I have never observed this in our brain. As I understand the voltage controls on V5, Each motor is allowed to draw up to 2.5 amps with 8 motors maxing out the capabilities of 20A discharge rate of the brain. If more motors draw current, the current will be limited among all motors. I don’t believe the battery over or undervolts. Not sure what happened on the DOOM problem. Was vex tech support able to help with this? That sounds like a bad firmware interaction with the game code which should never happen.
The way to prevent ESD damage from happening is very simple. Three passive components are required to prevent static damage to the RS-485 to UART transceiver chips. The transceiver chips probably cost them about 2 dollars per chip at the quanitity they order them. The three passive components needed are two resistor and a TVS Diode. All these components are pretty cheap and will cost about 60 cents per port or $13 per V5. Also the how to guide for preventing static damage to the chips is like the first result on google. Linked here: http://www.ti.com/lit/ug/tiduai4/tiduai4.pdf
so your telling me they could sell the V5 for $50 more with those chips and no one would have to complain about blowing ports ever again?
knowing how much vex likes to mark things up, that’ll probably be an extra 100 dollars for v5.
I don’t know if I’m willing to pay 100 bucks for esd protection
That’s an excellent write up @V5Wizard!
I think VEX could get those components much cheaper:
Last year I found a deal on EBay and bought 50 SMBJ43CA TVS diodes for about $6 including shipping, which is ~ $0.25 to protect one V5 port.
100 bucks is a cheap price to pay for not having to buy a new V5
Especially since VEX slaps their logo on it and says that you now have to pay $275 to get a new one
Good point. I was just using max quantity cost on mouser to estimate as a rough estimate. They would probably go straight to the manufacturer to get the parts. The point I was making is that its a cheap and very simple solution to a known problem and just looks very bad and sloppy to have overlooked. I think that point still stands if its 0.60 or 0.25 per port.
Thanks all for the ideas on the anti static. Our club will probably look at a way to make a TVS in-cable adapter. It would be legal in VexU and at the very least could be useful for others up to competition. Vex really should just sell the brain with this added or at the very least, sell a power distribution board with this implemented.
It won’t be legal in VEXU because custom electronics aren’t allowed to interface to the between motors and V5. I also don’t think you could make an effective in cable adapter since the chips are smd and should be placed on the board as close as possible to the transceiver chips. It wouldn’t have been hard to include it in the design from the start but would probably be pretty hard to add it in now.
What about grounding the metal heatsink on the motor to the frame of the bot? You could also attach a conductive wire from the frame and let it drag the floor.
The motors do not have a metal heatsink.
As @sazrocks mentioned, these motors do not have a metal heatsink. The heatsink looking shape on the motor sides are for rigidity of the plastic and not for cooling. Without them , the motor pcb could be damaged. Our club discussed an idea of wiring a ground wire from the circuit board the the metal screw insert in the motors and brain, which would in theory achieve the same effect of limiting the overall static potential of the robot. I still feel the best fix would be for vex to update the power distribution board on the brain with anti-statics components.
this is definitely worth looking into, since I belive my organization has a brain with 20 dead ports that is out of warranty, as well as several (6?) more unusable brains.
we currently have 3 unusable brains. they kept whitewashing and had at least 12 ports burnt on each
Sorry. Incorrect. One is plastic and decorative. The other is metal and directly contacts the motor housing.
I will look into this. I have a motor opened at our club. I thought both sides of the motor were just plastic.
This is a picture from the teardown by @sazrocks. I will look into it this evening as we have a couple of broken motors.
Looking at the pinout, the Analog LTC2862A seems to be compatible, since it is also a TIA-485 chip. It is claimed to have pretty good ESD protection built in, so it might be worth looking at for repairing brains (for classroom use, of course)
Only thing is, there are several models of that chip and I can’t figure out which one would be right for this use case.
You can hear the difference. Pull your fingernail, or any hard object, backwards across the fins. Significant difference in sound.