I’m curious as to what path static could take in its way into the motor from a shaft that would allow it to reach sensitive electronics. The shaft is metal, and the gears inside the planetary gear cartridge are metal, but that’s about it. The motor’s casing is plastic, and the gear that drives the gear cartridge is plastic. Grounding the shaft to the chassis makes sense for it sown reasons, but as for the motor itself it seems pretty well isolated from the shaft already.
Static at these levels does not need an uninterrupted metal path to ground.
The metal shaft gets the charge inside the motor casing… from that point, as yourself, what’s the quickest path back to ground? Through the motor’s wiring into the brain, which is what teams are seeing… dead motor ports and dead brain ports.
We saw charge levels over 8000 volts after dragging a mobile goal last year < 30 seconds across the field.
And if the motor had a grounding spot (are you listening vex?) that would be great. The next best solution would be to prevent charge levels from building to critical levels.
For those that didn’t read the whole ‘static’ thread, and are blowing motors/brains, I’d read the whole thread. worth your time…
Thanks for the help! just to make sure, the solutions are:
- static spray
- make sure each component contacts another metal part of the robot
- make each shaft collar touch a metal part of the robot
- have a piece of copper wire discharge the static into the ground? ( I’ve read that one elsewhere)
Am I correct?
Not each collar, but one on the motor shafts.
You can drag a ground wire. The AL metal has an oxide layer that’s a very good insulator, so sand a clean spot and make your connection mechanically (with a bolt/nut holding the wire TIGHTLY to the frame).
UPDATE:
we changed one of the wheels on each side of the drivetrain to a 2.75 omni-wheel and changed the gear ratio. this made one of the wheels have a speed of 4.27 feet per second, and the other have a speed of 4.31 feet per second.
Would this 0.04 feet per second difference affect how much strain the drivetrain motors have to handle( and thus the likelihood of a motor to blow)?
This is unlikely to be much of an issue, but if it it is, you can run the wheel moving 4.31 ft/s at 99.07% speed.
Our wheels are geared directly together, so I can’t change one wheel’s speed without that affecting the other wheel.
If the wheels were independent of each other, your solution would work.
I am wondering if VEX changed something in the electronics part inside new motors. We started burning new motors at an alarming rate.
Have anti-static tiles, anti-static wheels, anti-static spray and basically anything with the words anti-static in it. Until recently and ever since V5, we were consistently burning brain ports. Now we consistently burn motors. What changed?
We burned intake motors, flywheel motors, drive motors. No pattern whatsoever.
We are a privately financed team with reimbursement from the school. The school started being very suspicious about our brain/motor spendings. It is hard to convince non-technical people that it is not our fault. Also it is now impossible to get any parts in time as brains and motors and other electronics are constantly out of stock or on hold or whatever. It is assumed students did something wrong as we had asked for an abnormal amount of motors recently. Picture a teenager driving a modded sports car down the road. Here comes a nice old lady in an old modest SUV looking at her phone and smashing heads on into the sports car. Guess who society pins for the guilty one instantly without even looking at any facts?
While I read @turbodog threads and certainly agree with grounding everything and walking around these robots on tippy-toes here’s where my brain goes into skepticism mode: steel shaft collars rubbing against aluminum structures is so very cringy as it produces that one thing that is the enemy of all robots - horrible friction.
I understand spinning a square steel shaft onto a delrin piece of plastic produces static but is the shaft really the mechanism of transmission? After all the shaft contacts the gearbox which is connected to a plastic pinion on a plastic shaft going to another plastic gear so not a straight and easy path into the circuit board.
Or is the charge actually going through the cable insulation and onto the copper wires then straight into one of the RS-485 transceiver chips (the TI VP1782) frying it - can be the port on the brain or the one on the smart device, motor in this case? We have complained in the past that the TI specsheet says these chips can withstand 16KV from a human body but beyond that need a double-diode TVS circuit. Well that would only work if the TVS circuit were connected to a common ground. But all VEX V5 electronics without any exception are completely encapsulated in isolating plastic and there is no way to ground them without breaking all rules.
