Need help identifying this motor

I need to control a device that has three spinning wheels controlled by these motors. Printed on the outside of the motors is:

0T-RK-S4SSA-20134/71 11-04-25 24.0V

(I'm pretty sure that's correct, but it's possible that the 0's are O's and/or the 5's are S's)

The usual reliable google is coming up short for me.

Can anyone please identify this and refer me to information on the specs?

And any advice as to how to design a circuit to control them would be much appreciated! I am an electronics newbie.

Thanks!

  • Dave

Can you post a photo of the motor?

How many wires come out of the motor?

What is the device?

What power supply (volts and amps, or number and type of batteries) does the device use?

…R

It is in a ball machine. It's a cylinder, about 5cm x 3.5cm. Silver. Two wires going into it. The device gets 24V power coming in from a wall wart (I checked the power with a voltmeter). Not sure what power is sent to the motor, but since it says "24V" on the side, we have a clue.

Here's a picture (sorry about the poor quality, but you get the idea of what it looks like):

Does the plastic end bell (the white thing where the wires/terminals extend from) have any markings? Manufacturers generally put something there.

Personally, I would like to see a really clear photograph of the motor ends, and the markings on the side.

Most likely, though, those numbers are some kind of "house number" and bear no relation to the manufacturer of the motor (that is, it was made to order for the manufacturer of the ball machine).

If no other information can be found, the best way to get at least some idea about the motor's specs would be to measure the current the motor uses while running, while under a moderate load (perhaps in the machine), and when stalled (or as near as you can get it).

The best way to do this would be to use a shunt resistor and measure the voltage drop across the resistor, then do your Ohm's law to find the current. If you can find a large high-wattage sand resistor in a very low value (again around 0.1 ohms) you can use that.

Alternatively, you can make a shunt resistor:

Get a piece of wood and a couple of brass nails. Take a length of thick solid copper wire (like that used for house mains wiring), and note the gauge. Look up the resistivity value for the gauge of the wire, multiply that by the length, and you can find out how many ohms are in a given length, then wind a coil of wire to equal say 0.1 ohms or so (don't let the windings touch - it should look something like a spring). Attach the ends of the wire to the nails (wrap the ends around the shank of the nail, then solder). That's your shunt.

You can then measure the current needs of the motor while running, under a load, and stalled (or near enough), and that will get you enough information to decide on what to use as a motor driver.

At that point, you'll just need to get an h-bridge driver of some kind that can handle 24 volts, for the stall current (plus 15-20%).

Thanks Cr0sh! I really doubt that the motor was custom made. The ball machines don't do high enough volume to warrant custom parts, and I would think there would be dozens (hundreds?) of off the shelf motors that would meet its needs. It just has to spin a wheel, wouldn't ever stall during normal use, and has a very low load. But what do I know - I'm new to this electronics stuff.

If you could point me to a tutorial on how to control motors and what I need to figure out about its characteristics so I can control it without destroying it, I'd appreciate it. But regarding measuring the current, can't I use a multimeter for that? I have a good Fluke multimeter that can do current, max, avg, etc... Like I said, I'm new to this stuff, but if there are situations where you need to make a "shunt resister" (new term to me) to measure current, instead of using a multimeter, then I understand less than I thought. Or maybe you were assuming my multimeter didn't do current...?

That looks like a bog-standard Johnson or Mabuchi motor. They are made by the million. From your dimensions I suspect it is what is often referred to as a 540 motor. Google johnson 540 motor

If you look through the slot in the can you should get an idea of how thick is the wire in the armature winding. Thicker wire implies higher current and faster rotation speed. I suspect since it save 24v that it will have finer wire.

I would guess it is designed for about 60 to 80 watts so, about 3 amps at 24v. Stall current would be much higher.

...R

Thicker wire implies a lower voltage higher current - the rotation speed is a mechanical limit, not an electrical one.

Ok, I googled Johnson 540 motor. It does look like that. But just because it looks like that, is that enough to identify it? What I want to do is to order a few of these to use to test my Arduino control board on, rather than test on the actual ball machine itself.

Here is some more info that might be useful:

The power supply is 24V, 3 amps. And at max speed, the motor is at 20 volts. Is there anything else I can test in order to be able to find a suitable replacement motor to debug my board against?

