Determining motor specs

[Maker]

I'm posting this partially to ask for help, partially because I think it might be interesting to some, and partially because I find it quite helpful to write down my thoughts as I work though something like this.



I've got a handful of these cute little motors, they've got a geared output and a 6 pin connector, so presumably there's an encoder in there. They're probably frighteningly expensive new, but without knowing what they are they're not much use to me. The product code, 344515, brings up nothing on the Maxon website, I emailed them and it's a customer specific part and they can't give any details without the OEM's express permission. I'd email the OEM but I've got no idea who they are, I've just got a bag of loose motors.

Here's the connector, I've seen them before but no idea what it's called, I'll buy a few if anyone recognises it?






Poking it with a multimeter, the two outermost wires have about 30 ohms between them and open circuit to the other four, spinning the shaft by hand I can get as much as 10VDC out on these pins, clearly it's a brushed DC motor, these are power leads, and I think 12V supply is a safe bet. The other four wires have 10k, 20k and 1 meg between them and nothing changes turning the shaft. It's gonna need a sacrifice one to the tare down gods.



The back end came off with a bit of brute force and ignorance, there's tiny copper brushes on the other side of this piece which I forgot to take a picture of.



I chewed the black plastic off this to reveal a ferrite magnet encoder wheel. I can't tell how many poles it has, I think those 12 dots on it are just a feature on the die, I can't find my magnetic viewing film so I'm not sure if there's just two poles or something more clever going on.





The wheel sat between these two white things, which I assume are hall effect sensors. They each have 3 terminals, if you label the wires on the ribbon cable 1 to 6, the rightmost terminal on both these parts is connected to 2, the centres are both connected to 5 and the left hand pins get their own wires, 3 and 4. That looks like 2 and 5 are power and ground, 3 and 4 are signal. I was hoping to test it with a magnet but I seem to have broken this board so I hooked up another motor to an arduino running the Analogue Read example code, because I don't have an oscilloscope. I connected pin 2 to 5V, pin 5 to GND and pin 3 to an analogue input, just guessed the voltage and polarity. Here's a screenshot from the serial monitor while slowly turning the shaft:

Perfect! It alternates between logical high and low while turning, looks like a nice sharp square wave too, very pleased with that. Clearly I guessed the polarity right first try, I tried it the other way round and the output just sits at a little under the supply voltage.

Hooking both sensors up, and struggling to use the serial plotter in the Arduino IDE, you can see there is a phase difference, whether it's 90 degrees or not I've got no idea, it's clearly not 180 though which is what I thought when I saw the diametrically opposed sensors.

I really need an oscilloscope!


That's just turning the shaft by hand, I'm sure it would be easier to see what's going on if I just powered the motor up, but I don't have a power supply indoors and I'm very wary of running it off the Arduino, I killed this laptop a when it was new and still under warranty (Thank god!) ago testing motors on an Arduino.

 

[Maker]

I was gonna hit the picture limit, there's more glorious tare down to show off.

It turns out the gearbox is just screwed onto the face of the motor (I took the picture after I'd already ******** the thread).


There's a metal gear very securely pressed onto the motor shaft, so much so that trying to pull it off I pulled the shaft and gear in one piece out of the rotor. Inside the gearbox I can see 3 plastic planetary gears, there's probably two or three stages in there, I haven't managed to open it up yet. Getting the gear/shaft out lets me count the gear ratio though, it looks like it's 16:1



The middle part is a very strong permanent magnet, the shiny section at the front is a snug press into the housing, it doesn't rotate. The windings are a hollow tube which sits around the magnet, the shaft passes through tiny bushings inside the magnet and presses into the back of the winding tube, it's a really tidy design imo. The housing is steel and does a very good job of keeping the magneticness in, there's almost no attraction between an assembled motor and a piece of steel.



Here's the commutator on the back of the rotor, there's 7 segments on it, don't really know the significance of that. The little extended shaft on there is where the encoder wheel was sitting.

 

[Red'n'Black]

Can't help with the motor but the connector looks like a Molex Picoflex.

https://www.molex.com/molex/products/family/picoflex

 

[hotponyshoes]

Does the maxon website have a search with a filter option on it?
If you put in the info you know about yours you might be able to get a close match.
In my experience "oem products" are often small changes/customizations of an existing product so you might be able to get a spec sheet for something pretty close that is 99% the same

 

[Bullet2012]

Hope you wash your mits before you make my brew for me

 

[Maker]

Does the maxon website have a search with a filter option on it?
If you put in the info you know about yours you might be able to get a close match.
In my experience "oem products" are often small changes/customizations of an existing product so you might be able to get a spec sheet for something pretty close that is 99% the same

It does, and I was going to try exactly that once I've measured a bit more about it (No load current, speed constant, pulses per rev, etc). I suspect it's a standard motor, standard gearbox and standard encoder, sold as one "custom" product with it's own special code.

Hope you wash your mits before you make my brew for me

I'll make bread first and post you a loaf along with the beer.

 

[hotponyshoes]

They might even have a download section with information on what sort of custom options they offer.

I've even had offers from places to sell bog-standard items but "customised" with my own logo or part number. Presumably so I, as a manufacturer, can control supply of spare parts for my machines or something?

 

[Bullet2012]

It does, and I was going to try exactly that once I've measured a bit more about it (No load current and speed constant for exmaple). I suspect it's a standard motor, standard gearbox and standard encoder, sold as one "custom" product with it's own special code.


I'll make bread first and post you a loaf along with the beer.

All,ok for bread thanks

 

[Maker]

Looks like it's probably these, or very close.

