Rear Steered Adaptive Trike

This project is another bike I constructed for Shepherd of the Valley Lutheran Church’s bicycle ministry program which, in coordination with our local school district, builds custom adaptive bikes and trikes for special needs students. This program is funded through the church and the Merced (CA) Sunrise Rotary which provides these adaptive bikes free to students and adults who otherwise could not afford them. This Instructable is provided in the hopes that other volunteer organizations and churches might replicate this program in their own communities and use our plans and descriptions to provide similar bikes at low or no cost.

The student receiving this bike has very limited use of his hands and his legs. He can not walk but he CAN move his legs in a pedaling motion which his doctors advise he should do as much as possible. While this bike does not allow the student complete freedom to ride a bike on his own, it does provide him with the exhilaration of riding while providing much needed exercise for his limbs. As you will see, the bike has been custom built so that it can be pushed, steered and braked from the rear of the bike. A parent, teacher or friend walks along behind the bike to carry out those functions.

[Note: Some of the photos taken during construction of this bike were lost due to a hard drive failure. I will try to fill in the missing images with photos taken of the finished bike.]

A basic frame plan was drawn up and the component parts were cut from 1 1/2x1" and 1 1/2x1 ½” steel tubing. (Photo 1)

A steering head (see arrow in Photo 2) was cut from a salvaged bike and was incorporated into the frame pieces as they were welded up.

The rear axle is cut from 5/8" diameter keyed shaft stock (I got mine on the web from Surplus Center). Common 1 1/4" EMT conduit (Home Depot) is used to create carrier tubes to hold the axles (see red arrows in Photo 1) A 1 3/8" O.D x 5/8" I.D. sealed wheel bearing with retainer ring (Ebay) is fitted into each end of the conduit to keep the axle spinning straight and smooth. The conduit has an inside diameter of 1.380" and the bearing has an outside diameter or 1.375 but the fit is tight enough to keep everything solid. In fact, your conduit may need to ground down a bit to remove any seam weld if present. The axle is prevented from moving left or right within the carrier tube by 5/8" I.D. shaft collars (white arrow in Photo 1) which are held in place with allen set screws.
The wheels are fixed solid to the axle shaft using W series weld on sprocket hubs (black arrows in Photo 1). W series sprocket hubs have a 1 5/8" O.D on the smaller sprocket end of the hub (Photo 2). This end of the hub slips almost perfectly into the bearing pocket of my wheel hubs once the bearings are removed. If yours does not fit snug, you can cut shimming material from an aluminum soda can. Make sure the shimming material is long enough to wrap almost all the way around the sprocket hub so that the hub can not move out of alignment in any wheel position as it rolls. The sprocket hubs are keyed the same as the axle shaft material so the key prevents the wheel from spinning on the axle shaft. The sprocket hubs are held in place with a pair of allen set screws which are included with the hubs at purchase.

Once the axle carrying tubes are perfectly squared up with the frame and welded in place, the center section of the axle shaft (arrow in Photo 3) will be cut out and removed thus allowing the left and right wheels to spin independently. The pedals/chain will drive only the “driver’s side” wheel. The passenger side will freewheel.

A power bracket is cut from a donor bike and two pieces of 3/16" flat stock are positioned and welded to the bottom of the power bracket so that they slip snugly over the center frame rail. (see red arrow in Photo 1) Holes are drilled in the lower ends of the flat stock so that the power bracket can be tightened onto the frame. This configuration allows the power bracket to be adjusted forward or back to fit the size and leg length of the rider.
The bike has an intermediary or “middle” hub which serves two purposes (see white arrow in Photo 1). First it acts as a jack shaft to shift the chain from the “pedal sprocket” side of the bike to the “drive sprocket” side of the bike. Secondly, since it is an ordinary rear brake hub from a coaster bike, it allows the drive wheel to freewheel. A second sprocket is welded to the output side of the hub to provide the outgoing power to the rear wheel. (See Photo 2)

A couple more views of the frame and chain drive components. (Photos 3-5) Note that at this stage of construction we were hoping the student might be capable of operating some hand controls and we had installed a small hub motor on the front wheel. It was later determined this would not be a viable option and the electric motor was replaced with a normal front wheel.

