Irving wrote:Those are really interesting Lenny, I'll knock up some drawings later today.
@goose - the likely max torque from a wheelchair motor is around 60Nm at stall - even the smallest will work. A more concerning number is the PN value which is the outward force on the hub, we need to be sure the hub isn't overstressed around the stud/bolt holes. I'll run some numbers later on both steel and ally hubs on both the RT25 and RT70 for 19mm shaft. Looking at the design of the sliding taper I reckon there is a direct relationship between the torque of the locking bolt and the inward and outward forces so it may be 'tuneable'.
Thanks for the 60Nm figure, it makes me feel less worried about how much stress I'd be putting on these...
I would be somewhat surprised if the PN value was much of an issue... The 'spigot' section is 75mm OD, and the couplings from different brands seem to be about 47-50mm, so that gives about 12mm ~1/2" worth of 'meat' around the outside - even in aluminum that seems pretty stout...
I can't play with the diameters of the spigot or bolt circle as they are set by the wheel. I could turn the OD of the bolt face down, but it seems that would not be good... I could probably also cut out 'lobes' to get rid of some of the material between the bolt holes, but I'd want a good reason as it would potentially make the work holding harder and the machining mildly more complex.... I CAN play some with the thickness of the spigot or bolt surfaces.
Does it make any difference if the width of the hub is more or less than the width (length) of the coupling?
Even though 3/4" is not quite = 19mm (0.75" = 19.05mm, 19mm = 0.74805" according to my digi-micrometer) should I assume that it is close enough to be able to use a metric fitting (I have seen some inch versions as well)
I probably won't end up using the same parts that Lenny pointed at, but my first glance suggests that all are similar in size, so I'd expect any forces to also be about the same...
What is the PCD of the rims you are planning? Are they the BM monkeybike ones?
They are the 3.50-8 version but the same cast alloy style as the BM wheels - I got them from Shirley, just like BM did....
They have a 75mm center hole, and a 92.5mm bolt circle The bolt surface is about 8mm thick. The outer face of the center flange is centered on the rim, so the contact surface is inset from it that much.
Edit: just did a search, there are plenty of Stainless Steel versions
Glad to hear it, as I'd rather do stainless or alloy so I don't have to worry about rust issues -
In reference to your question of starting a new thread - We probably could start a new thread but unless BM can split this one to move what we have already said to a new thread, it is probably easier to stay with this one - which is sort of on the topic of doing different wheels / tires, and isn't seeing much other activity...
ex-Gooserider