Variable speed motor for lpi?

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sameal
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Variable speed motor for lpi?

Post: # 42729Unread post sameal
Thu May 26, 2016 11:12 am

Hello.
Im looking for a variable speed motor to adapt to a presto 8dg.

Any suggestions?

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Soulbear
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Re: Variable speed motor for lpi?

Post: # 42736Unread post Soulbear
Thu May 26, 2016 12:40 pm

Hi Sameal,
I'm currently having a Play Around with This Type of Motor/Gearbox Combination.
Lathe Feedscrew Drive Motor 24V 27RPM A.jpg
Lathe Leadscrew Motor1.jpg
Lathe Feedscrew Motor2.jpg
I actually bought this from a U.K. based company, but have since found them sold much cheaper and for far less cost on the Bay. The Ebay Seller is either Sellerbible or Assisi Electrics. They come in various Voltage and Speed Combinations from around 2RPM up to 500RPM. I'm currently checking out the 27RPM 24Volt Motor/Gearbox Combination, and seeing what it will Slow Down to without Juddering when Powered from a PWM Speed Controller. I got it to around 4RPM at 6Volts ish. Depending on what Pitch Leadscrew I finally settle on, I may go to the 50RPM Output Model, as I said it's Experimentation and Playtime at the Moment. It's not noisy, and with the Mounting Rubbers theres Very Little Vibration, and Driving the Leadscrew with a Belt Drive, should Further Reduce any Potential Vibration Transfer Problems. If you go on the Bay and Type in DC Gearmotor, I'm pretty sure you'll end up with Someone who sells these, as there are quite a number of Sellers of these items.
Hope This Helps.
:wink: :P :D Soulbear
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mischmerz
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Re: Variable speed motor for lpi?

Post: # 42745Unread post mischmerz
Thu May 26, 2016 6:47 pm

I did a lot of math on this question. The adjustable PWM range doesn't give you enough torque to cover all necessary revolutions for 33 1/3, 45 and 78rpm. Even if you concentrate on 33 and 45, you would need to be able to manually "rewind" the cutter head because the motor doesn't give you enough speed to do it for you. This motor can be (reliably) run at about 35% PWM. I tried a 5rpm and 10rpm motors and you'll get either the right speed to cut 33 and 45 .. but not 78 and no automatic rewind, or you can't get it slow enough for 20minutes at 33 1/3.

If you have the possibility to uncouple the cutting head from the lead screw to push it back manually, it may work for you if you just need the lower speeds. Calculated for a 1mm pitch lead screw.

Michaela

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sameal
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Re: Variable speed motor for lpi?

Post: # 42746Unread post sameal
Thu May 26, 2016 7:57 pm

Hrm. This is a bit complex.

So if not the pictured motor, what options do i have?

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markrob
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Re: Variable speed motor for lpi?

Post: # 42749Unread post markrob
Thu May 26, 2016 8:58 pm

Hi,

Its not so easy if you want to cover all conditions with a single motor and gear ratio. You really need a closed loop servo motor with tach feedback to do this right. Even then, its hard to get much better than 50:1 speed range. You won't come close to that range with a simple open loop PWM controller. That is really no different than driving the motor with a variable DC power supply. If you go with a closed loop system, you will get good repeatability when setting the LPI since you'll be able to command an exact speed. Open loop, its a crap shoot. If you want to cover the entire speed range required, you will probably need a dual motor setup or some sort of gear shift arrangement for lead in/lead out.

First thing to do is figure out the torque needed. Then you can narrow down your search. Pittman makes some very nice small gearhead brush and brushless DC motors , but once you add in a drive, you might see some sticker shock. eBay might be you friend here. Is this to be a pro application or are you looking for a budget solution?

Mark

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sameal
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Re: Variable speed motor for lpi?

Post: # 42755Unread post sameal
Thu May 26, 2016 10:30 pm

Well, as pro as i can go with this setup i suppose. It's a presto 8dg, so im limited a little bit. I don't have customers lined up or anything, but i would like a setup nice enough to get good results.

I guess id be looking to spend less then a grand if i could. But if theres something thats going to really get me there, i could save up over time.

