[Nathan Streeter]

While it will be helpful to use the JVN Mechanical Design Calculator, there are a couple important things to understand about designing a motor setup (# motors, motor selection, gearing, etc.)...

First, a few things to know about motors:
- @ Stall: no speed, max torque, no power, max current draw
- @ Max Power: half speed, half torque, max power, ~half current draw
- @ Free Speed: max speed, no torque, no power, min current draw

You never want to design a system to operate at motors' max torque, because this is only provided at stall (torque then decreases linearly until 0 @ free speed)... For a "heavy-lifting" operation, I'd recommend designing for a point a little faster than max power... about 55-60% of free speed (which is 45-40% max torque). Designing for this point means that unexpected losses will push the motor closer to max power rather than further.

Also, always take in to consideration some losses... probably about 10-20% loss. Remember to account for this in both speed and torque calculations.

You can also shrink the pulley radius to increase your mechanical advantage... I'd personally recommend a smaller pulley than 2" diam for this reason.

Also, are you sure you really need ~500 pounds of force in your surgical tubing?! That is a phenomenal force! How are you pulling that back currently on your prototype? Perhaps try using more travel in your surgical tubing to enable as much energy storage but with a lower max force... (U = 1/2 k * x^2).

I'm low on time right now, but perhaps I'll post again later with a worked out example...