Unfortunately, the photos of the seat construction were lost when a hard drive destroyed itself. But I will substitute as best I can. The seat shown in these photos was for a previous bike we built, but the process is the same.

The seat base is cut to the size and shape you want from ½" plywood or particle board. Tee nuts are installed to match the mounting position on your bike. (Photo 1)

Foam is cut to match the shape of the seat base and glued in place. For this seat we only had 1/4" foam on hand so you can see we have four pieces of foam glued on top of each other. To get a nice smooth edge, the foam can be sanded to shape once the glue has dried. About one inch of fairly solid foam is recommended for a comfortable seat. (Photo 2)

Select an upholstery material which feels pliable to the touch and is UV resistant. JoAnn fabrics carries a variety of marine grade material which is suitable of bike use. Lay the seat base on the back side of the upholstery material and trace around the base with a marker. Then draw a second line all the way around the first but ½" to the outside. The first line will be your “sew line” and the outer line will be your “cut line”. Cut out the pieces using the outermost line. Note the long rope like piece of material in the photo. This is called welting and is inserted at all the seams. The welting is not absolutely necessary and I have made many seats without it. But it does give a crisper look to the finished product and helps prevent wear and tear on the seam itself. (Photo 3)

Lay up the top piece and side piece inside out. The finish sides of the material should be facing each other and the back sides should be facing out. Pin and staple the two pieces together after you have lined up the outer edges. (Red arrow shows staples in Photo 4). The material must be worked around curved corners so that it comes out even as you move on to the next corner. It is a good idea to make guide marks on both pieces to insure they are staying even. Once the pieces are pinned or stapled together all the way around they can be sewn together by following the inner “sew line”. (See black arrow in Photo 4 for sewn seam) When you are done sewing your upholstery will look something like Photo 5.

Place the upholstery material on top of your seat base foam and turn it right side out while pulling the sides of the upholstery down over the sides of the base and foam. Once the top is fitting correctly you can begin to pull the upholstery over the plywood seat base and tack it in place with a staple gun on the back side of the wood base. Work your way around the base stapling in a few placed until you see the upholstery is even all the way around. Then go back and staple everything securely pulling out as many puckers as you can. (Photo 6)

Here is the finished seat for the bike in this Instructable. (Photo 7)

Adaptive bikes quite often require some sort of back support so the child can remain upright and secure on the seat. The type of back support will depend on the needs of the child. This particular back support is made basically the same as the seat using a plywood base with upholstery over it. A metal frame is made of 3/4"x3/4" tubing to hold the left, center and right sections of the seat back. The frame is angled so that the left and right sections of the seat back wrap around the rider’s torso and provide side support. The seat back is 18" tall to provide full support up to the neck and above (Photo 1 and 2) The seat back is bolted to a 1 x 1/12" upright post which is welded to the bike’s frame. The seat back can be moved higher or lower on the post by simply loosening the bolts. The seat back can also be tilted top to bottom to provide the most comfortable back rest buy fastening the seat back to the post using eye bolts. (See black arrows in Photo 1) Photo 4 is a close up of the adjustable eye bolts connecting to the bottom of the seat back and Photo 3 shows the adjustable eye bolts at the top of the seat back.

In almost all cases adaptive bikes are equipped with some sort of seat belt and/or shoulder harness. For this bike we are making a bib type harness. The bib is sized to the rider. In this case the bid is approximately 14" tall by 8" wide. The measurements need not be overly specific. The bib is there to distribute the load a bit in the event the rider is thrown forward for some reason. A bib pattern is drawn on heavy paper stock and then transferred to a piece of 1/4" foam and cut out. (Photo 1)

Heavy duty outdoor nylon material is used to cover the bib. This material is commonly used for backpacks or duffle bags and is available from many sources including JoAnn Fabrics. Once the covering is sewn in place over the foam core, 1" nylon webbing straps are sewn onto the bib to create the harness. (Photo 2) The webbing and snap clips for the webbing can be purchased on line from various sources including Amazon. The snap clips allow the harness to be adjusted so it holds the rider firmly but not overly tight. Once adjusted, the snap clips allow the harness to be put on and taken off easily without need for readjusting. The harness straps snap nylon webbing which is bolted to the frame of the bike. In addition to the bib harness there is an automotive type seat belt which also attaches to the frame. These seat belts are available on Amazon and on Ebay.

