Movement of the Fisher Price motors
 

This is a simple and rather dumb question, but suppose one uses the Fisher Price motors to rotate an arm. If one cuts power, does the arm simply dangle, or is it held in place?

Thank you.

Re: Movement of the Fisher Price motors
 

Simple and rather Dumb Reply: it depends.


How much torque are you dealing with?

Re: Movement of the Fisher Price motors
 

It depends on the weight of the arm. If you are holding up something like 10 pounds it will probably fall back down. It would only stay up if it is light and standing strait up.

Re: Movement of the Fisher Price motors
 

it really depends on the torque (gear ratio) and your design of lift, rotation, etc. They dont move that easily without power. However, with a 10lb ball to deal with, I'm sure it will not stand still with a loss of power.
This is actually our first year we dont intend on using those motors for our lift.

Re: Movement of the Fisher Price motors
 

We use a worm gear type reduction for lifts because they are typically harder to backdrive.

It shouldn't be hard to set up an experiment.

Re: Movement of the Fisher Price motors
 

You can put the Victor(s) on "brake" mode which will help a little bit. It might still fall but not as fast. Traditionally worm gear setups don't fall (backdrive). The Van Door motor is the exception.

Re: Movement of the Fisher Price motors
 

Whether or not a worm gear backdrives is dependent on the angle of the worm. If the angle is less than 5 degrees it probably won't backdrive. More than that and it probably will. This is an approximate number and how your system responds depends on many things including how smoothly your gears turn and how the load is applied.

If I recall correctly, the worm on the vandoor is around 10 degrees. I haven't looked closely at this year's motor, but older versions had an adjusting screw that could be used to increase the drag on the system and reduce a tendency to backdrive. I wouldn't reccommend making it too tight though!

Re: Movement of the Fisher Price motors
 

If you wanted to you could put some kind of a passive lift system to hold your arm up. This would be something like surgical tubing, a spring, or closed actuator. Also you can stall the motor by giving it constant power so it doesn't move. Stalling is not good for the motor if it last more than a second or two. The only issue you may encounter with using a worm gear is that when a match is over you may not be able to put the arm down without power.

Re: Movement of the Fisher Price motors
 

If you want it to be stable, use the blue speed reducer transmission... thing.
That's what we did on our robot, and the arm was very stable:
http://www.chiefdelphi.com/forums/sh...ad.php?t=56063
You should be able to see it on the third picture.

Of course, using the speed reducer it DOES reduce your speed along with the vibrations, so think carefully if you really want to have a stable but slow arm, or fast but unstable arm (or something that's half of each).

Hope that helps.

Re: Movement of the Fisher Price motors
 

hey where did u get that blue thing? and how does it work?

Re: Movement of the Fisher Price motors
 

Mikhail,
The simple answer is the Fisher Price even when used with the supplied transmission cannot hold itself in place when the power is removed especially with the weight of the arm and whatever it might be holding. You can couple to a worm gear system as some have discussed or you can use a pneumatic operated brake to hold the arm in place. You can even use a servo motor to operate a mechanical stopper, the choice is up to you.

Re: Movement of the Fisher Price motors
 

Another option is to use a Nothin' But Dewalts style gearbox and leave the anti-backdrive pins in.