Torque calculations for a small electric vehicle

[Lnewqban]

Should I consider them 0 ?

Yes.
No rolling resistance.
Pushing forward forces of two wheels balance rearward gravity force component, assuming your contact patches have enough traction, which depend on normal gravity force component acting on each of them.

 

[Lnewqban]

For beginning I will put the vehicle manually on the slope, and I expect to not roll down the slope.

Your wheels would be rotating while in the air, just to be precisely stopped when contacting the surface of the slope?

 

[domnu_filip]

Your wheels would be rotating while in the air, just to be precisely stopped when contacting the surface of the slope?

Yes, kind of.

 

[Lnewqban]

Yes, kind of.

Then, from previous tests, you should have narrowed how much amps your motors will need to receive in oder to provide the precise torque needed to compensate for the pulling rearwards gravity component.
Your modulating control should match that level of precision.
Otherwise, your car may still slowly move up or down the slope after you place it on it.

 

[domnu_filip]

Then, from previous tests, you should have narrowed how much amps your motors will need to receive in oder to provide the precise torque needed to compensate for the pulling rearwards gravity component.
Your modulating control should match that level of precision.
Otherwise, your car may still slowly move up or down the slope after you place it on it.

Ok, I used the steps described in that document, without Fa and RR, because there is no rolling, and no speed?
Is this correct?

 

[domnu_filip]

Then, from previous tests, you should have narrowed how much amps your motors will need to receive in oder to provide the precise torque needed to compensate for the pulling rearwards gravity component.
Your modulating control should match that level of precision.
Otherwise, your car may still slowly move up or down the slope after you place it on it.

And in up motion, I will use this for calculating the max angle.

And one more question, the calculation from that document, are valid for an angle smaller than maximum angle?
Thanks!

 

[Lnewqban]

I am not sure about those equations.
Could you show us what the terms mean and a free body diagram of forces?

 

[domnu_filip]

Right here, in my case FWD.

 

[Lnewqban]

Thank you.
I do not see the $F_r$ that is shown in the equations in that diagram.

Do you want to find the torque of each wheel as a function of those variables for your work rather than calculating a value for a determined slope?

 

[domnu_filip]

Thank you.
I do not see the $F_r$ that is shown in the equations in that diagram.

Do you want to find the torque of each wheel as a function of those variables for your work rather than calculating a value for a determined slope?

Yes, I want to find the torque of each wheel as a function of those variables.
Hope it helps; Do you know to should I calculate the rolling resistance on a slope?

 

[Lnewqban]

Yes, I want to find the torque of each wheel as a function of those variables.
Hope it helps; Do you know to should I calculate the rolling resistance on a slope?
View attachment 259933

But we are calculating for steady condition first: no rolling resistance.

 

[domnu_filip]

But we are calculating for steady condition first: no rolling resistance.

Yeah I know, I was just curious how can I do that in future.

 

[Lnewqban]

Yes, you could once you are ready to compute the dynamic condition of the car moving uphill.
For static conditions, the equation for finding the angle is correct, being $f_r=0$

That would be the maximum angle for which your driven wheels will keep traction.

The torque that each of both driven wheels should deliver in order to keep the car from rolling backwards should be equal to half the total weight (0.5 mg) times the sin of the angle of the slope times the radius of the wheel.

 

[domnu_filip]

The torque that each of both driven wheels should deliver in order to keep the car from rolling backwards should be equal to half the total weight (0.5 mg) times the sin of the angle of the slope times the radius of the wheel.

And for going uphill?

 

[Lnewqban]

And for going uphill?

For that, you will need to estimate a desired rate of acceleration.
That means an additional torque will be needed to overcome the inertia of the car.
The maximum slope will need to be a little less than for static condition, or wheels may slide under the increased torque, as tangential force may become bigger than the available friction on the contact points.
Unless you are rolling on deflated tires, I believe that rolling resistance at constant speed could be dusregarded.

 

[domnu_filip]

For that, you will need to estimate a desired rate of acceleration.
That means an additional torque will be needed to overcome the inertia of the car.
The maximum slope will need to be a little less than for static condition, or wheels may slide under the increased torque, as tangential force may become bigger than the available friction on the contact points.
Unless you are rolling on deflated tires, I believe that rolling resistance at constant speed could be dusregarded.

