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Old 10th April 2012, 12:24 AM   #1
cancon is offline cancon  Canada
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Default DC motors and speed control - vibraphone motor help

Application: 12-24v DC motor with gear-head needed for smooth and silent operation of a vibraphone mechanism, Ideally 20-200rpm.

Problem: replacement "vibraphone motor with controller" can retail for over $700!

I'm finding some good deals on ebay but need some direction on which motor and controller to buy. Currently i'm looking at a 5000rpm 12V motor with 200rpm gear-head. I believe the cheap ones are all brushed DC. The problem I'm having is choosing a proper speed control (PWM type). They typically list specs of voltage and current. Does the listed voltage (i.e. 12-24V) mean that the board can vary the output voltage between these two numbers? If so, a 12 V motor would be run at full speed at the minimum output level, and overloaded if turned up? Alternatively, a 24V motor would be able to be adjusted from 50% speed up to 100% speed? I'm a little hazy on electronics class as you can tell... any help would be appreciated! thanks!

adam
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Old 10th April 2012, 12:51 AM   #2
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Normally a PWM would range between no output and full output. Full output would mean the input voltage, or close to it.

12-24V almost certainly means the device will work with input voltages between these 2 values.

A 5000 rpm 12V motor with 200 rpm gearing sounds like what you want.

A brushed motor with 5000 rpm commutates at 10000 per minute or 166Hz so the PWM frequency probably wants to be, say, 5 times that, 1kHz. You'll have to pick a PWM that will pass sufficient current.

PWM is not the only way to go, you can just use a transistor (heatsinked) controlled by a pot. The question is, how much current does the motor draw?
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Old 10th April 2012, 02:41 AM   #3
cancon is offline cancon  Canada
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Thanks for your reply!
What would the difference be between a 12V and 24V motor, in terms of performance? (torque, operating noise...etc). It looks like the 24V is more robust. The "current rating" is 0.33 amps. Not sure if this is on or off load.

input "200rpm dc motor 24v" into ebay and you'll see what my selection is.
input "pwm controller 10A" and you'll see the bulk of them, most are more than 1kHz.

I know that 'you get what you pay for' and that cheap isn't always the best, but i'm still trying to figure out my options, and maybe these things will last the test of time... I'm just working my way through the options. So far a sewing machine motor and turntable motors (belt or DD) did not work properly. I hope these 24V motors aren't too loud though.

Thank you very very much for your time in helping me out. Can't wait to get this vibe up and running!
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Old 10th April 2012, 03:19 AM   #4
pixpop is offline pixpop  United States
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How much space do you have for the motor?
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Old 10th April 2012, 06:50 AM   #5
cancon is offline cancon  Canada
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about 2" or 3" of vertical clearance. The mounting plate can be customized to mate with a replacement motor - the current holes locations are 1.25" (wide) x 1.75" (tall). The existing pulleys are about 1" dia.

pics here;

jenco - a set on Flickr
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Old 10th April 2012, 06:54 AM   #6
pixpop is offline pixpop  United States
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Quote:
Originally Posted by cancon View Post
about 2" or 3" of vertical clearance. The mounting plate can be customized to mate with a replacement motor - the current holes locations are 1.25" (wide) x 1.75" (tall). The existing pulleys are about 1" dia.

pics here;

jenco - a set on Flickr
Ah OK, never mind. I have some beautiful motors that would probably work very well for this, but they are way bigger that what you have space for. They are about 5" diameter, and about 8" long. They are reel motors from 1/2" computer tape drives.
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Old 10th April 2012, 09:02 AM   #7
Enzo is offline Enzo  United States
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I occasionally repair vibe motor controllers for a school music program rep. The motor in this unit - says "Musser" on the controler circuit board - appears to be a small AC motor. ABout 60mm in diameter and about 93mm long (including bracket but not the shaft with pulley).

The kids break the switch and speed pot.

