With the warm weather finally here and the garage clean once again, I wasted no time, jumping right into the first project of the year, a tandem tadpole trike called the Viking. This tandem inline trike will be loosely based on our Warrior Trike, taking some of the frame geometry. I usually start with an idea on my mind and then just throw a bunch of scrap tubing around while I take notes to see what works and what doesn’t.
The first thing I wanted to improve was the way the captain and stoker have their cranks linked together, forcing them to fight each other if not in perfect harmony. If you have ever been on a standard tandem, then you know what happens when one rider needs a break from pedaling or loses their footing - a jerking of the other rider’s cranks. On a low recumbent, this can actually be a dangerous situation, causing a rider to have a foot fall to the ground and possibly end up under the frame.
I made the decision that the captain should always be in charge, and have the ability to stop pedaling at any time without having the stoker force the cranks back into motion. To solve this complex problem, an interesting crossover drive system was built and tested that uses only standard cycle parts, yet allows independent pedaling. This new drive system also puts 36 speeds at the captain’s control and solves yet another weakness in the standard tandem driveline – the rear chain.
On a standard tandem, the thin speed-bike chain must deliver the force of two riders to the rear wheel, but on the Viking, a BMX chain and freewheel is used at the rear, which puts a heavier chain where it is needed. This will greatly extend the life of the transmission.
On a “standard” tandem tadpole trike, a heavy main boom usually runs the length of the trike and then a lot of extra tubing is placed over top to allow a place for the two seats, stokes cranks, and the rear of the frame. This design requires a lot of tubing and also allows the main boom to flex in the center because the trussing is not complete.
The Viking will also use a large 2 inch main boom, but it will become the seat frame, crank support, and rear of the frame without needing any extra tubing! In addition to a small truss tube that will make the frame very strong, the entire length is just one piece. Not only does this look very slick (on paper), but it makes for a lighter and stiffer frame that will be capable of carrying more weight than a standard parallel boom design.
Updates on this project are posted on the Atomic Zombie blog: atomic-zombie-extreme-machines.blogspot.com