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charly17201 08-05-09 05:53 PM

'Bent Tadpole Frame Build
Cross-posting to Recumbents Forum

Okay, I've decided I want to try and build a 'bent tadpole trike - fall/winter project.

I've looked at tons of pics of trikes coming up with the vision for mine. I'd love to do a laminated 'Woodie' just because what I've seen look so darned sweet. But I'm going to settle for a metal build for now. I'm just trying to figure out CroMoly or Alum. I'm leaning to Alum but have yet to find any simple to follow guidance on thickness/weight/strength on choosing the materials. Any help here would be wonderful.

Weight/size considerations:
Me- Height 5'4"
Weight 160 lbs
x-seam 32"

Primary Use: Commuting - but I want to be quick. I carry about 25 lbs of stuff to and from work daily.

Frame Considerations: Tadpole
700c wheels
CroMoly or Alum???

I'm thinking of a 10-speed hub and maybe an over/under drive.

Any thoughts or recommendations would be appreciated.

rodar y rodar 08-07-09 10:08 AM

Do you already have the skills and equipment needed to fabricate an aluminum frame? If not, that would be a MAJOR hurdle to overcome.

charly17201 08-07-09 05:13 PM


Originally Posted by rodar y rodar (Post 9439215)
Do you already have the skills and equipment needed to fabricate an aluminum frame? If not, that would be a MAJOR hurdle to overcome.

I have a friend with the requisite welding skills.

rodar y rodar 08-08-09 12:33 AM

He might be able to pull it off. Still, I`d probably go with steel if it were me because you may need to change something later- especially since there isn`t as much info on tadpole geometry as there is for DF. I wouldn`t want to play "lets try it like this now" with aluminum. Or I could just be paranoid. In the interest of full disclosure, I`m not a frame builder either- I just like reading about the process and since the smart guys seem to be leaving this one alone I figured I might as well offer my gibberish.

scbvideoboy 08-08-09 09:44 AM

Yeah you get one shot with aluminum welding process...if it's wrong scrap it and start over. But there are bike supply places where you can buy alum BB shells and frame building stuff like drop outs and such. best idea is once you get a good rough layout and design...get someone who has experience building a trike look at it to offer some alternate ideas and suggestions.

jamesl 08-08-09 10:16 AM

I've built a few different recumbents, including a tadpole. I would strongly suggest steel as the better alternative, especially for a first time build. The difference in weight of the actual frame would be relatively small. Most of the weight in a tadpole design is in the things you attach to the frame, anyway, like seat, three wheels, steering, etc. has an active home builders forum and a trike forum, both good resources for q&A.

25hz 08-11-09 08:23 AM

Mild steel is more than strong enough for a trike build and it's easy to get a hold of and cheap. A tadpole is a simple design and easy to build. The hardest part is getting a welder. Using square tube makes the process even easier.

NoReg 08-11-09 11:29 AM

I looked at some pictures, and the design is truss form from what I could see. Lots of little parts with separation. With an alloy recumbent, the kind of thing you can do is make the backbone out of one bent alloy beercan of a tube. There you maximize the form advantage of oversize thin wall tubing. If you are going to make the backbone out of a thin tubed truss, then I don't see the point to going with Al. Myself I would use chromo, it isn't all that expensive, welds very nicely, and is stronger than mild steel.

charly17201 08-11-09 06:58 PM

Thanks for the input so far.... I'm getting more and more ideas on how to do a better design.

25hz 08-13-09 07:41 AM

Going to chromo is fine, but or being able to go to thinner wall, it MIGHT save you a couple pounds in frame weight, if you're lucky, generally, much less, and that is going from .063" walled mild down to .035" cromo. Chromo is definitely stronger than mild steel, but mild steel is also plenty strong enough. Making a simple cross shaped frame is quick and easy, or you can try a twin rail design. In the end, the weight is going to be nearly identical anyway.

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