Recumbent Trike
Part 1: Ideas and Design


 

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Great Bike and Trike Resources

Atomic Zombie

If you are interested in building recumbent (and other kinds) of bikes and trikes, check out Atomic Zombie.  I liked the Delta Runner and bought the plans.  I thought that I could get the frame welded, and assemble the rest. 

How wrong I was!  These great folks are welders at heart.  What I tell friends is that if you are following an AZ plan (beautifully written) and you are not welding, then you are doing something wrong.  I wanted to make, then ride, not weld.  It's just my nature.  This might be my only trike project...I have other things that I want to do.

Wood Recumbents

There are lots of sites on the web that describe home-built wood bikes.  Some used 2x4's other used bamboo.  There are high end ones for sale.  Here are some links:

2 x 4 Recumbents

Wood Bikes You Can Make

10 Free Wooden Bike Plans

Plywood Recumbent Building Workshop

But these are all two-wheelers.  The 2x4 Recumbents guy sent me some sketches of a trike idea.  They were very conceptual, and added little to my quest.

There are lots of great resources on the web about bicycles (those are the parts I used, with others added).  I like:

Sheldon Brown (recommended to me by someone working at Cycle Salvation in Ottawa)

I used "The Bicycling Guide to Complete Bicycle Maintenance and Repair", 5th edition and the above websites and forums for my external guidance.

My Trike

My trike's style would be DELTA, where there is one wheel in the front, and two in the back.  The other style is the tadpole where there are two wheels in the front.  Front steering is the only way to go regardless of the trike style.  It seems that a single front wheel would be easier to build (steering two wheels would be hard to work out).  That's how I like to work things.

I took long looks at the rear triangle of bikes (the triangle around the rear wheel, which includes the bottom bracket tube (where the cranks that your feet drive connect to the bike) and the tube holding the seat post.  (Pictures below.)

If I use a complete rear triangle, then look what I get:

If I could mount two rear triangles as the two rear wheels, I would be on the way.

Only drive ONE wheel.  If you drive both wheels, then you need a differential to handle the different wheel speeds during a turn.  So they tell me and I'll listen. 

Most trike builders would move the rear set of gears to the center of the trike, and run a long shaft from these gears to the wheel.  But our rear gears are set to the side of the trike, not in line with the chain.  We need some sort of displacer (shown in blue and labeled "jackshaft"), as shown in this top view diagram.

 

Some internet searching and forum questioning yielded two methods for displacing the chain energy to the wheel.

  1. Drive the left rear wheel, and make a threaded tube that would fit where a crank puller would go.  Attach a gear to the other end of this shaft and you're set.  I loved this idea, except that if the trike flexed, the shaft would bend, causing problems.  I rejected this idea.
  2. Use a jackshaft.  "Jackshaft" is a generic term for any shaft that transfers motion from one place to another.  My jackshaft (shown in blue in the above diagram) would use two sprockets (one to attach to the "long chain" from the pedals, the second to attach to the rear wheel setup), and two pillow blocks, which are simply bearings in a nice holder that I can bolt to the trike.  More about this now and later.

 Attaching the jackshaft chain to the driven rear triangle. 

My question was how do I attach this chain from the jackshaft to the gearing on the driven rear triangle.  Some forum-folks suggested that I put a captain's crank on the driven sprocket.  A captain's crank is simply a (left)crank (the piece that holds the pedals) that has a gear on it.  You see these on all the tandem bikes.  They enable two people to pedal together.  A search for "captain's crank" yielded pieces of over $100.  Way out of budget.

I thought that I could simply add a crank to the left side with the chainrings of a normal right crank.  Or, I could simply use one of the three existing chainrings (either the inner or the outer one) and only have two gears for this derailleur.  (That's the set of gears shown in the above diagram just above and to the left of the words "orig chain".)

Thus I would have a trike with three gearshifts (wow! count the gears):

  1. The front set of gears by my pedals: 3 chainrings
  2. The middle set near the words "orig chain" in the above diagram: 2 chainrings left after I used one to drive it
  3. The rear derailleur set: 6 gears.

This would give me 3 x 2 x 6 = 36 speeds.  But this is not really true, as the gear ranges overlap.  In addition, adding that middle set of gears would change how the existing bike gear ratios worked.

So I took that middle gearing out.  Leaving this:

 

Mounting Those Rear Triangles

Another reason why I did not want to use the middle set of gears is that I wanted to use that area of the rear triangle for mounting the rear triangle.  Let's look at some bikes.

I bought two unserviced bikes from the bike dungeon of Recyclore, a bike recycler here in Ottawa.  They were both Raleigh mountain bikes, and they cost $20 each.  I searched for two bikes that would be as similar to each other as possible.  These were 26 inch bikes with an 18 inch frame.  Here's what they looked like:

We see the rear triangles, still attached to the bikes.

A bit of terminology.  The pedals are connected to cranks, which are connected to a shaft that connects the cranks through the bike.  This shaft and its bearings are called the bottom bracket, and it sits in the bottom bracket tube.  The right crank holds the chainrings, which drive the chain.

My plan is to remove the cranks and the bottom bracket (save them for later) and use the bottom bracket tube to mount the rear triangles on my trike.  Here's a rear triangle already cut (I used an angle grinder to cut, but a hacksaw should be OK), showing the bottom bracket tube (at the top of the photo):

You can see where I made the cuts (two sharp tubes at the left of the rear triangle) and the bottom bracket tube at the top of the image (the seat would be at the bottom, as I have this in a vise upside down).

I measured  the bottom bracket tube's diameter to be about 1 5/16 inch which decimally is 1.3125 inches.  My Ottawa metal supplier, Loucon Metal has aluminum pipe which has a nominal diameter (inside of 1 inch, but an outside diameter of 1.315 inches.  This would do, and with my inaccurate measurement, fits well.

Here are the two bike's rear triangles cleaned up (with all parts carefully removed for possible later use) and  the aluminum pipe:  (I had to do a bit of grinding with a rotary tool to remove some burrs in the bottom bracket tube before the aluminum pipe would fit.

The red triangle will go on the right side.  I initially wanted to have the left wheel driven (opposite my sketches, above) but decided on driving the right wheel.

The bottom bracket tubes will be bolted to the aluminum pipe.  This will not be the only mounting for the rear triangles, due to the upward rotational forces when weight is on the trike.

Go to next page, Aaaargh the Front End.