Hello, does anyone know if it is possible to make a lockable transmission for the Fisher Price Motor? If so, how would you do it?
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Thanks and good luck to everyone,
Melissa W.
[Team 912]
Could you describe what you mean by ‘lockable transmission’ with a bit more clarity?
It’s possible to do nearly anything with enough resources and ingenuity.
Not backdrivable, probably… Like the winches of 2004.
I sure can. Our arm on our robot is going to be lifted up and down using a motor. The only suitable motor would be the Fisher Price motor so inorder to make it possible, we need to make the motor lock when the arm has reached a certain height because the weight of the arm will just bring it back down -quite fast.
Does that clear it up a bit?
Melissa W.
[Team 912]
If you use a PID loop to control the arm, it will be able to dynamically control the motor to hold the arm steady.
Look up PID in the whitepapers section or google it.
Additionally, you can set the “brake” jumper on the victor speed control, which will slow the rate of descent of your arm a little bit. However, if true non-backdrivability is what you want, a traditional way of achieving that is with a worm gear, like this. The Fisher Price motor (by itself) is a very high RPM motor though, and you’d probably want an additional stage of gearing in there somewhere. Also check out the FIRST mechanism library
The higher the gear ratio between the arm and the motor the easier it will be be hold the arm’s position. Of course the arm will also move much slower too. But that is the nature of engineering, pick your druther and go with it.
With a high gear ratio, you could add a brake to the arm mechanism somewhere. The closer to the motor the less force you need. I seem to remember WildStang using a servo to make a brake for their FPs one year, but as an Inspector I see so many robots I might be somewhat confused.
ChrisH
If you use a PID loop to control the arm, it will be able to dynamically control the motor to hold the arm steady.
Look up PID in the whitepapers section or google it.
Fisher Price motors are not well suited for dead-load (static load) applications, so a PID loop is not the best way to hold an arm steady. It could put you at risk of burning out your motor(s). Therefore, I recommend that you try using a Dewalt transmission with the non-backdrive pins in place. Here’s an example:
http://www.jmen.biz/Bees/2004-2005_PreShipping/medium/0043.jpg
Directions for interfacing an FP to a Dewalt Transmission:
http://www.chiefdelphi.com/media/papers/1592
Assuming you are going to be gearing the motor down, DeWalt drill transmissions can have anti-backdrive pins in them which do the job nicely. They also provide a 47:1 reduction in first gear, which helps to bring that massive rpm down to a manageable level. A whitepaper on how to adapt a DeWalt to a Fisher Price can be found here.
Edit: Hows that for a coincidence?
you could use a craftsman ratchet;)
just get a monster gear ratio and thats it!
althought that might weight a little too much
Worm gear.
Pluses, a single lead stays where you park it. Power off
Down sides, very high friction loss and gear ratio. things may move way slower than you want. I would stay away from FP’s on highly loaded arms, they smell real bad when stalled. Consider moving FP’s to drive along with a pair of Cims if you are doing tank drive. Andymark http://andymark.biz/am-0002.html Makes a gear box to match Fp’s to Cims. you only lose about 5 to 7%. Almost used one last year As a shooter motor.
Biff
I highly suggest using the disc brakes from preformance off road bikes. With one of those, you can stop solid a 4 CIM drivetrain to the point of stalling. It’s more than light and simple enough for your job.
I’m surprised no one has mentioned worm gears.
We’re going to have worm gears at every moving joint on our robot this year.
Like they’ve said… Worm Gear. Here’s our’s from 2004 used as a winch to lift ourselves up. A little video of it is here here