Not an electrical engineer by any means and mad respect for @turbodog trying to help the community, just attempting to understand things and to make sense of all of it to help my teams.
Thank you for saying this!! I have noticed the same thing, and I was beginning to think I was the only person having this issue, and that it was my fault that we were blowing motors. I’m relieved to know I am not the only one blowing motors.
Also, how do I change the topic of this thread? It doesn’t feel very descriptive.
Couple of things
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paragraphs are ALL our friends
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steel shaft locker LIGHTLY rubbing/touching the aluminum will not produce significant friction and, currently, is a necessary step
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we are talking static electricity at THOUSANDS of volts, not 12vdc, not 120vac, but many thousands. This voltage will go right through cable insulation, motor cases, etc. However, it still follows the path of least resistance… which for static from a moving part, is straight down the motor shaft, through the gearbox, into the electronics, and down the motor wire toward earth.
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aluminum creates an oxide layer immediately when exposed to air. This layer is a pretty good insulator, which makes the path through the motor, wiring, brain to ground a preferred path.
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post a photo of the bot in question: overall pic and some good close-up pics of motor shafts, flywheel shafts, etc. Any other pics showing grounding between robot subcomponents would be good also.
This is the robot I am working with:
There should be some good close-ups in there.
Noted. Thanks. Fixed.
I’m talking specific pictures of shaft ends, clearly showing the structural metal, shaft, bearings, spacers, shaft lockers, etc.
I caught a glimpse of a shaft on the bot in the video. It looked like you could hang a metal washer on the shaft where it would randomly touch the frame and bleed off any charges.
In our case pictures would definitely prove your point as we always make every effort to have Teflon or nylon washers between shaft collars and aluminum. While I still disagree with shaft collars rubbing against aluminum frame (one time we did that by accident and the shaft collar literally ate a thick layer of aluminum), you mention using metal washers in your post, that would be an acceptable compromise.
Also question to you and the rest of the community: would a very tight cable management help mitigate this? As in zip tying the cables along a c-channel for example? Also keeping cables away from shafts?
If charge can jump between 1 motor/brain wire into a group of them, you might end up with multiple burnt motors/ports.
If you leave space enough for a sheet of paper/fingernail between shaft locker and AL: 1) friction won’t be a problem 2) natural shaft movement back/forth will let the metal get close enough to ground the shaft.
If you had a shaft locker ‘bore into’ your AL previously, sounds like there were some loads on the shaft which generated an axial load up/down the shaft.
We also have encountered a higher failure rate with new motors (8 so far) , with 2 specific new brains received this summer - all on basic drive trains, and plenty of metal on metal 
The motors in question went completely dead after a couple of minutes. One team went through 5 motors, on different ports (all functional), with brand new V5 wires in the matter of 2 days. We swapped brains and the team has been fine since. A second new team had the same thing occur a few weeks later.
If your issue is with new motors and/or brains, recommend you contact VEX Support -they have been responsive and working through the RMA process. I have not heard back on whether it was brain problems, or a potentially bad batch of motors. All the motors that have failed for us so far have been in the same batch per imprinted code.
EDIT (all other teams using same fields, etc with existing gear are not encountering these type of failures)
Happy cake day!!! It has been 4 years of help!!!
The latest we fried just last night during an open house event, we literally had a robot on the field, just put a new battery, turned it on and drove for about 4-5 seconds. Same symptom. Motor port light suddenly goes black and that’s that, dead. No load, no overheating, no walking on the field and touching things. A bit upsetting, we have to get rid of an entire team for this season because we literally ran out of motors. All new motors are dead and the ones we use now were canibalized from a few old robots we decided to keep. The only source of VEX motors is in “ships in 8 weeks” mode.
So last night’s casualty says this on its board:
276-4840-901
REV 10
22 19.
Do you think that ‘22 19.’ is the manufacturing date (Year 22 week 19 format)?
Could @jpearman or somebody else who works on the v5 products comment on whether or not anything was changed in the production of the motors?