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Tuesday, December 1, 2009

More Broken Spokes, Need Rear Suspension

I'm pretty sure at this point that if I had rear suspension I wouldn't be having nearly the problems with the rear wheel that I do, so that is my next priority on this crazy bike.

Tonight I heard a rear spoke break TWANG as I hit a small 1" deep pothole around the diameter of my handspan, that I thought I avoided but didn't quite manage. As I stopped to see the damage, I could feel the tire rubbing against the frame in two spots, making it likely that there was at least one other broken spoke. There were four! All I could do at the time, about two miles from home, was to loosen some of the opposing spokes and tighten some of the ones around the broken ones on the same side, to eliminate the rubbing, and try not to abuse the wheel any more than necessary to get me home.

I'll have to take the wheel off and fix the spokes tonite, so I can head off to work tomorrow "worry free", as it were, but the worry that more spokes will break from the unsprung rear weight is not going to just go away.

I've had lots of ideas for rear suspension, most of which could be implemented reasonably easily if it weren't for the cargo pods needing to bolt the bottom rail to the rear triangle just above the dropouts. So I'll be creating a small piece of framework for the rear of the square tubing portion of the cargo pod rails, which are self-supporting, to "hang" the rest of the cargo pods structure from and keep them pushed outward at the bottom. I am not sure if this will work well until I try it out, but it is the only way short of a stiff tubing framework that will put the cargo pods fully outside the volume I need for the rear swingarm to move within.

Making a rear swingarm is technically not that hard, but may end up more difficult than I expect. The most compact option will simply remove the existing rear triangle and add a short extension to the front frame just under the seat that will hold the pivot point. The pivot point would be a BB and crank axle from a one-piece-crank type bike, of which I have several already disassembled for previous experiments. I'd leave the BB bearings partly exposed so I can get grease in there as needed, and then with no grease in it I'd weld the swingarm front end to the crank axle ends.

Alternately, I would cut a one-piece crank in half at it's center, then reweld it together as a U-shape instead of the S-shape it comes as. Then I can use the pedal holes in the cranks to bolt the swingarm to a little rearward of it's front end, and clamp it's front end to the cranks with some U-bolts, so that later on I can change things without cutting and rewelding, if necessary.

Either of those methods then requires a fairly compact spring, as there is not much room between the top of the ex-seatpost under the seat, and the front of the swingarm (perhaps 4 to 6"). I have a short and quite stout spring from a desk chair that is meant to preload it for tilting, which might help absorb a little bit of shock, but I would have to use something in addition to it to take up the preload of the bike weight plus myself, or there will be no compression left.

The other good springs I have are too long, and are meant to go outside a shock absorber from a motorcross bike (which I also have). These are about a foot long I also have the rear swingarm shock and spring from the Honda scooter, but it is also too long at around 10", and it is also probably not strong enough for this bike, as the Honda had a weight limit of only about 130 or 140 pounds, I think.

If I don't mind adding at least a foot to the length of the bike, I can bolt the front end of the swingarm *into the dropouts* of the existing rear triangle. This is easiest if I simply use the 24" rear triangle originally destined for the ReCycle that I never finished, as it uses square-taper cranks that I can easily just bolt to the dropouts.

This also makes it easy to use any of the shocks and springs I have; I could easily use the pair of motorcross shocks/springs, one on each side, and probably get a pretty good ride out of it.

Adding the new triangle plus the shocks would add at least 20 pounds to the bike, though. :-(

However, it is the best option, as it would also give me a place to put one more of those 17Ah batteries, for a 48V system and another 200Wh of power, which would give me about 18.6 miles of range at 80% DOD, with no recharge along the way, assuming 35Wh/mile. Right now, it's around 14 miles with three 17Ah batteries, by calculations. Realistically, I would get closer to 20-25 miles out of it, as I don't usually ride faster than 15-16MPH unless I'm in a hurry to get somewhere, and then it's 17-18MPH or maybe 19-20 for short trips--either of those eats up power too fast, though.

All told the battery plus the frame changes and shock and new triangle will add at least 35 pounds. So much for making it lighter. ;-)

But at least the weight will be sprung, so the rear wheel won't get destroyed by all the little holes and bigger potholes, plus the inch-or-more-high edges of driveways and such I must go over to get into parking lots and whatnot.

There aren't any pics for this post, as I need to get to fixing the problems now that I'm done with dinner, but there will be some of the spokes, and of some design ideas and parts, as soon as I can next post something. Also some pics of a couple of old 10-speed-type bikes I got for $5 at a yard sale a couple of days ago, one of which (a Schwinn 12-speed) has square-taper cranks (yay!), and both of which have lots of nice chromoly tubing, being very "tall" men's frames. I think that those bikes along with some other bits around here, including the old wooden seat from CrazyBike2, are going to become a Tour Easy clone, similar to that shown on the site. It'll be interesting to have a lightweight pedal-only recumbent not meant for cargo, but rather just for commuting.

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