View Full Version : are motor rpm and torque the right calcs for my design?
16th Oct '11, 20:13
I am designing an electrically powered drill; the reciprocating shaft, which connects the shank and drill bit, is driven by a CAM which connects to a motor through gears. How do i determine motor specifications from gear, cam and shaft weight, speeds and frictional resistances on bearings, bushings etc?
also, is rpm and torque the relevant motor properties?
21st Oct '11, 15:55
There are two motions...
1. The Power motion when the Axial thrust of the drill comes into play. The forces are... The axial thrust of the drill, The pressure angle that the cam makes with the slider, the gear reduction, efficiency of the gear and then the power of the motor.
2. The return motion, when the motor has to lift the weight of the reciprocating elements and the axial thrust is absent. However, you may consider a certain percentage of the axial thrust for "Scrap Friction".
Power of the motor does depend on the rpm. After all power is a function of Torque and speed.
24th Oct '11, 11:35
The motor torque is determined from two cases; Acceleration and Constant Torque Requirements. The inputs are the required drill output speed, time to accelerate, the required torque output of the drill and the inertia of the largest device attached to the drill bit.
The first case is to calculate the reflected rotational inertia (J) from the drill bit to the motor through the cam and gear train. (Don't forget to include efficiency). Then a torque calculation is done based on the time to get the drill bit up to the desired rpm and the Inertia (J) using T=J*Alpha where Alpha is the rotational acceleration.
The Second case is to calculate the motor torque based on the required drill output torque and efficiency of the gear train and cam mechanism. This is the constant running torque case.
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