I would have plenty of room in the cabinet for a dual motor setup.

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mischmerz
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Re: Variable speed motor for lpi?

Post: # 42765Unread post mischmerz
Fri May 27, 2016 12:15 am

The other way to go .. and I haven't investigated this yet, would be a stepper motor. Lots of torque, very good accuracy and highly flexible in terms of different speeds. Disadvantages are: More complicated to set up and to run - most likely need a computer (Arduino?), those things are noisy, you'll need good sound insulation and well, they are steppers, so there is no constant motion. But with the right stepper motor, one should be able to move the lead screw very flexible from very low to very fast.

I think.

Michaela

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Soulbear
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Re: Variable speed motor for lpi?

Post: # 42776Unread post Soulbear
Fri May 27, 2016 1:09 pm

Hi Michaela and Sameal,
Just some more info on the Gearmotor I'm Playing and Experimenting with. Experimentation being the Operative Word. I re-checked the values I mentioned in the earlier post and found the RPM was in fact 3.5RPM and I said this was at 6 Volts. The 6 Volts I mentioned was erroneous, what I actually meant to Type was 6%, this 6% being the indicated Duty Cycle of the PWM Speed Controller Display. Now for some other figures, I have a Small Centre Tapped Transformer Outputing 22.5 Volts A.C. each side through 2x 10 Amp Rated Diodes, and Smoothed with a Largish 10,000mf Electrolytic Capacitor. Now we'd expect the Voltage to be approaching the Peak of 1.41 ish the RMS Value of 22.5 = 31.7Volts ish, and in fact I'm actually reading 30.5 volts, all Values Read from a Fluke77 Multimeter, so I reckon they're right. Granted this is somewhat higher than the Motor's 24 Volt Rating, but I've run it at 50% Duty Cycle for 6 Full Days and Nights and The Thing has not gotten even remotely warm to the touch. Now I've not tested the Voltage with the Motor Fully Loaded as I've only got one pair of Hands. I would however suspect that once the motor is loaded, that this voltage will drop slightly, or more significantly, depending upon the VA Rating of the Transformer. Now as I bought my Transformer Second-Hand, with no rating plate, I have only the Sellers description to go on, and so I'm saying it's a 75VA Transformer. As for the Motor being Under-Nourished in the Grunt Department, well I can only share with you some of the results of my Experiments. I attached a Quite Large Timing Pulley to the end of around 8 inches of 3/8th Steel Bar and Taped this to the Output Shaft and Switched the Motor On. It swung it around with no trouble. I then raided my Larder for a 1.5Kg Bag of Baking Flour, I tied String around the Bag, Looped the other end of the String around the Gearbox Timing Pulley, and held on to the Motor. It managed to lift the 1.5Kg Flour Bag through a distance of around a Metre, I only stopped because I was in Danger of either getting entangled, or making a Real Mess . And YES this was at the aforementioned 6% Duty Cycle. I don't know How Stiff the Leadscrew you're proposing to Drive will be, but I cannot imagine it will need anywhere near the same effort from the Motor, As for Speed, again I can only share with you the Results of my Kitchen-Laboratory Tests and that is, at 100% Duty Cycle the this 27RPM Rated Motor actually Hits 65RPM. In this little PDF I've included the Data Sheet Lifted from here http://motionco.co.uk/ along with some images of my Somewhat "Nutty Professor" Type Experimentation. Additional information also, I've also Experimented with driving the Motor with It being connected to 2 of these Controllers simultaneously, the outputs of each being fed through a Power Diode to prevent "Reverse Powering" the PWM Controller set at a the Lower Duty Cycle, and thence to the Motor, this was done in an effort to resolve any "Switching Delay" and resultant "Groove Defects", when changing over from High Speed Lead-In/Run-Out to Low Speed Cutting. I can say that the Transition occurred very smoothly with no Ill-effects to either Motor or PWM Speed Controllers. For the budget concious I do think this Offers a Decent Solution to Driving a Fixed Pitch Leadscrew, with the added bonus that with a bit of trial and error and a little calculation, if you know your Leadscrew Pitch, you can Match the Duty Cycle Display to the Actual Cutting Time, and Maximise the Area you can cut.
Gearmotor Data2.pdf
Might be worth thinking about eh?
:wink: :P :D Soulbear
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mischmerz
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Re: Variable speed motor for lpi?

