Sproklegrommet - Aluminium Folding Triangular Electric Bicycle

Go Home!	Triangular Folding Aluminum Electric Bicycle	See All Photos
	I had built two or three electric scooters in the past, but they all suffered from too much of the wrong kind of attention from the Police if I happened to ride them on the road. There had been a certain amount of coverage in the press about different Police authorities taking different views of electric scooters - although technically they are mostly illegal. Many said that if they were ridden sensibly and safely the Police would 'turn a blind eye'. I rang Sussex Police and they take a hard line saying they are illegal and there is no excuse for riding them on the road. They will arrest and they will prosecute! I asked how an officer on the street decides what is legal and what is not and was given the answer "If it looks like a bike, it's a bike (hence possibly OK so long as built to the EPAC regs), if not, it's illegal." The scooters were a lot more fun than traditional bikes so my challenge was to build something as fun as a scooter, but with a bit of imagination, looks like a bike. This is what I came up with after months of scribbling on beer mats and drawing on my CAD package. I thought I'd come up with something completely novel - particularly the folding mechanism, but someone pointed out that is was fairly similar to a bike called a 'Strida'. The patent for the Strida seems to show a my folding system as one option. Maybe they didn't get it to work properly? Either way, I think mine works better than the Strida and will fold in less than a second! Pretty good compared to Bromptons and other folding cycles even if it does not fold quite as small.
	This was the end result of my CAD drawings. It uses 6" diameter wheels with a belt drive between the pedals and rear wheel. I had figured the pedals would only really be there to make it look like a bike. They would work, but didn't need to work well. It was originally conceived as a 'V' belt, but when I found out about the Strida, which uses a toothed belt, I bought a spare pedal crank and sprockets from them. They are nicely made and very light plastic construction. I wish I could make plastic moldings!
	The drive motor (an engine cooling fan motor from a truck) has a nominal power of 200w although the stall current is about 35A at 24v - giving a max power of 840w. The speed controller also limits to about 9A continuous giving a continuous power in the region of 200w - hence legal without the need for the motor to be disabled unless you pedal (pedal assist). It is connected, with a ratio of 1:8 via a 1/4" pitch chain to the rear wheel.
	If you click on any of the images, you can see them in full resolution. You can see that it came out fairly similar to the CAD drawing. It is made from Aluminum tube, which itself houses 20, 7Ah NiCd 'F' Cell batteries. The tube is actually what is used for supporting TV antennas and the like. It appears to be drawn or extruded, thin walled and very strong for the weight. It was sufficiently light that I could hold one end of a 6m length with one hand and wave it around! Try that with a steel tube!. It is 1 1/2" outside diameter and the batteries are a snug fit inside (35mm outside diameter)	Unfolded: Half Folded Fully Folded
	I have to thank my friend Simon Copsey, who milled this bit for me (before I bought a mill capable of doing it). If you look at the higher resolution images, you can see how this joint operates. The handle bars connect directly to the front leg of the triangle. This has a bearing at the top (in the white nylon bit in the photo). The milled Aluminum bit pivots on the side of the nylon bit allowing the angle at the apex of the triangle to change (part of the fold mechanism). The Mk1 version was OK, but the handle bars were not quite wide enough and not at all rigidly held in place. I milled up a couple of clasps that hold the handlebar tight and now it's much better. This photo shows how I have joined the tubes. Not having the capability to weld Aluminium - and needing to be able to get at the batteries, I machined a plug which is a tight fit in the end of the tube. There are four radial bolts through the tube holding the plug in place and five axial bolts to attach the plug to something else - the top bracket in this case. This spreads the load on the end of the tube a bit and seems pretty strong!	Mk1 Mk2
	The front leg of the triangle continues down to this joint which again allows rotation, but also allows the cross bar to slide up and down the steering column. The original version of this joint worked pretty well, but there was too much sticktion (is that a real word?). When you tried to move the steering it required a lot of force, but once moving, it was easy. The mark 2 employs PTFE rollers which surround the steering shaft sandwiched between two aluminium plates. The PTFE makes it slide up & down really easily and the rollers make the steering smooth and easy.	Mk1 Mk2
	The saddle is just a normal comfortable gel filled one from a local shop. The wheels are pretty small and you tend to feel ALL the bumps in the road - so a comfortable saddle is important!
	The speed controller provides regenerative braking which is amazingly effective. It now sports a shiny new disk brake on the front wheel, but in practice you don't need it - but a front brake is one of the requirements for the bike to be legal!
	You can see the Strida pedal assembly here with the toothed belt drive to the rear wheel. I made the bottom bracket out of a lump of Nylon which just clamps to the cross bar. It could not bolt to it as the bolts would interfere with the batteries. The little hump above the rear wheel currently houses the motor and speed controller. At some point I want to move the controller into the bracket which supports the saddle. The red rectangle is a 70A power connector to isolate the batteries from the motor and connect to the charger - a RipMax SuperNova. It provides a fully managed 'delta peak' charge for up to 25 cells. Seems to work pretty well and gives me a full charge in about 3 hours.
	What about the speed and range I hear you ask? "Err....It does no more than 15mph Officer". That's not far from the truth. I went for torque rather than speed. It will cope with hills up to about 25% and has enough acceleration to throw you off! I have now limited the acceleration with the speed controller - don't like landing in the prickly bushes! The range appears to be at least 7 miles which although not a lot compared to some, for a bike this light (it really is very very light!) it's not too bad. How many journeys you'd want to do on something like this are over 3.5 miles? It would lend itself to additional 'clip on' NiCd battery packs in tubes. They could potentially be attached to the three legs of the triangle. Like most of my projects, this is an ongoing development. I'll post some more photos as the improvements come.
	Click Here to see all the photos of the build process.