Jurassic Tandem, a two places vehicle for almost nothing

For the group of teachers who think about embarking on projects around electric vehicles, it was necessary that we figure out some detailes before committing one or more classes into uncertain projects.

That’s the reason why François Girardier and Jean-Philippe Chavey came up with the Jurassic Tandem, an electric bicycle with a solar panel on the back.

The solar panel came from the adventure of "Tour of Malta in 80 emails", so from 2001. Philippe Muller, professor of mechanical engineering, created a hinge that allowed the panel to tilt to maximize efficiency.

The tandem base belonged to JP Chavey. The BionX kit was assembled by NowFuture in Lausanne, with an arrangement to give it back if we didn’t keep it after the project (which would reduce the costs).

However there was still a problem, adjusting the voltage. The solar panel issued approximately 17V, and the NiMH battery operated in 24V (ie at least 27-28V to load). The end result is a little bit of a “do-it yourself” fix, but it worked well.

To adjust the voltage of the solar panel(17V) to the batteries, we could not find a MPPT. Instead of that, we added a small lead battery (12V, 4Ah). Charging is therefore done in two phases:

1. Charging the battery from the 12V solar panel.
2. Circuit using both the solar panel and the 12V battery to charge the 24V battery.

This system obviously isn’t optimal in terms of performance, because we charge a buffer battery, but at least it works. Switching between the two is possible via a manual button.

We participated in the solar Phebus rally 2007 with this bike, and you might see in the story that it was effective in terms of energy, but the aluminum casing of the engine broke mechanically.

The whole vehicle weighed only 40kg in total, what make it one of the lightest 2 seater electric vehicles in the world.

With two 200Wh batteries, we could have expected to travel 2 x 40km (moderate hills) being well assisted and in case of very sunny day, another 30km. That isn’t too bad, it is a good electric bicycle. But to go further, it would need to go from 30W solar to 150 or 200W, and start with 800 to 1000Wh.