Voltage on Frame
 

When we shipped the robot, there was one small problem remaining that we could not fix. When we checked the frame for voltage there was about 3V going through it. Last year we had a similar problem, but there was 12V. It turned out to be a limit switch with pins touching the frame. :)

This year we were unable to find the source of this mysterious voltage. I pulled all fuses out. There was still voltage. Unplugged the RC and all limit switches. Still there. I wasted about and hour on this before putting the bot into the crate. I think we'll need to eliminate this problem to pass inspection (the frame is not supposed to be used for power distribution). Any ideas on what to look for when we get to our first regional? :D

Re: Voltage on Frame
 

well if you dont tell them they probably wont check it. but thats bad GP :D . so to get rid of frame voltage...
*check all MOTORS. all connectios where wires touch motors. unplug the motor and see if it is going thrugh the winding or watever. if it is, thats a BIG problem.
*electronics board. last yeah i build my own "ground stud". all of the electronics were on lexan, but we had a huge frame-grounding problem. it turns out that the screws that held the standofs that held the groundstud were touching a structal member.
*check wires. sometimes wire can get pinched and short with the frame. bad striping jobs, exsessive heat... etc
*sensor circutry. as well as custom circutry. make sure it FAR away from the frame. be libral with your electrical tape use!
*and finaly, the battery. one year our battery holder was made out of aluminum. must i go farther?

Re: Voltage on Frame
 

There is no place to get 3 volts from the robot RC or power system, unless you have something like the tether cable (RS-232 port) or maybe the link to the radio shorting to the chassis.

chances are you are getting a false reading - ifyou put a digital voltmeter on something that has very high resistance, you can pick up stray static and false readings on the meter. try putting something like a thousand ohm resistor across the voltmeter leads, and Ill bet your "3 volts" dissapears.

If by some chance it remains, then the only place I can think that it could come from is the radio cable from the RC. Does it run through the frame anywhere? is it possible it got pinched or sliced somewhere?

BTW - Im assuming you measured this with the black lead from the voltmeter on the negative (gnd) lead of the battery? another way to check for shorts to the frame is to unplug the batterys (both) and use the ohm meter part of the DVM - see if you have low resistance from the +12 or the gnd posts to the frame anywhere - it should be in the thousands or ten thousands of ohms -if you see <100 ohms to the frame from either one, then you have a shorted cable to the frame somewhere.

Re: Voltage on Frame
 

or so one would think. resistance can drop voltage. it doesnt have to be a direct short. if a oxidized piece of aluminum 1/64 of a inch wide pierces a 5v wire partialy, it could have 3v on it easly.

just a thought.

Re: Voltage on Frame
 

only if the short was delivering power (currrent) to some device - but that would require two shorts, one to source the power and one to consume it.

Re: Voltage on Frame
 

power --> short --> multimeter --> ground

Re: Voltage on Frame
 

the impedance of a Digital Voltmeter (DVM) is over a million ohms - so the 'short' would have to have millions of ohms of resistance - that is a possiblility -if someone spilled something on the breaker or ground, and it was salty or only slightly condutive, then you would see voltage on the frame with a DVM - but if the resistance is that high its not a problem

you can put your fingers on the probes of a DVM and it will register several thousand ohms - much less than the input resistance of the meter iteself when its on the volts scale.

Re: Voltage on Frame
 

Each year, we build most of the robot on the frame before taking stuff off to have the frame welded (it's initially bolted together). We didn't take off electronics last year and the electromagnetic field caused by the welding completely fried all the electronics... that little messup cost us about $1000. Moral of story - large EM fields are bad around the electronics.

Re: Voltage on Frame
 

Just use a wood base.... duhHH!!!

Re: Voltage on Frame
 

................. or you could just build your robot out of plywood, the way all the real teams do.............. :D

on a side note, does anyone remember the HDPE at the top of the ramp last year creating some serious static charge on the robots? has anyone had any problems like that this year? just wondering.

Re: Voltage on Frame
 

i could only see it being a problem if you made your wheels out of something like wool, and had a wire running from them into your control board...

Re: Voltage on Frame
 

never underestimate the creativity of tired people...

Re: Voltage on Frame
 

lol its a shame EMP isnt alowed...

Re: Voltage on Frame
 

I'm guessing you are in the middle of checking electrical continuity while you discovered this little problem. The problem with this that I see is that the robot contains a closed electrical syetem. Whereas the battery is the ground and the supply.

The only suggestion I can offer as to the extra 3V is that possibly your electrical sub system parts are not mounted on a non conductive part like wood or lexan.

Their is a ground built into the system, but of course like I stated before it is a closed sytem, so this is just a precautionary ground I believe.

Re: Voltage on Frame
 

In 2002 we spent a good part of one regional figuring out why our frame had a voltage on it.

It turns out the "rubber" that went around the bottom of the light conducted electricity and we had the light mounted on metal assuming the rubber was sufficient insulation. So we just mounted it on lexan and it solved that problem.

Not that this applies to this year, but I just thought it was interesting.

[Edit]By the way you should check the screws you use to mount your speed controllers. Those are often very close to the connectors for the speed controllers and if you have your victors mounted on metal (or some metal part of your robot is touching the screw) it could be a problem.