I know we have a "be nice" policy around here, but that beater design has some major problems. If its done on the cheap, it probably won't survive even one match and it will cost a small fortune to make a part that will work reliably:

1) As described the beater is all one piece; how is the pulley going to be fitted to the central shaft? Cutting it in half and screwing it back together will add bulk and reduce its strength.

2) Placing the motor close to the central shaft means that the pulleys will have to be fairly small and the belt between them will be short - far too short to fit over the beaters on either side. The shortest belt that will slip over the beaters is about 400mm and that will place the motor too far out. The only solution to that problem is to use custom length urethane V belts that are joined in place. Having used those belts on smaller & lighter beaters, I know they will not transmit the torque needed to spin up this beater design. This problem is the real show stopper - I don't see any good solution without a major design change.

3) Fabricating the part is going to be difficult & expensive. Beaters are usually water-jetted from steel plate, then mounted between centres on a lathe so that the stub axles can be turned - no problem so far. Turning down the central portion from square to round will need a large lathe with at least a 250mm swing over the saddle. Getting a cutter in between the beaters will need over 100mm of tool stick-out which, together with the hardened steel, will create extreme tool chatter and a very poor surface finish. To do this operation successfully will take the sort of multi-axis CNC machinery normally used to make car crankshafts IE:

Of course, if the central shaft isn't supported, then it can be left square and the two-part pulley can be made with a square hole .

4) having a central support bearing is a good idea - the beater will very likely bend or snap without it. Two-part bearings are used on the crankshafts of cars and work well when properly lubed and the shaft running in them is well polished. Getting the central shaft polished is also going to need the sort of machinery used on crankshafts. The bearing itself is easy; just cut a plain bronze bearing in half. The mount for the bearing is much harder; it needs to be precisely made, probably requiring a CNC mill.

5) The 80mm space between the beaters is really a bit tight to fit a motor powerful enough to spin up the beater. The closest beater design I can think of is Conker 3 and Alex needs a monster out-runner to spin it up. Once you add a motor mount and a pulley with a hub, the 80mm is more than used up. The pulley width for even small belts is 14mm plus around 8 to 10mm for a hub. The pulley on the beater can't be hard up against the beater arm as the motor pulley needs clearance from the beater as it swings past - add another 2 to 5mm. Then there is a motor mount; it has the support the motor rigidly and should be 10mm thick aluminium. That all adds up to at least 34mm, leaving just 46mm for the motor. Let's not forget some clearance between the back of the motor and the other beater, so around a 40mm long motor is the longest that will fit. Finding a motor with enough power in a 40mm length is basically impossible. I think this beater will need a motor at least 60mm long to spin it up to an effective speed - A scorpion 4530 might be a good starting point.

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I hope this isn't too disheartening and that you can change the design a bit to make it easier and cheaper to build.