My Own Trainer Project

john979

The more I look at the Velotron braking unit, the more I am convinced it might be useable as-is on the PT300 Pro. As I am pure slow-twitch, I don't need 2500 watts. This gets me thinking that I don't need the copper conductor. The only problem I now see (other than buying a unit) is that the PT300 flywheel edge is beveled, further reducing the magnetic field. However, I really just want to be able to perform SST and VO2 Max intervals, so the Velotron unit might be able to produce enough braking power.

vladav

Re-read page 1 - yes indeedy, I'm wrong. Wahoo!

So you can simply fix one magnet on one side, and move the opposing magnet to & fro.


Maybe Dr W knows the answer: Should the opposing magnets have the poles opposed or sympatethic? N-N, or S-N?

Dave

john979

I have a PT300 Pro and the issue is mechnical braking. Too much fiddling to dial-in and it does not release well. In addition, if, and this is a big if, my Velotron contoller idea works, I can use VR software.

John

john979

This is crude but provides an image of my thoughts. Creating an adaptor bracket should be easy. Mounting points are readily available on the PT300.

Attached Thumbnails

 

Alex Simmons

Some interesting thoughts here. This is what I was thinking. Remember it's to be simple and cheap but effective:



The velotron idea on the PT300 is nice but I have my doubts you could get that unit and controller for low $.

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Steve_B

Depending upon how much you have to move the magnets to get significant changes in resistance, your corkscrew control may or may not be a pain in the backside to use.

WattsAMatta sounds right here. That being the case, you may or may not have to make huge adjustments on your control to change the resistance, depending upon how you implement the mechanism to move the magnets. I'm not going to tell you how to do it, just to take something like ease of use into consideration.

You will probably want to set some markings on your control to some place so that you can easily come back to some known resistance levels. Ability to easily see those markings when there's sweat in your eyes and you don't feel like moving too much (except for the legs ) may also be something to take into consideration too.

I was thinking a bit more about this idea of a solid flywheel vs. slotted as far as eddy current distribution goes. I was thinking that sloting might create some sort of pulsing to the resistance, which might become annoying. However, I was also thinking that beyond a certain velocity, you may not feel it at all. Also, the distribution of current density might be small enough (since the wheel is composed of a very low resistance material) that the effect is fairly localized and slotting it won't matter either.

I am also an EE and my in my senior year I was actually the lab instructor for the "energy conversion" course (transformers, generators, motors and three-phase power). However, 20 years of P-N junctions, GHz signals, microstrip designs and applied statistics has blown away any memory of this stuff.

Alex Simmons

Thanks for the comments. At least with cheap stuff it's easy to experiment. It is quite posible that we'll find the best placement of the magnet may be around the edge of the flywheel, so that the magnet moves from being out side the radius of the flywheel, to overlapping the outer rim.

When we trialed it with a crude approach (me holding the magnet close using a wooden lever to control location), I noticed pulsing when "holding" the magnet but the rider couldn't feel anything through the pedals - the flywheel is large enough that the pulses can't be felt.

Also - I will still have a gearing option, meaning I can set the resistance at the desired level (by way of some kind of marker) then use a bailout gear for recovery between efforts.

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john979

"Saritron" Update:

Racermate sells the Velotron control unit for $1200 undiscounted. Mounting the control unit to the PT300 Pro will require a custom aluminum plate, maybe $100 to have cut from stock aluminum. The second most expensive piece is the copper ring. That is $500, unless I can get the supplier to buy back the center cutout that I won't need (%80 of the copper sheet is not needed). At the max the conversion is $1800 plus the software. I might be able to get a 20% discount from Velotron, and sell back the copper reducing the cost to around $1300, maybe a bit less.

Next up, the cost of getting a non-PT flywheel from Saris -- I would prefer to test the drilling and alignment first.

Open issue: will gear ratio differences and weight difference between flywheel affect the Velotron software's power reading?

WattsAMatta

Would it be possible to use the 300pt flywheel as-is? Or is the gap in the Velotron too narrow? I don't think that there's anything special about copper -- any conductor should work fine, and other materials might be cheaper.

I think that it's more of an issue of magnetic field strength at the conductor (flywheel) and velocity of the conductor through the magnetic field rather than an issue of weight and ratios per se. I'm assuming that the Velotron has come sort of calibration capability within a certain range. If the resistance of the project's setup is too low, then it would be a simple matter to add a permanent magnet to bring the system's total resistance into the required range. If the resistance is too high then it might be a bit trickier.

-- Bryan

john979

Bryan;

From pictures, the Velotron contoller's gap appears too narrow to accomodate the PT300 flywheel. I was actually hoping this would not be the case, as I agree with the rest of your commentary and I am not too worried about resistance accuracy. However, I do like your idea of adding permanent fixed magnets, if necessary.

Another consideration is cadence. 1) The cadence sensor will add a small amount of cost to the project. 2) Some adjustment must be made to the Velotron software to set the PT300 gear ratio, but per the Veltron manual this can be done.

Thanks,

John

beerco

I like this idea. If you put the magnets on a lever with the pivot point "under" the flywheel it would be very easy to adjust. In fact, you could use an old fork you have lying around as the magnet holding thing. An acme screw could be used for adjustment.

Or, you could have a strong spring pulling the bracket away and use a cable to pull it in. This way you could have sort of a gear shift type thingy for preset levels. A screw with knob could provide the fine adjust for resistance. Come to think of it, this is really similar to an illustration someone provided earlier.

WattsAMatta

This is conceptually similar to what I had in mind. I plan to attach a small reversable cordless drill to the bolt to make the adjustments quick and easy.
-- Bryan

daveryanwyoming

Forget nuts and bolts, you want a ballscrew linear actuator something like this: http://cgi.ebay.com/KURODA-BALLSCRE...1QQcmdZViewItem

-Dave
P.S. This one's more expensive, but includes the necessesary end bearings to support the thing:
http://cgi.ebay.com/IKO-Linear-slid...1QQcmdZViewItem

You don't need all the tricky calibration scales, but you get the idea...

Alex Simmons

Very cool. There's lots of cheap stuff like this on ebay. Will keep in mind.

Thanks!

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