pic: Fischer Price motor are very powerful

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Thank goodness for spares

Our team decided to make this into an award for next year. “Most Robust Design” award. :smiley:

We’ve done even better with this. We have two f-p motors powering our arm, with a 16:1 reduction outside of the stock gearbox reduction, and during different points in testing we

  1. buckled arm
  2. tore gearbox mounting point out of chassis
  3. snapped a solid 44 tooth (35 chain) sproket.

Beware of the power.

We also use two FP motors, but only a 10:1 Reduction. We also had a vandoor motor with them until weight became a problem.

And this, class, is an illustration of what happens when you get too agressive with your lightening: Bad things!

Neat picture though.

So that’s what a “sprocket cam” looks like! :stuck_out_tongue:

Is that just from normal use, or did it bind/the movement was restricted somehow? I’ll also guess that the gear wasn’t hardened otherwise it would’ve snapped (or something else would’ve let go) instead of twisting like that.

I am confused about this picture. It looks as if the gear was designed that way. It appears to be bolted twice to an aluminum block that appears to be attatched to an arm. Some clarification would be nice.

I’m sure the two tabs used to be collinear. The tremendous moments about each of the bolts caused them to slip from their fastening and swing around bringing the rather thin rim with them. It is an easy fix. Just extend each tab so that it goes all the way across. That way, there is one member that can take some shearing and tension forces instead of all off the torque being transferred right to the two bolts in the form of a giant force couple.

Make no mistake: The Fisher-Price motor is an absolute beast. So be careful when pocketing sprockets! Leave some steel to help you out.

-Carl

this is what happened to our arm (322) durring one of our earlier attempts to hang. this particular sprocket wasnt directly connected to the fishers, but to two window motors that control our wrist. we tried to hang with our wrist slightly bent, and because window motors lock in place, the sprocket gave into the weight of a 130 lbs bot trying to hang. gravity tried to straighten the wrist, and the motors tried to hold the wrist in place, and crunch… there goes our sproket. …but yea, it was the fishers that lifted the robot up to begin with…

yep that pretty much what happened.

We have similar drive sprockets from last year, only it bent into a triangle because it had three mounting points. We learned Our lesson though, leave a ring around the center when you lighten sprokets.

one of our f-p motors got burned in the quarter finals, so we were not able to hang, they were powerful, but get too much heat in direct pulling.
So we lost 50 points and the chance to go to the semi finals.

We use the FP’s through the drill transmission and then reduce another 32.5 times for our use. It will viewable tommorrow at the UTC NE Regional.

I agree with those who discussed being too aggressive in lightening efforts.

In my opinion, this is a better example of a not leaving enough meat on the bone than the power of the F-P motors.

Actually power had nothing to do with this failure, I suppose it was torque that killed it not torque X speed (i.e. power).

Joe J.

You mean it’s not SUPPOSED to look like that??!? :rolleyes:

Actually, the first time I looked at this image, I thought that Team 322 had manufactured an elliptical gear to tailor the delivered torque to certain angles of inclination of their arm (similar to high-end/competition bicycle cranks and chain wheels). I saw the kink in the lower portion of the ellipse and thought “wow - they bent their chain gear; too bad after all that work to cut the custom gear shape.”

Then I realized that it really did start out as a round chain gear, and modified that reaction to “WOW!!!” Lessons learned: 1 - even more respect for the F-P motors. 2 - gotta go double-check strength calculations for lightening gears. 3 - elliptical gears could be very useful; something to remember for next year.

-dave

Yep, the sprocket was supposed to see only torque from the Window motors (very weak), but because we were still learning with the arm we hung incorrectly. This put the torque of 2 FP’s reduced 10:1 on the sprocket. Unfortunately when you try to do a lot of tasks (big ball, hang, climb, push) with your robot, weight becomes a big issue REAL FAST. This requires the team to lose a little bit of robustness. This is what it’s all about though, making the simple parts to replace the weak link. We replaced the sprocket within 5 minutes and had time to eat before our next match. We have learned a lot over the last 5 years. We also ripped off an robot finger trying hang incorrectly and blew out our trick wheels when the bot fell. It was awesome, our arm was still on the bar. I think we should have gotten 50 pts. for it. :stuck_out_tongue: :stuck_out_tongue:

Oh course Fisher price motors are powerful opens gear box and gazes at big gears! They also are made to move up to arund 150 pounds, so if its moving your arm…that alot of power for not so much weight.