Calculating Stopping Distance for a Small Buggy Using a Linear Actuator?

[mattm874]

I am trying to work out how long it would take a small buggy weighing 300kgs to stop when traveling at 10kph and then at 20kph with the operation of a linear actuator. The no load speed of the actuator is 11mm/s and fully loaded speed at (4000 Newtons) is 8mm/s. For the brake to be fully on there needs to be 1800Newtons of force.

For the sake of ease, let's say the force needed to apply the break will increase proportionally with respect to time and the speed of the actuator will decrease proportionally with respect to the force. Can anyone help me? This is purely theoretical and therefore disregarding, tyres, road surface and other similar conditions.

Thanks

 

[berkeman]

Hi mattm874,

You didn't answer my safety questions in your other thread: https://www.physicsforums.com/threads/stepper-motor-or-linear-actuator.778866/#post-4896418

Can you address those a bit here? The calculation you ask about here is fairly straightforward, but I'm still concerned about this autonomous ATV that you are working on designing. Thanks. :-)

 

[mattm874]

Hi mattm874,

You didn't answer my safety questions in your other thread: https://www.physicsforums.com/threads/stepper-motor-or-linear-actuator.778866/#post-4896418

Can you address those a bit here? The calculation you ask about here is fairly straightforward, but I'm still concerned about this autonomous ATV that you are working on designing. Thanks. :)

Can you say more about your project? Is it a school project in an ME course or something? Where exactly are you going to be running these autonomous ATVs? What safety interlocks are involved in the designs of the ATVs?

The design will be a one off, incorporated will be an emergency shut off meaning the brake will automatically be applied if needed and an engine kill switch will be incorporated. If the buggy passes the design stage it will be run in a cordoned off car park that will have been booked out so as to have no cars of people about. The buggy will be limited to 10kph. I hope that addresses some of your concerns.

 

[berkeman]

The design will be a one off, incorporated will be an emergency shut off meaning the brake will automatically be applied if needed and an engine kill switch will be incorporated. If the buggy passes the design stage it will be run in a cordoned off car park that will have been booked out so as to have no cars of people about. The buggy will be limited to 10kph. I hope that addresses some of your concerns.

Can you say more about how the kill switch mechanism will work? How will the ATV know if positive RF control has been lost?

On your question about how to calculate the stopping distance, the brake pads will exert a friction force on the brake rotors/drums according to the dynamic coefficient of friction for the pad & rotor materials. By applying the brakes, you exert a normal force between the pads and rotors, and that translates into a reverse torque that slows the vehicle. Just as the motor supplies a forward torque to accelerate the ATV, the brakes supply a reverse torque to decelerate the ATV. Do you know the coefficient of friction for your pad/rotor combination? What is the average radius that the pads are away from the axle?

 

[mattm874]

Can you say more about how the kill switch mechanism will work? How will the ATV know if positive RF control has been lost?

On your question about how to calculate the stopping distance, the brake pads will exert a friction force on the brake rotors/drums according to the dynamic coefficient of friction for the pad & rotor materials. By applying the brakes, you exert a normal force between the pads and rotors, and that translates into a reverse torque that slows the vehicle. Just as the motor supplies a forward torque to accelerate the ATV, the brakes supply a reverse torque to decelerate the ATV. Do you know the coefficient of friction for your pad/rotor combination? What is the average radius that the pads are away from the axle?

We are using Arduinos and Pi's and in the programming we will make sure we have a code to kill power and automatically apply break if RF signal is lost or if there is a fault with one of the other systems.

The average radius of the pads is 130mm and the coefficient of friction for the pad/rotor combination will have to be an estimate as I am still waiting to hear back from the manufacturer. Therefore I will assume for the moment it is 0.3mu.