DC motor conversion

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edma194
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Re: DC motor conversion

Post by edma194 »

The next type of motor speed control to consider is PWM (Pulse Width Modulation). This is a means of controlling motor speed through a series of full power pulses, with varying width and frequency of the pulses. It provides very high torque for a wide range of motor speeds.

Treadmills usually come with some type of PWM controller, but I have a lot of questions about how these controllers operate. Based on what I've found so far, it is unlikely they are producing 100+ volt pulses of varying width at full current. I suspect these controllers effectively derate the motor with lower voltage, current, and limited pulse control. My suspicions are reinforced by the lack of reasonably priced PWM controllers that can manage the high wattage these motors are rated to consume. This includes commercial controllers that cost hundreds of dollars. They all seem to top out in the range of 500-750 watts, which means the motors couldn't be producing more than 1 HP.

There is another 'feature' of treadmill motors that is undesirable to many, a soft start control that doesn't allow the treadmill to start at high speed which can result in the user getting thrown backward at high speed and suing the treadmill company. If you are using a simple potentiometer as the input to the controller to adjust speed the controller will ignore the potentiometer and start at a slow speed. You must dial your speed down on the pot and then bring it back up again. This shouldn't bother Shopsmith users too much since we all dial our speed down to Low before turning off the machine. We do that every single time, right? Anyway, there are workarounds to disable that feature if you want to use one of those controllers.

I do want to point out that this area of electronics is outside of my background and experience so at this point I have made a lot of assumptions that require further investigation. I do have a salvage motor and controller now and tried out a voltage controller. As soon as I can find a 5K pot I'll try out the MC60 motor treadmill controller to see what I get. I will try to find some way to measure the output of this motor with the different controllers. I definitely to work out a way to apply a load to them.

So, depending on how accurate my assumptions are, I think the use of common PWM controller will limit power output of these motors to no more than 1 HP equivalence with an AC induction motor. This is mot much worse than a 1-1/8 HP motor, and probably will be better than the 3/4 HP motor in a Greenie. The high end of the speed range should increase, but I don't know how much. The low end should definitely do much better. I suspect 250 RPM is achieveable without significant further decrease in power, maybe less. This would be something like a derated version of a PowerPro, possibly useful for some.

Even with the limitations of a PWM controller the motors could still be switched over to operation at full voltage and full speed over 6000 RPM, producing I think at least 1-1/2 HP in equivalence to an AC induction motor. What a reasonable voltage and duty cycle is in this mode is unknown. I suspect the motors will overheat even with additional cooling when run full blast like that and voltage and power still need to be diminished for continuous operation.

I see three different ways of using a PWM controller in a Shopsmith with whatever power they can produce:

1) Simply use PWM to run the motor at approximately 3450 RPM. The result is unlikely to have any advantage over a Shopsmith with 1-1/8 HP motor. Still an option if you need an inexpensive motor replacement.

2) Use PWM to control motor speeds in conjunction with the Shopsmith conventional belt and pulley speed control. This should extend the speed range at both the high end and low end, with considerably lower speeds possible.

3) Use a PWM controller for all speed control and remove the conventional belt and pulley speed system. This option leaves more space in the headstock for the electronics. The speed range should extend both higher and lower. Overall performance is an open question.

Any of these options could also have the secondary mode of running the motor at high speeds with full voltage to produce more power.
Ed from Rhode Island

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edma194
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Re: DC motor conversion

Post by edma194 »

A little follow-up, I finally found a little bit of solid info on two very common motor controllers found in treadmills, the MC-60 and MC-2100. Neither of these is a PWM controller per se.

A potentiometer can be connected to the MC-60 and it will function as a voltage controller, providing between 0 and 12 volts from the center tap to the controller will produce a relative output voltage from 0 to approx. 130 volts*. One data sheet for the controller indicates that signal could be pulsed, but there are no specifications for doing that. The same boards are often configured in different ways by disconnecting resistors or other parts at the factory so I don't know what kind of configuration might use that feature. It's not at all clear if a PWM signal could be supplied to this controller, I suspect it could not switch high voltages fast enough to work properly. Maybe I'll try to play with that some day.

