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-   -   Power loss problems? (http://www.chiefdelphi.com/forums/showthread.php?t=18965)

sanddrag 10-03-2003 01:23

Check for binding and drag in your drivetrain. You can tell a lot just by the sound of it running up on blocks under no load. Also, you can only have one Van Door motor.

Andy A. 10-03-2003 01:40

To repeat sanddrag, check for binding, worm gears are ineficent with out it.

Also, when my hands typed 'vandoor motors', my mind typed 'window motors'. Long story as to why I confuse the two so often, but it has to do with lazy programers who won't change their programs to reflect new motor selection.

So yes, steering is through two globe motors and two window motors. I don't suspect them as the problem, they never stall and run for less then a second at a time.

Perhaps the problem lays with those 8 little muffin fans on the victors constanly running, you never know...

-Andy A.

Al Skierkiewicz 10-03-2003 08:14

Quote:

Originally posted by Andy A.
95 has a problem much like this. We are using a 4 wheel 4 motor drive (2 CIMs and two drills, plus two van doors and globes being used as steering motors)...
At first, I suspected a short to the frame (why don't inspectors check for this?).
We to use worm gears. We did some current draw tests on our motors and found they were drawing around 10 amps, no load. Wow.
With no load on the battery, it will settle at around 11-12 volts... Doesn't that seem wrong? That is a very large voltage drop in so short a time...
We believe that attaching a capacitor across the power terminals of the RC helped prevent resets (when voltage dropped to low the capacitor would drop power into the RC to compensate). Yes, we checked with the inspectors and this was legal.
-Andy A.

Andy this is a lot to answer so here goes...
We have been calling for inspectors to check for frame shorts, but to no avail yet. This isn't a serious issue but can lead to problems in certain cases.
10 amps on your motors no load isn't bad, it's what they are drawing in competition especially on turns that is important. Many designs will max out motor current at 80-100 amps per motor while driving which may not trip any of the 40 amp breakers and not the 120 amp breaker if the current is short term. However, with the weight of the robot on the wheels there may be significant friction to run motor current up to 50 or 60 amps per motor which will not trip any breakers but will be drawing 240 amps out of the battery.
If you look at the data sheet on the battery, you will see that terminal voltage will fall after drawing current. The amp hour rating of the battery is determined by how long it takes for the voltage to fall to 8 volts. What you describe is normal for high current draws.
Adding the capacitor and passing inspection really surprises me. In past years the capacitor was strictly illegal. We believe that Innovation First responded to this problem and put a larger capacitor inside the robot controller as part of their improvements on this year's controller. A better fix is to make the leads between the battery and the controller the shortest on the robot and to not connect controller power downstream from motor supplies. The high current causes a voltage drop in the wiring. (Simple Ohm's Law V=I*R)
How to fix it at this point? You might have to scale the software back a bit. I would rather be slow and play all two minutes than to go fast and break fifteen seconds into the match.


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