Finding a controller to maximize torque in salvaged washing machine motor?

[ElectricLove1975]

I have a huge 310v, 2.8A, 0.92hp COM2000 direct drive motor from a Samsung washing machine, which I am trying to salvage in the process of turning the washing machine into a cannon.

The goal is to have the motor pull back the drum (which is attached to springs at the front of the gutted washing machine) like a sling shot, with some load in the drum (watermelon, lego millenium falcon, basketball, etc.), and then release it with a trigger mechanism. It functions like a giant sling shot. Everything is already built and works, I am just trying to make it more powerful, and figuring out how to access the beautiful torque in this motor is the bottleneck for me (previously I have just been turning the motor with my hand). I also have very redundant safety precautions, and a huge private property to do this on.

My goal is to find a motor controller that can maximize the torque of the motor, to maximize elastic potential energy in the springs.

This challenge (with almost an identical motor) has been attempted to be solved before on this blog, but their solution was to just use the original controller from the washing machine: https://www.eevblog.com/forum/projects/building-a-motor-controller-for-a-samsung-brushless-direct-drive-washer-motor/
^(This is a pretty long thread, but towards the end you can find the important detail- the hall effect sensors of these motors are different from most.)

I stupidly threw away the original controller when I first took it apart, so the only option here is to build/buy a new one. I know that people have successfully used e-bike ESC's like this one https://www.amazon.com/dp/B08HWF7MZ7?psc=1&ref=ppx_yo2ov_dt_b_product_details
to drive motors exactly like this. So it is definitely possible.

I am trying to figure out:
1. The optimal specs of such a motor controller in the interest of maximizing torque (there are no limitations on available power, rpm requirements, etc.- I only care about torque)
2. Would rewiring the stator like this unlock more possible torque?
My understanding is that this lowers the required voltage and increases possible current, and more current equals more torque. Is this correct? I am trying to educate myself on what rewiring the stator would accomplish, and other general theoretical info about this problem, but all online sources about it seem to just give instructions without diving into the theory.

Thanks!

[Siwastaja]

Rewiring/rewinding does not unlock any more torque because torque is finally limited by the iron saturating. The only thing you could do by rewiring is change the voltage/current relationship (i.e., change the motor from low-voltage high-current into high-voltage low-current or vice versa, with power and torque characteristics kept the same); this is useful if you have a power supply / battery pack of certain voltage too far away from what the motor was designed for. One could also increase the efficiency and maximum continuous power rating by rewiring if they are able to squeeze in more copper (factory-made motors have some empty room to allow easier machine insertion of windings), but this effect is small and it seems long-term power rating (in minutes, limited by heating of the windings) is not that important for you. Therefore, no rewinding needed.

The key to maximum torque is to forget sensorless drivers and sense the rotor position (hall sensors, encoder or something else, the exact type doesn't matter). Then any controller with suitable current/voltage ratings pretty much perform the same.

You can exceed the rated motor current by maybe 2-3 times, but after some point, the iron saturates hard enough that returns in torque are diminishing and any extra current is just increasing resistive losses without generating much incremental torque. Maximum current is best found out by testing. Keep the testing short (a few seconds) to avoid burning the windings at highest currents.

Your thinking mistake in rewiring business is that while you can indeed increase the current by lowering the number of turns, being able to wind with thicker wire, then again magnetic flux (and thus torque) is really not defined by current, but current * number of turns. This works out to a constant, meaning that given certain amount of copper and iron, motors can be wound for any voltage / current relationship, within some practical limits, and there is very little if any difference otherwise; a 1A, 100V motor with 100 meters of winding wire is very close in all performance parameters to a 10A, 10V motor with 10 parallel strands 10 meters in length each.

[ElectricLove1975]

Thank you very much for the response!

I ordered this controller a few days ago and it just came in:
https://www.amazon.com/dp/B08HWF7MZ7?psc=1&ref=ppx_yo2ov_dt_b_product_details

Here is the problem I am trying to solve. The motor has built-in hall effect sensors, but not in the traditional way. It has 4 pins- 2 for U and V, and one for voltage, one for Gnd.
This (and seemingly every other consumer ESC that would fit this application) has a 5-pin sensor, 3 for hall & 1 for voltage, 1 for GND.