And on an unrelated note - does anyone know if there's anything I can do in order to get email notifications on threads that I'm subscribed to? I have "Receive emails and alerts" set on this thread, but I'm not getting emailed about responses.

dptdpt: Ok, I googled Johnson 540 motor. It does look like that. But just because it looks like that, is that enough to identify it?

Have you a better idea?

These are cheap motors. There are significant variations within a standard size of can. If you can find a shop that stocks them take along your existing motor and look for one with the same number of armature poles and similar wire thickness.

If not suggest you find some convenient web site that supplies them and choose one that seems to meet your requirements as far as you know them. Then try it and see what happens. Maybe even deliberately buy two different ones so you can compare them.

I would be surprised if it is essential to have an absolutely identical motor.

...R

PS, I'm sure @MarkT knows a lot more about motor technology than I do. I just meant that for a given voltage (and plenty of available current) thicker wire will normally indicate a higher motor speed because it has lower back emf and therefore a higher current.

My goal is to make an Arduino control box to control the ball machine that I can offer for others to use to control theirs. So it’s not an option to swap out the motors. I do want to test against an external motor though, before I connect my control box to the actual ball machine. Hence my search for the motor. So this motor I’m buying is just for testing. I just don’t know enough about how these things work to know how similar my test motor needs to be. I just want to verify that my control box can - (A), control the motor, and (B), do so without burning it out eventually.

So if anyone could educate me as to how to match motors, and what characteristics are relevant to safe control of a motor - or point me to a site that explains all this, I’d appreciate it!

dptdpt: So if anyone could educate me as to how to match motors, and what characteristics are relevant to safe control of a motor - or point me to a site that explains all this, I'd appreciate it!

I honestly think you have a double problem here. ( A ) You don't know exactly what you have and ( B ) you are unlikely to know exactly what you are buying even if you do find a motor that is similar.

Try the websites for suppliers to industry and see if they have specs for the motors they supply. I guess if you want a motor with specifications you will have to pay more :)

What exactly will your control box need to be capable of doing? Perhaps you can design it with a bit of "slack" so that the exact spec of the motor is not important.

Can you be sure that other machines will have exactly the same motor that yours has?

...R

Yes, I am sure other machines will have the same motors.

My control box will be fairly complex, but for the purpose of controlling this motor, I just need to be able to control the speed of the motor rotation - from still to max rotation, and maybe 20 increments of rotation speed in between.

I don’t know much about motors, and I don’t know what I don’t know. I don’t even know if my questions are so newbie-ish that we have a disconnect here.

Can I assume, based on the fact that my multimeter shows 20 volts between the leads going into the motor, that all I need to do is to send it 0 volts up to 20 volts of power to control the speed of the motor?

Is there anything else I need to figure out about the characteristics of a motor to control its speed, and to make sure I don’t burn it out? If so, can I figure it out with a multimeter, or is there some other way I’ll need to reverse engineer the motor?

I was hoping that the numbers on the side of the motor would tell me all I needed to know, but I guess not. Rats!

One other thing, and this is probably not a clue that will help identify the motors, but if anyone could explain this, I'd appreciate it!

So again, there are three motors, each controlling a wheel in the ball machine. All are the same 24V motor, or so it appears. When I measure the voltage on the leads going to the motors, at max speed I get 20 volts. But when I measure the voltage being sent to the motors from the control control box, I get very different results. The control box sends 20 volts to one motor at max speed, 5 volts to the second, and half a volt to the third (I tested this with each motor running at max speed and the other two not spinning). Clearly, the machine itself is amplifying the voltage sent from the control box from two of the motors, but why? Why would they design it this way, instead of just having the control box send 20 volts to each?

dptdpt: Thanks Cr0sh! I really doubt that the motor was custom made. The ball machines don't do high enough volume to warrant custom parts, and I would think there would be dozens (hundreds?) of off the shelf motors that would meet its needs. It just has to spin a wheel, wouldn't ever stall during normal use, and has a very low load. But what do I know - I'm new to this electronics stuff.

