Torque calculations and motor size

  • I hope it's ok to post here. I'm working on a robot. I'm trying to calculate the torque and motor sizes needed. I'm no engineer so these are probably simple questions for most here. So..

    This machine is scalable to any size. For now I'm making a small version to see how it moves. It should be around 10-15 lbs and I want to make it RC controlled.

    There are motor driven main shafts connected to worm gears that help it move. Im looking at a 1,621 rpm brushed planetary gearmotor. 10.9 oz weight. 20 amp current stall and 97.2 oz-in torque stall.

    First question:

    If I gear it to the main shaft at 2:1 ratio will it double the torque to 194.4 oz-in? Then with the worm gears at 30:1 ratio does that mean torque is 194.4 x 30 = 5,832 oz-in?

    30 ft-lb?

    Will this be good to move 10-15lbs? It will run slow and smoothly with minimum friction.

    2nd question:

    I'm using 2 additional gear motors for turning it as it moves. Im looking at two brushed planetary gearmotors. 12V, 12rpm, 8,110 oz-in torque stall, 20 amp current stall motors. I will only use one at a time depending which direction it moves. I want to connect all 3 motors to one rc receiver. Am I ok as long as the receivers amp rating is high enough to cover all three motors combined? Say a 60 amp receiver? All 3 motors have 60 amp stall total.

    I hope I can get some help. Thank you!!

  • AD
  • using reducer (gear,belt etc) will reduce speed and increase torque. lowering speed is not an issue

    and when connected in reverse, it will do the opposite (increase speed and decrease torque) but in this case (increasing speed) there is a limit how far you can go before the system is not driveable any more.

    there are some small loses which are usually ignored since one adds safety margin anyway (20% for example).

    so using gear ratio of 100:1 you can get the output speeds and torque

    1600RPM * 0.8 = 1280 RPM

    where 0.8 is 80% of rated speed, just to make sure there are some reserves....

    1280RPM / gear ratio = 12.8RPM at output shaft

    motor torque = 97.2oz-in * gear ratio =9720 oz-in

    which exceeds required 8110 by some 17% or so.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

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