PWM Extention Cables: 4 Shall Be the Limit

From an e-mail between FIRST VEX Challenge teams:

Hey all,

 This is TJ from team -Stickshift FRV 51- (First 1688) .

We are experiencing a problem that I think you all might be having. The
rules say that were only allowed to use 4 pwm extension cables for the
servos and motors. These cables are nowhere near long enough to power the
manipulator to the full extended length and still have enough left to power
a drivetrain (with a 24 inch chassis…we would need at least 10-12 inches
of cable on each motor to safely route the wiring to the control module. Any
takers on this one, because were stumped as to why using more than 4
extension cables would be banned (as per the FRV robot inspection sheet). I
don’t know if were missing something…maybe we are…if so…shout out to



Dr Joe’s Answer:

As to his question, the 4 PWM extention cables are part of the design challenge.
I think it is probably an unreasonable restriction giving the size of the
robots (it effectively limits/makes impossible the use of powered end
effectors), but it is one of the limits. I could go with FIRST changing the
rules (in fact, I recommend it), but if they don’t, teams will have to work
around it.

Joe J.

Hope this helps.

If you have questions or answers or opinions or whatever feel free to join the conversation.

Joe J.

Team 48

It does seam a little strange. We designed our tower and drive train based on the available cable lengths. It is like the tail waging the dog.

Does this means that we can’t try to create our own extension cord using the parts from the kit? It would be hard but possible.

If what you are proposing is to use the wires in the kit to extend the wires on a motor or to extend an extension cord, very clever, but I don’t think it would be looked upon favorably by FIRST inspectors.

<R19> Motors, extension cords, sensors, controllers, battery packs, and any other electrical component of the
Vex Robotic Design System Kit may NOT be altered from it’s original state in any way.

I think that this rule would not allow you to do anything like you are proposing.

Joe J.

FVT-42 The Hitchhikers
Members of our team voiced similar grave problems with the lack of flexibility of parts. I love it. I have seen students come up with very creative solutions since they couldn’t just throw more resources at the problem. I love seeing these Apollo 13 moments flourish. I also like how it is a very economical, level playing field, especially for those of us in the first FIRST vex competition, where our up front cost was pretty low.

Being a teacher, I really like seeing the gray matter getting stirred up. I suspect teams such as our are going to play both games because they each foster a different kind of creativity.