A special bike for a special user.
I was asked to build a bicycle for a girl with special needs but who loves to go on bike rides.
Since i live by the phrase "By every one with the capabilty, for every one with the need", i simply couldnt resist.
The requirement list is as follows:
Not to heavy, not to expencive.
Two seats, next to eachother.
Dual steering, but break- and gear-shifters only on one side.
Passenger size fitted according to needs of the user.
Freewheel connected to the passenger side, so only the pilot is forced to pedal.
Modest luggage transport capability.
I have created a 3D-model of the HandyTandem that you can download from the link below.
A 3D-pdf must be downloaded and opened with Adobe Akrobat, right click the link above and select "Save as.."
A complete cad model is available upon request.
The project started with a production meeting with the orderer and the requirements list was specified, aswell as budget for the project.
We decided on a delta trike, with 2 rear wheels
and with pedals in front of the seat in a semi-reclined position.
I then spent a few months designing and improving the blueprint aswell as identify and solve any forseable problems.
The main problems were the gear and brake part, only the pilot is to control thease parts, and the gear"box" must affect both sides with perfect symetry.
Since the passenger side bottom bracket needs a freewheel, a power splitter is needed in order to power the both rear wheels regardless of who´s pedaling.
Initially the power transfer was designed with several intermediate axles to collect the pedal power, transfer it thru a single hub gear and then transfer and distribute the propulsion to the rear wheels.
This solution turned out to be very technically challenging and added alot of unecisary weight.
Eventually, after some brainstorming and fact-collectiong, i decided to use dual deraillours fitted on the rear wheels, with a cable splitter between the gear shifter and the deraillours.
Two greenfield full suspension frames were purchased from a used bike shop, and 3 6m sections of square tubes were purchased.
The frames were stripped and got the headtube removed.
The rear forks were welded together with a 25x25x2mm square tube between them.
Then we fabricated the two bent sections that makes up the outer section by cutting the tubes almost all the way thru, bending them and welding them back together.
Then we welded them together at the front and onto the rear frame.
The headtube was then fitted and welded onto the front of the bent tubes.
A diagonal square tube was then added between the upper part of the headtube and the square tube between the rear forks.
To be continiued..