Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Piston force required (Disk brake system)

  1. Jul 22, 2016 #1
    Hello everyone,

    I'm currently working on a project where we need to change the little manual wheel (shown by red arrow) and replace it by a cylinder (either pneumatic or hydraulic). Right now, when the manual wheel is adjusted by rotating it to the right, the contracting rim will come closer together, which slows down the shaft that is rotating the white fabric seen in the image. What I'm trying to figure out is how to calculate the output force needed by the piston in order to successfully bring the contracting rim closer together.

    I was looking for some ideas and I found the second image in this PDF (page 6) https://www3.nd.edu/~manufact/FME_pdf_files/FME3_Ch18.pdf [Broken]. The rims are not in the same location, but I guess that gives you an idea of what I'm looking for. I attached a third image just in case.

    I would really appreciate any ideas and general equations to estimate de force required by the piston, so I can select one with the right force range.

    Thank you in advance for your help!!

    Photo Jul 22, 11 06 23 AM.jpg

    Disk brakes.PNG

    Photo Jul 22, 11 31 38 AM.jpg
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Jul 22, 2016 #2

    jack action

    User Avatar
    Science Advisor
    Gold Member

    You show a disc brake, but you seem to have a band brake or a block/shoe brake.
  4. Jul 22, 2016 #3
    I attached a small 30 sec video for better reference. What do you think? Block/shoe?
    Thank you so much for your time.

  5. Jul 22, 2016 #4

    jack action

    User Avatar
    Science Advisor
    Gold Member

    It looks like a block/shoe, but I can't see much. If you want to make some calculations, you will have to take it apart to get measurements. It must be relatively easy because I would guess it should be done regularly for maintenance.

    Another (easier) way would be to measure the required force directly. You could also just measure the torque needed to turn the wheel and you can convert this to the applied force (quick estimate, detailed calculations).
  6. Jul 22, 2016 #5
    Jack's recommend to calculate using the torque on the existing screw is a good one. If you are replacing the screw with a piston type actuator the hydraulic side of the piston will be pressure adjustable to fine tune the braking required. As long as the piston is of adequate size to provide close to the correct effort the rest will come afterwards.
  7. Jul 24, 2016 #6
    Thank you for those links. I didn't think about considering the screw torque before, that is a good idea!

    I was doing some additional research and it occurred to me to take a look at my "Machine Elements in Mechanical Design" book by Robert L. Mott. I didn't have access to it during the week, so I had to wait until this weekend to read it. Anyways, there's a chapter on Clutches and Brakes and I found a brake similar to the one I'm working on but without the solenoid (I attached a picture from the book), and instead of the spring I have the screw which I'm looking to replace with a piston. They describe it as a long shoe drum brake. I also attached the section of the chapter that covers that topic.

    I'll take some measurements tomorrow and I'll let you know the approach we take!

    Thank you again.

    Attached Files:

  8. Jul 24, 2016 #7
    It is indeed a good idea to consider the torque on the screw. Although, I was looking at a slightly different approach. I attached the files that explain it in my previous reply if you want to take a look at those :) And yes, we do need to adjust the pressure so I've been looking for proportional valves that receive a signal range from 4 to 20 mA, so the input current will be proportional to the output pressure exerted by the piston.
  9. Jul 25, 2016 #8


    User Avatar
    Science Advisor
    Gold Member

    Have you considered turning the screw using a motor/gearbox combination? If you can estimate how much torque it takes to turn the wheel, you can likely find a motor with a gearbox that could turn it for you...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted