This is my first Instructable so we'll see how it goes.
I want to document the construction of my recumbent bicycle, herein after referred to as the Rec-liner, or more probably just the bike.
The bike has a number of unique features that may be of interest to other bike builders including;
- under-seat, remote steering
- intermediate drive with an elliptical front chain ring
- mostly standard bicycle parts to make replacing and upgrading parts easy
I built this bike around 18 months ago, but as I did not have Instructables in mind at that time so there are no actual build photos. I have however pulled the bike apart a little to take some photos so hopefully this should make the following easy to understand.
Step 1: Materials
You should be able to build the complete bike using only two donor bikes but there are a number of specific requirements for each.
Donor bike 1 - Mountain bike with 26in wheels
- rear end (rear triangle, bottom bracket, cranks, derailers etc.)
- handlebars, handlebar stem, head tube, fork tube
- an indexed gear system is recommended
Donor bike 2 - Mountain bike with 20in wheels
- front end (handlebar stem, head tube, forks, wheel)
- bottom bracket, cranks
Both bikes would ideally have triple chain rings that are removable from the cranks.
2.8m of 50mm x 25mm rectangular section steel tube (1.2mm thickness)
Plywood for seat
Foam rubber for seat
Scrap steel plate (3mm)
1m of 10mm threaded rod
2 x 10mm rod ends (female thread)
Plastic tubing (10mm inside diameter)
Welder (I used 130A arc welder with satisfactory results)
Usual tools required for bike maintenance
Step 2: The Frame
I designed the frame with only one rider in mind, but with some allowance to move the seat to fine tune the length. If you are planning to build a frame you can use the measurements I give as a starting point. To give you some idea I have an inner leg length of just a little over 80cm and there is room on the frame to move the seat back about a further 10cm.
Start by cutting the rear triangle from the larger bike, including the seat tube and bottom bracket, Weld a 1.3m section of 50mm x 25mm rectangular section steel tube at right angles to the seat tube 175mm above the bottom bracket. This is now the new top tube for the recumbent.
Next cut the bottom bracket off the smaller frame, this will become the front bottom bracket on the new frame. Weld the bottom bracket to a 1m section of 50mm x 25mm rectangular section steel tube to create the new down tube.
Cut the head tube off the larger frame and grind back the cut sections to leave just the tube. Remove the bearing races and shorten the tube to about 75mm. Drill and file a hole big enough to fit the head tube into the new down tube. This hole should be about 650mm behind the bottom bracket, Weld the head tube into the down tube and then refit the bearing races.
To join the top tube and the down tube first cut a slot 25mm wide in the centre of the front bottom bracket. The top tube fits into this slot and the down tube is welded to the rest of the frame (hopefully this is clear once you have looked at the images). Now file away the top tube that protrudes inside the bottom bracket to allow clearance for the bottom bracket workings.
Next we make the back stay for the seat. This is a piece of rectangular section that is welded to the top tube just in front of the seat tube and to the seat stays on the rear triangle. Fit the wheel to ensure the new back stay will clear it easily. I was lucky enough to find a frame where the seat stays joined to a single tube before meeting the seat tube which made this problem a lot easier.
Finally the frame is completed by adding the head tube. Cut the head tube off the smaller frame and weld it to the top tube. The angle at which it is welded makes it parallel to the other head tube.
To plug the hole in the seat tube I used a rubber foot off a table leg.
Step 3: Power Train
One of the interesting features of this bike is the intermediate drive. This has a couple of advantages over the usual designs for a recumbent power train.
Firstly the area around the cranks is clean with no front derailer, Secondly there is less slack in the chain; a number of recumbents I looked at when designing the bike had a bad habit of dropping the chain with some regularity.
Construction is straight forward. Cut the crank arm off one of the triple chain ring cranks and file back smooth to create the intermediate drive. Remove the inner chain ring and add some small washers to move it far enough from the middle chain ring so that there is no interference between the front chain and the rear chain.
Mount only the small chain ring on the front crank, I used the same spacers as I used on the intermediate drive small chain ring so they would line up, but this is probably unnecessary. I used an elliptical chain ring on the front so I spend more time on the power section of the stroke and this has worked well.
Finally you will probably need to tension the front chain to remove any slack. To do this I created an idler out of some scrap steel and an idler cog from a rear derailer. Adjust the 'front' derailer so that it does not allow you to shift to the smallest chain ring.
Step 4: Steering
The second interesting feature of this bike is the steering. When I designed the bike I decided I wanted under seat steering (to me it just looks more comfortable). On a long wheel based bike this requires remote steering.
The front of the steering arm is the simplest. Cut the end off one of the handlebar stems and weld on a piece of scrap steel for the lever arm. Place the stem in the front fork tube and tighten up the choke like normal.
The rear of the steering is a bit more complicated. Firstly cut the fork tube off the spare set of front forks. You will need to fabricate a new mount for the bearing race so that when the tube is inserted in the head tube about 30mm of thread sticks out the top. Next shorten the second handlebar stem so that it can be inserted in to the head tube, but remain as long as possible.
Insert the handlebar stem into the head tube, then insert the fork tube and mark where it comes up to on the stem. You want the top of the stem to be just below the bottom of the top tube so that your handlebars are not to low. Remove all the pieces and then weld some scrap steel just above the line you marked to create the lever arm. Reassemble as before.
Finally the steering rod is created from a piece of 10mm threaded rod with a rod end at each end. Once you have determined the appropriate length cover the rod with plastic tubing to make a smooth surface. The steering rod should run between the left crank and the frame, just above the bottom bracket.
Step 5: Seat
The seat is made of plywood, covered in high density foam rubber. The base of the seat clamps to either side of the top tube so that it adds no extra height between the rider and the handlebars.
Place the seat on the bike and move it forward or backward to get the desired length. Once I had the seat positioned I made up a mount to attach the back of the seat to the seat stay.
Drill holes in the top tube and seat stay and bolt the seat in place.
Step 6: Summary
As I said in the intro I built this bike about 18 months ago and since then I have traveled about 5000km on it commuting to and from work.
The bike is easy to ride with only the slightest pressure on the handlebars required to keep it going in the right direction. It has proven surprisingly agile despite its long wheelbase, and the height of the seat means its easy to see and be seen in traffic.
Please let me know if you find this Instructable useful, or if there is anything in this Instructable that is not clear.