12 V DC Motors

Thread Starter

Dyers

Joined Dec 11, 2013
21
Your belt drive appears to be driving at an angle to the pulley rather than truly perpendicular to each shaft?
Yes, this is true; there is a jog of the drive belt at both pulleys when either of the two outside steps are used. The middle step of the 3-step pulley is directly above the driver pulley on the motor shaft, and that means that the two outside steps are not. Now, I'm trying to decide if the stepped pulley is worth keeping, and if it is, to find a way to keep it aligned with the driver pulley, no matter which step is used.

For instance, I might use a lever to control a mechanical means to reposition the motor on the x-axis, make it easy to reposition the stepped pulley on it's shaft, replace the driver pulley with a stepped pulley on the drive shaft, or replace the driver pulley with a slightly wider pulley with three belt grooves on the drive shaft. I might also use the better idea you or someone else suggests.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Also an issue if you want quieter running is to replace the ball bearings with bronze Oilite sleeve bearings, these are traditionally much quieter.
Max.
 

Thread Starter

Dyers

Joined Dec 11, 2013
21
Also an issue if you want quieter running is to replace the ball bearings with bronze Oilite sleeve bearings, these are traditionally much quieter.
Max.
I did not know about these, had never heard of them. Thank you. I used epoxy to hold these steel ball bearings in place. Epoxy works well. It's not a very easy bond to break. I wonder how I'm going to get these bearings out to replace them? Maybe I won't. The loudest noise coming from this machine now is the sound of the flyer arms cutting through the air.

By the way, your .sig has not gone unnoticed. Good god, man; are you looking for some kind of nucular disaster by throwing words like those around? :eek:
 

Thread Starter

Dyers

Joined Dec 11, 2013
21
bronze Oilite sleeve bearings
Max.
What I'm finding is that Oilite was developed in the 30s, is about 20% SAE 30 motor oil by weight due to it's porosity, a characteristic that can be damaged or destroyed by using any but the sharpest cutting tools to machine it. What I'm not finding is how it might replace the sealed ball bearings I'm currently using.

The parts I can find that are identified as Oilite look like sleeves, bushings, flanged bushings, and other parts. Is your thinking re: this application to imbed one in the wood, and another around the aluminum shaft so as to provide a low friction coupling between the wood & rotating shaft, or would the aluminum simply glide inside an Oilite bronze sleeve that's imbedded in the wood?
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Looking at the application again, Oilite may not be the best alternative if the shaft is aluminum as I am not sure about the friction characteristics between the two?
Unless it is relatively low rpm.
BTW, a nice resource for components is Misumi, the huge (free) catalogue is worth it just for a reference book.
Max.
 

Thread Starter

Dyers

Joined Dec 11, 2013
21
Looking at the application again, Oilite may not be the best alternative if the shaft is aluminum as I am not sure about the friction characteristics between the two?
Unless it is relatively low rpm.
BTW, a nice resource for components is Misumi, the huge (free) catalogue is worth it just for a reference book.
Max.
In reading about Oilite since you introduced me to it last evening, I concur with your appraisal of it for this application, but I have another project, currently on the back burner pending a different way to approach it for which it seems perfectly suited. Bearings do make noise, and I would love to find an alternative if a reasonable one exists...but the bore in the bearing is so precise in it's match to the OD of the aluminum tube that there is no slippage, and therefore, no friction between the bearing, and the shaft.

Back to motors. Those brushless DC motors made for RC airplanes seem increasingly interesting to me, but I'm not finding much applicable data to help me narrow down the field. GopherT mentioned a large retailer not far from where I live. That's a good resource I want to follow.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Those brushless DC motors made for RC airplanes seem increasingly interesting to me, but I'm not finding much applicable data to help me narrow down the field. .
I have no experiience with RC motors, but my understanding is they require alot of power and alot of cooling, they appear to be designed for short - very high current operation.
I generally pick up high end servo's off of ebay, Tamagawa, Applied Motion etc.
These are mainly BLDC motors, and use the A-M-C servo drives.
Generally the advantage of AC or BLDC apart from no brushes is the higher RPM capability.
Max.
 

Thread Starter

Dyers

Joined Dec 11, 2013
21
Belaboring the point, constant torque ac motor seems perfect for your winding operation.:)
I've seen the phrase constant torque a couple of times in the last couple of days, and the association with winding seems strong, but now that I'm looking for such a motor, I'm not able to find anything small enough. I am seeing a lot of permanent magnet motors, but they seem to be DC. What brings you to making this particular suggestion; do you have something specific in mind? Your suggestion of an AC motor also has my attention, but why AC?

I have tried to pursue servo motors, and they may well be top notch, but I wonder about their cost effectiveness; at what point does the law of diminishing returns kick in?

I think this choice compounded in difficulty by the fact that I still need to better understand RPMs (both rated, and actual), torque, and their relationship. The Mabuchi that I'm currently using has a no load rating of 4600 RPMs. I don't know what to do with that number, and by extension, any other no load ratings, when the actual RPMs output is so much smaller.

I had a "duh" moment last night. WhenI said I didn't have any way to measure the actual RPM of this motor in this machine, I was mistaken. My son took two different colored balls of yarn to the other end of a long room while I attached their other ends to the spinner. I turned it on, and used stopwatch.com to measure 30 seconds at which time I turned off the spinner again, and calculated the total number of twists. Since one full rotation = exactly one twist, I could multiply my product by 2 to calculate actual RPMs with some degree of accuracy. This motor, measured in that way, rotates 465 times per minute under this load.

That's enough information to say that the motor I'm looking for will output 1,200 or more RPMs. I am not a spinner, but plying is comparatively easy to learn, and in the last few days, I've learned to manage. 465 RPM is slow even for a noob.

Does knowing the no-load, and loaded RPM of this motor operating as it does in this machine that tell me anything about another motor? For example, this motor's actual RPMs under this load are about 10% of it's no-load rating. Could I deduce that another motor with a similar torque rating would output a similar 10% of it's RPM rating? What happens to actual RPMs if a motor with a higher torque rating and similar RPM rating is used?

I haven't figure out a way to measure torque with what I already have lying around, but I'd like to find something that will output several times the current number of RPMs, and leave me with no less torque, and preferably more.

I can't tell you how much help it is to have a couple of people around with whom I can bounce questions and ideas around. I don't know anyone who's even mildly interested in this kind of stuff.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Personally I would be surprised if you see much difference between a AC servo which has a flat torque curve from zero rpm up to its max. rated rpm, and a decent DC brushed motor, which incidentally has a similar torque curve, when either are ran at that low a RPM.
And if you employ a quieter PWM drive rather than SCR/Triac etc, Any noise generated is most likely to be coming from the mechanical pulley/linkage etc.
Practically all motors are going to reduce rpm with a change in load, unless some kind of feedback element is used, this is why servo's use encoders to precisely control both torque and rpm.
Steppers are an exception, but these are exceptionally noisy down to zero RPM.
There are slightly more sophisticated drives than the simple open loop, variable speed control, that monitor the motor current as a form of feedback when set at a certain speed and increase the rpm accordingly when a load is sensed.
Max.
 
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