This post on this forum from about a year ago talks about this exact problem with this exact type of motor, but the OP had the original driver to use. I don't.
https://www.eevblog.com/forum/projects/building-a-motor-controller-for-a-samsung-brushless-direct-drive-washer-motor/
If you scroll to the bottom you can see them talk about these things.

Do you think there is any way I could connect this 4 pin hall effect sensor to a 5 pin one? Is my best option to just try to replace it with a 5 pin one? I am trying to see if there is a simple, less intrusive solution to this.

Thanks again

[Siwastaja]

Maybe it only has two hall sensors like Benta speculated on the linked thread. Converting that to simulate the expected three would be quite complicated, at that point I would consider rather designing your own controller or picking one of the "open source" ESC projects and modify their code.

Low-speed high-torque application would benefit from more accurate rotor angle sensing than achievable with just two hall sensors which will require interpolation. In the intended use of washing machine, motor always rotates at a significant enough speed so that even sensorless is an option. If I understood correctly, you want instantly full torque from nearly standstill, in which case not only sensorless goes out of window but 2-hall sensing is a bit iffy, too. You could always consider retrofitting more accurate angular sensing.

The 3 hall sensors give 6-step output per electrical revolution, meaning electrical angle will be at most +/-30 deg off from any instantaneous optimum value. With 2 sensors that would drop to 4 steps and +/- 45 deg respectively which is a big difference as 45 degree error from the optimum 90deg phase shift means significant drop in torque and increase in reactive current. So while 6-step sensing benefits from angular interpolation, it becomes nearly mandatory with 4-step sensing.

[ElectricLove1975]

I think it definitely is the case that it has 2 hall sensors.

It doesn't need to necessarily go straight to instantly full torque, it would fit the application needs if it started lower and worked its way up as it turned. Does this change the feasibility of trying to do this with 2 hall sensors? Also, I could easily implement a gear-lock system on the motor to prevent it from turning in the wrong direction if the motor stalls. Does having a motor that is allowed to stall mean it is ok to run it sensorless?

Could you elaborate on what you mean by retrofitting more accurate angular sensing? I don't have much experience with using/installing hall effect sensors, but from some research on it, it seems like this can be pretty tough to pull off right, especially without an oscilloscope. Am I wrong in perceiving that as a very complicated task?

[Infraviolet]

310V motor? In what country is 310V readily available?

[IanB]

310V motor? In what country is 310V readily available?

If you use a voltage doubling rectifier on 110 V AC, you get near enough 311 V DC.

[langwadt]

310V motor? In what country is 310V readily available?

If you use a voltage doubling rectifier on 110 V AC, you get near enough 311 V DC.

or rectified 230V,  ~325VDC

[ElectricLove1975]

Yeah, power is really not the issue. Just trying to figure out how to sensor it correctly.

I just ordered this:
https://www.amazon.com/gp/product/B0C1417P8J/ref=ox_sc_act_title_1?smid=A24XCO3ZAMI075&psc=1

It's a hall sensor for a different type of washing machine motor that has 5 pins, but the picture of it seems to still have 2 little sensors sticking up. Since it's only $10 I will give this a try by dremeling a bit to try to make it fit this motor.

I would appreciate a lot if anyone has some info for my questions in my previous post on this thread.

Thanks all!

[max_torque]

wait? If you only care about torque and not power then why not use some mechanical gears! For low cost you could increase torque 10 times easily, something that would be  impossible directly from the motor you have (and it's fixed active volume (ie magnets,iron and copper)

I suspect you do care about power though, as power is the rate at which work is done, and when it comes to throwing stuff, more power means more throw in any given time (although perhaps you don't care about the reload time at all in this instance)


"gears" in this case could be as simple as a smaller diameter drum on the motor to pull the cable or in fact a pulley block, that can double or quadruple the line pull without you having to touch the motor at all.....

[ElectricLove1975]

Thanks for the response, Max_Torque! (great name)

Believe it or not, I actually already have a 10x torque increase on this system from mechanical gears. I attached a picture.

These gears are great, but it kills me to only have access to such a tiny percentage of this motor's potential right now. I currently have only been able to drive the motor using the goofy mosfet driver in this youtube video:

What's funny is there is literally a second video with more views 'debunking' that exact other video that I happened to see years before, talking about how it only shows you how to turn a motor, not meaningfully drive it or have it bear any load:

As a beginner, I was totally misled by that original video, but am starting to have a better understanding. Even with that primitive driver, the motor is strong enough to lift a 45 lb weight off the ground. Can you imagine how strong this could be with the full torque unlocked + the gears?!

