Conversion of ALDI stick vac to brushless

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So I got one of these knowing it was a bit crap, thinking I could hot it up with a few bits ordered off the web. It has a 540 style 120W 22.2V motor (what a PITA figuring out how to get to it that was) which should be fairly easy to replace with a 3650 brushless job, if I can manage to remove the impeller without damaging it (seems to be a press fit).

My intention is to grab a battery clip to suit my DeWalt stuff, taking it down to 5s, so I’m trying to figure out the kV and number of turns I’m after, to get the power up to like 250-300W. I found this page: https://blog.ampow.com/amp/rc-brushless-motor-size-chart-choose-the-best/ but it doesn’t seem to completely make sense, with kV ratings in columns headed ‘speed’…

The other piece of the puzzle is a suitable controller. I’d imagine a sensorless motor would be fine for this application (although curious what happens when the rpm wants to soar when suction is blocked), and a very basic controller that only switches between two or three speeds if at all would do, but I have no idea what to search for. Seems I’d want to nail down the motor spec first anyway…

What sort of controller would be suitable? An RC ESC seems a bit OTT… what else is available at this power level, any idea?

Cheers

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Hi Kim,

Welcome to the forum!

What is it sitting at now given you’re stepping down to 5S? Also, I’m assuming that’s a 5S LiPo that you’re referring to given the power you’re talking about.

I reckon a 3650 should fit into a stick vac of that size, I agree it is interesting that they’ve gone with Kv as a unit of “speed”, considering Kv is actually a ratio of thousands of RPM to voltage, determined by RPM (i.e. a Rotational Period) at 1V with no load, nothing about that has anything to do with travelling distance over time :sweat_smile:.

But none the less, what I’d argue you should be interested in this case is the max current under load, the wattage, and its relationship to the Kv of the motor, if you check the those specs for other better performance vacs of similar size that should give you a pretty good idea for what to go for, then you can use that to determine what ESC you need.

I agree that an RC ESC will probably be overkill here, although to be honest, I wouldn’t be surprised if that ends up being the best value for money controller for a 3650 given that they’re quite popular, possibly with a fairly cheap microcontroller providing signals to it. But if anyone else has ideas, please feel free to shout out

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Thanks for the quick reply, Bryce! Nice place you’ve got here.

3650 seems a no-brainer physically. 1/8” shaft, 35x50mm size, doubtless 1" bolt spacing, although I haven’t got the impeller out of the way yet to confirm that. Hotting up a cordless gizmo with an aftermarket RC motor has been an idea of mine since before brushless was a thing, so pretty keen to give this a crack. Reckon I’d publish a guide too.

The vac uses 6s, and my DeWalt batteries (LiPo obvs) are the FlexVolt ones, so actually 3p5s or 15s depending on how you take the power from the battery. Can’t see why I’d want to go 54V/2Ah instead of 18V/6Ah tho.

Given I have the voltage I’ll be working with, and the 120W number on the standard motor, shouldn’t I be able to work something out from that, since I figure another 150% of the Watts plus the extra efficiency of brushless should be plenty of a boost?

I’m afraid I still don’t understand kV ratings despite your brief explanation; I had just kind of assumed that was kilovolts plain and simple. But given my little drone uses 11kV motors, I didn’t see anywhere near enough of a spark gap for that sort of voltage on its tiny SMD controller board… that was a head scratcher. Suspected it wasn’t so simple.

I’d like to identify a rough spec for the motor to give me around half an hour run time from my 6Ah batteries at max power. Speaking of which, maybe adapting an RC ESC to work without a radio is enough of a project to warrant choosing something a little less common and this more expensive, if it means less faff.

Perhaps the electronic guts from a cordless power tool is the go? Might do some googling on that score, see if replacement units are available.

…

Holy crap, we get screwed in this country… look at those prices.

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Absolutely no idea how comparable the RC motor would be to the bespoke unit in the drill, though… I suppose one could fry the other if the spec was too out of whack. Better rip open one of my tools and see if the motor has a sensor.

…

Hm, yeah.

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I guess that would be typical, since any hand tool would be subject to highly variable load. Sensorless (and waterproof!) RC motors can be had for a mere $30, guess I’ll see how much more expensive sensored ones are.

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How about this for a controller?

Is there any reason I’d want a hall sensor in the motor? Doesn’t seem like the sort of application that would warrant it, not that I have much idea what the exact advantage of one is…

Seems hard to go wrong for $20, and I can find a brushless motor for $30 and a battery clip for like $12, which is the sort of spend I was hopefully anticipating.

