I'm currently in the process of making a Halloween contraption. One of the components in the contraption is a Lightweight Conveyor Belt. It's not sexy, and I debated whether if it was even worth writing about. It is a very simple system, easy to build, and designed for lightweight items. However, it is not robust nor designed for long time use. I figure, though, someone might find it useful.
I needed a way to move 1 to 4 bite-sized wrapped candy from here to there in such a way that it fit with the theme of my Halloween contraption. An episode of I Love Lucy came to mind where Lucy and Ethel picked and wrapped candy as it went by on a conveyor belt. I found something in PBJ Mechanical Munchie Machine and modified it for my needs. My end goal was to make it tall, adjustable, inexpensive, and look kinda cool (for 3-10 yr old kids). I also wanted to be able to reuse most of the parts after Halloween was over.
Step 1: Parts and Tools
- Duck canvas, 76" x 7"
- Clear top coat fingernail polish
- 48" x 18" x 3/4" plywood
- 3/4" PVC pipe, ~6ft
- 3/4" PVC tee connector, qty 4
- 3/4" PVC cross
- 3/4" PVC 90 degree elbow, qty 1
- 3/4" PVC coupling
- Hanging strap, qty ~3ft
- 10 x 3/4" wood screw, qty 16
- 8" x 14" x 1/2" plywood
Motor and Mount
- 3/4" PVC Male Adapter MIPT x Slip
- 3 1/2 " x 1 1/2" x 3/4" wooden block
- 50mm pulley from Tamiya Large Pulley Set, $7
- 131.25:1 Pololu Gearmotor, $25
- Motor bracket, $8
- Rubber bands of various length and strengths
- 4 3/8" stiff spring
- 1/4" x 5 3/8" turnbuckle, preferably hook on both ends
- 3/16" x 4" turnbuckle, preferably hook on both ends
- Zip tie, optional, qty 2
- 3/4" eye wood screw, qty 2
- SparkFun RedBoard (Arduino UNO clone), $9 on Arduino Day
- SparkFun Ardumoto motor shield, $25
- 10K Ohm resistor
- Momentary push button
- LiPo battery, 11.1v
- Sewing machine (optional)
- Mallet or hammer
- PVC pipe cutter
These parts will make a conveyor belt about 72" long, 17" high in the back sloping down to 13" in the front. The rear tension system will reach back about 12". The belt will be 7" wide but the width of the PVC frame, rollers, and motor will be about 13".
Paint Roller Frames and PVC Connectors
The magic (or should I say luck) of the system is that the butt end of a cheap plastic paint roller frame handle fits very tightly into a 3/4" PVC pipe connector. The paint roller frame is rigid enough to hold a moderate length of canvas fairly taut. I tried fitting 9" and 7" cheap paint roller frames from 3 different hardware stores into various 3/4" PVC connectors and they all fit tightly. I figured if they were a tad too big, the connector could be widened, or if they were a tad too small, tape could be used as a shim. All of the connectors in this section are slip (i.e., not threaded).
The width of the system can be altered by changing the width of the paint roller frame, maybe using 4" or 9" rollers. The height of the system can be increased by extending PVC lengths, but it will be harder to make it any shorter than 12". It depends on diameter of the paint roller frame handle. As long as the cut handle fits tightly into the connector, possibly with the use of tape as a shim, then it should work.
Duck canvas is a moderately dense, non-stretchy fabric. It's very easy to work with. It comes in various vibrant colors. It's cheap when on sale, about $5 yd at Jo-Ann's. I tried making the belt with both duct tape and felt. Duct tape was way too heavy and felt was way too stretchy. If the belt fabric is stretchy, when pulled taut and the front and back rollers are not perfectly parallel with each other, the belt will stretch out of shape and move right or left on the roller, eventually falling off the roller.
When buying the canvas, consider buying it measured out the length, not the width, of the canvas. For example, if 72" are needed and the fabric bolt is 80" wide and if it's really cheap, buy 2 yards instead of 1/2 yard. The duck canvas has a nice, straight, finished edge that won't have to be prepared to keep it from unraveling.
