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maximum speed of a hydraulic brake disc

madrat27madrat27 Posts: 7
edited September 2014 in The workshop
Hi,

I am a Masterstudent Maschinenbau at the university of the IME RWTH Aachen Germany. For my Master's thesis I need to design and construct a 2-speed-gearbox as a didactic element for a course (https://drive.google.com/file/d/0B8PE0B ... sp=sharing). I am searching for a simple brake system to slow the system down and stop it. I was considering to use the shimano hydraulic brake BR-T665, but I can not find the maximum torque and the maximum velocity it can withstand. I can also use another type of hydraulic brake. The brand is not important. The highest velocity the shaft will have is 2000 rpm. I'm afraid that the disc will heat up to much. The gearbox will only run a few times a year and that only for a maximum of 4-5 minutes. Is there a place where I can find a good datasheet for this? Or maybe a review of a test done on these kind of brakes? I just need a general guideline. I'm considering this system for its simplicity and cost. If you would compare it to industrial brakes its quite cheap.

Thank you,
Koenraad

PS: I hope I made this thread in the right place. If not, my apologies.

Posts

  • ride_wheneverride_whenever Posts: 13,279
    One of the mags did a massive brakeset test with dynoing a while back.

    Use massive rotors, saint brakes and a big cooling fan and you'll be fine
  • thanks,

    already good to know that it should work. Would you by any chance still know what magazine and which edition?

    thanks again!
  • ride_wheneverride_whenever Posts: 13,279
    What mtb 2012 or 2013. Pm supersonic, he'll probably know
  • supersonicsupersonic Posts: 82,708 Lives Here
    I shall have a look into it. Can you work out the retarding force of your system?
  • nicklousenicklouse Posts: 50,675 Lives Here
    If that was a bike wheel you would be going a bit fast.

    But I don't see the rpm being to much of an issue. From the pics I would guess that the rotor would be quite a bit if the total rotating mass.

    I would do it.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • mr_evilmr_evil Posts: 234
    There might be a problem with overheating due to the lack of airflow for cooling. You could estimate whether this will be a problem by working out the total kinetic energy of the system at 2000rpm, calculating how much the rotor would heat up if all that energy was dumped into it at once, and comparing that temperature with the boiling point of the brake fluid.
  • deswellerdesweller Posts: 5,175
    You need to do an energy transfer calculation. I don't think centripetal force will be an issue; the question will be staying below the maximum heat transfer rate of the disc and caliper assembly. Without knowing the masses and speeds of the components of the gearbox then we can't really help you.

    If you used the energy of, say, a 120kg bike + rider stopping from 40mph as quickly as possible (i.e. with the back wheel just off the ground) on a level surface, with a tyre max mu of 1 then you might get close to the operating limit of the brake. Then multiply by, say, 1.7 to approximate the design limit.

    Edited for typo.
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  • Ok,

    a little bit more data: https://drive.google.com/file/d/0B8PE0B ... sp=sharing
    The shafts themselves have a diameter of 30mm and a length of 300mm. Everything is made of steel.

    Something I should have said from the beginning. The gearbox is a mechanical simulation. The brake would simulate for instance wheels of a car. The brake will be braking constantly. So for 5 minutes it needs to brake at around 5-8 Nm. The brake needs to produce a counter-torque, so that the force on the gears is high enough.

    So the purpose of the break is only to give a counter-torque. If the shaft would be turning at full speed: 1500rpm. And the motor is shut down the system should stop in let's say 20 seconds tops. It does not need to stop in a second or so.

    Thanks for your quick response!
  • mr_evilmr_evil Posts: 234
    5-8Nm is nothing. For a bicycle, if you take the 120kg mass suggested above and assume a deceleration of 0.5g (I think that's reasonable for a bike) and a wheel radius of 0.35m, then the braking torque will be over 200Nm. I would expect the brakes to be able to withstand substantially more than that.

    Heat is more likely to be a problem because cooling will be almost nothing without airflow, and brake fluid boils at a relatively low temperature. To get an idea of how much, taking 8Nm and 2000rpm, the brakes have to deal with something like 1.7kW for 5 minutes. If I was designing something to deal with that much power I would be looking for a very big heatsink and a very noisy fan.
  • deswellerdesweller Posts: 5,175
    OK I think he's got enough information to figure it out...it's supposed to be bloody homework!
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  • madrat27madrat27 Posts: 7
    edited August 2014
    DesWeller wrote:
    OK I think he's got enough information to figure it out...it's supposed to be bloody homework!
    Dear Mr. DesWeller, the reason of this thread was to give me more data on bicycle brakes. I do not expect a complete solution. I only hoped for a guideline and a collection of data on bicycle brakes. I do not have a lot of knowledge about hydraulic bicycle brakes, hence the thread. I posted solely because I did not know where to search for it. I had already contacted several bicycle companies before posting this thread. They did not reply. This is not homework. When I use a wrong brake and the system breaks down people could get hurt. It is a small part of my thesis, but an essential one. I have been working on my thesis for over 6 months. Nevertheless I thank you for your first input. It helped a lot.
  • supersonic wrote:
    I shall have a look into it. Can you work out the retarding force of your system?
    Dear Mr. Supersonic, would you by any chance already have an idea what article it was? I searched for it myself but had trouble finding it. The reason I ask is because I would like to use the article as reference in my thesis. I need a good data reference on the possible counter torque of a disc brake. The counter-torque would be around 5-8Nm. On a disc brake of 160mm, the retarding force that the brake pads should provide is 50N.

    When I have done my calculations I will let you know what type of brake I used. I will use dot5.1 braking fluid which has a boiling point of 205°C. I thank you all for the good information and tips!

    Thank you!!
  • supersonicsupersonic Posts: 82,708 Lives Here
    Might take me some time! I'll try and get some info for you.
  • Thank you Supersonic!
  • thistle_thistle_ Posts: 6,186
    I know you're after info on a disc brake, but what you're describing is similar to the resistance created by a turbo trainer. Might be worth looking into how they work and dissipate heat?
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