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Moz's Tandem Building

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seat building
I built the seats first, since they were going to be easy to store and entertaining to bend up. Giles offered to help bend the tubing, which saved me making a jig. That's when I began to realise I'd seriously over-spec'ed the tubing - Giles wasn't set up to bend the 22x1.2mm tube I was using, but we managed it anyway. In retrospect CI could have got away with lighter seats, but because I didn't think I'd have very good triangulation I wanted them to be fairly solid. They were... Also, 330mm wide is too narrow, even though it's wider than my TriSled, for touring 400mm or wider is more comfortable. These are designed to use sleeved joints to attach to the trike, so they're fairly simple to make as separate items.
making a sleeve joint for the main tube
Serious construction started with the rear part, as it is small and fairly simple. This meant building the first sleeving joint, and getting around the fact that I only had one size of tube, I couldn't get anything that would sleeve over the main tube so I had to make my own. A small circle of the tube, the spacer, and a big slot in the sleeve did the trick.
building chainstays
Then, cut a 50mm circular hole across one end of the 78mm tube to take the cross tube...
addiung dropouts to the rear rectangle
and add the chainstays as a rectangle of tube. That makes for a strong part, and it's also a bit easier to build since it sits flat while being put together.
a real rear rack
Once the basic shape is there, add the "rear triangle" and rack.
mid section
The center section was the easiest bit - a length of tube with a bottom bracket attached at one end. The second sleeved joint was definitely easier to put together. Cutting the slit is easy enough (10 minutes with a cutting disk in the grinder), but spreading the tube afterwards involves a lot of heating, levering and hitting.
getting nine degrees of lean on the cross member
Getting the cross member in straight, with the required 9 degrees of slope backwards took a while. I drew a line on the wall and moved the tubing to match. That's threaded rod through the kingpin holes to show exactly which way they're pointing. Then it was just a matter of filing, assembling, checking the angle, filing again and so on until it looked right. At which point I could start brazing - tack a little, check the angles, repeat... I was quite keen to have the front end of the trike correctly set up as well as strong.
steering setup
Which is where the steering geometry became entertainment in three dimensions. My frame lacks the second bend in the main tube that Greenspeed use, but it looked OK in CAD and turned out to work in practice, albeit with a bend in one steering arm.
steering setup
This turned out to be the main hiccup with the steering - the handlebar hits the steering connection, which limits the lock available. The connecting rod on the other side is far enough under the bars that it doesn't hit, but this one did. Hence the bend... which gave an extra few degrees of steering movement. You can also see the top of the recessed pivot bolt for the handlebars is this shot.
mounting seats - very busy at the front with steering and chain in
the same place as the seat mount
After only a couple of months I could put the bits together and start worrying about all the details that hadn't been obvious in the computer. The chain lines were the big hassle - things that looked fine on the PC seemed to have mysteriously grown ugly in the metal. The issue initially was that the drive-side chain ran at the same height as the seat fastenings, and spacing it out as here meant the bolts holding the idlers on flexed visibly under tension.
bolt on front seat
We came up with the bolt-on version for the front seat - I brazed a lump of steel strip (25mmx5mm) on the inside of the frame tube, then tapped it to take 10mm bolts at 30mm intervals. By putting two pairs of holes in the seat at 45mm spacing I could get reasonable adjustability without the seat extending more than half way down the main tube. So the chain could run close in the that tube.
sleeved joint
The sleeved joints seemed to work quite well, or at least I could put them together and they held while the trike was in the back yard.
long chain
But the 2m length of chain tended to flap in the breeze a bit, so I made the movable idler you can see here. It turned out to be essential, as after powder coating the chain ground on the underside of the seat when the trike was in solo mode (I discovered this about 100km south of Bidyadanga, in Western Australia)
I started the accessorising process early - mudguards are essential in Sydney, especially on a tandem (when it's the stoker who catches a lot of the front wheel spray).
wheel truing gadget
I also added these wee wheel truing guides, and finished building the front wheels using them. It's just a steel bolt and a bit off an old spoke, but it makes it very easy to true the wheel on the trike.
folding the trike
The first test ride meant carrying the trike through the house...
tight steering lock
And discovering just how tight the steering lock really is, especially in the solo mode. It turns really tightly. That's Ian Humphries riding it.
ridable, but not painted yet
loooong trike
As a tandem it became obvious just how long it really was - without the stokers seat it looks more like a truck than a trike.
all the bits together after painting
powder coated
I carried the bits down to the sand-blasting place, then to the powder-coater, then back again on foot (mostly). Once they got back I had this huge pile of very clean white bits to assemble. And now we own a collection of powder-coated steel bolts in a variety of sizes.
assembled after painting
first assembly
Note the way the rear rack is at a funny angle. That was the first problem I found once I started test riding the tandem - the back part tended to rotate on corners. I fixed it by putting three bolts through the sleeved tubes, which kind of made the actual sleeving irrelevant. But at least the trike worked...
bolting down the front seat
front seat attachment
This shows how the front seat bolts on. It's a fairly heavy system, and not exceptionally easy to adjust until you compare it to breaking chains and playing with other dirty bits, as Greenspeed and ICE make you do. In that sense it worked really well, and on CANC the seat seemed to get moved most days. This photo is looking forward from under the seat. Note that the front of the seat has two holes instead of a slot, and that this mounting is what stops the seat rotating around the main tube on corners. So it needs to be fairly beefy...
bottom bracket details
This photo is from when I got back to Sydney after 3500km of riding. You can see the twin derailleur posts (for small and large chain rings), the very oversize front boom tube (it should have been 60x1.2mm or so), and the bolt-in bottom bracket. That allowed me to swap from tandem (Mt Drive in front of stoker) to solo (Mt Drive at front) using only an allen key rather than having to pull cranks and undo bottom brackets. Much faster and easier this way... Oh, and the cheap 20W halogen "bike light", a standard household fitting, a bent spoke and some speaker wire (cheap and flexible).
chainline photo
The rear seat about as far forward as it will go, note the chain sitting about 20mm off the ground. A lot of the time I ran it over the mobile idler which normally sat just in front of the joint in the main tube. The pink MTB bar-end is to mount the rear brake lever on, as the older Hayes levers are a one-bolt style clamp that can't go onto a closed tube (like all the 22mm tube that you can see there). You can just see the "front" gear lever on the right of this photo. I mounted it in the end of the derailleur tube to make routing cables easier, and it seems to work quite well there. I wouldn't want to shift it every 10 minutes like that, but mostly I used the 9 speed cluster to do the bulk of the shifting, and the Mt Drive to get low gears for starting off.
all done
This is the assembled tandem.