Particle collection magnets

[Oran]

I recently came across a bargain on Ebay, a second hand hub listed as being for spares or repair, very little use, slight oil leak and comes built into a wheel. For £60 I thought it was worth getting because the rim and spokes must be worth more than half of that.

It arrived yesterday and appears to be an up to date version. It’s interesting to see what small modifications have been made, the engineers are always busy trying minor alterations and additions. On the drive side is a plastic cover which I discovered has 6 strong magnets, probably neodymium, underneath it. I assume these are to keep any steel particles away from the traction surfaces.



It’s a rather good idea and is cheaper and less wasteful than replacing the traction fluid. I know a lot of the particles are non magnetic aluminium and magnesium but these don’t do any damage to the traction components. I know there is steel in the traction fluid because I put a magnet next to some when I had it in a jar because I thought it would be a way of removing the particles. It collected some but not many of the particles so I gave up on the idea, what I hadn’t realized was that what it had collected were the most harmful ones.

I will stick a magnet to my hub and see what it collects. I have some spare large ferrite magnets from a wind turbine I’ll try first. Then I might buy some small ones made of samarium cobalt, neodymium is a bad idea because they corrode severely. Unless I can find a place to put them inside the hub then neodymium is the best option, I expect that is what Fallbrook intend to do in the future.

I will write another topic about the second hand hub as its going to need a few repairs, the freewheel has been completely destroyed and the leak is a significant one.

[Normand_Nadon]

That is a nice addition to the design!

I don't get any answer when I mail Fallbrook... had any luck lately?

[Oran]

To be honest I haven't got round to emailing them, I've been waiting until I decide what to do with the extra hubs I have.

The magnets are confusing me slightly as they are positioned under the thick metal beneath the lids screw thread. The nearest the traction fluid can get to the magnets could be as much as 8 - 10mm. If positioned slightly nearer the axle they would have only a few mm of aluminium to penetrate.

The part is definitely a NuVinci add-on so its not for a cycle computer unless its for the harmony kit.

Just checked Ebay photos and it is from the harmony kit. If nothing else it's given me a good idea adding magnets to collect any steel. There are plenty of places on the stator to fit a small neodymium magnet. I think some gear boxes have them but more as a way of checking for contamination.

[Oran]

I taped a 1 x 2 inch ferrite magnet to the hub I'm currently using with the bushings. I rode it half a mile and this is what was attracted to the magnet. I regretted doing it afterwards as I have magnetized the traction rings but its a weak magnet so its very slight.



The question is whether its worth worrying about such small particles. The traction fluid maintains a gap between the traction surfaces so can they do any harm.

[Normand_Nadon]

Since these particles alterate the nature of the fluid, I think that they absolutely are a problem!
The fluid is meant to change state under pressure and create traction.... but if this fluid has any contaminent in it, it looses it's properties...
Any particle has to be harmfull in such situation. Not to forget the slow "wet sanding" effect!

[Oran]

I suppose there are other factors, it can do no harm to add some magnets and hopefully some good. Whilst I'm using the repaired second hand hub I might as well install some on my current hub. I have found a place on the stator I can actually fit up to six 4mm dia by up to 8mm long rod neodymium magnets. They'll be out of the way of magnetizing anything, near the axle on the output side.

[Oran]

Ive now installed two neodymium magnets on the stator near the non-drive side bearing.


It was the only location I found that was far enough away from any of the steel parts. Its a little bit close to the overdrive end of the slot but the magnetism is weak on the sides of the magnet and a nail placed in the slot doesn't get attracted. The curved slots they are fitted into are just under 4mm wide and after drilling them out the magnets were a nice tight push fit.
I don't want to keep opening the hub too much so it will be a while until I see what they've collected. Unless something happens it will be at 2000 miles when I do the next inspection of the bushings. I'm currently at 1200 miles and the weathers not helping to increase that.

[Oran]

I'm planning to spend a bit of time on the mainland and it will be a chance to add up a few more miles. Before I take the hub with me I thought I would check the bushings and magnets, current mileage 1650.

This is what I found stuck to one of the two magnets. It's about a third of the total they have collected as a small amount is inside the stator at the opposite ends of the magnets. An impressive amount that's not getting in between places it shouldn't be. The traction fluid is still looking reasonably clean although it contains some non magnetic particles.
 

[Normand_Nadon]

Okay... you got me! I am opening my hub at the end of the season!

Do you rebuild your wheels yourself?

[Oran]

You should have a go I'd be interested to know how much stator wear has occurred.

I do build the wheels myself. However it's possible to open up and inspect a hub whilst still in a wheel if that's what you were thinking of. The hardest part is pouring out the traction fluid. I make a sort of spout from a piece of 2" wide sticky tape. The other thing I do first is give the whole wheel including tyre a good wash. Avoids any possible contamination from grains of dirt.