The Gearmotor, Pulley, and Shield
This was hit and miss. I didn't know exactly what to order so I ordered a motor at some speed and a pulley set. The motor arrived first and it was immediately too slow. Attaching the only pulley-like item I had, a sewing bobbin, it took about 18 secs for an item to travel the length of the belt, way too long for a kid to wait for candy. The 50mm pulley subsequently arrived and dropped the time down to about 7 secs.
The motor was the single most expensive part of this project. I didn't really know what I was doing when I ordered it new. Since then, I have ordered or found a number of used motors of varying speeds and quality and all of them were cheaper. This is definitely the way to go. For this project, the motor really only needs to be of moderate speed and have moderate torque. A pulley can easily increase the speed as desired. As for torque, take a conservative guess of how heavy the payload will be.
The Tensioning System
This was also hit and miss. At first I didn't use a spring. I relied on the friction of the mounted connectors. Talking to a few other makers, they recommended a spring to provide flexible constant tension. I really didn't know how long or strong the spring had to be. I took a guess and bought a number of used springs of different lengths and strengths from a salvage yard. Adding the turnbuckle was the secret sauce. It allowed finer adjustments to the spring tension.
Step 2: Conveyor Platform and Frame
The layout of the PVC and connectors is fairly relative. To help align them, draw a reference grid on the 48" x 18" plywood. I did every 12" along the long length (4 divisions) and then I created a 4" region down the center of the long length, since most of the fine tuning will be from the center.
Cut 8x 3" length of 3/4" PVC pipe. Build 4x feet: 3" + tee + 3". When building these feet, really push in, even hammer in, the pipe into the connector. They can be glued but I didn't because I want to use the tee's for another day.
This is for the shortest roller. It is the roller that things will roll off of. Mount it to the plywood using the hanging strap and wood screws about 4 1/4" from the edge and in the center of the 4" region. When mounting down, place the hanging strap in the center of the PVC length. This provides room to slide the foot back and forth when trying to fine tune the roller alignment. Also, mount the strap over the pipe so that it has a good bite down on the pipe. This will prevent the foot from unnecessarily spinning.
This is for the tallest roller, roller 4. This is where things will begin rolling from. Mount it down 31 1/2" measured from the same edge as foot 1.
This helps support the belt. It needs to be mounted 10 3/4" from the edge. But due to the belt slope, the foot needs to raised 1/2". Just cut some scrap wood, attach it to the platform, then mount the foot. In my system, I'm placing an item in this area so I need a bigger piece of scrap wood.
This also helps support the belt. It turns out that a PVC coupling will raise the roller just the right height, implying no shim is needed. This foot is mounted 23 1/2" from the edge.
Cut the following:
- A = 1 3/4" PVC length
- B = 5/8" PVC length
- C = 9 1/4" PVC length
Put A into the tee of the foot. Put the cross on A. Put B in a horizontal connector. Put 90 degree on B. Put C on 90 degree. Put 9" roller on frame. Put the frame in the cross such that the frame rod is closest to C. Really push down the frame handle into the connector. Use duct tape or something around the handle if there isn't enough bite. It should be very difficult (not impossible) to spin the handle in the connector. Also, don't bend the frame rod.
Put an uncut roller on the frame.
Cut the following:
- 1 3/4" PVC length
Put it into the tee of the foot. Put the coupling on it. Cut a roller down to 7" and put it onto a frame. Put the frame in the coupling such that the rod is on the opposite side as roller 4.
Roller 2 and 1
Cut rollers down to 7" and put them onto a frame. Put the frame of roller 1 oriented in the same was as roller 4. Orient roller 2 in the opposite direction.
Aligning the Rollers
Aligning the rollers now provides a good reference point to work from. But as the project progresses the alignment will probably have to be tweaked, or possibly the feet may have to be moved.
On the opposite side of the motor, place a long straightedge along the butt ends of the first and last paint rollers. Make sure the straightedge is parallel down the length of the platform. Hammer the feet on one side or the other so that the rollers are flush against the straightedge. Now make rollers 2 and 3 flush. Reposition any feet if it is too far off from being flushed and the strap is preventing any more movement or is falling off.
After the opposite side of the motor has been aligned, because the last roller is 9" long, 2" should be protruding further out. This is where the pulley band will be placed.
