Legal Counterweights
 

We're looking at our Logomotion Robot for design inspiration and it's been considered to use a counterweight for a trebuchet. We don't want to use dead weight, for obvious reasons. Is there anything (rule wise) against using the battery for this? R5 states cable length, but beyond that, nothing concrete.

Re: Legal Counterweights
 

I don't know if you can use the battery for a counterweight, but there's probably nothing specifically prohibiting it. IMHO, a Trebuchet is not the most practical way to hurl a two-foot ball. Trebuchets rely on the speed generated from the whipping action of the sling, which on a robot would probably exceed the 20" extension at some point.

However, if your heart is set on a Trebuchet thrower, I would recommend using a non-gravity powered method, such as using surgical tubing to pull the counterweight arm down. This allows you to save weight for other mechanisms.

Re: Legal Counterweights
 

I don't know of any specific reason why you cannot as long as you follow this rule:

However, I am not sure if Robot inspectors would approve of the system.

Also, it is all to common that from a collision in the final rounds, a well renowned team has their battery fly out of their robot and even rip the terminals.
Maybe if you have like a full out metal box around it that is bolted shut this would make it seem safe (not sure though).

Re: Legal Counterweights
 

*Usual last year's rules aren't this year's rules disclaimer*

That being said, check out team 23 from last year. They robot was a 30 point climber and their battery was mounted on one of their arms, so something like this has been done before. Your mileage may vary though, as their arm did not move very far or very fast, and a trebuchet definitely will.

Re: Legal Counterweights
 

If you're using one battery to both power your robot and act as a counterweight, that's allowed.

If you have one battery powering your robot and another as a counterweight, then that's unsafe by definition. One battery is dangerous enough.

Re: Legal Counterweights
 

It would probably be ruled unsafe by inspectors and disallowed. The batteries are sealed lead acid and have the potential to explode if a cell is damaged or ruptured. One of the easiest ways to rupture a battery is for it to see a hard impact, such as dropping it. By mounting the battery as your counterweight, you are necessarily lifting it up high and putting it through a rapid motion path which could cause it to come loose or collide with something.

Re: Legal Counterweights
 

For 2005, 857 had a 'tetra cannon' which was counterbalanced by the battery. So, since the rules haven't changed "that" much, so long as it's the only battery, is safe, and can be removed for robot weighing, it should be okay.

Re: Legal Counterweights
 

The rule is
R31
The only legal source of electrical energy for the ROBOT during the competition, the ROBOT battery, is one of the following approved 12VDC non-spillable lead acid batteries:

And

R35
The one ROBOT battery, the one main 120-amp (120A) circuit breaker...
Emphasis mine.

One and only one please. As to counter weight for your trebuchet, by definition that would add significant electrical loss through the long #6 or larger wire. If you were to mount the 120 amp circuit breaker on the robot, then a significant length of wire would be unprotected should a short occur. While this is not specifically addressed in the rules, it is bad electrical practice to do so.

Re: Legal Counterweights
 

You'll be spending a lot of time justifying that the design is safe to the inspectors. I would suggest focusing on a different approach.

Re: Legal Counterweights
 

Shifting the battery around to move the CG is one thing. The shock from it being a counter weight for a trebuchet is another. It already gets banged around enough just being on the robot.