Arm Design advices

Hi everyone, my team and I are using JVN to design an arm but we still have doubts about what gearbox could be a nice aproximation to have, so, does your team have advices to what we can take on to design the arm, and the gearbox?

Aprox. specifications:

  • 2 joint arm
  • Total lenght in max extension: 47 in
  • Weight: 12 lbs
  • Possible motors for the first joint gearbox: 2 Falcon 500 or 2 CIM or 2 AM Redline (It would be placed below, on the chasis)

Thank you so much!

You don’t want to know your max extension length, you want to know the distance between the pivot point and the arm’s center of gravity.

Also, some advice you didn’t ask for: it’s almost week 1 of competition. If you don’t have a solved and functional design for your double jointed arm, do not make a double jointed arm. You are competing in 4.5 weeks. Re-evaluate your scope and simplify to get something done.


We stopped using the JVN calculator a few years ago. and the AMB Robotics Calculator are newer versions of the tool that are pretty great.

I like the Sport gearbox. Max Planetary is also a great choice, but is struggling to stay in stock.

As far as motor choices, If I had falcons sitting in a drawer I’d use them. Cims are also a good choice - lots of thermal mass if you stall them out. I’d stay away from redlines for an arm personally. Too easy to burn them up.

It sounds like you’re trying to have a long stretch of chain from your gearbox on the chassis to the joint. Be aware that the propensity to skip teeth will increase with distance. We are mounting our motors close to the joint to avoid this. Our gearboxes are 2x Andymark Sports, each driven by a Neo, and a final reduction from a smaller to a larger sprocket via chain.

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