Fisher Price Gear Box Problem

[kevinbrice]

Hi. We constructed a gear box for our fisher price motor to spin a set of rollers out of plastic (delrin) pulleys and rubber cords. This technique worked well for us last year, but we desired a lower spin speed then. Right now the gearbox is set at a 9:1 reduction which is the desired speed of our rollers. However, whenever the system interacts with a ball, it is moving at such I high speed the frictional torque is easily overcome in the outer pulleys of the system. We have debated migrating the drive to timing belts or chain... Also, what is the minimum reduction we could use with the fisher price to still keep some (a good level) of torque? Any ideas or different roller powering options would be much appreciated.

[MFS766]

We ran into a similar problem with our roller too. We had two fisher price (way overpowered) roughly 9:1 gear reduction to a roller 1.5 inch in diameter. We used polycord pulleys. The roller was covered in rubber, so we would stall the motors or shred the polycord due to slippage. In fact, our roller would chew up soccer balls way too much.

I see two solutions:

1. We reduced the friction for the roller by using a pvc pipe. We also found the fabric from the bumpers and the rug material the arena are very good. Despite our high speed/low torque, we had excellent control and could even spin our robot in a circle. Also, its a lot nicer on the soccer balls.

2. If you really need more torque, try reducing the roller diameter without reducing the final pulley. This will increase your gear reduction. We couldn't do this because our roller is also our final pulley.

What is you material and diameter of the roller? I ask this because we also found that roller tangential velocity is more important than the rpm of the roller. I hope this can help. Best of luck.

[joeweber]

We were able to remove the largest gear of the fisher price gear box and than attached a 2 inch aluminum pully to the next gear set down. We than ran a belt to a 3/4 PVC pipe and it works great.

[kevinbrice]

Can you please post more pictures from your modified gear box...we are interested. Also it powers dual 2 inch delrin rollers which are the last pulley as well.

[Akash Rastogi]

Originally Posted by joeweber

We were able to remove the largest gear of the fisher price gear box and than attached a 2 inch aluminum pully to the next gear set down. We than ran a belt to a 3/4 PVC pipe and it works great.

Joe was it similar to this? (hope the picture shows up)

http://www.facebook.com/photo.php?pi...5&id=645471640

[dtengineering]

We're using a banebots 26:1 planetary gearbox running off an FP to a 2" diameter roller with roughtop tread on it. It might be just a touch slow... we're going to work with it on our practice robot to try and optimize it.

When the ball is in "full backspin", we draw about 3-4 amps on the FP... which doesn't drop all that much when there is no ball in the system, so I'd have to say that the force requirements to put backspin on the ball (at least in our stationary testing application) are fairly minimal relative to the gearing and frictional losses.

I hope that provides some useful comparison data. Good luck getting it up and running smoothly. Hooray for the witholding limit!

Jason

[joeweber]

Originally Posted by Akash Rastogi

Joe was it similar to this? (hope the picture shows up)

http://www.facebook.com/photo.php?pi...5&id=645471640

Yes. We used the same gear shown but slide the small gear in that set into a 2 in pully. We than cut out the gear box to allow it all to fit. I will not have other pictures until we unbag it. You can dig through our build pictures if you like http://www.team1322.org/robotics_09-10.htm

[kevinbrice]

very cool. we are trying that right now. I will post back if it works!

[jspatz1]

Originally Posted by joeweber

We were able to remove the largest gear of the fisher price gear box and than attached a 2 inch aluminum pully to the next gear set down. We than ran a belt to a 3/4 PVC pipe and it works great.

We made a similar modification to run our roller. Cut the FP gearbox case in half, removed the last two gears, attached a 1" timing pulley to the 2nd gear. I believe the result runs about 400 rpm. Sorry, no pictures of this before we bagged it.

[Al Skierkiewicz]

Just so everyone keeps this one thing in mind. The FP motor has an internal thermal cutout. When it opens, there is a 2-4 second delay before the motor comes back to life. Just be aware when it occurs.