Quote:
Originally Posted by Al Skierkiewicz
Dave,
You are correct in your assumption that the main battery regularly falls below the 8 volt cutout for the RC ( we have seen robots that take this down below 4 volts on pulses). Generally a condition like reversing the motors will cause this as they fight to slow down momentum and then traverse a stall condition to change direction. However these are usually short duration pulses that the power supply in the RC can weather just fine. Since the modems are powered by the backup battery they should be relatively immune to power fluctuations on the main battery. The RC is a different story and I have seen teams that can improve life support for the RC by simply rearranging things in their electrical design. Frequently teams will take off power for the RC at the end of a long string of wiring that supplies power for high current devices. By feeding the small breaker panels with their own #6 input and return wiring (from the power distro blocks) and by using one of the first breaker positions to feed the RC, low voltage can be reduced. With four and six motor drives, it is very easy to loose 2 volts in the wiring and battery internal impedance on a fresh battery.
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Hi Al,
With the bench lab supply connected to the backup battery terminals, I did not notice any current being drawn while the RC was powered by the primary battery, but if it was less than 20mA it may not have been noticed on the 3A analog meter movement. Since the radios will work without a backup battery connected, my assumption is that the backup battery is only being tasked as the primary sagged below the backup batteries threshold.
As to our wiring, it couldn't get much shorter. We have about 12" total of 6AWG between the battery and Maxi-Block, with maybe 6" additional on the positive side to account for the main circuit breaker.
Each of the 2.5" CIM speed controllers negative leads are 10AWG return to the Maxi-Block and are also in the 6" range. The positive side connections between the speed controllers and the quad 40A blade type fuse/breaker block are probably no more than 6", and the input to the fuse block is 6AWG again about 4-6" long. The CIM's then directly attach to the speed controllers using the manufactuer supplied pigtails, which look to be about 14AWG.
The robot controller was the only thing tied to the smaller ATC fuse block, and the connections to that fuse block are also 6AWG connections back to the Maxi-Block with lengths on the order of 8-10".
Other than the Maxi-block compression connections, with one wire per clamp, and the 1/4" spade connections on the RC and smaller fuse block, all other connections are ring lug type compression fittings that are crimped/compressed and then soldered (in that order) to not only reduce impedance, but also to avoid vibration induced failures at a compression only junction.
All in all, the wiring could not be made much shorter than it already is and the only way to further reduce impedance would be to start eliminating some of the 'required' components, nor do I believe that increasing the wire size would substantially improve the electrical noise situation.
Recall that something as subtle as replacing the NiCd pack with a bench supply improved the situation, but did not eliminate the problem. Without measuring the supplied AA NiCd, I would presume that the ESR is already on the order of 0.1 Ohms.
Something that I did not try was adding some .01uF caps across the output terminals of the Victors to see if that improved the situation at all. Without opening up the motors (not permitted) to add them close to the brush assembly, we couldn't get them any closer to the motor without cutting and splicing the motor wiring.