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-   -   Homebuilt recumbent V.2.0 (https://www.bikeforums.net/recumbent/183944-homebuilt-recumbent-v-2-0-a.html)

Bikewer 03-26-06 09:00 PM

Homebuilt recumbent V.2.0
 
Here’s my Version 2.0 homebuilt. The first one, made of the finest Chinese steel, weighed in at a rather portly 48 pounds. My goal was to refine the thing, and shed as much weight as possible. This one is 38 pounds, so I shed 10 pounds of ugly fat. Compare to 29 pounds (manufacturer’s claim) for a Rans Rocket.

I found an aluminum V-frame, and tossed the “shock absorber”. Built an all-aluminum stem, and threw away the original crank and refined the chain routing. The new boom is from a CroMo-framed MTB, with a more-compact Alivio crankset. The chain guides are pretty standard skate-wheel constructions, using the extra-hard wheels.

The seat is a marvel of engineering, it’s from my lawnmower. The back is the frame for the bag, and the seat cover is the bag itself, suitably cut, sewn, and grommetted. A couple of aluminum tubes run to the dropout eyelets provide bracing.

I want to loose the old, heavy SPD pedals; I have a pair of eggbeaters I may try.
Trying to figure out where to mount a water-bottle!
Total investment for this thing is still under a hundred dollars.

The weather was good enough for an initial road test, and everything seems to be pretty much in order. A little bit of front DR adjustment needed, but it seems quite comfortable, and a bit more stable than my initial effort. I've lowered the center of gravity a bit, with a lower seat position and making my strut a bit shorter than the original shock absorber. By my seat-of-the-pants engineering, this should increase rake a bit as well, perhaps increasing high-speed stability. (Version one was a bit twitchy near 30 MPH)

http://im1.shutterfly.com/procserv/4...108AcNGzhu3bNn

kapnk 03-26-06 10:41 PM

http://im1.shutterfly.com/procserv/47b6dd07b3127cce97a2a5aa1ee800000016108AcNGzhu3bNn

Thanks for sharing. I love to see other people's homebuilts! This past weekend I did some work on building my first one. I took a bike with 20" wheels and chopped off the chain and seat stays and attached others from a 27" road bike. What I gained there was a larger rear wheel for smoother ride, and the ability to (easily) have multiple speeds. I brazed a seat post to the head tube so I can slip the boom on. Unfortunately I got it really crooked, so I'll have to go back and re-do that. I also brazed on some braces for mounting the seat. Sorry I don't have any pictures to share, it will be about 3 weeks until I can get back to the project.

Couple questions:

How high is your seat from the ground?

Why are your handlebars at that height? (comfort for your hands/arms, or do your knees really go up that high?)

Keep up the great work!

Bikewer 03-27-06 09:04 PM

Seat height is about 26". I measure the handlebar height right at 48", which gives my knees "just enough" clearance. Looks higher in the pic, because I cleverly cut off the top....

I spent a lot of time getting the position right, as it's not particularly adjustable. One annoying thing is that the chain tends to hit my calf, leaving gooey ick on same... I'm considering running that section through a plastic tube.

Floyd 03-28-06 03:23 PM

thanks for the pic. I too like to see what others are doing. I got started after seeing the "ground hugger" way back when. Yours looks good and the chain thing is a minor setback... keep up the good work

atombikes 03-29-06 10:02 AM

idlers
 
Floyd,

You could probably move the idler mount a little lower, and do away with the power side idler altogether. That may give a little more clearance for your leg?

World Tour 03-29-06 11:40 AM

How do you keep the chain on the skateboard wheels?

atombikes 03-29-06 02:01 PM

There is a groove cut in the outer circumference. Easy to make: chuck the skateboard/rollerblade wheel into a drill press, and use a cutter tool to remove material to create a groove.
===============================================================

One question: do you notice a lot of boom flex?

Bikewer 03-30-06 06:48 AM

Actually, the boom seems quite rigid. the frame tube is a pretty good fit on the steering stem, and there's a pair of pretty stout bolts there. I could have used a bit of shim stock to get a really tight fit, and if I notice any creaking I'll try that.

One thing about the skate wheels (there's a lot of info on making them on the web) is to get the hard ones. The first ones I made from a pair of cast-off skates were rather soft, and the drive-side wheel failed within 10 miles. These are very hard, "machine" quite nicely using a small square-end chisel and a jig chucked into my power drill. A drill press would be better if you have access to one.

I may look into just dropping the drive-side wheel. It does look as if the chainline would be a straight shot from the cassete to the crank!

PaPa 03-30-06 12:01 PM


Originally Posted by Bikewer
One thing about the skate wheels (there's a lot of info on making them on the web) is to get the hard ones. The first ones I made from a pair of cast-off skates were rather soft, and the drive-side wheel failed within 10 miles. These are very hard, "machine" quite nicely using a small square-end chisel and a jig chucked into my power drill. A drill press would be better if you have access to one.

I may look into just dropping the drive-side wheel. It does look as if the chainline would be a straight shot from the cassete to the crank!

Ideally, no idlers is preferred - and if idler(s) are required, then try to restrict them to the return side.

Converted skate or rollerbade wheels are poor choices. Although easy to convert, the compound is usually incorrect and longevity and efficiency suffers because of it. Also, the more the chain line is deflected, the greater the efficiency loss and decreased life span of the idler. Although more difficult to make, 15t and larger cogs are a better choice.

World Tour 03-30-06 08:46 PM

Papa, are you the same papa in yahoogrouops power-assist?

World Tour 03-30-06 08:46 PM

Papa, are you the same papa in yahoogrouops power-assist?

PaPa 03-30-06 09:24 PM


Originally Posted by World Tour
Papa, are you the same papa in yahoogrouops power-assist?

I don't do "Yahoo", so must be somebody else. So far, the only power assist I use, is one leg assisting the other.

BlazingPedals 03-31-06 06:44 AM

I agree about the idler on the power side. here is a how-to on making one.

http://www.biketcba.org/TRICORR/proj...ler/idler.html

For about the same price as buying the parts retail, you can get a Greenspeed idler from Hostelshoppe.com. I think the actual placement of the idlers could be tweaked, but you're on the right track there. It's not a bad idea to have a top idler, just to help prevent chain slap; but the whole double idler assembly could be moved lower.

I wondered about the boom, too. It is awfully skinny and I would expect it to deflect under heavy pedaling. You say it's just bolted on?

Bikewer 03-31-06 07:12 PM

Yep, 2 bolts. Seemed to work OK on the previous version as well. I tend to "spin", so there's perhaps not as much pressure on the thing as would be the case with someone who mashes the pedals.

The guy with the site I stole most of the original design from cut slots in the boom and secured it with radiator clamps! Didn't look sturdy to me.... I plan to study the thing a bit more this weekend and see if I can't get a yet-more-efficient chain routing.


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