neptronix wrote: ↑
Jan 16 2019 9:08am
The problem with smaller spokes is the interface between the hub and the spokes.
I've built 2 500-750w geared motors with standard 14 gauge spokes, and even that power level had them pinging and loosening from the get go.
Strange...what kind of rims were used?
I haven't seen these kinds of problems on wheels I've built (or rebuilt) with geared or DD hubs, in anything from 20" to 26" rims (cheap or good) (and my bikes are heavy enough, especially with me and cargo on them, to cause problems on bad wheels *without* adding motor power to the mix).
On my MXUS 450x motors, because the holes were so huge that even 12g spokes rattle around in there, I drilled new holes between the existing ones, sized for the 13-14g butted spokes I used from Grin, to the 20" (16"MC) rims.
If spokes ping and loosen, then commonly either they weren't stress-relieved when built, or the rim is deforming as it rotates, and allowing the nipples to turn. The latter usually happens when the spokes were insufficiently tensioned to start with, but can also happen if the nipple holes have cracks in them (often from too *high* a tension for the rim strength, especially with an average or below average rim quality). It's the sort of thing I see with 12g spokes on OEM hubmotor wheels. (I think I have seen it on every one of the ones I've had so far, with at least one spoke, and the same thing on wheels I rebuilt with 12g spokes).
1) a majority of hubs are drilled with a certain spoke diameter in mind - 12 gauge. <snip>
2) a majority of hubs also have a divot that's large enough for the head end ( or whatever it's called ) of a 12 gauge spoke. This is meant to give a lot of metal to metal contact also, since a hub motor produces far more torque than a human being and all.
While both of those are true, the smaller diameter spokes will still hold tension better, and make a better wheel, when using common average-to-below-average quality bicycle rims (like those used on OEM hubmotor wheels), because the tension required doesn't damage the rims.
If you're using a good enough rim, it doesn't matter if you use thick spokes, if it's designed for the tensions required. Many rims are not good enough, however.
Myself, I wouldn't let the hubs' holes dictate how to build the wheel, unless using rims that are designed for the higher spoke tensions required on the larger spokes. I'd rather use washers like I would on even a regular bicycle hub that had similar issues (some do).
Washers dont' work in all situations. But they can work in most. i've been using them for years on the HSR3548 wheel build that was used on CrazyBike2 and then on SB Cruiser (is still presently on SBC due to axle issues with the other motor that should be there). Bent the rim up on potholes, crushing the bead flange in flat in at least two places, but it's still a functional wheel.
1) <snip> 13 gauge is just barely close enough for low power builds..
Unsure of exactly what you mean, but: If you mean that 13g spokes themselves can't handle more than low power...that's definitely not correct (unless we're talking low-power motorcycle class power
). If it were, then I'd have spoke failures all the time on SB Cruiser--but I don't have any spoke failures on it, with 13/14 butted spokes on the rear, where the side-loading and potholes and bumps all create more than significant strain on the wheels, not even counting the motor power.
I break axles...but not spokes.
I suspect I could use 14/15g butted spokes, and still have reliable wheels, which is a test I'll do eventually when I build the 26"-29" rear-wheel version of the trike.
FWIW, I had some cheap BMX's wheels with 44 spokes, 15g, that I used on SB Cruiser's rear wheels for a while (when I had a front hubmotor on it), and broke a number of spokes, because the rims were not made for anything like the loads I was putting on them, and deformed while rolling allowing spokes to loosen, and then break at the elbow. They could also have had damage from their previous life on the BMX, but I expect my overloading of the rims was the primary cause.