Hi all!
Im building a social tandem trike with two rear wheels and i have some questions that needs answers.
The project is for a family who´s daughter has special needs, so she cannot use any brakes or gears due to congnitive dificulties, witch further complicates the project.
Since it will be a rear wheel drive, it will require some constructive thinking regarding the power transmission and gears, but also a way to brake both wheels with one brake lever.
The setup is as follows:
Two sets of pedals rotates an axle (located under the seats), one or both sides has a freewheel. I call this axle a collecting or front axle.
The rear wheels are both chain driven and connected to the rear output axle (no freewheel).
Option A means installing a internal gear hub with aditional sprocked fixed on its output part (instead of a rim), the gear hub would be installed between the both above mentioned axles, so it would power both wheels regardless of who´s doing the pedaling.
Option B would be dual external gears on the rear wheels, possibly with only one axle between the rear wheels and the pedals.
This single axle would have 4 sprockets, 2 for the pedals (one or both with freewheel) aswell as 2 fixed sprockets for the rear wheel chains.
Option B would mean alot (!!) less work, lighter weight and simpler mechanics exept from one big problem; how to control two derrailours from one shifter (the handlebar mounted gear controller, whatever its proper name is).
My logic dictates that STI derrailours are indexed so i could, at least in theory create a Y-cable to solve this.
But its not totally unusual that reality fails to follow my logic so therefore im writing to ask if anybody else has tryed this.
Regardless of what option i build, the rear wheels will have freewheels.
This will allow only the slower wheel to be powered when turning or while driving on slippery surfaces.
This means that the inside wheel will be powered while turning, rendering the turning radius a bit big, but i simply cannot afford a rear differential that probably would be a better option.
The second, lesser, problem is the rear brake assembly.
I would very much like to control both rear brakes from one lever, since i would need the other lever to control the single front wheel brake.
The idea is similar, a single wire from the handlebar that splits up into two behind the seats.
This could be done in two ways, eather fix the wires with a cable lock (two screws with paralell plates that locks two or more wires onto eachother) or with one cable between both rear brakes and a pulley system that pulls on the cable with a wheel or a hook as found on many 90´s mtb brakes.
Cable lock:
the cable hook (top of picture)
I know that i wont be able to perfectly balance the brake forces but i think that ok is good enough, since this wont be a speedster.
I just dont want it to turn in any direction while braking.
This would probably mean constant adjustment of the individual brakes but i could live with that as long as i dont have to use two levers.
As a side question, im looking for pushrods, connectors and such that i could use for steering, where do you guys purchase such things?
and whats the required dimensions on such things? i figure the forces arent huge, but still, i would hate to loose steering due to pushrod failure..
The trike will have two handlebars and both can control steering, so the control mechanics looks like a T when looked on from above, with front facing down.
..see the 3d-pdf below for specifics..
Has anyone used pull-pull wires for steering?
I figure it could be a good idea to use pull-pull-wires since that would allow me to better hide the control mechanics..
Im including a link to a 3d-PDF that shows my project with the above mentioned option A gear solution, save the PDF and open with acrobat reader since 3D wont work on any of the browsers ive tested..
http://liggist.se/other/stuff/h3mligt/handytandem3D.PDF
As i mentioned earlier, im building this thing, here´s a recent build picture
the whole thing was created in cad so if anyone wants to build one for themselves, just drop me a message and i´ll share my work
Im building a social tandem trike with two rear wheels and i have some questions that needs answers.
The project is for a family who´s daughter has special needs, so she cannot use any brakes or gears due to congnitive dificulties, witch further complicates the project.
Since it will be a rear wheel drive, it will require some constructive thinking regarding the power transmission and gears, but also a way to brake both wheels with one brake lever.
The setup is as follows:
Two sets of pedals rotates an axle (located under the seats), one or both sides has a freewheel. I call this axle a collecting or front axle.
The rear wheels are both chain driven and connected to the rear output axle (no freewheel).
Option A means installing a internal gear hub with aditional sprocked fixed on its output part (instead of a rim), the gear hub would be installed between the both above mentioned axles, so it would power both wheels regardless of who´s doing the pedaling.
Option B would be dual external gears on the rear wheels, possibly with only one axle between the rear wheels and the pedals.
This single axle would have 4 sprockets, 2 for the pedals (one or both with freewheel) aswell as 2 fixed sprockets for the rear wheel chains.
Option B would mean alot (!!) less work, lighter weight and simpler mechanics exept from one big problem; how to control two derrailours from one shifter (the handlebar mounted gear controller, whatever its proper name is).
My logic dictates that STI derrailours are indexed so i could, at least in theory create a Y-cable to solve this.
But its not totally unusual that reality fails to follow my logic so therefore im writing to ask if anybody else has tryed this.
Regardless of what option i build, the rear wheels will have freewheels.
This will allow only the slower wheel to be powered when turning or while driving on slippery surfaces.
This means that the inside wheel will be powered while turning, rendering the turning radius a bit big, but i simply cannot afford a rear differential that probably would be a better option.
The second, lesser, problem is the rear brake assembly.
I would very much like to control both rear brakes from one lever, since i would need the other lever to control the single front wheel brake.
The idea is similar, a single wire from the handlebar that splits up into two behind the seats.
This could be done in two ways, eather fix the wires with a cable lock (two screws with paralell plates that locks two or more wires onto eachother) or with one cable between both rear brakes and a pulley system that pulls on the cable with a wheel or a hook as found on many 90´s mtb brakes.
Cable lock:
the cable hook (top of picture)
I know that i wont be able to perfectly balance the brake forces but i think that ok is good enough, since this wont be a speedster.
I just dont want it to turn in any direction while braking.
This would probably mean constant adjustment of the individual brakes but i could live with that as long as i dont have to use two levers.
As a side question, im looking for pushrods, connectors and such that i could use for steering, where do you guys purchase such things?
and whats the required dimensions on such things? i figure the forces arent huge, but still, i would hate to loose steering due to pushrod failure..
The trike will have two handlebars and both can control steering, so the control mechanics looks like a T when looked on from above, with front facing down.
..see the 3d-pdf below for specifics..
Has anyone used pull-pull wires for steering?
I figure it could be a good idea to use pull-pull-wires since that would allow me to better hide the control mechanics..
Im including a link to a 3d-PDF that shows my project with the above mentioned option A gear solution, save the PDF and open with acrobat reader since 3D wont work on any of the browsers ive tested..
http://liggist.se/other/stuff/h3mligt/handytandem3D.PDF
As i mentioned earlier, im building this thing, here´s a recent build picture
the whole thing was created in cad so if anyone wants to build one for themselves, just drop me a message and i´ll share my work
