Answered: Can you post pictures of VEX arm in Turntable Bearing Kit video?

The YouTube video that you did to show off the new Turntable Bearing Kit was great! I have always wanted to build an arm like that and it might work good for Gateway. BTW - whoever built it did an awesome job!

I was just wondering if it would be possible for you to post some details about the arm (aluminum or steel, how many turntable kits, motors used, etc.) and maybe some pictures. I thought you might have put something on the Wiki page with your other robots, but I didn’t see anything.


The Turntable Arm wiki page is now up. If you have any more questions, feel free to ask!


Thanks Parker, the Turntable Arm wiki page is great!

I do have a question though. In the description of degree 4 (wrist), it lists just 1 motor, 1 pot, and 1 small turntable bearing. In the pictures however there are 2 motors and 2 pots - what’s the extra motor and pot for?

I’ve re-watched the video several times, but I’m still not sure.

The extra Motor 269 and potentiometer you see were part of another degree of freedom that the robot currently does not have. Their intended use can be found on the wiki under the “Ideas for Future Revisions” section as a co-axial wrist.

The Motor 269 will drive a shaft through the center of the small turntable, through the potentiometer for position, and into some mechanism that will tilt the VEX Claw up and down. After two iterations prior to the World Championship, I scrapped the tilting function to complete the robot in time.

I hope you’ve learned a bit about how to use the new Turntable Bearing Kit from the new wiki. Let me know if you have any more questions or ideas to improve the Arm!


Thanks for answering my question about the arm. I do have a few ideas, but you have already thought of some of them:

  1. Use aluminum parts to reduce the weight.
  2. Run the cables up through the center of the base turntable bearing - degree 1
  3. Use aluminum 1x2x1 C channels for the frame work between degree 2 and degree 3 instead of the 1x5x1 C channels to reduce weight further.
  4. Move degree 4 (wrist rotation) closer to claw.

I didn’t know what kind of arm you were trying to build - a human like arm or a regular robot arm. If you put the wrist tilt after the rotation, the arm will perform just like your own arm. If you put the tilt first and then the rotation, you would be able to do things like turning a lightbulb or door knob for example.

There is a way to put both motors down toward degree 3 and use chain to power the wrist in both axes, but I don’t know how well the VEX bevel gears would work. You would use 3 bevel gears in a “C” shaped bracket. The 2 side ones are driven and the axle in the center one attaches to the claw. The bracket is free floating and moves up or down depending on the rotation of the side bevels. Depending on which way the motors are turning the wrist will either go up or down or spin CW or CCW. It might make the wrist too weak though.

I was thinking about using 1x2x1 C channel for my arm from degree 3 to degree 4 and moving degree 4 to the end to reduce side load. I was also thinking of using a single-acting pneumatic cylinder for opening and closing my claw. I thought I might be able to run the air tubing through the center hole of the small turntable.

What do you think? I don’t know if any of these ideas will help or not - they may not even work.

This arm was modeled after the FANUC 1000iA, an industrial robotic arm typically used in the auto industry. It’s definitely a cool feat of engineering and you should check it out.

As far as the wrist goes, we tried using bevel gears to do exactly what you proposed, but the slop in the gears couldn’t support the weight of the claw and the teeth would skip. I want to point out that if you placed bevel gears on both sides of the perpendicular bevel, the whole system would immediately lock up. When the center bevel rotates, it actually spins the side bevels opposite directions of each other. You could, of course, put them on separate shafts (think differentials), but that would be useless in this application.

I think all of your ideas are great and on the right track. Tubing through the turntable is a great use of the center hole! If you end up building an arm yourself be sure to post it; I’d love to see your own creative twist on this robot.