Using scooter brakes

[packtim]

Im currently trying to sort out braking systems for a Formula Student car. Initially I was going to use 200mm discs all round with AP 2 pot calipers.

I have decided to use 200mm moped discs, which are 6mm thick. Problem is most small motobike calipers will only accommodate up to 5.5mm (Ap racing's 2 pot will only take up to 4.5mm). All previous braking calculations were based around these, and seemed fine.
I have tried looking for moped from disc calipers for these brakes, but they are hard to find, hard to find information for, and therefore I cant be certain that they will be up to the task performance wise.

Also, because of the lack of info I can find on them, they are incredibly hard to model for the car in CAD. Are manufacturers usually willing to give all these dimensions out or is it better to approximate dimensions, given that they are being bought in, not made. However, I will still need mounting dimensions for them


Does anybody have any pointers for me??

Thanks a lot


Tim

[Perry Harrington]

Originally posted by packtim:
Im currently trying to sort out braking systems for a Formula Student car. Initially I was going to use 200mm discs all round with AP 2 pot calipers.

I have decided to use 200mm moped discs, which are 6mm thick. Problem is most small motobike calipers will only accommodate up to 5.5mm (Ap racing's 2 pot will only take up to 4.5mm). All previous braking calculations were based around these, and seemed fine.
I have tried looking for moped from disc calipers for these brakes, but they are hard to find, hard to find information for, and therefore I cant be certain that they will be up to the task performance wise.

Also, because of the lack of info I can find on them, they are incredibly hard to model for the car in CAD. Are manufacturers usually willing to give all these dimensions out or is it better to approximate dimensions, given that they are being bought in, not made. However, I will still need mounting dimensions for them


Does anybody have any pointers for me??

Thanks a lot


Tim

Take them to your local machine shop and have them turn them on the flywheel grinder. It should be able to cut down the braking surface easily.

--Perry

[packtim]

I can get it skimmed down in our workshop, but there are 2 problems with this

1)This will have a very high tolerance on it for the thickness of the disc, due to it rubbing on the pad. Each disc is £30, and I can buy moto discs for 75. With time spent on this @£20/hr, im not sure it will be worthwhile.

2)This will not be easy to fit in a lathe accurately, due to its thickness and diameter.

[Rob.C]

why dont you use the mounting holes for the rotors and make a jig that sits in your lathe nicely!?

alternatively, why not just make your own rotors?

we have been doing that for years, you can then customise them to work at optimum temps and drill them out aswell!

[packtim]

I wanted to make the rotors, but am seriously contrained on time. Initially I had 5 people in my group to do all the control systems, brakes, etc, but 2 have dropped out. The uni wants the final design in 3 weeks. With the increased work load I dont have time to design the brakes.

Anyway, decided in a meeting this morning to stick with those rotors, but probably change to a Wilwood GP 320 caliper. Thanks for your suggestions

[drivetrainUW-Platt]

have them custom lazered out, you can do any design you want and it doesnt take long at all, we get ours done for free

[Cement Legs]

You may want to consider motorcycle rotors. Most rear rotors are 200 mm or less(some are close to 220 mm). Ours are roughly 190 thou or 4.83 mm.

[packtim]

I have been considering motorcycle rotors, but am worried, as the seem to be about twice the price of the moped rotors (around £75). Also, my group has been told today we have a budget of $4000 to spec all the braking systems, gear system, pedal box, safety systems, fuel tank, dashboard gauges. Therefore im trying to cut back on what I can, although I realise the braking system is one of the most important parts ofthe car.

[drivetrainUW-Platt]

4k, my budget for the drivetrain is around $500, enjoy man

[packtim]

You cant even buy the engine for $500, so I think you better have some words with the project manager!

[Perry Harrington]

Originally posted by packtim:
I can get it skimmed down in our workshop, but there are 2 problems with this

1)This will have a very high tolerance on it for the thickness of the disc, due to it rubbing on the pad. Each disc is £30, and I can buy moto discs for 75. With time spent on this @£20/hr, im not sure it will be worthwhile.

2)This will not be easy to fit in a lathe accurately, due to its thickness and diameter.

That's why I said to take them to a machine shop and have them turned on a flywheel grinder. A flywheel grinder consists of a rotary table and a blanchard grinding head. The disc is laid flat, clamped in the middle, and the grinder makes a pass as the table rotates. It's very accurate and cheap. If they charge you more than $20 to do 2 discs, they're ripping you off.

--Perry

[B]

I agree with Perry.

I had our rotors growd down from 6.5mm to 4.3mm for the front and down to 3.3mm for the rear! And they only changed $7.50 (AUS) a face and did it in a coupld of hours. Any braking place or machine shop should be able to do it.