Ultimately, we want the trike rider to be able to pedal the pedals before him, and have that energy transferred to the right rear wheel.
The system will use the normal bicycle shift system. There will be three chainrings (gears) attached to the cranks which are attached to the pedals. In the rear wheel (only the right rear wheel is powered), the pedal energy will be applied to the rear wheel as it normally is in an 18 speed mountain bike.
Bicycles are such specialized things, that if you want this all to work, you have to do everything possible to make the bike parts think that there is another bike part at the end of that chain. Instead, there is the jackshaft (evil laugh).
So this repetition of an earlier picture shows us the power layout of the trike:
In reality, the "long chain" in the picture above is just a bit shorter than a normal bike chain. When I drew this I did not know how the sizes would work out in life (I'm a trial and error "engineer").
Let's call the long chain (the front one in the figure above) the "front chain", and the other chain the "rear chain."
The blue "jackshaft" in the diagram above, is simply a shaft that is rotated by the front chain and turns the chain to the existing rear triangle, driven. Each chain meets the shaft via a sprocket. The chainrings by the pedals and the cogs on the rear wheel are sprockets. Unfortunately, it would be a problem to grab some sprockets from a bike and attach them to a shaft (you would have to build something to connect the shaft to the exact center of the bike sprockets.
The shaft is mounted on two "pillow blocks" which are simply a bearing in a housing that lets you mount it easily:
This picture is a happy face from the materials I originally bought for this project: 3/4 inch keyed shaft, two pillow blocks (only one shown) and two sprockets (Martin Sprocket 41BS15) and a piece of chain. If I did this again, I would definitely use a smaller diameter keyed shaft. 3/4 inch it total overkill, and it weighs a lot.
Observant eyes might catch that the teeth of the sprockets (and that the one in the foreground is partially ground down) are WAY too thick for the chain links. There will be grinding, but it's not really so bad with a rotary tool.
So in action, the jackshaft is a shaft with two sprockets, mounted on two pillow blocks. The sprockets are keyed to the shaft with a piece of steel. The pillow blocks are BOLTED to the trike at right angles to the two chains. The front chain attaches to one sprocket, and at the distant end of the jackshaft, the other sprocket attaches to the rear chain.
The sprockets have to be ground using a rotary tool and a stone (I found that the reddish or grey stones worked well, the white one I had just ground itself to dust).
- Wear eye protection. Grinding emits sparks and metallic dust, and if your luck is lousy a piece of metal.
- Wear hand protection. The sprocket gets hot, there are sparks flying, there is a spinning object. And proper other clothes.
- No flammables around. Sparks
- Proper Electrical Safety. The rotary tool uses electricity and you could get hurt.
I promise to discuss this some more :-(
Essentially you grind down the flat side of the sprocket until you can have chain move along the sprocket when you turn the sprocket in your hand. With the rotary tool I did a sprocket in two sessions of less than one hour each. I originally tried this with my angle grinder, but found that the rotary tool (e.g., Dremel) with a stone works much better. In fact, I broke a tooth on one of my original sprockets with my angle grinder, had to get a new sprocket. Each sprocket cost me about $10.00. I used cheap pillow blocks (about $8.something each), and the steel shaft and little piece of key steel cost me about $30.
I put a plastic tube over the jackshaft so my leg would not hit the rotating shaft. The tube is mounted on a spacer of plywood so it doesn't touch the shaft.
The pillow block that is near the centre of the trike is actually bolted to the piece of perforated angle iron that runs partway down the length of the trike. The outer pillow block is bolted to the plywood with washers and lock washer on the bottom of the trike.
Note the cut out of the plywood so that my right foot doesn't hit the trike when I pedal.
Front Chain Setup
It starts off as a normal chain, going from the front chainrings through the normal front derailleur, through a hole in the plywood see the pictures above, to the sprocket on the jackshaft.
Aside about the rear derailleur on a bike. The rear derailleur serves two purposes:1: to move the chain across the cogs when you change gears, and 2: to keep tension on the chain as the chain has to work with differing size chainrings (as you shift gears). In this second function the rear derailleur, both keeps tension on the chain, and provides storage for the extra chain as you shift onto smaller chainrings and cogs. Take away the tensioning functions of the rear derailleur, and you have a front derailleur.
So I knew I needed a tensioner for my front chain. It had to deal with three different size chainrings as I shift. I decided to take one of my extra rear derailleurs and just keep its tensioning function (or most of the tensioning functions). I mounted it on a small piece of plywood, so it would mount and space nicely on the bottom of the trike. Look:
It gets mounted just about under the sprocket which is on the jackshaft. Unfortunately I did not have a long enough chain (I don't know why) and I could not switch to the highest chainring. I'll work on that later.
Even worse, the chain jumped on the sprocket. FAILURE (my pessimist part appearing stage left). I reground the sprocket to make it as good as possible, checked for stiff links in the chain and loosened them, and finally realized that I needed to increase the spring on the tensioner. I did this with a spring attached (slid over) the end of the tensioner and attached to the bottom of the trike, as:
Works well, but I still only have two front gears. So for now it's a 12-speed trike, not an 18-speed trike. (Early June update: I lengthened the front chain a bit, so I can shift to all three front chainrings, and now have 18 speeds.)
Rear Chain Setup
This is easy. A chain, the length of a normal bicycle chain goes from the sprocket on the jackshaft to the rear gear cluster (cassette) via the rear derailleur as is normal on a bike. I controlled the rear derailleur from the handlebar via shift cable completely enclosed in shift cable sheathing (shift cable sheathing is different from brake cable sheathing). Thus I could easily shape it the way I wanted it to go.
I bought a beach chair (looks like a folding lawn chair but with shorter legs) at a garage sale for $1.00. I attached two pieces of 2x3 lumber as shown in the pictures (the lumber is blue). After screwing all of it (including the little flat piece of metal on the bottom of the back of each side of the chair, I cut off its legs, leaving the front one a bit longer.
I have to get a better colour seat ;-)
The wood attached to the seat is screwed to the plywood of the trike.
(early June, 2010)
Next, Ride that Trike, and make changes to it