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Wednesday, August 27, 2008

Recumbent Bike From Scrapped Bikes

The treadmill motor idea is going to be implemented on a new bike I thought of only a few days ago, and have been working out in sketches since then at breaks and lunch at work (no other spare time so far). This bike will be made as much as possible from only old bike frames, with a seat frame made of the remains of an old bedside toilet seat holder frame whose plastic bits were all sunrotted off. It's a recumbent type, bike instead of trike, mostly because I really can't make the complex steering mechanism for a trike properly right now--I just don't have the tools or knowledge yet.

I actually want to build an airshock-based recumbent trike, which I've already drawn up, but I simply can't afford the tools and materials needed to build it.

Today I am cutting up the old scrap frames I already have for a few parts, and will hopefully get some more scrap frames for the rest of the parts I need later this week from a fellow Freecyler. There'll be pics once I have them ready for pre-assembly fitting and filing, hopefully of all stages from "whole" frame to just the parts I will use. Some of the frames I got as pieces and such, so they're not all whole to start with. At least one was pretty trashed and bent up and I'd already cut those parts off months ago, so it's also not whole.

In the meantime I'll put the basic sketches up here:

The steering idea is still in progress, as currently both drawn methods conflict with my legs pedalling at anything but mild steering angles, and I think the trail is probably totally wrong for this setup. I had planned to use a 24" shock front fork with a 20" tire or smaller, with some serious modifications to the fork's headstock mounting end, but I discovered one of the tiny kid's bikes I've got a frame for actually has shocks in front, and it uses (I think) a 20" tire or smaller. Have to actually measure it (doesnt' have a wheel in it of course). Anyway, it's definitely short enough to not have to use such an extreme angle to keep the front end lower than the pedals, which will both help the shocks work better (more vertically) and let the steering work more easily.

I'll probably have to cut and weld a set of handlebars for the steering to make it work out right, because I don't think anything I have will either reach far enough back or be bent in the right shape to be out of the way of my legs, the bike frame, etc.

Not sure exactly what I'll do for the rear spring between the seatback frame and the rear triangle, but possibly the intact side of a bent-up 24" front shock fork could be used, if mounted correctly.

The seat will just be a lawn-chair style tube frame with material strung across it that won't hold water in, and allows as much airflow as possible (to keep from getting sweatsoaked back and thighs).

Since the pedals won't be in the way, I can have battery mounts along the bottom edge of the rear frame triangle, and my cargo pods or baskets (haven't decided) can be mounted much lower, with only the rear derailer to worry about clearing.

The seatpost from the rear triangle will be sticking up as far as I can get it (probably nearly a foot above where a seat would normally be), with a lighting module for visibility in place of the seat. There'll also be lights elsewhere on the bike, to ensure as full a visibility as possible, and it'll be painted the same DayGlo Avenger style as my current bike (which will remain intact for use when this one undergoes alterations, as is nearly certain to be required).

There will be 3 chains, the first runs from the pedals (above the front wheel, with a single chainring) to the first bearing set you see hanging down just behind the front wheel. That is where the front derailer and chainrings will be, mounted on a freewheel. That freewheel will prevent the pedals from being moved if the motor is running faster than the pedals, since they'll all be on the same drivetrain. The second chain runs from a fixed chainring on there to the bearing set (actually the motor) just in front of the rear wheel. That motor shaft will have a freewheel on it mounted so that the pedals don't turn the motor if pedalling only with no motor power, but instead only pass power to the 3rd chain that runs the rear wheel cassette (which will be a standard one with typical derailer and freewheel, etc).

I'd originally thought of putting the front derailer/chainrings on the motor so that it could also benefit from those additional ratios, but the inital sketch-scribbles showed me it was too complex and would be difficult to adjust and maintain, especially if the motor had any issues requiring it's removal. It will be difficult enough to setup the freewheel on it.

It's even possible I may not use front shifting at all, depending on the complexity and clearances of working out a tensioning scheme for that chain loop.

3 separate chains instead of one long chain is partly to make derailing the chain accidentally harder to do, as well as keeping the chains tensioned properly. It's also so I don't have to go buy a bunch of thin chain, and can instead use for the front two chains some of the single-chainring-width chain I already have off these scrapped bikes, and then just the single regular thin multi-chainring-width chain I have off one of them.

Should be interesting to see how different the actual bike is from those idea sketches above. :-)


  1. An old bedside toilet seat, Mike?

    Is that to facilitate... um... "dropping ballast" (shall we say?) during transit to gain more power on hills?

  2. Ah, no, but I thought it might be in the spirit of the 80's Popular Science that had a "methane powered" car--with toilet seats to collect the methane from the occupants. :P

    It's actually only because it's good enough steel to hold *my* weight, spread out across it via the cloth strapping, without itself contributing much weight to the bike. If I could weld aluminum, I'd rather use that, and I have some old folding cots with rotted-out plasticanvas that would be perfect for a supply of tubing. Since I can only weld steel with my equipment, then steel bedside toilet frame it is. :-)


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