So if that controller is appropriate, I just need to work out the kV and turns (poles too?) of the motor I need.

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I had not seen this Kv term before but the explanation is clear. The more Volts applied to a brushless motor, the faster it goes. How much faster? Kv revolutions per minute EXTRA for every volt applied. So if your power supply is 5s (5 LiPo batteries in Series) the Volts = about 18V. You want a motor to run at (for example) 30,000 rpm then the Kv value is 30,000/18 = 1667Kv. This is a no load value so the actual rpm will be less (but not much. We start talking about back emf and winding resistance and a whole lot of complication which is better summed up as “not much”).

The current drawn by the motor is dependent on the torque required to drive the load at the stated rpm. So swapping a 100W motor driving a load at 30,000 rpm for a 150W motor driving the same load at the same speed will not actually draw more current. It just gives a bigger margin if the load is increased.

As a completely pedantic aside, Kv should not mean kilo volt. Units named after people (V for Voltare, A for Ampere, W for Watt) are capital letters. Units not named for people have small letters - s for second (S is for Siemens), h for hours etc except for Litre when it seems either l or L are acceptable. The size prefix (e.g Mega, Giga, pico, nano) are capitals if Mega or bigger, small otherwise (so that Mega and milli don’t get confused, if for no other reason). So kilo volt should always be kV and Kv is something else.

Comment for no particular reason.

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Sensored brushless is great for startup torque. You don’t need that.

This guy is cheapish, can handle 6s lipo, and has a variety of input signal types. And for a parlour trick, it can play musical tones on startup by rapidly toggling the motor :slight_smile:

All you need to do to make it go is feed it a “servo” type pwm signal. There’s an arduino library for that. Simple.

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I was thinking stuff it, let’s see how that $20 controller goes, but I had to pay another $10 to avoid a long shipping delay, so I had a look what there was for $30. This one comes with a direction switch.

It occurred to me yesterday while banging dust out of the filter, being able to chuck it in reverse could be a good thing. I assume a centrifugal impeller isn’t completely useless in reverse…?

ETA: a centrifugal impeller isn’t completely useless in reverse… but the centrifugal aspect is key. Still sucks, but poorly.

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DIY vacuum gauge, goes up to about 2.7m, so plenty of room for improvement, if can achieve it

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Hi Kimmo
If that red stuff is coloured water a perfect vacuum will be something like 10 metres at sea level.
Cheers Bob
If you seal off the upper end of the tube and fill it completely and stand it upright with the lower open end in a bucket of water you will have a barometer (a perfect vacuum at the top) albeit a rather tall one (nearly 10m). That is why a realistic one uses something heavier like mercury. Before hectopascal the scale used to be mm Hg or mm of mercury as a means of measuring air pressure.
The really old scale was inches Hg.

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I actually have a proper vacuum pump around somewhere…

Found it on the street! Only recognised it because years ago I used to work for a mob who made carbon fibre yacht stuff.

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Yeah, whoops…

Turns out that ESC I got could only handle half the current the motor needed, and fried itself as I wound up the the revs.

That one you linked would probably cook itself too; it’s 35A and the motor is 41A.

Now that I have a clue, I’m thinking this one is the go, in 50A.

I have some Arduino nanos around somewhere, have to dig them up… I gather a RC ESC like this won’t start if it’s getting a part- or full-throttle signal; it has to wake up to zero throttle. And I’ll be using a pot to work out the best speed to run the motor at with my vacuum gauge, but once I figure that out the pot will be redundant, so after that I’ll just need to write a bit of code to ramp up from zero throttle to whatever that optimum value is.

I never got beyond a basic level with Arduino, and it was years ago - how do I see what signal I’m sending the servo? IIRC, you can get a real-time look at what’s going on with the Arduino by leaving it plugged into the programming PC, is that right?

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Hi Kimmo

That is a hell of a current requirement for a battery operated motor. Equates to about 900W, over 1 horsepower. Quite a large motor physically too.

Are you sure that it is not 4.1A? That I could believe but might still have a large inrush current. A brushed motor could approach 30 0r 40A inrush but a brushless motor I don’t know. Inrush can be overcome with a soft start.

The original was apparently 120W and at 22V this equates to about 5.5A.
Cheers Bob

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It’s the maximum as quoted by the supplier (900W @ 22V), but whether that is startup, stall or run is not stated.

