DC motor conversion

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edma194
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Re: DC motor conversion

Post by edma194 »

bill50cal wrote: ↑Tue Aug 24, 2021 6:14 pm I would never think of trying to convert a shopsmith to a metal lathe. if you have spent any time on a metal lathe you will soon find out the shopsmith is not near strong enough for the forces put into the tool holder and that is just a start as to why i would not do it.
I agree with you. I threw lathe into the mix for no particular reason. I actually have a mini-lathe but never used it. The most I've done in metal turning is use a grindstone to turn a motor shaft down by 1/16" while it ran. I do want to do some small scale milling, but I think the speed reducer should be sufficient for my needs.
Ed from Rhode Island

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RFGuy
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Re: DC motor conversion

Post by RFGuy »

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

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One of the things I'd say is a clear advantage of a DC conversion is a reversible motor. But I've been studying this thread: G.E. Motor Reversing and it looks quite feasible to add reverse operation. I think if I read that thread over carefully 10 more times I'd understand it well enough to pay a motor shop to do it for me.
Ed from Rhode Island

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Re: DC motor conversion

Post by JPG »

Other than locating and separating the start winding, it is merely a matter of reversing the start winding polarity.
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10
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edma194
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Re: DC motor conversion

Post by edma194 »

JPG wrote: ↑Thu Aug 26, 2021 12:05 pm Other than locating and separating the start winding, it is merely a matter of reversing the start winding polarity.
I'm sure it's just that simple. But for now it looks like this blackboard from The Day the Earth Stood Still to me.
Ed from Rhode Island

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Sawsmith 2000 Ultra, 10ER in progress, 10ER undetermined future
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JPG
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Re: DC motor conversion

Post by JPG »

Looks like some stuff I was exposed to back in college.
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10
E[/size](SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange
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Re: DC motor conversion

Post by RFGuy »

The 1951 movie or the 2008 remake? I really enjoyed the 2008 movie, but had to go to your link to remember the scene. Below is an explanation of where the equations came from...

Excerpt from: https://www.quora.com/What-was-the-math ... tood-Still
"The scene in the 1951 movie took place in the home of Professor Barnhardt, a character who was modelled after Albert Einstein. Barnhardt had a blackboard that contained equations from Einstein's theory of gravity. The alien changed some of the equations to explain how his star ship could travel between the planets.

The 2008 remake of "The Day the Earth Stood Still" contains equations from a paper published by William Hiscock and his graduate student Hector Calderon. Hiscock is director of NASA's Montana Space Grant Consortium. Calderon is visiting assistant professor of physics at Carleton College in Northfield, Minnesota.

The new movie needed to update the equations so they represented the cutting edge of knowledge in 2008 and not Einstein's equations from 60 years earlier. To find such equations, Seth Shostak, senior astronomer at the SETI Institute and a scientific consultant for the movie, contacted Calderon and Hiscock. Shostak said the new script mentions the "Big Rip" possibility in General Relativity, and that led him to read their paper about it.

The Big Rip refers to the possibility that galaxies, stars, planets and atoms would be ripped apart and their parts accelerate away from each other at ever-increasing speeds due to the "dark energy" in the universe."
📶RF Guy

Mark V 520 (Bought New '98) | 4" jointer | 6" beltsander | 12" planer | bandsaw | router table | speed reducer | univ. tool rest
Porter Cable 12" Compound Miter Saw | Rikon 8" Low Speed Bench Grinder w/CBN wheels | Jessem Clear-Cut TS™ Stock Guides
Festool (Emerald): DF 500 Q | RO 150 FEQ | OF 1400 EQ | TS 55 REQ | CT 26 E
DC3300 | Shopvac w/ClearVue CV06 Mini Cyclone | JDS AirTech 2000 | Sundstrom PAPR | Dylos DC1100 Pro particulate monitor
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Re: DC motor conversion

Post by DLB »

edma194 wrote: ↑Thu Aug 26, 2021 12:01 pm One of the things I'd say is a clear advantage of a DC conversion is a reversible motor. But I've been studying this thread: G.E. Motor Reversing and it looks quite feasible to add reverse operation. I think if I read that thread over carefully 10 more times I'd understand it well enough to pay a motor shop to do it for me.
Even easier on your PowerPro. ;) IIRC I read that the start winding connections are not accessible on all motors (Emerson?). I'm sure that depends a little on one's definition of accessible...

- David
edma194
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Re: DC motor conversion

Post by edma194 »

DLB wrote: ↑Thu Aug 26, 2021 2:14 pm Even easier on your PowerPro.

- David
That's the best DC motor conversion available for the Shopsmith. You may have noticed it's a bit pricey though. A PowerPro upgrade kit cost me more than all the used Shopsmiths I've obtained.
Ed from Rhode Island

Mark V 510 with PowerPro headstock, Mark V Greenie with 510 headstock, Mark V 500 in progress
Sawsmith 2000 Ultra, 10ER in progress, 10ER undetermined future
edma194
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Re: DC motor conversion

Post by edma194 »

Up to this point in the story I had only looked at simple voltage controllers for the motors. These will produce maximum power at maximum speed. What the maximum speed is as a practical matter is unknown. I think without additional cooling running them at 100+ volts will overheat the motor, and I don't think it's designed for that kind of duty at all.

Summing up, the use of treadmill motor with simple voltage control in a Shopsmith has limited appeal. It will allow higher top speeds with possibly more power, but somewhere below 1500RPM power is lost rapidly when reducing spindle speed. At the high end there are questions about the duty cycle, heat production, and life of the motor.

A possible compromise is to limit the voltage to around 50% so the motor tops at 3450RPM like a Shopsmith motor. This makes it a cheap motor replacement, certainly with diminished performance overall. At least in this derated mode the motor is unlikely to overheat or burn out it's bearings rapidly. I don't think in this mode the motor would keep up with 1-1/8 AC induction motor normally found in Shopsmiths when heavily loaded though. The result will be a low performing Shopsmith, I suppose still an option if you can't afford to replace a burned out AC motor.

As another option, if a treadmill motor was installed with another reduction step of approximately 2:1 so the Shopsmith speed controller is being run at about 3450 RPM at with the motor at full power there could be increased power performance across the range of Shopsmith speeds and the ability to further reduce speed with voltage control, albeit while sacrificing power. I don't know if there's room in the headstock for another step down pulley. The motors typically have 1" Poly-V type multi-grooved pulley. I suppose this could be positioned fairly close to a 2" pulley, no idea what the minimum belt length available is. It certainly adds another level of complexity.

In general, the use of treadmill motor with simple voltage control in a multi-purpose application like the Shopsmith will likely lead to disappointment. DC motors don't perform the same way as AC synchronous motors and really aren't designed for this purpose. Still, the low price of the motor, often $0, gives it some appeal.

OTOH a treadmill motor could be a fine motor replacement in tools where variable speed is not needed, or only a limited speed range is needed.
Ed from Rhode Island

Mark V 510 with PowerPro headstock, Mark V Greenie with 510 headstock, Mark V 500 in progress
Sawsmith 2000 Ultra, 10ER in progress, 10ER undetermined future
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