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Unread 03-07-2003, 22:32
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
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Quote:
Originally posted by Adam Y.
I have done this before besides a little bit of sparks nothing really was destroyed. The only time you risk destroying a battery from hooking it up to a motor is if you stall the motor.

OK, we have discussed this before but to prevent any further confusion...

When a motor is in stall, one or two windings are in contact with the brush assembly. Each winding has some resistance which limits the amount of current flowing. For the drill motor this year, stall current was rated at 129 amps. However, the SLA battery is capable of supplying in excess of 400 amps in short circuit! That is sufficient to weld wire, sending sparks (fire and skin burning hazard) bright arcing light (retinal burns) high temperature on the conductor (creating poisonous gasses) and the possible explosion of the battery. High temperatures are not only generated in the wire you use. Remember that the circuit is a series one. Current, everywhere in a series circuit, is the same. 400 amps flowing through a wire is also flowing through the battery. That amount of current will rapidly raise the internal temperature of the battery, resulting in damage to the case if you are lucky. When high currents are flowing in the battery, you boil the electrolyte and deform the lead plates. Use circuit protection when testing motors! Hot sulphuric acid and plastic shrapnel is not my idea of a fun time.

Now back to the problem. Something is drawing the power supply down below reset on the RC. Remove all the circuit breakers that feed motors and repower the robot. If moving the joystick still causes reset, then suspect a bad PWM cable or a bad PWM input on a controller. You can isolate this by removing PWM cables one at a time and repeating the joystick test.
If the RC does not reset with all the breakers removed, then add the breakers back one at a time until you isolate the bad circuit. I think you will find a wire or connector has come loose and/or is touching another contact. There has been trouble with the drill motor brush assembly and it is possible to cause a short in this area if the plastic at the brush end of the motor is damaged or out of alignment.
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Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Storming the Tower since 1996.
 


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