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Hi Kimmo
Just had a look at that link. I don’t think that “50A” means “50 Amperes”. I think that is the model number as down further this appears
Bidirectional 20A 2-4s 2A 5V
Bidirectional 30A 2-4s 2A 5V
Bidirectional 40A 2-6s 3A 5V
Bidirectional 50A 2-6s 5A 5V
Bidirectional 60A 2-6s 5A 5V
Bidirectional 80A 2-6s 5A 5V

Which seems to indicate that the “50A” is actually 5A @ 5V.
Cheers Bob

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Hi Jeff
Just looked at that link.

Yes agreed. But this specification also quotes a resistance of 0.0182Ω which suggests 1200A current @ 22V.
I know brushless motors are different to brushed but something does not seem right here.

The first thing that comes to mind is how did they manage to measure a resistance like that. Outside some super laboratory I could not see that happening. Consider the practical size of the wire and the number of turns (the length of the wire) that would be in the motor and I doubt that even silver wire would get down to that figure. For a small motor such as this I would believe 0.0182kΩ possibly.
Cheers Bob

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I’m guessing my cheapo meter isn’t anywhere near accurate enough to give a reliable reading at such low resistance… but it’s definitely well under an ohm.

What’s IO?

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I think you’ll find the 2-5A 5V columns refer to the BEC output (BEC stands for battery eliminator circuit, so an RC receiver can get its power from the motor battery via a third wire from the ESC, rather than requiring its own battery pack).

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Hi kimmo
depends exactly what you are measuring here. That 0.2Ω could well be mostly your meter leads. I think to measure 0.0182Ω you would have to be in a very well equipped Lab and it would not be an ordinary ohm meter.

I dug up a couple of brushed motors I had laying around. One is new and fitted with a 30:1 gear box made by Johnston Electric. The gear box prevents me from turning the motor so I can’t get any idea of the winding resistance. From the data sheet which says stall current of 69.49A I calculate the coil resistance to be 0.2072Ω and the dynamic resistance is quoted as 0.2070Ω so this has to be correct.

I have another one ex a power tool which is visually identical without the gear box and would, by virtue of its use, operate in a similar voltage range, 7.2 to 18V. I can turn this one and measure resistance of between 0.8 and 1.8Ω with meter leads being 0.1Ω.

I remember golf buggy motor which are robust 12V brushed motors being about 0.5 to 0.6Ω when in good condition. They had a stall current of a bit north of 20A

I think I will need to do quite a bit of research into brushless motors as they seem to be the go these days.
Cheers Bob

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Correct. Upon bootup, the ESC will not arm until it sees a safe value. Typically zero throttle for one second, or thereabouts. It can tell you this via motor beeps if you like.
Alternatively, if you configure the ESC to bidirectional mode, an input of 50% is required to arm it. Then you move up to 51% to start moving forwards, or down to 49% to start moving backwards.

The “knob” textbook example is basically perfect for your situation. https://docs.arduino.cc/learn/electronics/servo-motors

This seems like the same thing, but in a little more detail. Arduino Brushless Motor Control Tutorial | ESC | BLDC - How To Mechatronics

Dumping variables to the serial console is trivial. Just put
Serial.begin(9600); //or other baud rate of your choosing
inside of the setup function, and then
Serial.println(val); //or whatever the name of your variable is
in your loop function whenever you want to print it.

Will the 35A ESC handle your 41A motor safely? Probably, if you don’t thrash it. But I ain’t taking responsibility for that.

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Hm, anyone know an Arduino IDE that runs on Android 13?

Never mind, I’ve got Arduino Studio installed… But now it’s asking for a platform?

Okay, Arduino AVR for my pro minis… geez.

Starting from scratch again, forgotten everything. Now I’ve gotta figure out what the deal is with the extra wire on the FTDI cable…

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I don’t think it’s meant to be on there all the time; I had it taped up out of the way. Hmm… I also have no idea why it has that bodged connector I obviously put on there; the reason is lost in the mists of time.

…Geez, what a faff. Seems Arduino coding on Android isn’t that popular anymore; OTG is just broken in Arduino Studio; no way to grant permission for USB access. Stuff-all else worth a damn as far as Android Arduino IDEs, except ArduinoDroid, which Play Store says isn’t compatible with my phone, because updates have ceased, so I had to dig up an APK elsewhere…

But now I’m in business. Successfully installed a couple of example sketches, good to go. Glad I didn’t have to use Windows; hanging off a desktop machine is inconvenient, and my laptop isn’t much better because it only works off mains power… :face_with_diagonal_mouth:

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