Friction Brakes Ergometer: Novel Application

[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

 

[KataKoniK]

Dear Darren,

Thank you for reaching out to us with your project. It sounds like you are on the right track with your calculations and approach. However, there are a few things you may want to consider when using a disk brake system for your ergometer in an MRI machine.

Firstly, as you mentioned, the disk brake system may not be designed for constant dragging and could overheat and fail. This is a valid concern and could potentially lead to safety hazards for the subject using the ergometer. It may be worthwhile to look into alternative braking systems that are specifically designed for continuous use, such as eddy current brakes or electromagnetic brakes.

Secondly, the coefficient of friction is an important factor to consider when calculating heat dissipation. The higher the coefficient of friction, the more heat will be generated. This is important to keep in mind when selecting a brake system and determining the maximum power output for the ergometer.

In terms of using MATLAB for a more accurate calculation, you could set up a model using the equations for heat dissipation in a solid object. This would involve calculating the heat transfer coefficient, convective heat transfer coefficient, and the thermal conductivity of the materials involved. You could also incorporate the specific heat capacity and mass of the brake pads and rotor in your calculations.

I hope this helps guide you in your project. If you have any further questions, please don't hesitate to reach out to us. Best of luck with your project!

 

[piercas]

Dear Darren,

Thank you for sharing your project with me and for seeking my input. I am glad to hear that you are interested in using a friction brake system for your ergometer application. It is certainly a novel and innovative approach, and I believe it has the potential to be successful if properly designed and tested.

Firstly, I would like to address your concerns about the potential overheating and failure of the brake system. It is true that traditional hydraulic brakes used in mountain bikes are not designed to be used continuously and may overheat if subjected to prolonged use. However, there are other types of friction brakes that are specifically designed for continuous use, such as electromagnetic brakes or eddy current brakes. These types of brakes are commonly used in applications where precise control of resistance and power output is required, such as in exercise equipment or industrial machinery. I would recommend considering these types of brakes for your ergometer, as they are designed to withstand continuous use and can be made non-magnetic by using appropriate materials such as aluminum and stainless steel.

In terms of calculating heat dissipation, your approach of using the formula Qm=m*c*T is correct. The heat will be dissipated through both the brake pads and the rotor, so you will need to consider both in your calculations. The coefficient of friction will also play a role in the heat dissipation, as it determines the amount of friction and therefore the amount of heat generated. You can use the following equation to calculate the heat dissipated by the brake pads:

Qp = (μ*m*v^2)/2

Where μ is the coefficient of friction, m is the mass of the brake pads, and v is the velocity at which the pads are moving. Similarly, you can use the following equation to calculate the heat dissipated by the rotor:

Qr = (μ*m*v^2)/2

Where μ is the coefficient of friction, m is the mass of the rotor, and v is the velocity at which the rotor is moving. These equations assume that all of the kinetic energy is converted into heat, so they may overestimate the actual heat dissipation. You may also need to consider other factors such as heat transfer to the surrounding air and the cooling effects of the MRI machine.

In terms of using MATLAB to model and simulate your system, you can use the equations mentioned above along with other relevant equations to create a model that can accurately predict the heat dissipation and temperature changes in your brake system. I would recommend