The MC-2100 is a different story. It was made to be supplied with an external PWM signal. Very simple circuits using a 555 timer have been used to produce this signal, there are inexpensive PWM signal generators, and there is popular software used to make computers and micro-controllers into PWM generators for this device. MC-2100 controllers can be found in free treadmills, but new and used controllers approach the $200 mark as compared to $60 for the MC-60 controller. There are still questions about how what maximum speed and duty cycle is for these motors so I still question the ability of a $200 controller paired with a $15 signal generator to outperform PWM controllers that cost several times as much.
Ed from Rhode Island

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RFGuy
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Re: DC motor conversion

Post by RFGuy »

edma194 wrote: Wed Sep 15, 2021 11:01 am A little follow-up, I finally found a little bit of solid info on two very common motor controllers found in treadmills, the MC-60 and MC-2100. Neither of these is a PWM controller per se.

A potentiometer can be connected to the MC-60 and it will function as a voltage controller, providing between 0 and 12 volts from the center tap to the controller will produce a relative output voltage from 0 to approx. 130 volts*. One data sheet for the controller indicates that signal could be pulsed, but there are no specifications for doing that. The same boards are often configured in different ways by disconnecting resistors or other parts at the factory so I don't know what kind of configuration might use that feature. It's not at all clear if a PWM signal could be supplied to this controller, I suspect it could not switch high voltages fast enough to work properly. Maybe I'll try to play with that some day.

The MC-2100 is a different story. It was made to be supplied with an external PWM signal. Very simple circuits using a 555 timer have been used to produce this signal, there are inexpensive PWM signal generators, and there is popular software used to make computers and micro-controllers into PWM generators for this device. MC-2100 controllers can be found in free treadmills, but new and used controllers approach the $200 mark as compared to $60 for the MC-60 controller. There are still questions about how what maximum speed and duty cycle is for these motors so I still question the ability of a $200 controller paired with a $15 signal generator to outperform PWM controllers that cost several times as much.
I am not that familiar with treadmill motors, but my understanding is they are permanent magnet DC motors. So, I would presume that some of the controllers are powered by linear power supplies while others have some form of switched supply (likely PWM control). You would need a motor expert to understand design differences, but to a first order I think you are fine with anything that gives the desired output voltage/RPM. In other words, cheap and dirty may be sufficient for this endeavor. There is no doubt that signal generators (any application) get progressively more expensive as you try to get a cleaner, more pristine output waveform, so you can spend as much money as your bank account will allow on them. For this application though, the PWM is just switching on & off the switches (FET's) that power the treadmill motor. Provided the PWM generation is clean enough not to overstress the FET's then it doesn't really matter. Another factor is if the PWM generation is sloppy your efficiency could suffer. IF you have a linear power supply that gives the control range needed over the motor then PWM may not be needed. I believe one advantage of PWM control in this application is that you can have the motor rotate very slow without stalling, but then this can also overstress the motor, e.g. low speed but heavy load. Probably not a concern for this application unless you intend to turn a large Forstner bit or a large bowl at low speeds.
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lahola1
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Re: DC motor conversion

Post by lahola1 »

1. If you use the controller that came with the treadmill motor (mc60, mc2100), you should have no problems controlling the motor.
2. Basically you throw out the 1st and last 15% of the control band as unusable; low power or low torque.
The mc2100 board needs a PWM signal of 20hz. I replaced the big treadmill control panel with the a small PWM signal generator (amazon approx $12).
My setup in the threads is a temporary one made to slow the SS down so I could drill thru steel.

Here are some links to threads I've commented on this subject.
viewtopic.php?p=266610#p266610

viewtopic.php?f=10&t=23268

viewtopic.php?p=281441#p281441
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lahola1
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Re: DC motor conversion

Post by lahola1 »

I asked a question about comparable power to a std SS mkV on the FB digital motor conversion group about being able to rip 2X or hardwood stock.
Norman Harrison (Admin) said he can cut 6x3 hard oak(or metric equivalent) without any problems. He also said he would try and do a side by side test comparing the digital conversion one with his std SS 520.
RFGuy wrote: Wed Aug 25, 2021 6:56 pm
edma194 wrote: Wed Aug 25, 2021 5:00 pm So you guys have looked at this. I'm tempted to join Facebook and see what is over there.

