# Calculating torque on a wheelchair

1. Mar 29, 2016

### Hovda

Hi!

I would like to apologize in advance, for my english.

I am working on a gear reducer for a manual wheelchair, and are trying to figure out what kind of design I think would work. But as I am calculating there are a few (simple) things I could need some help with.

As a test I've chosen a "wheelchair + person - system" with a total mass of 110 kg (95 for the person and 15 for chair and wheels). I am simply trying to calculate the torque needed to push this system 30 degrees uphill, and this is where I have a couple of questions:

When calculating the tourqe, is it enough just to use Tourque = RadiusOfWheel * MassOfSystem * gravity * sin(30) ? In my case this gives me T = 0.6m * 110 kg * 9.81 m/s^2 * sin(30) = 323,73 Nm. Devided by two wheels the torque would be 161,865 Nm.

I'm wondering if this is the correct way to do it? As these are wheels, do I have to take the rolling into account when calculating the tourque? All the books I have are in English, and believe it or not, it is not always easy to find the correct (relevant) information as English is not my fist language :) .

I need the tourque to be able to design gears that would do the job.

I know these questions might seem simple, but I would really appreciate if someone could give me some pointers here.

And if everything is completely off, let me know!

Thank you!

Mats

2. Mar 29, 2016

### SteamKing

Staff Emeritus
I must say it's rather ambitious for a person to try to climb a 30-degree slope in a wheelchair without any assist.

Most of the grades I have seen specified for wheelchair access are limited to about 1:12, or say 5 degrees maximum.

Even the famously steep streets in San Francisco max out at about 17.5 degrees.

http://www.datapointed.net/2009/11/the-steeps-of-san-francisco/

3. Mar 29, 2016

### Hovda

Hi!

Yes, I know 30 degrees is alot, but the number of degrees is not the point itself. It was simply a "random" number i put in. Allthough the point of the gear i am designing, is just that it should be able to reduce the "force" needed to climb so much that one could get up steep hills. But anyways, again, the degrees is not the point here :)

But thank you for pointing it out :)

Mats

4. Mar 29, 2016

### SteamKing

Staff Emeritus
Whew! It's a good thing you didn't pull out a number like 90 degrees, or even more.

Good design should account for what is feasible versus what is not.

5. Apr 1, 2016