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Friday, January 15, 2010

More Trike Thoughts

spinningmagnets on ES is looking out for internally-geared hubs, which would greatly simplify the switching-gears on the front wheels, and ought to be able to take the nominally 300-350W per wheel I would be putting thru them, as long as I set it up to cut power during shifting.

So I will probably build the front setups simply using regular rear hubs on both front wheels, and any multi-gear drivetrain I come up with for temporary use will be easily removable. I still need a ratio change of around 1:5 to get the 20MPH top speed, from the gearbox output that's intended to directly drive wheels half the size of the ones I'm using for 8MPH.

I have been pondering a way to swap the gears in the gearboxes so that they output closer to what I want to start with. I cannot remember exactly what ratios they are inside for which parts, but basically the main reduction is from the motor shaft's helical gear to the first right-angle gear in the box. Then that has another gear on the same shaft that meshes with the output gear, which is on a lever-type clutch to disengage the gearbox for manually pushing the wheelchairs these came from. I'm pretty sure that the last two gears are different sizes, with the larger of the two on the output shaft.

If the shaft diameters are the same between the output shaft and the first shaft, I can swap the gears so the larger one is on the first shaft, which will give me some amount of anti-reduction (gain?) within the gearbox itself. If they're not the same ID but I have or can make a collar adapter for the difference, I can still use the gears swapped; just have to lathe out the smaller one to fit.

Then I have just that much less anti-reduction to do from the gearbox to the wheels. If the gears are the same OD/teeth or the larger is already on the first shaft, I'll have to do all the work outside the gearbox.

I've also considered taking the motors off the gearboxes and affixing a timing-type pulley directly to the motor shaft but this would require creating a drive-end plate for the motor that supported the shaft, as right now that bearing is part of the gearbox. This is not that trivial a matter to do, for me.

I would then need a much larger pulley on the wheel itself. I can't recall offhand the motor RPM, but somewhere in the 3000 range, I think. That would be a ratio of about 9:1. The smallest belt pulley I have around here is for a V-groove, and it's around 1.5". So I'd need a 13.5" diameter pulley on the wheel!

I can't recall the way to figure minimum number of teeth I'd need engaged for a timing pulley, but I suspect it'd be at least an inch or two in diameter.

Can't really use chain; at 3000RPM at the motor end that would be a helluva noise.

Basically, at 9:1 reduction, compared to 1:5 anti-reduction, I'm better off sticking with the gearboxes and using bike chain/sprockets for output shaft to wheel transmission. It's not as "efficient" as less stages of changing ratios around would be, and it's heavier, but it is a lot easier to do, with less stuff I have to build from scratch to make it work.

Now, one problem I have is that for the right side wheel, to get power from the motor to the wheel, I need the motor on the right side of the wheel, just like it will be on the left side wheel. But that would be problematic for reasons of safety, clearance, and keeping the motor itself safe from damage. So the motor must go on the left side of the right side wheel.

That leaves the issue of how to get power to it. To use a regular bike hub for it isn't that big a deal, as I can just bolt a sprocket (or weld it) to the left side of the hub. But I will want to use the internally-geared hubs for this later, and those will need the sprocket on the right side of the hub. Meaning I have to get power around the wheel somehow.

Thus, I will probably end up using an extra hub at the rear of the fork, to act as a jackshaft and pass motor power thru to the other side of the wheel. I can simply use a front hub since I don't need to put any freewheels on there, or spoke a wheel to it, and just bolt the sprockets on thru drilled-out spoke holes if they line up right. An adapter plate if they don't. Or weld them on, one on each end.

I just weld on some little dropout tabs to the fork near the U end of it, just clear of the wheel.

For the fork itself, I'm going to need to take some 24" or 26" U-forks, and cut them in half at the stem end. Then weld a tube across there to space them far enough apart for a rear hub to fit in the dropouts up front. But since the internally-geared hubs need dropouts that are slotted to fit them, and I will need enough dropout length to use to adjust chain tension (no derailers), I'll need to remove the original dropouts and put on some from scratch or from BMX bike frames.

Alternately, I can just build the forks from scratch, which would simplify making them significantly, and give me control over every part of their design, as well as make them the same for each side, mirrored. (well, mostly)

Another thing I've been pondering, and that is which way to make the forks--vertical or horizontal.

Horizontal will keep more weight down low, which is very good for a trike. But it means the motor mounted on there will have to have it's weight swung back and forth on the pivot every time I turn, which will act as a pendulum weight and make steering a tad more difficult--it will tend to resist starting to change the wheels direction, and resist stopping that change, too.

Vertical will essentially fix the latter, but will place at least a little more weight up higher. I can still mount the motor itself so that it is centered about the axle, and that will keep most of it's weight low, but the fork will still be higher up and that weight will be above the centerline, giving the trike just that much more susceptibility to tipping in turns, especially if I use the kingpins/pivots up at the top end of the forks.

If I mount the motor vertically on a horizontal fork, it will end up as the best compromise, but it will interfere with the steering pivots and kingpins, unless I move it farther forward, and then the pendulum problem reappears.

Probably I will go with the horizontal fork, and change it if it doesn't work out right.

I've been going back to my old trike research and rereading info I found then but didn't apparently fully comprehend at the time. Now I have seen enough stuff in action and worked with various things in steering, and I understand them better. I think if I had built a trike before, unless I had simply copied someone else's design, I would have ended up with an unsafe or unrideable trike. :( Now I think I know enough to make a passable first shot at it. ;)

I am certain that I got lucky with CrazyBike2, in that it's configuration ended up working fantastically well for something so randomly chosen at each point in the process. I'm fairly good at the by-guess-and-by-gosh process, but it doesn't always work. :roll: The trike needs more thought put into it, and more choices of parts based on design rather than just whatever I have laying around. That said, I think I have a handle on it, and might be able to start building it in a month or so. Less if I'm lucky enough to figure the rest of the design out sooner.

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