My current plan is I've ordered a 5-pin hall effect sensor from a different style washing machine with a very similar motor, and am going to try to dremel it a bit so it fits under my motor.

I am trying to educate myself on how to correctly install a hall effect sensor on a motor like this and would very much appreciate any info!

[max_torque]

You already may be actually developing peak stall torque with that basic driver!

Without any phase current control, your peak phase current will occur at zero rpm (because there is no backemf) if you driver can energise a phase in the right axis (ie in the Q axis ie at 90 degree electrical to the magnets in the rotor) then you will be making peak torque at zero rpm ie stall!

More advanced motor controllers acheive higher efficiency, higher power, and higher speed but ultimate stall torque is set by the zero speed phase current and the saturation of the iron in the system.

What is your the peak phase current at the moment.


A simple rig to measure the motor characterstics is easy. Energise one set of phases with a variable power supply (start at a low current, say 1 amp to avoid overheating)  Mount the motor with a simple torque arm to which you can attach a weight on a string,  apply more current until the weight is just lifted. You know what the torque is (force x radius) and you know what the current is, so you can calculate kT for the eMachine ie the Nm/amp.  This will be linear until the motor starts to saturate, playing around with phase current and weights allows you to work this out.  Be sure to have the toque arm at 90 deg to the string and ensure that the torque arm is mounted at the correct angle on the rotor so the phase is proiperly aligned (this is easy, simply energise the rotor on one phase, which will spin the rotor to this position and hold it their when it is not loaded

[ElectricLove1975]

Thank you for the info-

By variable power supply are you talking about a variable frequency driver? I just have a regular DC power supply. Is it impossible to determine this without a vfd?

With that information assuming I was able to successfully determine the Nm/amp, would that just serve to help me choose a current to operate it at from a controller?

My priority right now is just getting it to run in general from the controller. My difficulty is in determining how to set up the new hall effect sensor I got for it correctly. I am trying to educate myself on how people use back emf/an oscilloscope to finely tune these sensors (i. e. what tunings can be made, how do you know if the sensor is in the right place on the motor?)

Thanks!

[IanB]

I think max_torque is suggesting a variable DC power supply.

If you apply a DC current to just one set of coils (blue, yellow, white, your choice), it will lock in the rotor at that position. The maximum torque of the motor will be similar to the pull out torque, which it is the torque required to move the rotor out of its locked position. This torque can be measured with a torque arm and weights.

You can progressively apply more current to the coils until increasing the current produces no more torque. At that point the core will be saturated and the magnetic  field will be at its maximum. You will also want to keep an eye on the temperature at the same time, as this is not the normal way the motor operates.

I think perhaps, that such a motor could be driven like a stepper motor, by applying current to the coils in an appropriate sequence. It may not necessarily need a VFD drive.

[max_torque]

yes, use a normal dc varriable power supply, ideally with a decent current capacity because phase current is likely to be in the range of 50 amps or more, but a normal 10amp supply will at least allow you to work out the basic linear specific torque


simply connect any two of the 3 phase wires to the supply, turn it on at say 1 amp, the rotor will spin round till it reaches the point of highest inductance (like a solenoid, the rotor always tries to increase it's inductance) which is also the exact position at which peak torque is made.   Mark that point and clamp the motor to a table and work out how to bolt on a simple torque arm that when the arm is 90deg to the table the rotor sits on the mark you made earlier

Now rig up a weight on a string, that hangs off the arm downwards

Now you can apply some current and find the current that juuuuust can hold the weight with the arm horizontal and the mark aligned, ie the rotor alignment is at its max torque geometery position

From those three values (mass (remember to include the mass of the arm acting at half it's radius too....), arm radius and current) you can then calculate the Nm/Amp for the motor at it's optimum.



You can use the same measurement rig with some thing like a car battery and a long length of copper pipe (used to make a basic resistor to varry the current) to find out the absolutely maximum saturated torque, which for this motor is likely to be in the 100amp or so i'd guess. Obviously this set up cannot be used for anything more than a couple of sec before the entire rig overheats but it should be enough to establish the abs max torque of the machine