A cheap DIY conveyor for moving small loads with precision, all made from common hardware shop parts.
I was doing a pick n place type machine, but became tired of the time needed in a xyz style of machine to travel back and forth. It seemed to make more sense for the part to move close to the dispenser.
Conveyors are a basic element of many production systems, and needed a simple open source hardware design. Commercially available conveyors of similar size (with much higher quality engineering) seem to cost around $1000 onto which you need to add $200+ for a variable speed controller! It seemed possible to make a sufficiently good one for less than about 80$ and control it properly from a stepper motor.
This is a small contribution toward a low-cost Open Conveyor.
Similar designs have been used in the context of T-shirt dryers e.g.
These tend to use rotisserie motors for continuous motion, whereas I needed the precise control of a stepper motor.
Design your conveyor
The strength, length and width of your conveyor needs to be determined. I cut the steel bar down to 180cm so it would fit on my desk, and chose a width of 40 cm with rollers every 15 cm which required 12 rollers. If it needs to be stronger you could triple the density of rollers.
Step 1: Prepare Your Parts
- 2 long pieces of steel bar or L-bar, preferably with 8 mm holes or slots. This should be wider than 30 mm - I used 38 mm L bar.
- Lengths of 25 mm outer diameter PVC tube often sold in 2 meter lengths with a tulip end.
- Roller skate bearings - cheap ones are fine
- 8 mm nuts n bolts
- 8 mm threaded rod. 1 m was enough for me.
- 2 cable tighteners with 8 mm holes
- Some 'waxed' table cloth cut to size
- Some sandpaper or anti-slip sticky tape
- Some wide sticky tape or a needle and thread
- A 22 mm rubber bung with no hole, or a hole <8 mm
- Some plywood
- A stepper motor and suitable controller
Total cost without electronics ~ 70 euros
Some of these parts have special qualities that make the project possible.
Cheap electrical tubing (IRL 25 mm) is used to make the rollers. Buy the cheapest quality with the 1.5 mm walls. Wise to take a bearing with you when buying this to make sure that it fits. It should push in with a gentle to medium push. You should not have to force.
This is what is going to give most of the rigidity and allow you to attach it to a table or attach other tools to the conveyor. You need it to have a dimension that will allow a roller plus the belt to move freely. You'll also be attaching lots of 8 mm bolts, so it will help enormously if it has 8 mm slots in it.
The classic 608 bearing has an outer diameter of 22 mm that corresponds with the inner diameter of the PVC tube. It also has an inner diameter of 8 mm which allows strong 8 mm bolts to be used. These can be picked up from sporty discount shops or ebay in packs of 8-10 for about 0.5 euros each.
22 mm Rubber Bung / washer
Somewhat rare but available in decent hardware shops, these allow you to grip to the inside of the plastic tube. They act as a coupler between a drive shaft and the tube. You probably can't find them with ~7 mm inner diameter, so you'll have to drill out the middle a little
Anti-slip sticky tape
This is an expensive luxury but works very well. It is like sandpaper on one side and very sticky on the other side. This is what grips the underneath of the table cloth. You may be able to just stick sandpaper onto one of your rollers, or use paint/varnish/glue and some sand.
'Waxed' Table cloth
These days they are made of a soft plastic coating with a fabric underside. They are generally sold in 1.5m widths which is far too large. The fabric side helps grip the grippy roller. The plastic top is flexible and relatively durable. This was the cheapest material I could find that had the right properties.
Stepper motor and controller
Typically this might be a NEMA 17 motor + Arduino + Motor shield. I won't go into this side of things.
Step 2: Construction
Construction is pretty easy, no special tools needed except for the drive part: I needed a 22 mm drill bit to make a hole for a bearing.
The rigidity of the conveyor comes from the steel bars plus at least 2 lengths of 8 mm threaded rod that pass through the middle of the tubes. For longer lengths, additional pieces of threaded rod would increase rigidity. I used threaded rod at the two ends: 1 all the way through the roller that acts as a belt tightener, and 1 all the way through the drive roller.
Cut your pvc tube to length with a saw. Measure well or make a jig, as it helps to have them all the same length.
Prepare an 8 mm slot at one end of each steel bar to allow the tightener to work. The bar I bought only had 6 mm slots, so I needed to drill 8 mm holes for each roller and create an 8 mm slot for the tightener.
Attach a roller bearing assembly to your metal bars at each roller position.
Prepare the drive roller. This needs to have high friction. You could paint the pvc with something sticky and cover it in coarse sand, or just cheat and stick on some anti-slip tape. Once grippy, you need a way to drive it from the stepper motor.
A 22 mm bung, with the center drilled out to 7 mm can be stretched onto an 8 mm threaded rod. When this is pushed into the inside of a pvc pipe, it provides enough friction to turn the pipe. You then need to find a way to drive this rod. I happened to have the luxury of some timing belt and cogs left over from a previous machine, so I hacked up some plywood to support this.
A neater design would be to use a small length of some hollow metal 8mm tube as a support guide with the shaft of a NEMA 17 though the middle to a rubber bung. This would avoid the use of other cogs and belts.
Your stepper can probably drive your belt way faster than you need, so using a large drive cog from a small stepper cog is an advantage.
Once all your bearings are in place, and you have prepared the drive roller and the tightener roller, you can install the plastic pipes on one side, then push the assembly together. This can take a little patience.
Cut your table cloth with a sharpie a little less wide than the rollers, and leave 5-10 cm extra length for attaching. Slip the cloth into place and sow or use wide tape to secure it. Tighten the tensioner and you should be ready.
Tune your motor controller
Once assembled, you should tune your motor controller for low acceleration, as there may be much weight on the conveyor.
Areas for improvement
- Find a common steel L bar which has 8 mm slots
- Avoid the stepper motor being above the belt (not below either, nor should it be higher than the L bar )
- Avoid the use of cogs and drive belts (hollow 8 mm tube with stepper shaft through the middle?)
- Find a way to attach an 8mm threaded rod via a bearing directly to the steel bar without the need for plywood adapter