Reference
The calculators start at a motor stalled against its current limit and follow that torque joint by joint. Losses are ignored on purpose: for a load check, the worst case is all of the torque arriving.
Shared math
Section titled “Shared math”Kt = T_stall / (I_stall - I_free)T_motor = n * min( Kt * (I_limit - I_free), T_stall )T_out = T_in * (N_driven / N_driver)r_pitch = N * p / (2*pi)F_belt = T / r_pitchF_corner ≈ T / (6 * r_c) r_c ≈ 3.7 mm for 1/2 in hexF_rack = T / r_piniontheta = T * L / (G * J)The shock factor multiplies full-stall loads. That is the jam spike the current limit cannot catch. The code lives in src/lib/loadpath.ts.
Assumptions we shipped with
Section titled “Assumptions we shipped with”The spec left a few choices open. This site uses:
- Shock factor defaults to 2.0 and is labeled as an estimate.
- A check fails when the load is over the allowable, is marginal under 2x, and passes at 2x or more.
- Stick lengths and comparison objects are the list in the spec.
- Arm lift margin fails under 1x and is marginal from 1x up to 1.5x. Other material checks stay at 2x.
- The elevator hard-stop factor multiplies current-limit tension, and only when soft limits are off.
- Flywheel surface speed is a rule of thumb: about twice exit speed for a hooded wheel, about equal to exit speed for two wheels.
- Calculators 2–6 follow
content/calculators-2-6-spec.md. Their math is insrc/lib/mechanisms/.
Motor library
Every row is unverified. Approximate figures from memory, Oct 11, 2026. Verify every row against the vendor sheet.
| Motor | Stall torque (N·m) | Stall current (A) | Free speed (rpm) | Free current (A) | Verified |
|---|---|---|---|---|---|
| Kraken X60 | 7.09 | 366 | 6000 | 2 | No |
| Falcon 500 | 4.69 | 257 | 6380 | 1.5 | No |
| NEO Vortex | 3.6 | 211 | 6784 | 3.6 | No |
| NEO | 2.6 | 105 | 5676 | 1.8 | No |
| CIM | 2.42 | 133 | 5330 | 2.7 | No |
| NEO 550 | 0.97 | 100 | 11000 | 1.4 | No |
Human terms
1 N·m = 0.738 ft·lb = 8.85 in·lb. 1 N = 0.225 lbf. 1 kg = 2.2 lb. Torque under 1 ft·lb is shown in in·lb. Stick lengths are 1 in, 6 in, 1 ft, and 2 ft, whichever puts the weight between about 2 and 50 lb.
Comparison objects are fixed: a gallon of milk is 8.6 lb, a bowling ball is about 12 lb, and a bag of salt is 40 lb. A check under 2x the load is marginal. That threshold is a team choice, not a measured material limit.
Allowables
None of these are verified. Until a row has a number and verified is true, calculators say "Allowable not yet verified" instead of pass or fail.
| Allowable | Used in | Value | Source | Verified |
|---|---|---|---|---|
| HTD 5 mm belt, 9 mm wide, working tension | Mechanisms 1–5 | Not filled in | Belt maker or FRC vendor load data | No |
| HTD 5 mm belt, 15 mm wide, working tension | Mechanisms 1–5 | Not filled in | Belt maker or FRC vendor load data | No |
| GT2 3 mm belt working tension | Mechanisms 1–5 | Not filled in | Belt maker or FRC vendor load data | No |
| Aluminum 1/2 in hex bore crush force | All bore checks | Not filled in | Vendor data or conservative textbook value | No |
| Printed 1/2 in hex bore crush force (PLA, PETG, nylon) | All bore checks | Not filled in | Our own bench test (torque-wrench session) | No |
| Planetary gearbox torque rating per stage | Arm, elevator | Not filled in | VersaPlanetary, MAXPlanetary, UltraPlanetary charts | No |
| #25 chain working load | Arm, elevator | Not filled in | Chain vendor data | No |
| #35 chain working load | Arm, elevator | Not filled in | Chain vendor data | No |
| Gear tooth load by pitch and material | Belt to rack | Not filled in | Gear vendor data or Lewis equation | No |
| Rope or cord rigging working load | Elevator | Not filled in | Rope maker working-load data | No |
Twist constants
Textbook shear moduli: carbon steel about 79.3 GPa, aluminum about 26 GPa. Not measured on team stock.
Steel 79.3 GPa. Aluminum 26 GPa. The hex polar moment is calculated from a 1/2 in across-flats section. These are inputs to the twist formula, not allowables.