[peterbranton]

The axle weights 5 kg it is 6 ' wide, it is a vertical axle with a magnetic barring at the base of the axle working on opposing energy, the axle is also in a vacuum of 3lb sq inch? Around the axle are nine 3 " wheels connected to the main central axle each of these weighs 0.4 kg each with a verticle axle and in the same vacuum system of 3lb sq inch?

[ebaines]

If you want to calculate the torque required you need to tell us (a) what speed you want it to spin at, (b) how quickly you need the axle to spin up to speed from a stop, (c) its diameter, and (d) what torque is opposing its turning. And I don't understand what that nine wheels are doing - are these gears that are being turned by the axle? It would really help for you include a sketch of this apparatus. Finally - you seem to think that the vacuum is important, which makes me think that you think that air resistance is an issue - why?

[peterbranton]

I will quickly draw a scetch, A) it has to main tain a speed of 2000 rpm with an acceleration rate of 30 minutes from stop, I mainly need the amount of torque needed to maintain it at 2000 rpm please. It uses ball barrings to centralise the axle

[peterbranton]

The air pressure is reduced to maximize the airo dynamic efficiency, I will prepare a scetch for the extra wheels , the magnetic barring is only beneath the main axle

[ebaines]

OK - I'll wait for the sketch. You'll need to provide an estimate of the drag caused by the main bearing. Also be sure to indicate what this axle is actually doing - is it making something else turn? What forces besides aero drag must it overcome? Finally, next time you post please use the "answer this question" box rather than the comment box.

[peterbranton]

Hello you asked for a scetch but I am unable to load it to the site, do you or this site have a email address I can send it to, or please tell me of how I work do it , obiously it is too much for a copy and paste, it is most important I answer this Q?

[ebaines]

If you respond to this thread using the "Answer this question" box rather than the comment box you should be able to load a graphic file of your sketch. Alternatively - I sent you a PM earlier today with my email.

[Unknown008]

If the image is not so big, you can upload to tinypic.com, copy then paste the link given to you after uploading, here.

Otherwise, if it's really big (some MB size), I'll recommend p1cture.me which can take up to 5 MB pictures when you are as guest, and 10 MB when you created an account.

[peterbranton]

Thank you very much this is most helpful

[ebaines]

Rough calculation: it takes about 1 N-M of torque to get the apparatus up to speed in one minute. But the real issue is the air resistance that needs to be overcome at speed:



where:
is the force of drag to due air resistance
= denisty of air at 3 PSI, which is about 1/5 of air density of 1 atmosphere, or about 0.24 Kg/m^3. = coefficient of drag, which is perhaps around 0.7 (total guess)
= frontal area of the 9 magnetic assemblies. These are each 4 inches wide by - what? If I assume that they are 5 feet long, then the frontal area for all nine is about 1.5 m^2
is 32 m/s, for an object 6 inches from the center turning at 2000 RPM.

So


and the torque needed is:



The power needed at this speed is



Again - all this is really a SWAG. It probably overestimates the drag based on the fact that if the assembly is housed inside a cylinder, the air in that cylinder will be pushed along and so the drag against the 9 wheels would be less than what I calculated. Until you build this and actually measure the resistance, it's impossible to say with any accuracy.

**EDIT** Also - PB: it's important o know what the frontal area of each of eh 9 wheels is. I assumed they are 4 inches wide by 5 feet long - please confirm.

[peterbranton]

Thank you. I will use this as a guide, much abliged