Test hub

[Oran]

I have now got two NuVinci hubs built in to wheels. This means i can preform short term potentially destructive tests on the hub I had been using until recently. Previously I had only one set of spokes which got passed on to the next hub. By luck I realized that a wheel from a child's bike I dismantled for the disc brake hubs had spokes of almost the right length. The rim came from a wheel that had gone out of true and the rusty spokes prevented any attempt at straightening. Altogether cost me nothing but time.

Possible tests I've thought of so far.

Trying a different traction fluid like SANTOTRAC 50 or Shell Morlina S2 BL 10

Simulating a bushing failure by removing the end from one of the planet axles. Can a hub function with 5 planets?

I'm sure there are plenty of others I can't think of at the moment. The aim is to see how a hub responds to various situations to get a better idea of the reliability. When can it keep going and when does it fail.

I would like to have the hub for spares if possible so I will not be doing any tests that obviously destroy part of it if it can be avoided.

The hub currently has no planets so I'll probably wait until I can get them back from the modified new hub. That way the new hub can get new modified planets and be sealed up for long term testing if the bushing have been a success.

[Normand_Nadon]

I can't wait to see the results with the Sanotrac fluid... If it turns out to work, I will be ordering enough for a couple of flush and I will maintain this hub on a regular basis!

Unfortunately, since I only own one bike now, I can't affort a test that can go wrong by myself for the moment! I will wait for your results... Take your time, but do it fast!!!!

[Oran]

So far the only Santotrac 50 I have found on the internet is from skygeek.com. The minimum quantity is a quart (1litre) which costs $80 (£50). That’s a bit more than I want to pay for something that my calculates say won’t work. I’m still keen to try it though and I’ll try a bit harder to find a smaller quantity, £5 for an oil change is very reasonable I think.

[Oran]

I have just tested the worlds lightest N360 as I have removed one of the planets. Don't bother trying it as the drop in efficiency is no where near made up for by to reduction in weight. It worked though which I'm rather impressed by. It means that if something happened to one of the ends of an axle and the planet could no longer transmit torque the hub will still work. Its unlikely because the planets are well supported between the rings and sun.



It got me thinking about the clamping force and traction coefficient. The hub is obviously designed for the load to be shared between 6 planets. If there are only 5 the force per planet will greater. As the torque is also only transferred by 5 planets the overall traction coefficient remains the same. Because of the increased forces the contact patches are larger and efficiency will be reduced. So if you wanted a lighter but also much less efficient hub you could remove 3 of the planets. It would be like doubling the torque all the time. I could try 3 planets next, I might learn something about the efficiency.

[Oran]

This is just to say that I haven’t forgotten about finding a replacement traction fluid. The problem I have come across is that shipping from the US is prohibitively expensive especially considering that nowhere so far can supply less than 10 times what I actually need. I have been unable to find a supplier in the UK at the moment.