Torque for Steering Wheel Using BLDC Motor

[WhyWhy]

Hi,

I want to calculate the torque of my Steering wheel using the BLDC Motor and i believe the torque formula which is :

Torque = Angular Velocity x Radius

But i don't have any idea how to calculate it from my steering shaft to steering wheel require how much of torque. Therefore, i can't buy the BLDC motor right now because unable to count the torque. Please Help and Thanks

Regards,
YY

 

[KlausST]

Hi,

My recomendation:
Find out how fast you want to turn your steering wheel.
Find out the torque. It is F x s (Force in N x distance to center in m)
Now you look for a motor with that or higer values.
If you dont find any, then you may consider an additional gear box for your motor.

Hope this helps
Klaus

 

[WimRFP]

KlausST has a good point, besides the torque, you need to know how fast you want to rotate the wheel, as this also determines the required mechanical output power the motor must have.

Just an example:
Steering wheel diameter 0.2 m
required force at 0.2 m radius to make a full turn within 2s: 30N

Torque = 0.2m*30N = 6 Nm.

angular velocity is 2*pi* 1/2 = 3.14 rad/s = 2*pi*revolutions/s

Mechanical power = (angular velocity)*(torque) = 3.14*6 = 19W.

You may need higher power as accelerating from 0 to 3.14 rad/s may require additional torque in case of heavy structures. You also need more power to overcome the losses in the gear box.

The gear box:
If your motor has 2000 RPM at nominal output power. 2000 RPM = 2000/60 = 33.3 rev/s

you require a full turn in 2s, so that is 0.5 rev/s.

Gear box ratio = 33.3/0.5 = 66.6.

If your steering wheel requires static torque, the motor needs to deliver torque without turning. This may overheat the motor as there is no cooling. This can be solved by using a torque limited brake.

Other option is to use a self-locking worm gear/drive. The main disadvantage is its low efficiency (<50%) to enable safety self-locking. you need more motor power to compensate for the mechanical (heat) loss in the worm gear.

There are other solutions when you search for back driving self locking, but these come with a price.