Introduction: DIY Free Motion Bike Training Rollers
This project got started a while ago with a rainy day and the urge to go for a ride. I took a look at how some other people on youtube, and here on instructables, put together their rollers for inspiration and started from there.
I wanted to make this project with off-the-shelf components where I could and not have to struggle cutting things perfectly round or getting too complicated with construction. I was also intrigued with the free motion idea (putting the roller frame on rollers itself). Others have accomplished this with wooden tracks and skateboard wheels, but I wanted to see if I could make a one-piece system with the free-motion mechanism integral to the frame. From there my spools and spring idea came to life (outlined below). I don't have anything to compare it to (this is the first rollers I have ever ridden), but the mechanism seems to work fine so far. The final thing I wanted to accomplish with this project was to find an easy way to make drive belts from old inner tubes. First, I had plenty around, and second, I didn't want to be bound to commercial drive bands. So far the old tubes are working fine.
I'll take you through the steps I went through below and provide some thoughts on build options where I have them.
Step 1: Motion Return Mechanism
This is a description of the free motion part of the project (see image). It works fairly well and lets the frame roll back and forth and doesn't require a track to roll in.
Step 2: Frame
I made my frame from 2x4's, but others have used hardwood. Make sure there are is no warping in your lumber. If I were to remake the frame I would use hardwood myself.
The most important thing is to keep all the holes aligned. I'd also advise clamping the side boards together when drilling them and using a drill press if possible to keep the holes straight. I have notched out all the holes on the frame for the rollers and center support so I can change belts easily. You can use just holes if you prefer. I have shown a range of holes for adjustability which you are free to ignore. You should check the wheelbase(s) of any bicycle(s) you intend on using to make sure the holes are ideal. The front roller should be set just slightly ahead of the front axle of your bicycle.
My frame came out with some slightly misaligned holes (lag bolt end holes in 2x4's) and slots. As a result my frame has some racking in it, but it wasn't the end of the world. If it doesn't come out perfect, it can still work.
Step 3: Rollers
The rollers are made from PVC pipe, skateboard wheels (and bearings), and a steel axle.
The roller shell is 2" schedule 40 PVC pipe. It is cut to fit inside the frame: the ones used here are 17-3/4" to fit inside the frame with an internal dimension of 18" (1/8" clear each side).
52mm skateboard wheels are epoxied into the PVC pipe ends, with enough inset to allow for a washer and shaft collar (see drawing). For 2" PVC pipe the outside diameter is 2.375" and the inner diameter is 2.067"+/-. The magic here is that the skateboard wheels are 52mm = 2.04" diameter which should just fit in the PVC pipe. Unfortunately I have found that with skateboard wheels 52mm is not always 52mm. Bones, Series 100, 52mm wheels had a snug press fit into the PVC (great fit), whereas DGK Street Formula wheels slipped right in with clearance (poor fit). I tried pinning the DGK wheels in place with two wood screws through the PVC and into the wheel from both sides without epoxy, but it wasn't a great solution (pinched section / poor fit) and the screws tried to work themselves out. I epoxied up a test roller with the DGK wheels and the epoxy did work, but it was very slightly eccentric. It was not hugely noticeable, but it was not as smooth as the roller with well-fitting Bones wheels. If you do end up with wheels that are slightly small, I would try wrapping them in thread (or tape) until they fit centered in the PVC. You can then glue the wheels with the thread in place holding them centered and use enough glue fill the voids. I only used a thin coat of epoxy on the well fitting wheels. Note: Take special care not to get any epoxy on the bearings. Once the rollers are glued up, the inner bearings will be in accessible. I kept a clean cloth and some alcohol on hand just in case. In retrospect, it's probably better to apply the epoxy to the inside of the PVC and not the wheel.
I originally intended to use a 1" drive belt made from an old inner tube. I imagined the belt would ride between it's two PVC bands (see photos and drawing) and everything would be great. This was not the case. My belts would not track in the groove. I'm assuming that this is from frame/roller misalignment (blame the builder). The happy accident was that the belts worked perfect when centered over the inner PVC ring. I left both rings so I can try different belt ideas, but you could just use one ring and move it in if you are only going to use inner tubes. I have tested belts made from 700x35, 700x18-25, and 700x20-28 and they all track on the ring. Do remember to file the edges round so the PVC ring doesn't cut into the inner tube.
The original axle is a 24" long, 5/16" diameter steel rod (fits skateboard bearings: 8x22x7mm), with 1-1/2" of the ends threaded for 5/16-18. This is a bit too long (see frame photos). I am planning on cutting off the extra threading later. I did the threading on the axle myself. I did consider using 5/16" threaded rod, but it felt too flimsy and allows for more play in the wheel. Threading the axle ends has the advantage of allowing you to tension the axle in the frame. If you aren't interested in cutting threads, there are some options:
1) Pin the ends of the axle into blocks on the outside of the frame: design from Sky-Monkey: https://www.instructables.com/DIY-Bike-Rollers/
2) Use shaft collars with washers on the ends of the axle outside the frame (I haven't tested this).
Step 4: Wheel Spools
The wheels used for this project were inline skate wheels that had 5 split spokes of soft plastic which #6-32 threaded into. The spoke configuration drove the design a bit. The wheel spool is made from a 3/4" long section of 2" Schedule 40 PVC Pipe. A notch is made in one end to allow for the end of para cord to be inserted and a figure eight tied. An end cap was made using ABS to hold the bolts in place. The end cap also has a center hole to allow for the passage of a 5/16" cap head screw used for the axle and to access the para-cord end passed into the spool.