It's an interesting concept but there are just more questions around every corner. The link from Ron up above is something I've seen before. There isn't much detail there on how he did it. How did he mount the motor and mate it to the shaft for the lower sheave? And while he has an impressive looking control display, it's driven by software, and a complication that's not really necessary for me. I believe I've seen a video where he has the reduced the size of the controller but even less detail was shown there.

So far I'm not getting a good idea of how effective these motors are in a Shopsmith headstock. I've seen videos of several metal lathe conversions that seemed to satisfy their creators, but I I think they were replacing smaller motors. How do these motors perform under full load? Are there overheating problems? There may be a lot of specific applications that could do fine with a highly affordable DC motor, but the Shopsmith is not a simple application, it has to perform in numerous modes with varying conditions.
I revisited the Shopsmith Digital Motor Conversions group to review some of the past posts out of curiosity. The guy in that video also has a PowerPro 520, so I don't know what applications he uses the treadmill DC motor powered Mark V for; maybe he only uses it for sanding? No one seems to talk about what they are doing with them after the conversion, or how the performance compares to a stock headstock. A few comments confirmed that torque at low speed range is a problem, but that is why they try to find as big of a DC motor as they can. Some even started looking for motors larger than 2.5HP to mitigate the low speed torque problem. He used the original motor mount holes in the motor pan and created a pivot on one side with bolts to apply tension on the other. Another guy in the group welded a mount to the motor pan. Some reuse the sheaves for speed control, but the guy in the video bypassed them and made his own touchscreen LCD control with custom SW in Python. Supposedly the files section in that FB group have more details both on the electronics and the motor mounting that some of them did.
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edma194
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Re: DC motor conversion

Post by edma194 »

RFGuy wrote: Wed Sep 15, 2021 2:12 pm I believe one advantage of PWM control in this application is that you can have the motor rotate very slow without stalling, but then this can also overstress the motor, e.g. low speed but heavy load. Probably not a concern for this application unless you intend to turn a large Forstner bit or a large bowl at low speeds.
I'd think that would be needed in most slow speed operations on a Shopsmith. The Shopsmith speed changer can give you about a 5:1 additional reduction from the motor speed, but to get down to only 700RPM you've given up half the power of the motor already. If it's just low speed you're after without much torque then voltage control would be fine but I don't see a lot of utility that way.
Ed from Rhode Island

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edma194
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Re: DC motor conversion

Post by edma194 »

lahola1 wrote: Wed Sep 15, 2021 4:54 pm 1. If you use the controller that came with the treadmill motor (mc60, mc2100), you should have no problems controlling the motor.
2. Basically you throw out the 1st and last 15% of the control band as unusable; low power or low torque.
The mc2100 board needs a PWM signal of 20hz. I replaced the big treadmill control panel with the a small PWM signal generator (amazon approx $12).
Excellent info in your links, I'll have some questions for you in a while.

In reference to the MC60 controller, have you heard of any use of PWM with this board? Here's some info of unknown origin hinting at that possibility. Note the comments on D7, the LED labeled SPD CTRL:

