high. If you add on a 3rd stage to the ball shifter, you’ll immediately see faster acceleration as well because your robot will be able to more easily accelerate to its intended speed.

[sgeckler]

Ah yep, that would be your issue.

Egads. Did we really do that? Sighh. I keep telling the kids to get better mentors, but they just won’t listen.

We actually ran a 8.45:1 last year. So tonight I’ll compare our Steamworks chassis at that ratio to our Power Up chassis in “low gear” which is basically the same. May expect little difference and better performance.

Thanks Ryan. Congratulations on a great showing at the District Championship! Another solid year by PhyXTgears!

I’ll be in Muncie soon, so maybe we can get together? Would love to see your shop.

Sam

[Ryan_Dognaux]

We actually ran a 8.45:1 last year. So tonight I’ll compare our Steamworks chassis at that ratio to our Power Up chassis in “low gear” which is basically the same. May expect little difference and better performance.

Thanks Ryan. Congratulations on a great showing at the District Championship! Another solid year by PhyXTgears!

I’ll be in Muncie soon, so maybe we can get together? Would love to see your shop.

Sam

Did last year’s robot weigh the same as your robot this year? If your 2018 bot was heavier that would definitely be a factor on why it didn’t work as well this year.

Thank you! Absolutely, feel free to let us know when you’re coming up and we can show you our build space.

[GeeTwo]

our Power Up chassis in “low gear”

This right here. Just changing to running in low gear at startup, and only shifting to high gear for cross-field sprints, and changing those now-likely-too-sensitive breakers may get you where you want to be – and leave more battery for longer practices or a climb at the end of a match. We’ve run 4 CIMs, 8.45:1 and 6" wheels the past two years with no problems, and excellent acceleration in 2017 (~75 lb **with **batteries and bumpers) and acceleration in 2018 (125-130 with batteries and bumpers) that was more limited by our high center of gravity than by the torque we could generate.