If your roller wheels don't have spokes or some other convenient bolt-on points, I have drilled into the rubber side-walls of the wheels themselves. The spools can be any diameter, they really just need to be smaller than the wheel to make sure that the spool allows for some winding of cord or wire without potentially rolling over it. The first prototype used a single bolt in the sidewall and an extended axle to wrap around (see photos). The disadvantage was that you could feel it "flop over" as the single bolt spooled the cord around the axle. The spools were used for smoother feeling motion.
Once the PVC pipe spool and cap were bolted into place, the threads of the #6-32 screws were glued in place (super-glue / cyano acrylic) from the non-spool side for extra strength. Epoxy would have been a better choice to fill in around the screws ends. Remember to be careful with the glue around the bearings in the wheel.
Future Notes: I would like to try to make these with 5"x1" wide caster wheels. I think they will have better traction on floors, and the larger diameter may make for smoother motion. The inline skate wheels have a small contact patch and can slip under torque on the wrong surface (i.e. irregular concrete floor).
Step 5: Motion Return Spring
The motion return spring is a simple construction of shock-cord (Bungee Cord) and two lengths of paracord. The tension is controlled by the number of cords in the bundle and the length. I have found two cords bundled at about 24" long work well for me (yellow cord in photo). I have been using off the shelf bungee cords then cutting off the hooks (the metal hooks get sucked under the spools and jam up). Make a loop of cord at the ends and then secure them using cable ties (or possibly wire). I used cable ties to secure my loops. A single large one or multiple small ones both work.
To assemble, take one length of para-cord and insert it into the roller spool and fish it out the center hole. Tie a figure eight in the paracord and pull the knot into the roller drum so the end isn't hanging out. Next, I tied a loop in the paracord to use as a cinch, but this is optional. Take the other end of the paracord and pass through the shock-cord end loop and tie off while tensioning the shock-cord. Repeat this for the other side.
Note: You may want to play with the length and number of sections in your shock-cord to find a responsiveness you like. Remember that you will need a section of paracord that is knot free to spool properly. If the shock-cord is too long it may interfere with the spool, but if it is too short it will reach it's elastic limits too soon. These lengths need to be balanced to work well.
Step 6: Drive Band
I have been making my drive bands from old inner tubes. Thanks to the metal recycling plant next door, I have had plenty of flats and have a lot of old tubes on hand. My local bike shop was also happy to supply me with some as well.
I found a tension length that worked well for me which was to take the distance from the front roller to the rear roller and subtract a couple of inches. This is the length of the drive band folded flat (half the total circumference of the belt). Four inches of overlap was left and glued into the other end of the inner tube using vulcanizing cement. I have also tested with E600. So far the E600 is holding up, but I feel a lot better about the vulcanizing cement. The vulcanizing cement is also less gummy, so it's easier to work into the other end. I also tried a glue up with Elmer's rubber cement, but I didn't get good results.
I'll outline the process below, but before you get started you are going to want disposable gloves, a disposable work surface (piece of paper or cardboard), and make sure you work in a well ventilated area (some fumes). You are going to need a couple of blocks of wood and a clamp to finish the gluing. I cover the wood blocks with masking tape so they don't get glued to anything.
Take the inner tube and cut off the value on both sides so you are left with a length of tube. Carefully blow out the extra dust inside, aiming it away from you. I have no idea what the powder inside is (hopefully just chalk), but you don't want to breath it. I blow it out because I don't want the excess to interfere with the gluing. Cut the tube down to the length you need.
Clean the inside of one end 4" and outside of the other end 4" (our glue overlap). I use rubbing alcohol and paper towels. For the inside clean, I wrap a small stick (chopstick) with a paper towel, soak some alcohol in the paper towel, and use that to scrub the inside walls. Clean the rubber really well, make sure no residue is left over. I mark off the end that is to be inserted by wrapping a piece of masking tape around the tube 4" from the end. This serves as a depth guide when you insert it.
Set yourself up well for the gluing. Align the tube so that there are no twists in it. When it is glued, it should lay flat. You can follow the seams on the tube and use them as a guide. Lay your tube out so you can inset the ends without having to handle the inner tube too much.
I apply a liberal coating of vulcanizing cement to the end to be inserted. This makes it pretty slippery, but it can still be tricky to work all the way in. After the glue is applied I fold the end of the tube in half lengthwise, which makes it easier to insert. You can also use a stick to help work it in. Insert the glued end to your depth guide (masking tape). After the end is inserted, there are two important steps: First, check that your seams align and there is no twist in the tube. Rotate the tube around to adjust. Second, work the overlap flat by massaging it out to the sides. The outer tube does not stretch to accommodate the inner end, so the inner end tends to fold at the end inside the tube (especially after you fold it in half). This makes a bump for the rollers if glued in place. Massage the glued overlap so that the center is flat. When it is flat in the center, place the overlap between your clamp blocks and apply clamp. I don't know what the official cure time is, but I have been letting the belt cure overnight in the clamp. So far the belts are holding up well.
Some other DIY drive belt ideas:
Sewn loop of nylon webbing (https://www.instructables.com/DIY-Bike-Rollers/).
Sewn loop of inner tube (recommendation in comments from another post).
Step 7: All Done
Install your drive band and you are ready to ride!