I don't mean "custom made" - rather, some manufacturers of motors (and other components) will allow a buyer (in a large enough volume) to have custom numbers stamped onto the part being sold (instead of a standard reference part) to allow for stock control by that buyer in their own system. Other times, manufacturers can allow a buyer (again, provided the volume is large enough) to specify certain particular "options" (most available via the datasheet, but again - if the volume is large enough, slight customizations are allowed as well) to get a slightly custom motor; in this case, the number may again be stamped onto the motor to reflect this customization at the client's request, or simply to make it clear that it isn't a standard part made by the manufacturer. In both of these cases, these are typically referred to as "in-house numbering" - you will find this on a lot of typical "surplus" parts, and trying to figure out what a part really is can be a great frustration.

That said - I do agree with you that if the volume was low enough, or if the application is generic enough (and this seems to be the case here - though I am at a loss at exactly what you mean by a "ball machine"?) - then such semi-custom parts likely wouldn't be needed. You could then be looking at something completely different - a case where the manufacturer, for whatever reason (though typically because of a sale, merger, or just to "differentiate" the product and freshen it up) - decides to completely change the part numbering scheme. I've seen this before on motors - notably the Pittman line; the brand and company have been sold/merged more than once over the years (from what I could gather - but I am not an expert here), and certain motors from the 1980s which are still made today have a completely different part number today vs then. Generally, the only way you can get information on these older parts is to get in contact with the company and/or a local sales distributor for the company - and hope/pray that they created and kept a cross-reference (which in most cases they don't).

dptdpt: If you could point me to a tutorial on how to control motors and what I need to figure out about its characteristics so I can control it without destroying it, I'd appreciate it.

Well - google "How to measure DC brushed motor stall current" and I am sure you will find something...

dptdpt: But regarding measuring the current, can't I use a multimeter for that? I have a good Fluke multimeter that can do current, max, avg, etc... Like I said, I'm new to this stuff, but if there are situations where you need to make a "shunt resister" (new term to me) to measure current, instead of using a multimeter, then I understand less than I thought. Or maybe you were assuming my multimeter didn't do current...?

The typical way to measure a motor's current consumption (and you will learn this as you google) is via what is known as a "pony brake" - this is basically taking the motor, mounting it solidly so that it can't move (period), then clamping the shaft so it can't move (or can just barely slip - in a real setup, the force on the shaft can be varied to simulate different loads - but this isn't so practical "at home" - but there are ways to do it; some easy, some interesting, some difficult). All of this needs to be mounted very solidly.

Then you use a power supply capable of supply the voltage needed and at the minimum the same amount of current or more that the motor will use under this heavy load (which may be a "stalled" load - that is, a load so great the motor can't turn, and thus it uses maximum current).

Since you don't know the current this motor will take under this condition - it very well may be larger than what your meter can handle (most meters can only handle 10-15, maybe 20 amps for very brief periods - under a couple of seconds - at least via the leads; those with clamp-on current measuring can sustain much larger currents of course). So - if you are running the current through those leads with the meter inline - and the current needed is larger than what the meter can handle, then pop goes the weasel and you're out a meter.

By using a shunt, you are only limited by the maximum amount of voltage the meter can show, and since you are actually measure the voltage drop across the resistor, then as long as your meter can show you the supply voltage, it will work to show you the lesser voltage.

All of that said - a pony brake on a motor can be a bad thing - if things are mounted very solidly (or you misjudge the power of the motor) - you can have a dangerous situation on your hands. If the shaft is locked solid, and you power the motor for more than a second (and maybe even less!) - you can end up with a blown or damaged motor, power supply, or maybe even a fire situation (which is why it is better to allow some shaft slippage if possible, then add on a percentage). Suffice to say, also, that you can't measure a gear-motor this way - only the base motor - because in a gear motor, you can easily break gears and whatnot under such a stall condition (I did this once with a Pittman gear motor accidentally - which is how I came to know that my part number wasn't standard - and I did get in contact with a local sales rep - but they wanted to sell me a minimum of 50 of those steel gears at $7.00 each - for a motor I had paid $10.00 for as surplus).

So - there are other ways to measure the stall current - some indirect, and some relying on slightly specialized tools (like a way to sample and hold an initial measurement from startup of the motor - because a motor at rest is -at- stall current conditions, and so if you can measure that instantaneous application of current to the motor, you can get a good idea about the stall current needs). As you google, you will find out about some of these other methods - some of which can be easily done with motors at home - others you can't without spending more money than it is generally worth.

