pic: Vex Teaser: What's Art been up to lately?

[Jay H 237]

Are you going to set this frame up as two or four wheel drive? Or do you just have other plans?

Be sure to post pics of the finished project.

[artdutra04]

Originally Posted by Jay H 237

Are you going to set this frame up as two or four wheel drive? Or do you just have other plans?

Be sure to post pics of the finished project.

This was mostly just an idea concept of how to simply and efficiently use a worm-gear drive in a small compact space, although I do have enough motors, motor mounting clips, and worm gears to make a 4WD robot using the worm gears.

The motor here has a fairly high amount of torque for something it's size. Under a moderate load it runs at about 2,500 rpm, which is geared down through the worm gear 36:1 to about 69.4 rpm. Just to see how powerful it was, I geared it down an additional stage (using two 60t and two 12t gears, so as to split the load between them) using a 5:1 reduction. It was practically impossible to stop the output shaft of the stump-pulling second reduction.

At the moment I am working on a much more complicated design that mechanically will calculate the difference between two input shafts. For example if both shafts were rotating CCW at the same RPM, the difference between the two would be zero. But if the two input shafts were moving at different speeds the output shaft would rotate in one direction (CW if shaft A is faster, and CCW is shaft B is faster) at a speed proportional to the difference of the two shafts.

[Dan Petrovic]

Where did you get the worm gears?

I was a bit frustrated at the lack of worm gears when my arm kept backdriving when I picked up mini tetras.

[artdutra04]

Originally Posted by InfernoX14

Where did you get the worm gears?

I was a bit frustrated at the lack of worm gears when my arm kept backdriving when I picked up mini tetras.

http://catalog.pitsco.com/store/

Note: I bought them about two years ago for another project, so I'm not sure if they still carry the exact same gears.

Any 24 pitch (or close enough) gear can mesh with Vex gears...

[John Gutmann]

you can also go to kelvin

[jgraber]

Originally Posted by artdutra04

...
At the moment I am working on a much more complicated design that mechanically will calculate the difference between two input shafts. For example if both shafts were rotating CCW at the same RPM, the difference between the two would be zero. But if the two input shafts were moving at different speeds the output shaft would rotate in one direction (CW if shaft A is faster, and CCW is shaft B is faster) at a speed proportional to the difference of the two shafts.

Nice work on the worm gear. Now that it is a few months later, how did it go?
Were you able to make a "South Pointing Chariot"?
Was it to make your holonomic drive "driver centric"?
Links from here might give you some ideas on differentials.
http://en.wikipedia.org/wiki/South_Pointing_Chariot
I thought the screwdrive one has some promise due to no requirement for bevel or planetary gears. You might also consider just doing the integration computationally, based on optical wheel encoders on the drive wheels or drag wheels.

[artdutra04]

Originally Posted by jgraber

Nice work on the worm gear. Now that it is a few months later, how did it go?
Were you able to make a "South Pointing Chariot"?

Somewhat. I got about 70% done with it, but at that point the number of gears required to mechanically keep it "pointing South" was taking a toll on the motors and causing the robot to drift badly. This was just meant as a kind of interesting experiment in gearing, and nothing more really.

Was it to make your holonomic drive "driver centric"?

That's still a work in progress; I have the a KoP gyro at my house, and I'm waiting on an order from Futaba for keyed connectors to make a jumper cable to go from FRC-style female leads on their sensors to the Vex-style male leads. Even once I get them, it probably wouldn't be until a vacation break, like Thanksgiving, when I would actually have enough time to start programming an absolute holonomic drive.

You might also consider just doing the integration computationally, based on optical wheel encoders on the drive wheels or drag wheels.

I could of did that, but I just wanted to play around with differential gearing to create a complex mechanical-computer type of thing, just for fun. If I was serious about finding the exact location of the robot, I would have picked something much simpler.

[Sislith]

I'm guessing torque.

[Jared W]

hey

hows it coming?

I'd really like to see a movie of the bot in action.

To see how much faster a bigger motor will be.

I hope next season Vex will release beefier motors for torque or speed.