I started repairing an old dryer I made that was just right angled pieces of timber, the battery sat on the back of it and the motor was mounted through the tight hole drill in the timber. Worked a treat and cost about $10 for the motor.
This dryer I did with the intention of being self contained because the old one got a bit trashed getting thrown in the tying gear all the time.
I made this a bit bigger and heavier by still using the 6v and I also used a 90mm foam plug, which meant the body of the dryer needed to be big enough to hold both. You could make this alot smaller using Li-ion battery or a 9v battery. Could also use a 240v power supply. I wasn't worried about weight etc so made it a bit chunky.
The motor I used was from ebay $10ish with a reduction gearbox. I used a 12v motor. Now using this with a 6v battery halves the speed so it turns really slowly, about 15RPM. You can by 6v 30RPM set ups. I dont think speed matters too much. Certainly no slower than 15 and I would not use something doing 300RPM. There will be flies stuck all over your roof and walls.
Start by getting all of your pieces together. I used 110mm pvc pipe and 2 push on ends for the base. Take you piece of pipe, fit one end cap. Place all the other bits of the dryer inside the pipe (make sure nothing shorts your battery!!!). Make roughly how high you want the dryer to stand or as high as required to contain everything once the second cap is fitted. Cut the pipe.
Step 2: Battery Placement
I used a large 6v battery. These things go forever but use what ever you want. Using a hot glue gun, glue the base from the packing the battery comes in. If you dont have a base you can either let it just sit in there or glue the battery down.
Next I cut the terminals short on the battery and soldered two wires on. Give yourself a good length of wire, approx 400mm and i just used speaker wire. Cover the terminals with hot glue to prevent shorts.
Step 3: Make the Spindle
I grabbed a poly threaded coupling and matching plug. To mount the motor shaft flange I drilled a center hole in the plug. To get dead center, use the largest drill that will fit inside the plug. Drill a very small make to use as a pilot. Use drill size same or size larger than motor shaft and drill hole.
Place flange on the flat surface of plug. Note: If your plug has a rounded end, just sand it flat.
Drill pilot hole for the screws and screw it down. You could hot glue it on if you wanted.
Step 4: Motor Setup
I wanted to remove the motor from the top easily so I used velcro glued to a bit of flat bar. Then hotglued the motor to the bar. Works pretty well and no mounting screws or holes in my end caps.
Apologies for upside down pic, but I've tried everything but it keeps turning up that way.
Step 5: Motor Fitting
Cut a slot the width of your wire into the top of your pipe. Make the slot half the width of the end cap lip, about 10mm or so. Make a similar slot in your end cap. The end result should be that once the end cap is fitted and the slots aligned, there should be a hole just big enough for the wire to fit through.
Place the wire into the slot and fit the cap. 180 degrees from the slot glue the velcro in place for the motor mount.
Place the motor on. Solder the wires to the motor and the switch. Hot glue the switch to the motor. Place hot glue over all terminals and wires that may cause a short.
Step 6: Foam Wheel
To make the foam wheel I used a 90mm pvc plug I got from Bunnings. I think my old once was made from a mat or old thongs. Doesn't matter as long as the foam can grip the fly hook. You can use styrofoam but its not real durable.
Find the center of the circle. Quickest way, if you want it pretty spot on, is to draw three cords of same length. Make the middle and using a square draw a line through the center. Where the 3 lines intersect is the middle (google for a better explanation and pictures).
Drill the hole out big enough for your coupling. If you dont have a hole saw use a metal pipe a bit small than your coupling. Heat it up with a blow torch or stove and punch the hole out. You can also melt a hole with your soldering iron.
Fit the coupling in the hole. I hot glued mine but it was a really tight fit and wasn't going anywhere.
Lastly, if you want you can cut small slots for the hooks to be gripped by the wheel. You can poke the hooks into the foam but it wont last as long.
Screw the foam wheel onto the motor and your in business.