"These SCR motor controllers are physically identical. The only difference is in the components used to allow a
higher Current Limit on the MC-64 and a lower Current Limit on the MC-67. The MC-60M controller is a variation of the
MC-60 controller that allows a single wire harness to carry signals between the console and controller. The treadmill’s reed
switch plugs into the controller, then the tach signal from the reed switch and the speed control signal are sent to the console.
These controllers can be configured to operate at different speeds and with various consoles by clipping one or more
resistors on the controller. Configuring the controller is done at the factory and should not be attempted in the field.
Clipping a resistor changes the part number of the controller. Always be sure to order the controller configu red correctly
for the Model number treadmill you are working on by referencing the model number's part list.
A new feature of these controllers is four troubleshooting LEDs that can be used to troubleshoot the controller when
repairing a treadmill. They indicated when the controller is receiving the expected control signals and outputting the required
voltages. Each LED is displayed below:
D6- Labeled SCR. Indicates that the SCR is triggering on the controller. If this light is out, no voltage will be sent to the
motor. Note that this LED will vary in brightness, depending on the speed setting. If this LED does not light when the
safety key is inserted and D7 is lit (indicating a speed setting other than zero MPH), the controller will need to be
replaced.
D7- Labeled SPD CTRL. This LED indicates that the controller is receiving a speed signal from the console. Note that on
consoles without a power board that use a speed pot, the LED will light solidly, but vary in intensity at different speed
settings. On consoles that use a power board, the LED will flicker with the PWM control signal. The brightness of the
LED will vary with the speed setting. NOTE: On consoles with speed potentiometers that require a power board, this
light may be seen to flicker even when speed is set to zero MPH. This is due to a small signal being sent from the
console. MC-60 controllers with this console and power board configuration will have RPS 1 clipped to operate
normally and keep the treadmill from running at all times. If this LED is not lit when the speed is set above zero MPH,
but D11 is, it indicates a problem with the console, power board, or wire harness."
Ed from Rhode Island

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lahola1
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Re: DC motor conversion

Post by lahola1 »

edma194,
looks like the info you posted came from the FB SS dig conversion group. I have a few other files from there that may interest you.
As far as mc60 board and PWM, I did not see any info and I am no elec expert so I can't help there but I don't know why you would want to use PWM control instead of a potentiometer. It's so simple. That's what I have on my Smithy Supershop with a 90v DC motor and a Dart control board. It works great.
I have 4 treadmill motor packages in storage. I was careless one day and fried my mc60 board.
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edma194
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Re: DC motor conversion

Post by edma194 »

The most important reason to research PWM for me personally is to learn. Since I have a PowerPro I don't have much motivation to actually try putting a treadmill motor in a headstock. A voltage controller is easy. I have a salvaged MC60 and motor from a treadmill and before I had any info about the controller I had the motor running with a variable AC supply and a full wave bridge. It is that simple, but at low enough speeds I could grab the flywheel and stop the motor with gloved hands (I still can't get that @#$% flywheel off in reverse, I think it may be a press fit).

PWM would maintain torque across the speed range. The typical motor runs in excess of 6000RPM and if installed in a Shopsmith has plenty of power at the high end of the speed range. However, even to get to the ordinary low speed of ~700RPM the motor would be running at 50% power or less. Still decent performance I think, but bringing the spindle speed down to 250RPM and lower may not leave enough useful power. I mentioned above several ways to use a treadmill motor and simple voltage controller in a Shopsmith with decent results, but with some compromises. Now I am looking at this with a comparative eye to the PowerPro performance, if you really want that I don't think a treadmill motor in a conventional headstock will get you there.
Ed from Rhode Island

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lahola1
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Re: DC motor conversion

Post by lahola1 »

the Powerpro motor is pretty robust to get 250-10000 RPM. I don't think your going to find that in any treadmill motor. I also appears to be 2-3X bigger in size/volume of any treadmill motor. Maybe that has something to do with it.
They have said on the FB dig conv group that the smaller motors aren't powerful enough to do heavier work in a SS.
Norman Harrison has a 2.25HP cont duty 130v motor in his. He seems happy with it.
The setup I had on the end of my SS is a 3HP, 130v, 2975RPM ,MC2100 PWM control, with 2"/6" pulleys.With that setup I got 188 RPM @15% and 3564RPM @85% speed at the SS quill.
The smaller motors have the mc60; larger motors have the mc2100 control generally.
I don't think your going to get anywhere near what you are looking for out of your mc60 setup but I think you can get close with a larger motor ( I've seen them up to 4.25 hp) and an mc2100.
I've found mine on craigslist free section. They come up 3-4 times a year where I live. Generally, the treadmills with the big panels with lots of speed buttons are the big motor/mc2100 ones.
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