The bike is controlled from behind the rider by an individual walking along and/or pushing the bike. The steering mechanism is much like a tiller and tubular linkage connects the tiller to the front wheel fork. To create the tiller will require a junk, discarded or flea market BMX style bike. Look for one that does NOT have chromed bearing seats fitted into the ends of the steering head. You will be using parts from the steering head, front fork, handlebars and handlebar stem. The rest of the bike can be a basket case.

The tiller is created by first fabricating a steering “column” (see arrow in Photo 1). The column is cut from a piece of 1" EMT conduit to the length needed to place the tiller at a comfortable height for the person pushing. Something in the neighborhood of 32-36" should be about right. Next, remove the bearing seats from each end of the flea market bike’s steering head. (See arrows Photo 2) The seats will pop out with a solid hammer blow. Depending on the donor steering head the bearing seats may be slightly larger, slightly smaller or exactly the same size as the 1" conduit. The bearing seats must be aligned so the bearings themselves, top and bottom, will be exactly perpendicular to the pipe’s length. The seats are then welded to each end of the conduit. (Photo 3) A note of caution: when welding on any galvanized material such as conduit, you should first sand off as much of the galvanized coating as possible. Also, the welding should be done outdoors or with plenty of ventilation. Breathing the welding fumes can cause some people irritation and is potentially dangerous to the lungs.

The tiller handle is made of two parts, the stem and the steering arm. The stem portion of the handle is simply the stem from your flea market bike. (Photo 4) The steering arm portion of the handle is made of two pieces. First, cut a section out of your flea market handlebars using the lines shown in Photo 5. You want to be sure to keep the center mounting point of the handlebars in tact and cut the other end before it begins to curve. Then cut as long of a section as possible off the end of one handlebar as shown by the mark in Photo 6. The two pieces are then welded together. Fortunately, for most handlebars a short length of ½" EMT conduit will slip nicely into the two pieces so that the joint will not only be held straight but will have additional internal support when it is butt welded together. (Photo 7) Mount the arm in the stem, tighten the nut, slip on a brake lever and install a handlebar grip. (Photo 8)

The stem of the tiller handle you constructed in the prior step will be inserted into a "stem tube".
This stem tube is cut off the front fork of the flea market bike. Make this cut 4 ½" down from the threaded end of the steering tube. Your cut will be near the line shown in (Photo 1). The threaded end of the stem tube will be going on the top or your steering column while the fork end of the stem tube will be going at the bottom of the column. What you are actually doing here is just making an incredibly long steering head.

To lengthen the steering tube to reach the full length of your steering column, 1" black pipe (Home Depot or Lowes etc) will be used. But do not cut the pipe quite yet. Leave it longer than your steering column. Fortunately black pipe slips into the stem tube with only a small gap around the pipe. (Photo 2) This gap can either be eliminated by using the thin aluminum material from a soda can as shimming or, if you are feeling really confident, simply align the two pieces and weld them up. But they need to be absolutely straight when done. If you use the soda can shim trick, make sure that the shim is ½" wide or less so that it does not extent too far up into the steering tube and interfere with the depth the stem can be inserted. Insert the black pipe ½" into the steering tube, check that it is true and straight AND that the threaded end of the tube is opposite from your joint and then weld it up. You will need to grind down this weld pretty cleanly to get everything to fit later.

Next, cut off both legs of the flea market front fork (marked with red X's in Photo 3) ) leaving only the center section of the fork (red arrow in Photo 3). Grind down where your cuts were made so the center section is nice and smooth (mostly for looks).

