Introduction: Tandem Mixed : Seated/bent
EDIT : After fews modifications, the tandem is really working and has done 2000km. we are currently in a bike trip since July to December in France. You can see pictures of the current version in the final step. soon more details !
New project : a new tandem, but not a regular one, a mixed tandem !
Yes ! Here, the driver is behind and manage the steering. He's as on a normal bike : on the seat/saddle.
The stocker (the passenger) is, this time in front of the bike and seated or bent like a recumbent bike.
The main advantage of this bike, compared to a normal tandem is the fact that both cyclists can see the landscape. The cyclist qt the back doesn't have a blind view and they can speak easily. You can also kiss your girlfriend quietly without any risk of dying !
Of course this bike's purpose is not racing, it's more made for touring
My build is a simply copy of the commercial bike Pino Hase. (cf picture)
For this instructables, you will need :
* a 26 inch moutain bike (for the rear triangle, the head tube and the fork)
* a seat for the stocker
* a 20 inch fork with the wheel
* a second bottom bracket for the stocker
* some tubes for the frame
* a steering ball and a pivot for the steering, I used a steering ball of an old car
I used two bikes for this tandem : an old mountain bike (for the driver and the steering) and a child bike (20inch) for the stocker.
Step 1: Frame
To build the frame, you need to keep only the rear triangle of the moutain bike.
After that, I welded the main tube (white) from the bottom bracket with the good angle : I took measurements from the model (Pino hase).
I made a hole in the main tube for the head tube. You have to check the head tube angle : I took 72° because it's really nice for this type of bike : pretty steady at low speed and manageable. It's a touring bike, you will have two people and little luggage, in order to have to keep right your bike. You don't need to go fast with it.
I made a hole in the main tube for the fork to keep the rigidity of the tube, of course you have to correct the angle of front part of the tube. I cut a slice, bent it according to my convenience and welded it.
The second tube is useful to strenghten the whole and to support the front seat and the steering. As the previous head tube, I pierced a hole for the second one.
Previously, I put the front seat behind the fork. According to me, this is the best option, in order to keep a good steering. But, I didn't keep any space behind for the handlebar. I had to move a bit the front seat.
The front seat was built from an old steel chair. I simply decrease the width of the seat and cut the feet. The seat is attached to the bike only with bolts. So as to, you can easily remove the chair and your bike could become a porter.
The seat is blocked on the front and the back with hooks welded to the main tube. I added a transversal tube
to prevent side shifting.
he seat and the back are not finished yet : I have to improve the comfort now.
Step 2: Steering
With 2 cargo bikes and 1 recumbent, I began to know shifting effect while steering.
You need a pivot and a steering ball to make the liaison between the handlebar and the fork.
For the front part, I welded a piece of metal to attach the steering ball.
This steering ball is also screwed in a thin tube. I welded the bolt to the thin tube. Thanks to that, I can dismount the steering ball and adjust the length of the tube (and so, adjust your steering).
On the other side, I cut the old moutain bike fork to only keep the upper part. This part is going inside of the head tube and you will put your stem inside. I welded at the end of the fork tube the same piece of steel that the front fork to attach the thin tube. Here you only need a pivot. I made it with a cone and a wheel axe. As the thread is really thin, this is a good pivot.
Of course, you have to keep the same size between the center of your front fork to your steering ball attach and the center of your head tube and the pivot. If not, by turning the handlebar, the wheel will not rotate exactly in the same way.
Step 3: Handle Bar, THE Problem !
This was my main issue : to find the correct handlebar. In fact, that's because, you need to find a compromise between :
* maximum steering angle possible, reached when the handlebar is locked against the seat
* the posture of the driver (more or less bent = more or less powerful) You also have to avoid hitting your knees to the handlebar.
Pretty complex, I have tried 3 handlebar to find the good one. This one is not perfect, however I can improve it by expand the width, again and again.
Step 4: Transmission
Like a normal tandem, the two cranks have to be connected.
The driver has two cranks : the right one is connected to the rear wheel, the left one is connected to the stocker.
The Pino (the model) includes a freewheel between the two cranks : cyclists can pedale separately and especially, the stocker can stop pedaling, which can, for instance, be handy for starting.
I don't have a free wheel on the left crank, it was too expensive or too difficult to build. The two cranks are simply connected by a chain, the size of the cranks are identical : 22 theeth.
With this length of chain, you need a chain tensionner. I simply put a rear derailleur below the seat. The chain is tight and there is no problem in order to pedal.
I just have to add roll-on to protect the chain from the stocker and roulette to guide the chain when no one is pedaling.
Pictures are shown green roll-on. It was just a test. I will post a new picture with the chain tensionner and roulettes.
Step 5: Test and Ride
After adding crutch, speeds and brakes (v-brakes), it was time to ride !
Driving this bike is really nice and the two positions are comfortable. This new tandem promises some beautiful rides !
Thanks to that, you will love tandem !
Soon, new pictures !
To improve :
* a better handlebar ?
* I have to paint it !