Step 3: Motor and Mount
Drill out a 1" hole about 1/2" deep into a wooden block that's 3 1/2 " x 1 1/2" x 3/4". Use a Forstner bit or something to create a flat bottom hole. Center the hole along the short axis and offset it about 3/8" along the long axis.
Fill the hole with water and let it soak. Once the wood inside is soft enough, dump the water and carefully screw in the 3/4" MIPT x slip connector. Make sure it screws in squarely. Once it is far enough in, let it dry overnight. The process may need to be repeated so that the connector screws in and out nicely.
Next, screw the motor bracket onto the other side of the wooden block. Screw the motor into the motor bracket.
The hole in the pulley is smaller than the shaft diameter of the motor. Use an X-Acto knife to widen the hole just large enough so that the pulley is an extremely tight fit onto the shaft.
Attach the connector on the mount to the upright pipe. Attach a rubber band to the pulley and the roller. To have enough tension in the band, pull back the motor's PVC pipe, or replace the band with one that's less elastic or smaller. It does not have to be super tight over the roller, but it does have to have a little bite.
Step 4: Electronics
This Instructable is less about the electronics and more about the build. So the electronics for this project is very simple. What I'm using is probably overkill, but it is what I have laying around. Basically, a button is pushed which starts and runs the motor for 5 secs and then stops. Not rocket science.
The sketch assumes a motor shield is being used. It also makes use of the Bounce library to deal with bouncing. If a button isn't used, then there's no need to use the Bounce library.
At this point, the motor, rubber band, and roller movement can be tested. It'll be tuned in the final step.
Step 5: Belt
The last major piece of the build is the belt. It took me a few tries with different fabrics. Duck canvas worked the best.
Cut 76" x 7" of the duck canvas. Make sure the ends are perfectly square. Use any right angle tool to help with accuracy.
For any edge that was cut, apply a layer or two of top coat fingernail polish on the edge. This will prevent unraveling.
Bring one edge to the other overlapping them by 2". Make sure it is completely flat and squarely overlapping. If it is off by a little bit, the belt will gradually make its way off the roller. Pin it into position. Sew both edges (top and bottom side) down onto itself about 1/4" in from the edge. Use a sewing machine if possible. If there is any puffiness in the overlap, unstitch one edge, flatten, and restitch. Do not glue them together. The glue will make the area stiff and it bump around roller 1 and 4 possibly throwing the alignment off.
Put the belt on the rollers. Make sure the rollers are square with each other. Turn on the microcontroller and press the button.
Step 6: Tension
Constant tension has to be applied to the rollers to keep the belt taut. The easiest way is to lock down position of the Roller 1 and add a spring to Roller 4. Turnbuckles are used to fine tune the locked position of the rollers.
In the center of Roller 1, attach an eye bolt 1" from the edge. Zip tie together the paint roller frame handle and the eye bolt side of the turnbuckle. Open the turnbuckle mid-way and then attach the hook to the eye bolt in the platform. You will probably have to rotate the foot to get the hook to reach the eye bolt.
In the center of Roller 4, attach an eye bolt 12" away from the foot. Zip tie the spring onto the paint roller frame. Zip tie the turnbuckle eye bolt to the spring. Open the turnbuckle mid-way and then attach the hook to the eye bolt in the platform, rotating the foot as necessary.
Step 7: Tweaking
Finally, the entire system has to be tweaked here and there and possibly have parts replaced to get the belt moving really well and consistently.
If the belt is too taut such that the rods of the paint roller frames are twisting, reduce the tension. To reduce the tension, either adjust the turnbuckles, use a weaker spring, get a longer spring or turnbuckle, or reposition the platform eye bolt for Roller 4.
Make sure Roller 1 and 4 are square with one another. If they are not, the belt will roll off. Adjust Roller 2 and 3 so that they support the items moving across the belt. If they are too low, then raise the handle or add a shim underneath the foot. If they are too high, cut the handle.
Once the belt is taut, try to move it with the motor. If the motor can't move it, use one with more torque or increase the voltage to the motor. If the rubber band is slipping, adjust its tension by moving the motor PVC pipe or use a different band. If the belt isn't moving fast enough, increase the power voltage, get a faster motor, or increase the size of the pulley.
If 5 secs isn't the right amount of time to move items across the belt, either modify the Arduino code or increase the voltage.