190 euros, taring one down was a lot less painful before I knew that!

 

[mike os]

Almost always a standard part or combination thereof

Maxon are nice drives

 

[Maker]

I managed to crack the gearbox open, two identical epicyclic gearsets inside, the first stage uses plastic planets and the second stage has metal ones. The metal ones look like proper metal too, not sintered powder like you usually see in gearboxes like this. The carrier for the first stage is powder metal but the second stage carrier and output shaft are machined from solid material. There's two ball bearings on the output too, for scale, the output shaft is 2mm, the OD of the whole thing is 10mm.





The sun and planets have 12 teeth, the ring has 36, so definitely 1:4 on each stage, 16:1 overall.

 

[bricol]

They might even have a download section with information on what sort of custom options they offer.

I've even had offers from places to sell bog-standard items but "customised" with my own logo or part number. Presumably so I, as a manufacturer, can control supply of spare parts for my machines or something?

Exactly - you make money from the spares sales, and so do they. Plenty of companies will flog you de-badged components if you buy enough.

Although, amusingly, to me anyway, for stuff such as pneumatic valves, it's usually pretty easy to spot who makes them, and if you are familiar enough with their stuff, exactly what it is anyway - and if you aren't a quick flip through their catalogue usually reveals all - and then how much you can save be going direct . . .

 

[mike 109444]

It's like AvE but in miniature

Sort of motor you might find in a small thermal printer (think tills or parking payment machines) maybe.

 

[Maker]

Sort of motor you might find in a small thermal printer (think tills or parking payment machines) maybe.

I don't think so, these are far too expensive, every printer I've had apart used stepper motors, no need for an expensive gearbox, encoder or feedback circuitry with a stepper. I was given these by someone in EBME (Electro and BioMedical Engineering), so some sort of medical equipment, but beyond that I've got no idea.


I wrote some Arduino code to count rising edges on the encoder output, 1 turn gives 192 pulses per channel, there's a 16:1 gearbox there so the encoder is 12 pulses per revolution. Those 12 dots on the encoder wheel must be magnetic poles (Which is what I thought when I first saw it, but playing with it near a magnet made me think there was only two poles on it). Using both channels of the encoder you get 384 PPR, so the positional resolution is just under 1 degree.

 

[Maker]

Using both channels of the encoder you get 384 PPR, so the positional resolution is just under 1 degree.

That's not right, I was only counting rising edges, if you count level transitions you get twice as many, so a resolution just under half a degree.

I measured the no load current, 5mA, steadily rising with load (pinching the shaft in my fingers (Ooer sounds a bit rude)) to around 350mA when it stalls. Assuming it's a rebadged Maxon 256105, no load should be 5.5mA and it should stall at 360mA, close enough.

As for speed, I'm measuring about 12620 RPM on the motor (So 791 RPM through the gearbox), but I don't think that's a very reliable number. My power supply puts out 12.23V so I'm PWMing it to as close to 12V as I can get (Multimeter reads 11.98V), but that's probably not the same as actually giving it a continuous 12V. I'm also counting the revolutions and timing it with an Arduino and my code might be dodgy.


I think that's about all the testing of the motors I want to do, now I need a use for them, I'm open to ideas.

What needs loads of low powered, very precise motors?

 

[eLuSiVeMiTe]

That's not right, I was only counting rising edges, if you count level transitions you get twice as many, so a resolution just under half a degree.

I measured the no load current, 5mA, steadily rising with load (pinching the shaft in my fingers (Ooer sounds a bit rude)) to around 350mA when it stalls. Assuming it's a rebadged Maxon 256105, no load should be 5.5mA and it should stall at 360mA, close enough.

As for speed, I'm measuring about 12620 RPM on the motor (So 791 RPM through the gearbox), but I don't think that's a very reliable number. My power supply puts out 12.23V so I'm PWMing it to as close to 12V as I can get (Multimeter reads 11.98V), but that's probably not the same as actually giving it a continuous 12V. I'm also counting the revolutions and timing it with an Arduino and my code might be dodgy.


I think that's about all the testing of the motors I want to do, now I need a use for them, I'm open to ideas.

What needs loads of low powered, very precise motors?

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Dunno but made me think of this. Cool bit of hardware

Got loads of bits kicking around that might be useful but I can't find a use for

 

[Maker]

That's interesting, I'd never have thought of that.

I'd been thinking something along the lines of this:

They'd make pretty cool input devices, like the motorised pots you used to get on amplifiers, but much cooler.

Or, I've always wanted to build a hexapod/Stuart platform, these are probably the ideal motor to make a tiny one suitable for a microscope stage or something like that, but I'd have to machine six leadscrews & nuts and make tiny linear actuators, which sounds like a bit too much effort for something I don't need. Some kind of tiny motion control like that is interesting, I wonder how small a 3D printer could feasibly be.

 

[eLuSiVeMiTe]

That's interesting, I'd never have thought of that.

I'd been thinking something along the lines of this:

They'd make pretty cool input devices, like the motorised pots you used to get on amplifiers, but much cooler.

Or, I've always wanted to build a hexapod/Stuart platform, these are probably the ideal motor to make a tiny one suitable for a microscope stage or something like that, but I'd have to machine six leadscrews & nuts and make tiny linear actuators, which sounds like a bit too much effort for something I don't need. Some kind of tiny motion control like that is interesting, I wonder how small a 3D printer could feasibly be.

Saw someone build a Stuart platform for a CNC pool cue the other day. Very cool.


Im tempted with the synth just for how interesting it is. Never seen anything like it