I doubt it is what you want, but this one is made by Oriental Motor, part 21K6RA-AULA (or perhaps 2IK6RA-AULA)

But it is only a 6 watt motor according to the label, and I wonder just how much torque do you really need to spin the thing?


DO you have an existing motor and control? And if it has failed, can we consider repair? Even without a schematic, if my motor itself were OK, I could replace every component on this controller board for under $5 total. Leaving me $695 to spend on... oh something or other.

I used to do a lot of work in another industry, and we used lots of small motors. I found that WW Grainger had just pages and pages of small motors (and large ones too) of all types and capacities. They have branch stores all over the place.

To answer one of your questions, motors can be had in most any voltage and at most any performance level. Whether it runs on 12v or 24v doesn't much matter. if you took a straight DC motor with no controlling circuits inside and doubled the voltage applied, yes, it would spin faster, but using a 24v motor with a 24v supply versus 12v motor on 12v supply really doesn't matter. I can find anything from a toy train motor that works on 12v to a starting motor for my truck that runs on 12v. VOltage is not the issue, other than what voltages does your unit already have inside.

Probably nothing wrong with a plain old unregulated DC motor with a variable DC supply, really.
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Old 10th April 2012, 05:58 PM   #8
cancon is offline cancon  Canada
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There is no motor or control board on this unit - it was stripped of these parts before the instrument came into my possession - hence why I'm so lost on this project. Musser is the brand that sells the replacement gear I was talking about (very expensive), good to know they use a ~$100 motor! (2IK6RA-AULA is what pops up results).

If a working example is employing an AC motor, should we stick with that?

I can't stress enough that quiet operation is a must. Not sure if the motor needs to be synchronous either, but a constant speed is also necessary, no matter what rpm is selected. So far we've settled on a 200rpm gear-head, but what type of motor and control system for the necessary specs? Do you think you could harvest more info about what kind of unit is run at that school?

Thanks again,
adam
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Old 10th April 2012, 06:20 PM   #9
cancon is offline cancon  Canada
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Also, about it being a 6W motor, is that too strong or too weak for the application?

I called a local distributor of Oriental motors, says that the AC motor is cheap for these kind of specs.

Motor: 2IK6RA-AWU - about $85
Gear-head: 2GN-7.5-KA - about $85, 12 to 213rpm
Motor control: ES01 - about $75...
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Old 11th April 2012, 01:42 AM   #10
Enzo is offline Enzo  United States
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I have no idea what the equipment is, they just bring me the control box and the motor. I work through an intermediary, so I have no contact with the school itself or the staff there. The motor shaft just has a pulley on it, no gear reductions.

I mentioned the 6 watt rating of the motor because it seemed you were concerned with the horsepower so to speak. I was thinking that there wouod be very little load on this motor.

I agree you don;t want the speed drifting around, but a couple percents probably would not be noticed. One would also want to keep the instrument at a constant temperature so the metal parts don't expand or contract and change the pitch. I doubt that ever becomes an issue either.

But the load on the motor really doesn;t change much, so regardless of motor type, a regulated DC supply would stay constant, and this AC motor appears to have a speed sensor on the other end of the shaft. Aha, the end cover even says "Speed Control Motor" printed on it.

I see in your photo a couple small pulleys on the rotating parts. The diameter of those in ratio to the diameter of the motor pulley will set speed. I wonder what the speed range of the motor is by itself, and iof the motor maker also can provice a speed controler, what range does it give the motor. MY thinking is that reducing gears may not be needed. Reduction gears is a way to trade motor speed for torque, and right or wrong, in my head, torque is not your hurdle.


I don;t think you want a synchronous motor, because you want to be able to vary the speed.


Ultimately I don't think the type of motor matters a lot as long as it matches your speed range needs - and don;t forget pulley sizes in the calculations. There are smooth running quiet motors of all types.


Just a note, the control board with this motor is labelled Musser and has the number MUS001-A. I could probably trace out the circuit easy enough, but have you tried contacting the Musser people to see if they would part with a schematic? AN $85 motor and a home cloned control board might be an inexpensive approach.
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