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#1
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Stiffening Capacitors
Any chance we can use a stiffening cap (0.5F - 2F) to offset the immense instantaneous draw by the drivetrain and pnuematic system on our battery?
Looking at putting 2 one-Farad capacitors on the robot. Is this legal? |
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#2
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Re: Stiffening Capacitors
I think that would violate the safety rule, so I would give that a "no."
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#3
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Re: Stiffening Capacitors
This would fail rule R02 on Page 7 of the robot rules
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#4
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Re: Stiffening Capacitors
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As for your cap idea, I'm afraid it is illegal, although awesome. Quote:
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#5
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Re: Stiffening Capacitors
It is a bad idea. Most of the 1F capacitors (usually called supercaps) have low voltage ratings (5V, 3.3V, etc) and they are extremely intolerant to overvoltage conditions. They'll blow up thus violating the safety rules.
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#6
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Re: Stiffening Capacitors
Actually, the capacitors I had in mind are car-fi capacitors, designed to work at 14 volts, tolerant up to 20. Perfectly safe, aside from the potential to weld metal should they be shorted. Definitely no more dangerous than a lead-acid battery in that regard (the welding-when-shorted bit).
When hooked up to a high-resolution voltmeter, there is a significant drop in voltage with the motors and compressor running, down to about 10v on a full-charged system. Tests with two 1-Farad Rockford Fosgate capacitors from my car resulted in the voltage staying above 11.5V, thus ruling out wiring as a potential fault. In accordance to <R02>, the energy would infact be derived from the batteries, since that is where it would charge from. I don't see how this effects <R63>, because it does not alter the pathway. Regardless, the safety could be called into check, and that's a big one on FIRST's list. Just an idea :-D. |
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#7
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Re: Stiffening Capacitors
Zach,
Yes they violate the rules stated above and therefore cannot be used. Capacitors to my knowledge have always been illegal. The drop you are seeing is the voltage drop across the internal resistance of the battery which is .011 ohms. When you draw large currents, a voltage drop will occur. The caps are holding up the power supply but only in a way that the current from the battery is reduced and so the voltage drop is reduced. All teams suffer this indignity and that is why the backup battery is reguired. If this was an allowable device, I would recommend that they could only be used with a suitable bleeder resistor in parallel with each one. You can minimize the drop in a variety of ways. A clean electrical design following the Tips and Guidelines is a good start. Short wires and a mechanical design that does not put significant loads on the drive train during turns are also a big help. Remember that any time the power supply falls below about 8 volts for a short period, the RC will go into standby and draw current from the backup battery. During this time, the PWM outputs will be disabled. |
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#8
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Re: Stiffening Capacitors
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You never know... Mike |
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#9
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Re: Stiffening Capacitors
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Uh-huh. Reeeeaally. Did not know that. Hopefully the omni's will help when they get here. |
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