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

 

[Achy47]

Dear Darren,

Thank you for sharing your project with us. Building an ergometer for an MRI machine is a fascinating project and I am happy to provide some guidance on your question about using a disk brake system for resistance control.

Firstly, I would like to address your concern about the system overheating and failing due to constant dragging. This is a valid concern, as most disk brake systems are not designed for continuous use. However, there are disk brake systems available specifically designed for ergometers and exercise equipment, which can withstand constant use without overheating. I would recommend looking into these options to ensure the safety and reliability of your project.

Moving on to your calculation of heat dissipation, you are on the right track. The formula you mentioned, Q=m*c*T, is the correct way to calculate heat dissipation, where m is the mass, c is the specific heat capacity, and T is the temperature change. In your case, the mass would be the combined mass of the brake pads and the rotor. The specific heat capacity would depend on the material of the brake pads and rotor, which you can find in their respective specifications. As for the temperature change, it would depend on the amount of power dissipated and the thermal conductivity of the materials.

In terms of how the heat is dissipated, it would be a combination of the brake pads and the rotor. The brake pads would absorb some of the heat generated by friction, while the rotor would also absorb some heat due to its contact with the pads. The coefficient of friction would play a role in this, as it determines the amount of heat generated by the friction between the pads and the rotor. You can find this coefficient in the specifications of the brake pads and rotor.

To accurately model and simulate the heat dissipation in this system, you can use the Simulink MATLAB software at your disposal. You would need to set up a model that includes the heat generated by the power dissipated, the heat absorbed by the brake pads and rotor, and the heat dissipated to the environment. You can use equations such as the heat transfer equation and the thermal conductivity equation to calculate these values. I would also recommend consulting with a mechanical engineer or a specialist in heat transfer to ensure the accuracy of your model.

I hope this helps guide you in your project. Best of luck and I am looking forward to hearing about your progress.

 

[ravenprp]

Dear Darren,

Thank you for sharing your project and questions with us. It sounds like you have a unique and interesting application for a friction brake ergometer. Using a disk brake system for this purpose is definitely a novel idea and I can see why you would want to utilize readily available components for your project. However, as you mentioned, there are some concerns about the system's ability to withstand constant use and potential overheating.

It is important to consider the specific design and capabilities of the hydraulic brake system you are looking to use. As you mentioned, these systems are designed for mountain bikes and may not be suitable for your application. The main concern with using a hydraulic brake system in this way is the potential for overheating, as these systems are not meant to be used continuously and may not have the necessary cooling mechanisms in place. Additionally, the materials used in the brake pads and rotor may not be suitable for use in an MRI machine, as they could potentially interfere with the magnetic field. It may be worth exploring other options for creating resistance in your ergometer, such as an electromagnetic brake system, which could be more suitable for use in an MRI environment.

In terms of calculating the heat dissipation and temperature change, your approach seems to be on the right track. However, it may be more accurate to use a thermal analysis software, such as ANSYS or COMSOL, to model the heat dissipation and temperature change in your system. This will take into account factors such as the specific materials and design of your brake system, as well as the airflow and cooling in the MRI environment. You can also use these software programs to model different scenarios and make adjustments to optimize the design and prevent overheating.

I hope this helps guide you in the right direction for your project. Good luck with your project and please feel free to reach out with any further questions.