# BLDC Motor force in reverse

Hello,

I am trying to build a force feedback yoke for Flight Simulator X. The yoke is supposed to be as close to a Cessna 172 as possible. Because of that the torque for the aileron system has to be about 5Nm and the force for the elevator control has to be about 50N. I have finished my mechanical build and the only thing missing are the motors to produce the force.

Is there any way to calculate the needed power of the motors or do they only need to apply the needed torque at 0 revolutions? Since the motor doesnt spin by itself, but i spin it by foce.

Here is an example to calrrify what i mean. Lets say the motor spins clockwise if no torque is applied. Now i apply a torque that is greater than the produced torque of the motor. The motor will stop spinning and i will feel the motortorque as a torque on whatever is stopping the motor. If i force the motor to spin counterclockwise now. Can i calculate how much power it would need? Or is the power just the coilresistance in conjunction with the applied current during stall speeds?

I hope somebody can help me.

You need to search for a motor designed to not overheat when stalled for a long time. Might be pretty hard to find. I have only seen a one very small AC sync motor designed to do that.

Paul

DC motors are normally rated for full speed full power for cooling - the fan on the rotor aids cooling.

Thus the torque rating at stationary will be less than the power rating implies. The actual derating ratio may not be documented as most motors are not designed to be stalled for more than a fraction of a second.

You need to figure out the maximum speeds involved to get a rough handle on the gear ratios you'll need, as gearing trades speed for torque.

For linear force you'll have to figure out a back-drivable linear motion setup (standard linear actuators are designed not to be back-drivable deliberately, which is no use for force feedback).

Sounds like you need a "torque motor" (designed for full torque output at 0 RPM) but don't know if they're available in small sizes and low voltages. Google it.

Any DC motor can do this, its figuring out the max safe stall current/torque that's the issue. Brushless DC motors will have significant cogging in stall mode if commutated via hall-sensors, which will be odd for force feedback, unless geared down significantly (which you probably need anyway). I think some experimentation might be needed, start on a smaller scale and see what you can get away with without generating smoke or flames!

Brushless motors are capable of beautiful smooth torque when driven correctly. Witness the camera gimbals hanging off zillions of drones.

But "correctly" is the hard part.

I expect a lot of other people have done this exact thing for other home cockpits. What did you find on Google?

MorganS: Brushless motors are capable of beautiful smooth torque when driven correctly. Witness the camera gimbals hanging off zillions of drones.

That's position control, not torque control, the feedback is hiding/compensating for the cogging.

As I think about it more, it seems like torque control is more difficult. That would require sensors on a brushless motor.

How do the commercial force-feedback joysticks do it?

DC motor with current control?

Yea as far as i know they use normal DC motors with current control.