My Own Trainer Project

Squint

I'm pretty sure they're not insulated. The bolts go into the flywheel and would probably conduct. Also, there is enough play around the bolts that adjacent copper fins could (and probably do) contact each other.

Alex Simmons

OK - thanks. Then it was just easier to make them that way and bolt on rather than for some special e-m purpose.

__________________
http://alex-cycle.blogspot.com/
http://www.cyclecoach.com/

rmur17

could be an expansion issue as well I guess though I don't know how much a flywheel of *that* size is going to heat up spinning at say 40 kph.

Re your project, I'm certainly willing to offer time to help Alex. I'm an EE by degree but not by work experience so I've been out of the true hardware design end for too long now. However, I'm pretty good at reviewing and criticizing if you need someone to do a design review etc...

Are you actually hoping to construct a full-blown ergometer with power regulation (load x speed) or more of an extremely heavy-duty mag-trainer with widely adjustable resistance?

__________________
rmur

Squint

A friend measured his at 10F above ambient.

WattsAMatta

That would be me.

I'm an EE, but I'm afraid I must have slept through most of my electromagnetics courses. I made a few attempts at store-bought and home-wound electromagnets and didn't have much luck. So, although it's not rocket science, unless you've got a lot of time for trial and error, or a working model you could reverse engineer, or know somebody with a bit of experience in the matter, it might prove to be tricky to get an electromagnet powerful enough to provide the resistance you'll require. With the electromagnets I wound, it was looking like the voltage and current required was going to be in the potentially lethal range, so I changed my plans.
My current efforts involve using some strong neodymium magnets mounted on a swing-arm that I can swing closer of further from the flywheel. My ultimate goal is to add a 'constant power' feature to my 300PT. The magnetic braking wouldn't necessarily provide all of the resistance, but it would increase or decrease as needed to compensate for a decrease or increase in cadence.
Here's a link to a commercial spin bike that only uses the permanent-magnet/proximity idea. Click on the photo and it will pop-up a slide show, one of the slides is a close up of the magnetic brake assembly.
http://valorathleticsinc.com/store/...&cat=105&page=1
Those magnets would need to be pretty strong, so I would think the lateral force would cause premature failure of the bearings. A better design would be to have the magnets on both sides of the flywheel in order to balance out that effect.
I'll post more once I have some successful results,
-- Bryan

MIHECH

Nice pics Alex, where do you keep the trainer?In the basement?

Miha

Alex Simmons

Well I'm now investigating the use of hysteresis brakes and power controls, which would enable quite fine and regulated torque control. They would simply be an extension to the axle and would remove all lateral forces. Control down to 5W increments could well be possible. Torque from these brakes is independent of the rotational speed of the brake and the power control auto adjusts for changes due to heating.

Will let you know how that goes. They are probably quite expensive though.

The pic I posted is not my trainer but a mate's. It was the inspiration for what I'm looking at though. I'll try to get a pic of the prototype unit this will be based on.

I am assuming the flywheel will be rotating at something like 200-800rpm depending on gearing. The flywheel and hub weighs in at 44kg by the way

One thing is for sure - I'm not a mechanical / electrical / engineer anything

This is fun though.

__________________
http://alex-cycle.blogspot.com/
http://www.cyclecoach.com/

Alex Simmons

BTW - the intended location for my trainer is in a new attic room I've had built into my home. Will be quite fun to get it up there though!

__________________
http://alex-cycle.blogspot.com/
http://www.cyclecoach.com/

Sillyoldtwit

It would probably be easier to take the roof off and hire a crane for the afternoon. Anyway, it looks like an AWESOME setup. Tyson

__________________

Alex Simmons

Holy crap!! I only just had a whole new roof put on - I'm not pulling it off again

__________________
http://alex-cycle.blogspot.com/
http://www.cyclecoach.com/

frenchyge

...or a structural engineer, apparently.

swampy1970

That looks similar to something my old coach used to have but in reverse:

http://www.abcc.co.uk/Articles/int_train1.html

He went on to integrate it into a box section "frame" where the bars and seat were free from the contraints of a standard bike frame. You could put the saddle anywhere between an effective seat angle of 40 and 100 degrees if you'd so wish. Due to the massively over engineered design, flex wasn't apparent either - you could probably stick Michael Hubner or Curt Harnett on that and it'd stay solid. LOL

Alex Simmons

Update:

1. I have just picked up a 2nd hand SRM Pro / PCV to put on the trainer.

2. No response from hysterisis brake rep here in Oz. The US guy was quick but local guy has not exactly been forthcoming. Need to follow up again.... I may just go back to the idea of some strong magnet proximity. It's cheap to try. Magnets like those found on the home trainer in earlier post are ~$4 -$5 each.

3. Some pics of the prototype. Mine is yet to be built. I won't be cutting out sections on the flywheel like this one - rather I'll reduce the diameter an inch or so.

__________________
http://alex-cycle.blogspot.com/
http://www.cyclecoach.com/

Squint

Have you considered putting an SRM on a good spinning bike?

For example, this one has a 46 lb geared flywheel and seems like it could emulate the fit of a road bike. Many spin bikes have English threaded BBs so you can install your choice of BBs.



The new Lemond indoor bikes have powermeters and aren't terribly expensive either.