# Homework Help: Friction Brakes Ergometer: Novel Application

1. Jan 20, 2008

### dalvares

Dear All.

I am working on a uni project building an ergometer for an MRI machine. I was interested in purchasing a disk brake system to control the resistance and the power output for the ergometer. The application requires that all parts to be non magnetic as it will be used in an MRI machine (Aluminium and Stainless Steel ok). Because of the hydraulic brakes for mountain bikes are readily available I was hoping to purchase one and just replace the bolts etc. I understand given the usual application of these systems that it unlikely that the brakes conform.

I was given feedback that the system might overheat and fail as they are not design to be dragged constantly. I understand this is probably true in a mountain bike however the pedal will operate at a max of 90rpm and subjects will dissipate only 100W of power. I would still like to calculate the heat dissipation and the temperature change in the pads and disk.

So far I know the power so I can calculate the work done by the subject when the brakes are fully depressed over the duration of the experiment. Assuming all is dissipated as heat I can then use the formula

Qm=m*c*T
mass=m
specific heat cap=c
Temp=t

Assuming that I am on the right track so far, I was lost when I tried to figure out how the heat would be dissipated. There's 2 brakes pads (Caliper brakes) 25mm*25mm and the rotor is 160mm OD. (Assuming its a flat disk with no ventillation). Is it half on the brake pads and the other half on the rotor. Also where does the coefficient of friction come in or is that not really important for this aspect.

I have simulink MATLAB at my disposal. If you think I might be able to do a more accurate job on that can you guide as to how I would set up a model and what equations I would use.

Really appreciate any help I could get.

Looking forward to hearing from you soon.

Cheers
Darren