Fixing N360 guide slot wear.

[Oran]

Just a quick update to say the modified hub is still working. The mileage is only 1500 as I spent a couple of months with relatives and was riding a different bike. I'm now back home and continuing to add up the miles.

The stator is made from magnesium. When I was installing the magnets I burnt some of the drill filings. They burnt with a very bright flash.

If I can get an idea of what traction coefficient the hub is operating at I'll considering getting some traction fluid. Santotrac-50 costs $80 for a quart. I made a mistake with my previous calculation of traction coefficient. Understanding how the forces are transferred though the planets is a little complicated and all the angles involved.

[mattijs.stuijk]

Just a quick update to say the modified hub is still working. The mileage is only 1500 as I spent a couple of months with relatives and was riding a different bike. I'm now back home and continuing to add up the miles.

The stator is made from magnesium. When I was installing the magnets I burnt some of the drill filings. They burnt with a very bright flash.

If I can get an idea of what traction coefficient the hub is operating at I'll considering getting some traction fluid. Santotrac-50 costs $80 for a quart. I made a mistake with my previous calculation of traction coefficient. Understanding how the forces are transferred though the planets is a little complicated and all the angles involved.

So you found/calculated a formula for the traction coefficiënt of the Nuvinci N360 traction fluid? It seems to me these kind of calculations are quite hard (http://ntrs.nasa.gov/archive/nasa/casi.n...016591.pdf). On an update off my project to make the nuvinci Bi-directional, thins are looking good. Made some new traction rings en coged up the freewheel. This weekend i am testing it with the fluid inside!

[Oran]

Thanks for the link, I haven't had much luck finding a formula. I had a go at some calculations but failed to fully understand how complicated it is.

Good to have an update from you and that its going well. That's impressive that you've made some new traction rings of a different design. When you say testing do use mean with it installed on a bicycle and going for a ride?

[Oran]

My time on the mainland is nearly over but its been good for hub testing. Wales has a lot of hills and the roads are often steep. Its been more about pushing the limits of torque transfer rather then mileage which is currently 2300 miles. I started out not braking the minimum sprocket ratio but as I met steeper hills I decided to use the smallest sprocket. A 28t on to an 18t instead of the 38t which is just within limits. So it will be interesting to see what's happened to the input side without the bushings. I now tend to use the 28t and have the hub near the 1:1 ratio instead of the 38t and have it in full underdrive.

Before I moved and transferred the hub between bicycles I checked it's condition at a mileage of 1650.
I'm was pleased with how looked. The traction fluid was looking reasonably clean thanks to the magnets. It contains some bronze from the bushings and some magnesium from the input side of the stator. These metals are soft so I'm not bothered about it. The fluid still had it's green colour not gray and nasty.
The bushings are continuing to wear but the rate has slowed. I reckon after another 1000miles (which I'm now a good way through completing) it will probably be worth considering replacing them. Its going to be interesting to see what happens. There is no damage to the stator on the bushing (output) side. I should gain more of a ratio range although temporary.

I reckon by now the bushings should be close to needing replaced. The hubs still working great although it leaked a bit on night after a steep 400m climb.

Once I get home I'll have a look and give them a measure. Will make some graphs of the data and post them here.

For those who are interested the bushings are wearing unevenly. It differs between the ID and the OD and between the side next to the planet or the side nearest the axles end.
Here's a few things I've noticed looking at the numbers.

The axle end side ODs are showing no significant wear over the last 650miles.

The IDs are wearing more and the side furthest from the planet is worn the most.

Over the past 650 miles the planet side ODs and IDs have equally shared a third of the total wear, the other two thirds is the opposite sides IDs.

The planet side is wearing half as fast even though the opposite sides ODs have shown almost no wear.

Planet 3 has the least and planet 6 has the most wear suggesting there is something off centered.

[Normand_Nadon]

Nice write-up Oran! So these magnets ARE the solution to reducing wear!
Hope Fallbrook will move on with this solution too!

Any luck finding a traction fluid?

[Oran]

Thanks, the description of bushing wear is like one of those puzzles where if I specified one dimension and its possible to work out the rest. :-)

The magnets are part of the solution. I don't know why but I hadn't considered that the reduced bushings wear might have something to do with the magnets. I thought it was to do with them wearing in to their proffered shape. However perhaps that's not the entire story.

It still doesn't get around the problem that the magnesium stator simply isn't hard enough. I expect for the majority of riders living in a flat place its not an issue. Also there's the debate as to whether a bit of wear has any effect on the efficiency. They seem very tolerant of wear and I believe designed to tolerate some.

At the moment the only source of traction fluid I keep ending up at is the Santotrac 50 from skygeek.com. It has a traction coefficient of 0.1 but minimum order is a quart costing $80! If I can get enough evidence to suggest the N360s traction coefficient is below 0.1 I will give it a go.

[Oran]

Finally I have arrived home and back to my workshop. I have given the bushings a check as I had done 700 miles whilst away. The results are much better than I had expected considering I had broken the minimum sprocket ratio rule and climbed a lot of steep hills.  
The rate of wear has reduced considerably since the previous 650 miles. The input, non bushing side appears to show no signs of continuing wear. I was going to replace the bushings but judging by the graphs that won't be necessary for a while. 



The traction fluid has lost some of its transparency and turned a darker colour despite the magnets. There are very few larger non-magnetic particles, it’s all been crushed down to a fine powder. I recon fresh traction fluid would be beneficial, looks like I might have to go for the Santotrac 50.  

[Oran]

At nearly 3000 miles and with the overdrive ratio having dropped to 1.35 I decided to replace the bushings, the underdrive ratio is unaffected. The actual bushing swap is very easy the most time consuming part is stripping down a reassembling the hub. I’m really pleased with how there has been no more wear to the stator and the output side slots are almost unworn just a little polished by the bushings. The traction fluid is looking ok thanks to the magnets which I cleaned at the 2350 miles inspection.

With everything reassembled a test ride revealed just how much of the overdrive ratio it has regained, back to 1.7, and how it’s performing as good as new. A great success considering how destroyed an unmodified hub was after 2800 miles. I've found noise is a good indicator of the condition and efficiency of a hub. That unmodified hub made a rumbling noise at slow speeds and high torque and felt inefficient.

[Normand_Nadon]

Did you finally try another traction fluid?

My hub is starting to become harder and harder to shift and feels sluggish... I might as well be forced to disassemble it!

Do you have any part number for the oilite bushing you used in the hub?

[Oran]

Did you finally try another traction fluid?

My hub is starting to become harder and harder to shift and feels sluggish... I might as well be forced to disassemble it!

Do you have any part number for the oilite bushing you used in the hub?

I've not got any traction fluid yet but would like to once the new bushings have gone through their period of fastest wear. At the moment the cost is prohibitive as I have to buy 10 times what I need and the shipping costs from America.

Do you know roughly how many miles your hub has done? It must be a couple of years old by now and out of warranty anyway. Have a go at opening it, I think it would be worth checking its condition.

The Oilite bushings are AM050804 the dimensions I.D 5mm, O.D 8mm, length 4mm. Do you have any ideas about how to repair the stator before fitting the bushings?