So, I have too add this to my stationary torque? Torque= ( m*g*sin_angle+(m*g*cos_angle*Crr) +Fa)*wheel_radius*resistance_factor?

 

[Lnewqban]

No need to add torques up.
The value of the torque for stationary condition is smaller than the one needed for acceleration.

 

[domnu_filip]

No need to add torques up.
The value of the torque for stationary condition is smaller than the one needed for acceleration.

Ok, what is the condition for acceleration?
I mean, how should I calculate the torque for starting from resting on the slope (previous case), to move uphill?

 

[Lnewqban]

I believe that we already have covered that.
Please, see:

https://www.engineeringtoolbox.com/cars-power-torque-d_1784.html

https://www.engineeringtoolbox.com/tractive-effort-d_1783.html

https://www.engineeringtoolbox.com/car-acceleration-d_1309.html

 

[domnu_filip]

I believe that we already have covered that.

Could you repeat please? I understand a little slow I guess :D

 

[domnu_filip]

I believe that we already have covered that.
Please, see:

https://www.engineeringtoolbox.com/cars-power-torque-d_1784.html

https://www.engineeringtoolbox.com/tractive-effort-d_1783.html

https://www.engineeringtoolbox.com/car-acceleration-d_1309.html

If I have the wheels mounted directly on the BLDC motor axle, how should I calculate the wheel torque?
I ask this because, if I send the command to the motor, e.g. 5 Nm necessary to keep the vehicle steady on the incline, how do I get the feedback for the control loop?
So, if I calculated that the vehicle needs 5 Nm to rest on the slope, it is correct to measure the wheel torque and consider it as feedback to my torque control loop?
And how do I should I calculate the wheel torque in this case?

 

[jack action]

Wouldn't your feedback come from an accelerometer? You set a certain amount of torque, expecting a certain amount of acceleration. If the resulting acceleration is different from what is expected, you apply the necessary correction.

 

[domnu_filip]

Wouldn't your feedback come from an accelerometer? You set a certain amount of torque, expecting a certain amount of acceleration. If the resulting acceleration is different from what is expected, you apply the necessary correction.

Yes, but how do I convert it? And btw I want it to rest...

 

[jack action]

If you want the acceleration to be zero (at rest), then you have calculated a constant value for your torque $C$, say 5 N.m. If the vehicle accelerate (+ve or -ve), then you need to counterbalance your torque by the amount of acceleration $a$ that is measured (it should be zero).

So you get your new torque value $T$ to apply with $T = C + rma$ where $r$ is your wheel radius, $m$ is the vehicle mass and $a$ the measured acceleration.

If you can measure the velocity $v$, that is even better, because your trying to reach for $v = 0$, which is your true objective. then the desired acceleration might be to reach for $\frac{dv}{dt}$ where $dv$ will be some fraction of $v$ and $dt$ will be based on your feedback loop time interval.

 

[domnu_filip]

If you want the acceleration to be zero (at rest), then you have calculated a constant value for your torque $C$, say 5 N.m. If the vehicle accelerate (+ve or -ve), then you need to counterbalance your torque by the amount of acceleration $a$ that is measured (it should be zero).

So you get your new torque value $T$ to apply with $T = C + rma$ where $r$ is your wheel radius, $m$ is the vehicle mass and $a$ the measured acceleration.

If you can measure the velocity $v$, that is even better, because your trying to reach for $v = 0$, which is your true objective. then the desired acceleration might be to reach for $\frac{dv}{dt}$ where $dv$ will be some fraction of $v$ and $dt$ will be based on your feedback loop time interval.

I have the speed of the motor axle is spining, in rad/s, if I have the wheel directly on that axle, or a hub-motor (segway), can I use that value?

 

[jack action]

Yes

 

[domnu_filip]

Hello guys, I'm working for a home project and I want to made a simulation on a BLDC motor, which have a wheel attached to it's axle. (It is a part of small cart, 2 BLDC motors with 2 wheels directly mounted on the axle). So can I control the torque this way? What regulator should I use? How to integrate the load torque in motor subsystem?

 

[domnu_filip]

No one?..

 

[anorlunda]

What regulator should I use?

When I shop for BLDC motors online, I see that many of the include the manufacturer's regulator as part of the package.