Hi, my teams are facing an issue with testing our V5 motors on our flywheel and we are loosing motors at an unstainable rate. In the last two days we have lost ~180$ worth of motors and 2 blown ports on different brains and if we continue to face this problem we are unlikely to make it to our first comp only a few weeks away.
Two of our four teams have just finished building their flywheels and were testing over the past two days and finding correct compression, RPM, and angle to run at. While testing suddenly one of the motors stopped responding on one teams flywheel, the team replaced the motor and made sure to ground their flywheel and started testing again. Again the motor died after a few minutes of testing, the team then wanted to test if the port on the brain would work and grabbed a motor from their base and drove it while holding the motor in their hand. Motor again died, a few hours later with the assumption that the brain or something else was the issue another team tested their flywheel and about 30 minutes into testing the motor died. Our program has decided to suspend flywheel testing until we figure out the issue but with our competition coming up soon we need a fix quickly.
All the motors that died no longer have a red light on them while given power, did not make a high pitched noise before shutting off, and were working fine seconds before dying. I would assume that other people have run into this issue but have not found any other threads about this specific problem. Any suggestions are helpful, Thanks.
sounds likely to be a static issue. If there is no electrical connection between the flywheel subsystem and whatever subsystem your brain is attached to, electrical charge can build up between the systems until the difference becomes so great that static will discharge through the cable between the motor and brain, which usually results in the brain port frying, but can also sometimes damage the motor.
The best way to address this is to provide the charge with an alternative route between the flywheel and the brain. This means there needs to be a direct conductive connection between the systems. There is no well-established way to do this, but there are a few potential solutions.
One is to make sure that there is metal-on-metal contact from the flywheel to the area around the brain. things like bearings, spacers, and other non-conductive components can cause breaks in the connection that don’t allow charge through. So you could work around these areas by using metal screws, nuts, washers, and other things to bridge this contact. Some people recommend using metal shaft collars on your motor shaft which rub against the metal c channel, but this is undesirable for friction reasons. If you put a metal washer loosely between them, it’s still not ideal but the washer will probably bridge the connection with enough frequency to prevent charge from building up too much. Keep in mind that while aluminum is highly conductive, the outer layer of aluminum oxide which covers c channels is very much not conductive, and you’ll likely have to do something like scratch away the oxide layer and then tighten a steel nut against the exposed region to ensure good electrical contact.
Another idea that’s been thrown around but as far as I’m aware, not tested, is to use some sort of conductive cable to connect the two regions. Using something like steel cable is legal under the rules that permit the use of rope/string (a q&a last year explicitly permitted steel cable, and though the q&a isn’t current to this season, the rule hasn’t changed and the logic assumingly still applies). By attaching a length of conductive cable between say the c channel the motor is on and the c channel the brain is on, you might be able to provide a path for static charges to flow without them going through your ports.
Things like anti-static tiles and anti-static spray, as well as higher humidity will also help, though these could be far less in your control.
We initially thought the static was the issue as well and made sure that we had one member ground the flywheel assembly to the rest of the robot after the first motor died. But we tested afterwards and had another die on us, plus we had one die while a member was holding it in his hand and I’m not sure that static would build up while the motor was being held.
no, it’s not likely for static to kill a motor not in use on a robot.
was there any common factor between all the instances of failure? the cable used? the brain used? brain port used?
The first three motors were all using the same brain & brain port but different wires. The fourth was on a different brain, brain port, wire, and flywheel design.
Also the motor was being used when it died in the member’s hand. He wanted to test if the port was dead and while testing the motor it died.
is the port used on the first three instances also dead? are the first three motors confirmed to be truly dead? (tested on other brains with other cables)
Sadly we tested the first three motors on other ports, cables, and brains to confirm it was truly dead. The port died after the 3rd instance on the first brain and on the second brain it died instantly.
well, the closest thing you have to a common factor between the instances is the first brain and port, present for 3 out of the 4 failures. It’s plausible then that the port or the brain was the cause of the issue for these failures, and the fourth failure was a completely unrelated coincidence. That’s about as much as I can help you I’m afraid.
are these new brains and/or motors?
What was the gearbox ratio of each motor?
Did you build a fly wheel with a single motor or two motors in tandem?
What % (or other unit) where the motors run at?
What was the gear ratio between the motor and the fly wheel?
I can easily believe if you had a single motor with 600 PRM gear box and 84:12 tooth gear ratio between motor shaft and flywheel shaft that the motor overloads and burns out something.
Did you burn out the motors and/or brain port due to overload?
The gearbox was 600 RPM with a 60:12 gear ratio on both flywheels.
Both were running with two motors and only one motor died at a time.
I believe both teams we running at ~100% full power when the motors died. Teams were using voltage but im not sure what voltage it was.
The motors were in pristine condition (No damage) but i’m unsure when we got them so they could be a few weeks old or a few years old.
Tbh if it is static that’s just really disappointing, a $45 motor should not be dying because of static electricity and we shouldn’t have to buy Anti-static wheels, spray, tiles, and be required to not wear socks within a five mile radius of these things because they could die on us.
In my most helpful tone… Go look up my thread on static electricity and READ it.
It’s entirely possible to have a significant static charge on the bot chassis which is then discharged through the handheld motor, frying the motor and/or brain port.
A spinning mechanism is an IDEAL device for generating static charge.
How exactly did you ground the flywheel motor? Pics preferred.
Strong, data-supported, recommendation is to have a metal shaft locker directly touching (not too tight) your chassis/ground on the motor shaft. This will ground charges before they come down the motor shaft, into the motor, and exit to the brain via the motor wire.
A lot of the thread is focused on static as the cause. It very well may be, but there are also other possibilities. What brake mode was the flywheel set to? Did it undergo any sudden stops? Many teams have found ratcheting flywheels a good idea for a variety of reasons.
The second flywheel (4th motor) was racheting, the first (1-3) was not but i believe that the motor was set to coast.
I have already talked to the head of Rolling Robots about the issues that we are facing and will be talking with a eletrical engineer who mentors our local FRC team about the possiblity of satic on wenesday. We are also going to test a multimeter on the circuit board to find out where the fault is. So any information about where faults are when satic is involved would be helpful, specifically components on the circuit board.
My thread includes some notes in the chips and their allowable Esd levels
It would be great if you could tell me what failed on you and what your findings were as I cannot find what resistors & chips failed in your thread.
I know from another thread that one of our mentors found, FB1 & FB2 were common places that failed. In your testing was this true? If so what was the ESD level that they failed at? Again any information would be helpful regarding this.
According to the datasheet published, the brain chips are good, if I recall, to around 14kv. We saw static produced in excess of 8kv in under 30 seconds of running.
All of that is interesting reading, but moot to some degree. If you are blowing motors/brains then it’s 98% due to static.
I would make sure the metal drive insert on the flywheel is touching the bare AL. It will add a minor amount of friction, but will help bleed off static from the flywheel itself.
Same advice applies for drive wheel motors are they contact the playing field.
And SPRAY the field w/ anti-static spray.
Going to quickly end this thread with a solution. As @levipope stated in the thread linked here vex engineers are looking into the problem and it is a common problem with motors ordered in 2022 that have a PCB marked rev 10. Out the 12-16 motors we bought over the summer we have now had 8 die. We will be sending the motors back to vex where they will be replaced and we have reached out to a local defunt middle school team that we have been buying motors off. Also thanks for the advice on static electricity we made some changes to our feild and robots to help negate static issues that we could have faced.