# Stepper Motor or Linear Actuator

## Main Question or Discussion Point

Hi,

I am trying to design a simple autonomous braking system for a 4 wheel drive ATV. The system needs to be as cheap as possible. I have come up with two possible solutions. The use of a linear Actuator to activate the brake or a stepper motor attached in someway to the master cylinder. It needs to operate quickly and with enough force to completely depress the pedal.

I am having problems with both options due to budget, torque and speed requirements. The force needed to depress the brake pedal fully is 420 Newton’s acting 0.12m away from the pivot point. There are plenty of Linear Actuators that have enough force but I am struggling to find ones that operate fast enough (I understand that there is a trade off, the greater the force the slower the speed). I started to wonder if you could use a stepper motor, but when sourcing one, I again encounter this speed force trade off in the opposite way, steppers are fast enough but I cannot find one with enough torque.

Can anyone suggest another method I have not thought of or a possible solution using one of the two ideas I have proposed?

Any help would be greatly appreciated.

Thanks

M

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Danger
Gold Member
Just at a glance, my first thought would be to use a pneumatic ram triggered by a solenoid valve. Depending upon your proposed driving course, however, you might not be able to carry a large enough air tank. That is assuming that: A) you don't need proportional braking, because this would just slam them on, and B) on the plus side, if you are willing to put out a bit extra, you could use a smaller tank with an onboard 12VDC compressor.
More detail as to your requirements, please... and don't hold your breath waiting for me because I have to go to sleep now.

The brake needs to work proportionally, just as in human operation. Therefore slamming on the brake, although would bring it to a stop, would not be favourable as it would mean the buggy would not be ale to slow down gradually or slow to a small velocity and then release the break to carry on moving. What other requirements would be best to include in this post?

Danger
Gold Member
What other requirements would be best to include in this post?
The only one that comes to mind, which I hinted at but didn't actually ask, is how frequently, and how many total times, does it have to operate? My reason for asking that is that resources such as space and electrical power need to be considered. if you were to use a hydraulic ram rather than a pneumatic one, there are proportional solenoid valves available for them, and 12VDC "power packs" which include the motor, pump, and reservoir in one compact unit, are not all that expensive. They are, however, quite heavy. If you are looking for a high-speed machine, that might be counterproductive.

If steppers don't have enough power (speed*torque) have you considered a servo? They tend to be more powerful.

berkeman
Mentor
Hi,

I am trying to design a simple autonomous braking system for a 4 wheel drive ATV. The system needs to be as cheap as possible. I have come up with two possible solutions. The use of a linear Actuator to activate the brake or a stepper motor attached in someway to the master cylinder. It needs to operate quickly and with enough force to completely depress the pedal.

I am having problems with both options due to budget, torque and speed requirements. The force needed to depress the brake pedal fully is 420 Newton’s acting 0.12m away from the pivot point. There are plenty of Linear Actuators that have enough force but I am struggling to find ones that operate fast enough (I understand that there is a trade off, the greater the force the slower the speed). I started to wonder if you could use a stepper motor, but when sourcing one, I again encounter this speed force trade off in the opposite way, steppers are fast enough but I cannot find one with enough torque.

Can anyone suggest another method I have not thought of or a possible solution using one of the two ideas I have proposed?

Any help would be greatly appreciated.

Thanks

M

The brake needs to work proportionally, just as in human operation. Therefore slamming on the brake, although would bring it to a stop, would not be favourable as it would mean the buggy would not be ale to slow down gradually or slow to a small velocity and then release the break to carry on moving. What other requirements would be best to include in this post?
Welcome to the PF.

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?

Danger
Gold Member
What safety interlocks are involved in the designs of the ATVs?
Oh, jeez, Mike... of course. Safety is paramount. For some reason, I had just thought of this thing running around on a motocross track or something all by its lonesome. The possible interaction with other vehicles or people didn't occur to me. That brings a whole different set of parameters into play.
To start with, Matt, is this thing autonomous or under external radio control? (I know that you said autonomous braking in your original post, but didn't specify whether or not that applies to the whole vehicle. I mean, real road vehicles such as some Mercedes models have autonomous braking, but are still driven by a human.)

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