Electronics > Beginners
How to control dc motor torque using H Bridge?
rstofer:
--- Quote from: Benta on November 13, 2018, 08:58:41 pm ---There's a lot wrong with that circuit. Power transistors with the same part number are depicted as both N- and P-channel, the drive circuit is ridiculous etc.
But the OP states it's Microsoft, knowing their software it could be real. :-DD
--- End quote ---
The HAT3004R device contains both a P and N channel device. Note parts IDs Q1 and Q1' - they are in the same package. Same for Q2 and Q2'.
http://www.ic72.com/pdf_file/h/564630.pdf
I'm guessing that the NPN transistors could be 2N2222A but I don't know that. I also find it odd that the designers added capacitance to the MOSFET gate capacitance ad then used a very low value series resistor to overcome the capacitance (27R). I'm thinking they truly fine tuned the potential for punch through.
It's actually a pretty clever circuit. I have a wheel around here but I don't know if it has force feedback. It would be worth looking at.
lion032:
Got it!
Thank you very much!
max_torque:
--- Quote from: rstofer on November 14, 2018, 10:24:51 pm ---
--- Quote from: max_torque on November 14, 2018, 06:28:35 pm ---The motor obviously rotates as it is attached to the steering wheel! And as it rotates, it DOES generate a Backemf (otherwise it is breaking the laws of physics, and even for microsoft, that'd be reasonably difficult......).
--- End quote ---
How much does the motor rotate as I attempt a land speed record at Bonneville Salt Flats, Utah? The point being that the wheel is often held stationary for long periods and the motor does not rotate and back-emf is a non-issue. But the motor is still energized to achieve braking.
Given no back-emf, the current is only limited by the applied voltage and the armature resistance and this is a very good reason for having current feedback. Something has to prevent the motor from burning up since the stalled rotor current will be several (or more) times higher than nominal full load current.
--- End quote ---
The motor rotational speed is clearly the steering wheel angular velocity multiplied by the physical gear ratio between the two components. To get a high steeringwheel torque, you either need a high turn count motor (high KT, but also high KE as a result) or a low turn count motor (low KT & KE) driving the steering wheel though a significant gear reduction, which, guess what, ends up with the same effective KT/KE !!
No way are you going to get anything like realistic force feedback if you fail to consider the most important characteristic in the system....
(the good news, is that if you use a current control topology (in hardware or software) then you get the Bemf compensation for free, the issue simply becomes one of control bandwidth and accuracy)
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