- #1
Runei
- 193
- 17
Hello
Im doing a physics project and I am trying to come up with an idea for calculating the torque done by an electric motor on the wheels of an RC-car, and the resulting acceleration of the car.
We have modified the car with some stronger batteries, and now we are in a dilemma.
Each rear wheel is driven by its own motor and when we set the car to go forwards the motors turn fully on (Theres no gradual rise in the current).
This means that the wheels at first begin to slide.
All we need to to is make some measurements, and we need to find out how torque has something to do with the cars translational motion.
---- WHEELS SPINNING ----
I have deduced so far, that when the motors turn on, and the wheels begin to spin, the force exerted on the road by the wheels must be greater than the force the static friction is capable of exerting on the wheels. And thus, the wheels begin to spin, and the force exerted on the wheels is now the kinetic friction.
[tex]F_{k,fric}[/tex]=[tex]\mu_{k}\cdot m_{car}[/tex][tex]\cdot g[/tex] (Because the normal force is equal to the gravitational force.
The force due to kinetic friction exerts a force on the wheels and thus applying a torque on the wheels, slowing the angular velocity. Also the friction force accelerations the center of mass of the wheels (the axle) and thus the car accelerates, with an acceleration given by
[tex]\frac{F_{k,fric}}{m_{car}}[/tex]
I know that at some point when the car has picked up some speed, the wheels "grip" the road and then it is the static friction that accelerates the car.
If that is correct the force exerted on the road by the wheels must decrease with increasing velocity of the car, and at some point the force must come below a given point, and the static friction kicks in.
How can I calculate how the force exerted on the road? (I did it with torque, since force is torque dividid by the distance to the place where the contact is)
How can I calculate when the velocity of the car is high enough for the static frictio to kick in?
Im doing a physics project and I am trying to come up with an idea for calculating the torque done by an electric motor on the wheels of an RC-car, and the resulting acceleration of the car.
We have modified the car with some stronger batteries, and now we are in a dilemma.
Each rear wheel is driven by its own motor and when we set the car to go forwards the motors turn fully on (Theres no gradual rise in the current).
This means that the wheels at first begin to slide.
All we need to to is make some measurements, and we need to find out how torque has something to do with the cars translational motion.
---- WHEELS SPINNING ----
I have deduced so far, that when the motors turn on, and the wheels begin to spin, the force exerted on the road by the wheels must be greater than the force the static friction is capable of exerting on the wheels. And thus, the wheels begin to spin, and the force exerted on the wheels is now the kinetic friction.
[tex]F_{k,fric}[/tex]=[tex]\mu_{k}\cdot m_{car}[/tex][tex]\cdot g[/tex] (Because the normal force is equal to the gravitational force.
The force due to kinetic friction exerts a force on the wheels and thus applying a torque on the wheels, slowing the angular velocity. Also the friction force accelerations the center of mass of the wheels (the axle) and thus the car accelerates, with an acceleration given by
[tex]\frac{F_{k,fric}}{m_{car}}[/tex]
I know that at some point when the car has picked up some speed, the wheels "grip" the road and then it is the static friction that accelerates the car.
If that is correct the force exerted on the road by the wheels must decrease with increasing velocity of the car, and at some point the force must come below a given point, and the static friction kicks in.
How can I calculate how the force exerted on the road? (I did it with torque, since force is torque dividid by the distance to the place where the contact is)
How can I calculate when the velocity of the car is high enough for the static frictio to kick in?