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Topic: Screwdriver motor (Read 2161 times) previous topic - next topic

michinyon

I'd also make the obvious observation,   that the speed and torque requirements of a cordless drill and an electric screwdriver,   and,  specifically,   the ability to start turning while under load,   are quite different.

Your practise may vary,  but I find it is always better to turn the drill on before I attack the piece of wood with it,   but the screwdriver works better if you put the tip of the screwdriver into the slot or star-shaped hole on the end of the screw,  before you turn the screwdriver on.

DonMilne


I would suggest this be a technical learning moment.

Just so's you know, I'm a professional engineer with 34 years experience. Though admittedly very little experience with motors. You can suggest anything you like. But, I personally have lost all respect for your opinions. You are a self important buffoon.

DonMilne

@michinyon: Yes, the cordless screwdriver turns in both directions. Obviously a drill and a screwdriver may behave differently as they're different applications. The attraction of this particular motor is that it runs on 6V, specifically 4xAA batteries, and it has very high torque - at least with the screwdriver gearbox attached. Unfortunately I don't have a pulley that fits this motor, so measuring the motor torque by itself is tricky. The other noticeable feature of the motor is how powerful the permanent magnets are. My other motors may have magnets inside, but none of them will pick up objects off my desk. I can't find any references that say that (large) permanent magnet motors have higher torque, but that seems intuitive to me. And of course the gearbox will magnify that... though I'm not certain how to calculate the gear ratio for a two stage epicyclic gearbox (*).

(*) Each stage has three planets with 19 teeth each. The motor pinion has 6 teeth. The annular ring has 48 teeth I think.

Robin2


though I'm not certain how to calculate the gear ratio for a two stage epicyclic gearbox (*).


As usual Wikipedia knows but I don't have the will to work through the complexities.

...R

DonMilne

I've seen the formula on Wikipedia, and while I could apply it blind I would prefer to understand it better. Frankly, I don't trust Wikipedia on things like this.  I guess I won't understand it until I write a software simulation, but that would be a fair bit of work and I have only so much free time!

DonMilne

#20
May 01, 2014, 02:17 pm Last Edit: May 01, 2014, 02:42 pm by DonMilne Reason: 1
Hi folks. I thought I might bring you up to date on my efforts to repurpose a cheap screwdriver motor. I have to say that it looks like a complete success. See the attached picture below. I have only tested it with 1kg and 2kg weights since I don't have any larger water bottles, but the motor easily handles that load and supports it without power at any intermediate height (in the photo the bottle is suspended about 600mm off the ground). I have no doubt that the motor would be happy with 3kg (my original design wish), though the same might not be said of my temporary mount - it isn't fixed down so needs a heavy counterweight to avoid any risk of tipping.

Oh yeah, tips for others about the importance of the spindle!  I made my spool on a small metal lathe I have. You want one which has as narrow a diameter as possible, consistent with the load, as that maximizes motor torque. The bevelled sides resist the potential of the thread jumping off the end. I also found it worked much better with that blue guide beneath the spool, which steers the thread back towards the center, otherwise it'll want to keep winding in one direction. It would actually work better if the guide was a small hole instead of a V, I'll do that next time. Oh, and the "thread" is actually 100lb (45kg) braided fishing line, only 0.25mm thick - you want narrow thread to keep the spindle diameter down and torque up.


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