We were wondering if having the battery move would be allowed, as long as the battery is securely attached to the mechanism. We checked and didn’t see anything in the rules forbidding it, but we thought we should check to be sure.
Thanks, team 3636.
yassi,
I normally would recommend against this for a few reasons. If you are controlling the motion of the battery carrier you have to be careful to keep shocks to the case at a minimum. Hard hits can damage battery internals.
Secure mounting takes on new meaning when the battery motion can exceed the speed of the robot. Inspectors will be watching for battery mounting in these situations.
Any motion will require that the wiring to the battery be extended. This brings up special issues. If you splice wires to make them longer, then the splice must be secure and insulated. Added wire length will affect maximum current. Figure at 100 amps, every 2 feet of #6 will drop an additional 0.1 volts. Typical currents during pushing or hard driving will drop 4 times that. Make sure to account for the length of both the red and black wiring.
The last thing is you need to consider the possibility of the wiring getting caught in the moving mechanism and causing a short to the robot frame should the wire insulation get damaged.
The appropriate robot rule on this question is you may only have 1 foot of wire attached to the battery. All other wiring must be counted in the weight of the robot.
Teams have used the battery to change robot center of gravity in the past.
Any possibility of using the compressor for the same purpose? Still difficult and full of its own issues, but it’s the only other common large weight on the robot that I think might have a chance of working.
Also please understand that ChiefDelphi is NOT an official place to check the legality of things. What anyone says here is not official, and if you count on something you got off ChiefDelphi, you might be better off just asking a random stranger at the local 7-11.
FIRST has a forum for official questions. That’s the only place to get an official answer.
BTW, Al’s answer is pretty good.
this concept of moving the battery to aid balance came up during a brainstorm for our team too. other than the legality of the issue, with a 120lb robot and a 12lb battery, through simple physics, the battery would have to move 10x inches as far to get the same change as the robot moving x inches.
move the robot 1 inch or the battery 10 inches? its a question of how fine the drive train’s movements are and how fine you need to balance your robot.
EDIT: this is assuming most bots are going to have similar weights.
Our team is using a program that moves our chassis up or down the bridge in correlation to which side of the bridge it is on and the angle of the chassis compared to the direction of gravity, the technique is being called “dithering” by our mentors.
are you using a gyro for this?
We had the same idea. Thanks for the great comments.
How “fine” can the regular drive-train CIMs move the robot without a “low” gear. Can they do 0.5" steps? Or do we need a separate mechanism for fine adjustments? (sorry for the newbie Q)
On the angle/gravity autonomous action, make sure you don’t start oscillating, or just the music up & we’ll have a dance 
Dean
Thanks for the replies. We’ve decided against moving the battery, we’re pretty sure.
Dean,
The CIM motor has more than the three poles that the FP motors have but the amount that any motor can move an object is dependent on the gear reduction ratio as well. While some motors offer better fine control, you should have no problem getting a CIM fine tuned to 1/2". You might want to look at the AM gear motor or a seat or a door motor for this application.