Bicycle Mechanics - senior design project - Human Powered Vehicle (a.k.a bicycle) - help?

allright, so we were assigned our senior deisgn project a couple of weeks ago. it is the ASME human powered vehicle (http://www.asme.org/hpv). we have an awesome concept, but are looking to cut down the money that we are going to have to spend in the machine shop.

we are basically going to build a three-wheeled recumbent with two wheels in the rear and one in the front - the front used to steer and the back used for propulsion. the vehicle must be able to reverse, but we also want it to have the ability to freewheel at speed (so you don't knock your feet off when the pedals sping out of control). we have a slick little jackshaft made up that will allow us to choose to drive one side of the vehicle at a time. one rear wheel will be mounted so that the freewheel allows it to propel the vehicle forward, and the opposite wheel will be mounted so that the freewheel allows it to be pedaled in reverse.

anyway, this opens up the possibility for independent rear suspension. a perfect solution for this involves bolting on the rear tringle of two full suspension bikes. however, our budget is severely limited and i've been trying to find wholesale/surplus frame shops online that would just sell me the rear triangle of the bike (the other option is buying two walmart bikes and just taking the triangles off of them, but that would eat up $200 easy).

anybody got any thoughts or ideas? i'd be happy to discuss our design with you if you are so inclined.

thanks guys (and gals). :D

greetings fellow mechanical engineer..

My thesis was an HPV too. With enough support from out Department of Energy, we were able to make a prototype. We were a team of 4, where I was assigned team leader.. the project was finished last 2001..

We made two prototypes, a tandem and a single. both recumbent.

Although, up to this point, we are bound not to discuss specific details, I can help you with certain aspects with regards to steering, and drive, and design concepts..

Unfortunately, a university thesis will not be submitted in contests, but may be displayed as exhibits only.

Good luck!! I hope you win! you have an edge! you're a cyclist! ;)

BTW, with regards to suspension.. travel was limited to material flex(same principle as carbon fiber forks and carbon rear chain stays and seat stays) which we computed.. The protoypes we made were roadies.. not MTBs :D :D

How fast? it was fast enough!

Dex.

I just drew it now.. Its not drawn to scale.. But it will give you an idea on how we did it.

BTW, it was as wide as a car so it can corner fast.

If you want to see the steering mech. PM me.

Forgot to draw the seat stay. :( , but its there on the actual thing.

If you have limited funds but good access to a machine shop and a decent weldor(The guy doing the welding) or other fabricator, it would be easier to make up your frame to fit your need rather than trying to make some other stuff work. With parts like freewheels it is easier to buy and mod but with a frame, it is just a couple of measured and mitered tubes. Dropouts can be cut out with a sabre saw and finished with a grinder and file.
Also if the budget is limited, leave off the suspension.

Seems to me, the easiest way to have gears and reverse. would be chain drive from cranks to an internal shift hub (Like a Shimano Nexus) driving one wheel and a dog clutch on the axle to lock the other wheel, directly to the cog, for reverse.

if you choose one wheel in the front and 2 in the back the vehicle will be very prone to tipping at higher speeds.

Recumbent designs are too low for tipping to be a problem. Its not such a big problem with upright trike designs.
Two front wheels are perhaps a better way of doing a trike.
You can cut up old garage sale bikes for rear triangles. You may want to consider using a mono-stay axle (supported on one side).