How to calculate Torque for exoskeleton suit that drives human leg

[jeeloong]

Dear Robot Expert,

I need help on calculating torque of an human leg for exoskeleton suit. Where can I get a reliable formula.
My issue is to calculate the torque required to actuate hip and knee of a person with mass of 80 kg for instance
so that I could determine the motor max torque and size

Thanks

[newInRobotics]

To get min torque required You multiply weight motor has to lift by distance from the center of the shaft at which that weight has to be lifted. For example, if You want to duck with exo suit, then that means knee joint have to support (if full support is required) almost 80kg of mass at around 30cm (length of thigh) away from its shaft, that gives us 80kg * 30cm = 2400kg-cm ~= 235.36N-m. Taking into consideration that You have two motors (one at each knee) means that knee joint motors will have to work at half load is one decides to duck, which is what You want. You never want to make motors work at 100% of their capabilities as that leaves no margin for error.