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Ridgebotics

Arm on a pivot

Guide 2

An arm's worst load is at horizontal, where gravity has the longest lever. The tool checks whether the motor can lift it there, what current it takes just to hold, and whether the gearbox and hub survive a stall or a hit.

Gravity torque = mass × g × pivot-to-CG × cos(angle).

Where the arm's load goes

Example inputs; the calculator updates these with yours. Imperial first, metric in parentheses.

6.6 lbf(29 N)Motor + gearbox: 42.6 ft·lbJam: 230.3 ft·lb(57.7 N·m at 40 A)Gravity, arm level: 11.0 ft·lb(15.0 N·m)3.9x lift margin11.7 A just to hold levelHub on ½ in hex: 585 lbf per cornerJam: 3162.2 lbf per corner(2,600 N) → use a bolted hub, not hex alone
appliedcalculatedwatchfailure point

Example inputs from the calculator defaults. Losses ignored.

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Gravity torque peaks at horizontal; the gearbox and hub carry it

  • Inputs
  • Joint
  • Calc
  • Check
  • Motor type and quantity
  • Current limit

Motor

  • Motor torque at limit and stall
  • Free speed
  • Calc
  • Planetary stages and ratios
  • Gearbox model

Gearbox

  • Torque per stage vs rating
  • Weakest stage flagged
  • Check
  • Hub material
  • Bore: hex, keyed, or bolted

Arm hub on hex

  • Hub bore corner force
  • Pass or fail
  • Check
  • Pivot-to-CG length
  • Arm and piece mass

Arm

  • Gravity torque at horizontal
  • Max lift torque at the pivot
  • Calc
  • Hold angle
  • Shock factor for a hit

Holding position

  • Holding current
  • Lift margin
  • Calc

What it teaches

A mechanism can be fine at rest and overloaded mid-swing. Gearbox ratings are per stage, and the last stage carries the most torque.

Session hook

Hang a weight on a test arm, read holding current at three angles, and compare it to the prediction.

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