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Automatic brake applying system

  1. Nov 8, 2015 #1
    Hi fellas!

    I need to develop a system for a self driving car which involves automatically presses brake,clutch and accelerator when required.I am planning to use a servo for this purpose and have some trouble identifying the torque requirements!

    How much torque do i need?assume the lever arm(distance of brake from servo shaft is around 10-15 cm.)
    If not known.. kindly share any method available so i can measure the torque required.

    If force needed to press the pedal is known..dividing by lever arm should give my torque requirment.

    I will be using a car which has vaccum assisted power brake i guess.

    Any help would be much appreciated :)
    Have a great day!
  2. jcsd
  3. Nov 8, 2015 #2

    Simon Bridge

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    You should be able to answer your own questions by finding a car like the one you need to design and looking at it's systems.
    i.e. how much torque is required to break at what rate for the cars you are most familiar with?

    Those cars probably have a foot-pedal ... so you could design a device that acts as the foot+leg part and keep everything else the same ... refine the design by looking to see how much of the mechanism you can replace. Basically though, there is no substitute for climbing into a car and just looking.

    You probably should not be guessing about the type of breaking system i the car you use - the possible variables are too wide otherwise, and it will be impossible to answer your questions.
  4. Nov 8, 2015 #3
    Why not use automatic transmission and ABS-Automatic Braking System. This is a serious engineering job I advice you hire a pro or consult a buddy engineer.
    This will involve controls and mechanical engineering stuff. But if you like to pursue, there is no limit to interest, you may sort out by studying machine design and controls system or the easy way but the expensive and time consuming : Trial and error.
  5. Nov 8, 2015 #4
    Right now our focus is testing the AI part. We need a quick and dirty fix for the parts I have mentioned. We have the design planned out, but need the torque rating of the three servo required, hence the thread

    Take a look at the picture uploaded!

    Attached Files:

  6. Nov 8, 2015 #5
    Also, the car has already been purchased and we need not just automatic breaking, but also clutch accelerator steering and gear box.
  7. Nov 8, 2015 #6
    Hi , you have misunderstood my question I think. I am not concerned on how to design it as we are prepared with that. Take a look at the image posted below. Also, the car in question has already been purchased (manual transmission) and we can only make changes it in the external part.

    For the servo used in the picture, I want to know a way to know the torque rating of the servo needed.
  8. Nov 8, 2015 #7
    There's no way, to tell how much torque is needed, as you see, forces and energy is dependent on geometrics (dimensions). There's no way to tell how much magnitude is enough with out seeing your design.
    Any how, I believe I am only limited with the advice on directions I can give you, serious engineering involve cost you know and should not be practice on forums like this.
  9. Nov 8, 2015 #8


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    Practical tests will yield better and quicker answers than any Q+A on PF . If there is an unknown force in a real piece of equipment then do whatever it takes to measure it .

    Pedal - put a brick on it - if it doesn't move put another brick on it . When pedal floors count the bricks .
  10. Nov 8, 2015 #9
    Hi, I have attached picture of design for brake pedal. Kindly take a look and see if it helps you make any conclusion. It is okay if the servo we buy is underworked. Lever arm is around 15 cm!
  11. Nov 8, 2015 #10


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    I can't see any attachment.
    Unless you've done what Nidium suggested or have otherwise found the required force for your particular car then we can't help.

    Engineering design almost always starts with defining the design specifications.At the absolute minimum you must know:
    - How fast must the brake be pushed (milliseconds between min and max extension)
    -How hard must the brake be pushed (Newtons, this likely varies with extension)

    If you can't answer these questions then you can't select a servo.
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