Cut a piece of 1"x3/16" flat stock 3" long. Drill a 3/8" hole in one end and weld the other end to the bottom or side of the center section of the cut down front fork (Photo 4).

Now you will measure and cut off the black pipe extension of the steering tube. Place the upper bearing into the upper cup of the steering column and slip the black pipe steering tube down into the column with the threaded end up. Put the washer and nut on the top end and tighten so that the tube sits in its final position as if ready for inserting the stem. Slip the lower bearing over the black pipe and then slip the lower tube section (the part you just made from the front fork) over the end of the black pipe as well. Let the bearing rest in the lower bearing cup and measure as precisely as possible the distance from the bearing to the bearing cup fitted in the lower end of the steering column. This will give you the amount of black pipe you need to cut off. Mark the black pipe accordingly, remove it from the steering column and cut it off. Once again insert the steering tube into the steering column and with the lower bearing in place, slip the lower tube section over the black pipe as far as it will go. If your measurements were correct, the steering tube should be relatively snug in the steering column, able to spin but not move up or down in the column. If necessary you may need to trim a bit more off the black pipe until everything fits snug. Once you have the right length, remove the steering tube from the steering column and weld the lower tube section (the part made from the front fork) to the lower end of the steering tube. When finished you should be able to insert the tube and bearing into the bottom of the column, push it in all the way and then install the top bearing, lock washer and top nut. Hopefully it will turn with ease while having no up or down movement. A slight bit of movement can be removed by tightening or loosening the top nut.

The steering column is attached to the 1 1/2x1" vertical post which holds the seat back. A spacer is cut from 1 1/2x 1" tubing and welded to the steering column (see white arrow Photo 5). Using 1x3/16" flat stock cut four tabs approximately 4" long. Drill 1/4" holes in one end of each tab. Then weld the tabs to the column spacer so that bolts can be inserted through the holes. (See blue arrows in Photo 5) Slip the steering column onto the vertical post and move it up or down so that the bottom arm (see black arrow in Photo 5) clears any obstructions. Then bolt the column in place.

The linkage from the rear steering tiller to the front wheel is made of ½" conduit which is cut and rewelded at the major bends. The linkage closely follows the frame of the bike (See white arrows in Photo 1) and is supported at various points along the way with eye bolts. A 2 ½" steering arm cut from 3/16" flat stock is welded to the front fork (see white arrow Photo 2) Heim joints are used to connect the steering arm to the linkage from the rear of the bike (see black arrow Photo 2) A “slider guide” is made from 1/4" rod to keep the linkage in a vertical position while allowing it to move forward and backward and turn the front wheel (see blue arrow Photo 2)
Heim joints are also used to connect the rear end of the steering linkage to the steering column. (Photo 3)

Pedal platforms are cut from plywood using the rider's shoe size (we go to Wal Mart, find a pair of shows the correct size, and trace around both the left and right shoes right there in the store). Then draw a second line adding approximately ½" - 3/4" around the perimeter of the first line. Use this outer line as a pattern for cutting your plywood platforms. The platforms are covered with fiberglass to protect them from the elements and then sanded smooth. The platforms are positioned on the pedals and bolt holes are drilled. Tee nuts are inserted from the top side of each platform. Rubber material (we use thick rubber shelving material found at Target) is cut and glued to the top surface of the platform covering the tee nuts. A heal guide is cut from thicker rubber material then glued and nailed to the rear end of the pedal. 1" nylon webbing is used to make an ankle strap and an instep strap. Velcro is sewn to the straps so that they are adjustable yet secure. (Photo 1)
With the pedal flipped over the underside shows the positioning of the bolt holes and large washers which insure the bolt heads do not slip into the gaps in the pedals. (Photo 2)

The handlebars are fixed in position on the frame and are used to steady the rider rather than for steering. The handlebars do not turn. The front steering head is retained, however, and the handlebars could be shifted from their fixed position into the steering head is a rider would be capable of steering on their own. ( Photo 1)

Here's the finished bike and it's proud new owner.