One other simple method I have head about to measure the current of an unknown motor, is to measure the resistance of the windings while rotating the shaft, noting the resistance values as they change, and getting an average (well, some say an average, others say take the lowest value) - then use that resistance measurement with your supplied voltage amount to calculate the current; I am not sure if this really works, or what current it is supposed to measure (running current, loaded current, or stall current - or something else).

Thanks Cr0sh. To clear some things up:

This device is currently in production and was recently released, so it isn't a case of the motors being old or out of production, I don't think.

Your suggestions for testing the motor are enlightening (thanks!), but I'm thinking I don't need to go through all that. You're describing how to find the characteristics of the motor under extreme loads, maybe for the purposes of comparing motors. I don't want to mess with the motors like that, and am only interested in the loads that the machine actually provides in normal use. But since the power supply is only a 4 amp power supply, and I have a 20 amp Fluke multimeter, I don't think I need to worry about blowing the fuse in the multimeter, and even if I did, I'd just replace the fuse, right?

Anyway, my outstanding questions are: 1) Can I assume that this motor is "brushless"?

2) Could you point me to a reasonable substitute that I can test my Arduino control box against? Should I just get one of those Johnsons?

3) Any ideas as to why the control box sends 20 volts max to one motor, 5 volts to the other, and .5 volts to the third - and they all turn at the same speed? Clearly the voltages are being attenuated in the last two motors, inside the control box - but why do it that way?

  • Dave

dptdpt: Anyway, my outstanding questions are: 1) Can I assume that this motor is "brushless"?

2) Could you point me to a reasonable substitute that I can test my Arduino control box against? Should I just get one of those Johnsons?

3) Any ideas as to why the control box sends 20 volts max to one motor, 5 volts to the other, and .5 volts to the third - and they all turn at the same speed? Clearly the voltages are being attenuated in the last two motors, inside the control box - but why do it that way?

I haven't read all of @crOsh's post but it looks like the "proper" way to do things.

You can be absolutely CERTAIN that what you have is a BRUSHED motor - I have two in my bits-that-might-be-useful-some-day box. You can see the brushes through the hole in the can. I don't mean to be at all rude, but if you don't already know that it suggests you are at the very bottom of the learning curve.

Measuring the voltage from the existing controller is unlikely to tell you anything. At the very least you need to measure the current at the same time. If it is a PWM controller you would need an oscilloscope to monitor the varying voltage and current - and the latter will be very complex.

I suspect that an engineer with experience of making the commercial devices with small electric motors would have an instinct for what is required and what is going on. He would also know where to find manufacturers' specifications and, perhaps more importantly, he would know how precisely the specifications must be matched to get equivalent performance.

As far as I can see you are not in that position (and nor am I). So all I can suggest, from a practical hobby point of view is suck-it-and-see. Buy a few different motors and learn how they behave.

...R

Thanks, Robin!

To your point, no offense taken - I am absolutely at the bottom of the learning curve. I'm a software guy with no electronics experience, trying to teach myself electronics so I can do this project. So if you could point me to anything I can read to climb a little up the learning curve, I'd appreciate it! For example, I know what PWM is, roughly, but didn't know it applied when controlling motors. I thought motor speed was controlled simply by varying the voltage - no?

As for testing different motors - again, I'm not looking to replace this motor. I just want to figure out how to control it so I can build my own replacement of the PCB that's controlling it now.

Ok, I just read up on PWM for motor control. Thanks for pointing me in that direction! That looks like the way to do it. The fog continues to lift, bit by bit... I'm now wondering if I should attempt to design the PWM motor control circuitry myself, or buy a shield. The problem is that I need to control 4-5 motors total, so I'd need 5 shields - right?

Still wondering about those strange voltage measurements too.

dptdpt: I'm now wondering if I should attempt to design the PWM motor control circuitry myself, or buy a shield.

The Arduino produces the PWM signal. That needs to feed into a h-bridge motor controller. For example, see this Pololu page.

If you have no electronics experience you will release a great deal of smoke before you build a successful h-bridge board. The good ones are quite sophisticated. Just buy one.

Whether you buy the sort of driver in that webpage or a shield is a matter of choice. If you need more than one shield just make sure that they can work together on one Arduino.

...R