Pulling too much voltage?

Recently my team has been running into an issue none of us have faced in our involvement with vex.

Background: We have a 4 motor single flywheel with a total gear ratio of 33.6:1. We have been running the setup for a long time and it has worked well in the past however this past week we have had a problem that lead us to replace our power expander, motor controllers, motors and even our cortex with no avail.

Problem: Whenever I try to run our flywheel at our full field velocity (around 80 power) the flywheel motors will function fine however after turning the flywheel off and then trying to ramp it back up again they die out quickly. I do not believe that we are tripping PTC’s on the motors or tripping breakers in the cortex due to the fact that the motor are not hot to the touch, also not twitching as they would normally do when burning out and that our chassis still runs fine being on the same breaker. It seems on this second ramp up the motors do not even try and I am thouroughly confused.

Any help would be greatly appreciated as it has been frustrating facing this issue for a week having a tournament on Saturday. Thanks!

If the motors don’t seem like they are even trying to ramp up again, is it perhaps your code?

33.6 is a pretty high ratio, and it seems most likely that it is the PTCs either in the motors or Cortex.

Why do you want to turn the flywheel off and back on again?

I don’t know about the ratio being too high…
We have 2 teams using 35-1 single Flywheels and they work fine and don’t trip ptcs until after the 3 min mark of non stop shooting (if even then)

We also assumed it was the code at first. We created a program that only sets motors to 127 or 0 and ran into the same problem.

Another reason I don’t believe it is the PTC’s is because it has literally ran fine for over a month and one of the other teams at our school is running the same ratio currently.

We do not normally turn them off and on constantly however it does happen a few times in a match and we were doing this to test for a problem.

What happens if you just wait a few minutes and then try?

That’s probably in San Diego, see you there !

You could try and see if it is a friction problem by using a small amount of vex legal grease/lubricant on your shafts and a small amount of Graphite in the bearings and gears

If we wait a few minutes and try it will ramp up fine again but then do the same thing if we turn it off.

That’s the one! Look forward to seeing you there!

This is one of the things that we have identified as being a possible problem and are going to take a closer look tomorrow.

So what’s probably happening is that PTC’s are hot after running the flywheel even though they are not hot enough to trip. Flywheel ramp up pulls a lot of current and is enough to trip them. Waiting a few minutes lets them cool down.

Think it is the PTC.
But of course it could be either the gear ratio and/or friction that caused the motors to draw more current.

And like what jpearman mentioned, it could be right at the borderline.
If the flywheel works again after resting, then it shouldn’t be a problem with the cortex or power expander, etc.

Btw, sorry for being picky (job hazard) - it is drawing too much current. The voltage remains the same for this case.

Pull the shafts a little bit out of the motors so they spin freely then give the flywheel a good fast spin by hand. It should coast freely for a good amount of time after that, if not there is too much friction in the system.

It seems to me this is most likely the problem via a square bar that has recently bent or something like that. I will take a look at it today and post an update here later. Thanks for all the suggestions!

I should have known this especially after taking AP Physics last year! I guess its been too long outside of that class.

Turns out the friction in our flywheel was the main offender. Thanks once again for all of the help because we are up and running for tomorrow!

Guess that means you will beat my teams now :slight_smile: