Hi Craig,
Good innovative thinking!
Try taking a look at north American domestic piston type water pumps that are used with rural shallow wells.
These use a vee belt and small vee pulley on the electric motor, but a flat driven cast iron pulley on the pump itself that the inner surface of the vee belt rides on.
To my recollection, there is no crown on the ( large ) driven flat pulley.
And on the 'Duro' brand, the flat pulley bore, to my recollection, is 1" diameter.
Timing belts from cars might be a better option. You could maybe run the toothed surface on a flat pulley, assuming that the pulley diameter was large enough, yet at the same time have the belt driven by a toothed pulley on the motor.
Be aware that some tensioner pulleys such as on Toyotas, are locked once adjusted, and others, such as Ford, and I think GM, are always pulling the belt tight with spring pressure.
Be aware that some timing belts have a square tooth profile, whereas others seem to have rounded teeth, which would give less flat pulley contact area. An easy way to see this is to check the toothed pulley teeth to see if the 'valleys' between teeth are squared off or not.
But in my own opinion, I would think that the best set up is a simple toothed belt with both the driven and the driver pulleys toothed.
This would allow low belt tension, locked as opposed to constant spring loaded adjustment, and so the main side load on the shafts would then be the torque of the drive.
A key factor in that case would be belt size selection.
For instance, small rechargeable floor sweepers use a toothed belt that is only maybe 2 mm wide. These smaller belts are very flexible, and would presumably rob very little HP in the deforming of the belt as it runs.
My own plan is to use vee belts until I verify the ratios needed, as they are more easily obtainable, then change to toothed belt once I know the pulley sizes, which in my case are critical due to the HP being used being small.
Another option would be the 'serpentine' style belts used on car accessory drives, where there are multiple grooves running around the belt, thus increasing the surface area. These are obtainable in smaller widths, such as on Toyota power steering drives.
Hehehe, dare I say it, all belt drives should have guards on them, then there is no need to calculate finger damage!
Shallow plastic tote boxes (or Tupperware?) might make good guards!
John
1.1. Flat drive belts with PP strapping Posted by: "Craig Carmichael" craig@saers.com craigcarmichaelis Date: Wed Dec 19, 2012 12:43 pm ((PST)) Recently drive systems - belts and chains - were being discussed. I'm becoming increasingly excited by the properties and possibilities of flat drive belts. So, FWIW: Flat drive belt systems simply need enough grip on the pulleys not to slip, and then they're almost 99% efficient through most of the power range - better than any other type. Wikipedia says that with 'modern materials', thin flat drive belts operate with reasonable belt tension and transfer up to 100 HP per inch of width. (Larger pulleys obviously will have more grip on the belt than small ones.) I've been searching, rather fruitlessly, for satisfactory "modern" flat drive belts. It has just occurred to me that the black polypropylene strapping one buys off rolls in various widths at, eg, fabric shops, is very strong with little stretch (like the yellow PP ropes), flexible enough to go around the smallest pulley virtually without friction, and cheap. (How about a 1" x 40" drive belt for 1$?) If the PP cloth has insufficient 'grip' without excessive tension, it can probably be increased by spraying it with urethane, or maybe some sort of rubbery material. (Urethane flat belts are relatively common as flat belts go, but are elastic. Urethane paint spray cans are common.) The ends could be melted, glued or sewn together to form a continuous drive belt. Flat drive belts auto-center on slightly "barrel" or "egg" shaped pulleys, always running towards the highest spot. I'm making ABS pulleys for 1" flat belts on my 3D printer, but may start molding them from (what else?) PP-epoxy composite to get bigger ones than I can print (~7" O.D.) - which will also be very tough and strong. (A sanded plastic pulley has more grip than a metal one and causes little belt wear - I'm sure it's part of the key to using flat belts.) And a clutch or (spring tensioner) can easily be made with an idler pulley on a spring, pressing on the outside of the belt. Finally on a rather unpleasant safety note, I would think that a hand caught in a flat belt and dragged through a pulley with no sides would probably emerge much less mangled than with a V-belt, toothed belt or a chain drive. (Especially if it's one that's tensioned with a spring.) (I mention this point as I've seen but thankfully not experienced savage accident results with both V-belt and chain drives in people I've known.) Cheers, Craig
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