Post: # 42779Unread post mischmerz
Fri May 27, 2016 3:09 pm

Hmm .. thanks for the in-depth info @soulbear . My motors are 12V and I am running them at 12V with a PWM controller. The have no torque at all below 20% duty cycle. If I understand you correctly, you "over" powered your motors?

m.

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Soulbear
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Re: Variable speed motor for lpi?

Post: # 42781Unread post Soulbear
Fri May 27, 2016 3:34 pm

Hi Michaela,
In the sense that the Drive Voltage is 25% Higher than Motor Specification, Yes, But as I noted, I've let it run Night and Day Continuously with no Ill-Effects. Not the merest suggestion of Overheating, though I might add, the Higher Drive Voltage must also have Increased the Upper Output RPM a Goodly Chunk. But 65RPM is what I got when I Taped an Indexing Mark of some Masking Tape, on the edge of the Timing Pulley and then Set my Kitchen Cooking Timer/Alarm to 60 Seconds and started counting. I repeated this 100% Duty Cycle "High Speed" check 3 Times so I know the value I'm quoting is correct.
Best Regards :wink: :P :D Soulbear

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mischmerz
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Re: Variable speed motor for lpi?

Post: # 42784Unread post mischmerz
Sat May 28, 2016 1:06 am

All right. I am going to try this. Will report back.

m.

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Soulbear
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Re: Variable speed motor for lpi?

Post: # 42786Unread post Soulbear
Sat May 28, 2016 6:57 am

Hi Michaela,
Yup please do that, I think you could be pleasantly suprised. The Motor I bought from Motionco (Link in earlier post) was Given the Type Number GMW40W290. The Proprietor is called Gavin and He also Supplies a mounting bracket for this Gearmotor (Too Pricey if you asked me) Thats if you don't fancy making a Bracket for yourself (I made mine fairly easily from Aluminium Angle). The China based Ebay seller who sells these Gearmotors at a much lower cost is sellerbible(272742) From this supplier, the Gearmotor is designated 634JSX290-31ZY
This is the PWM Controller/Display I'm using:-
PWM and Display.JPG
This again came from China and the Ebay Seller was globaldealshop(9543) and you'll find them for under 10 Bucks. I went way back and checked into my purchase history, and found that the Transformer that I mentioned I'm using, was actually sold to me as a 50VA Transformer, I knew it was under 100VA and thought it was 75VA for whatever reason. Lordy my memory keeps playin' tricks on me HUMPF!! :( Anyhow M, I look forward with real interest to reading the results of your own Obsevations/Testing/Experimentation with this potentially promising Low Cost "Variable Speed Leadscrew Drive" set-up.
Best Regards
:wink: :P :D Soulbear
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Soulbear
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Re: Variable speed motor for lpi?

Post: # 42788Unread post Soulbear
Sat May 28, 2016 8:04 am

Hi M,
I forgot to add this image (Lordy, I'd forget my head if it was loose!!) :-
PWM Reverse Power Diodes1.jpg
This is my Set-up to run the Gearmotor at 2 Speeds without a Switching/Changeover Delay which would show up within the Grooves of the Finished Cut. One of the PWM Controllers can be Set at a much Higher Duty Cycle for the Lead-in and Run-out, the other PWM Controller being set at a Lower Duty Cycle for Cutting. On the changeover you would "Make" the Supply to 1 Controller before you "Break" the Supply to the Other, I'm thinking of ways to use one of these Cam Operated Switch Cycle Timers in conjunction with Leadscrew/Overhead Mounted Microswitches, to Semi-Automate this Changeover:-
Switch Cycle Timer.jpg
Ordinarily the Switch Cycle Timer might have a Clock/Motor to Drive it, but I've got a 50:1 Mechanical Worm Gearbox which I'm figuring out how to connect to the Leadscrew Drive System. A much simpler and easier solution which I'm also considering, would be to simply use a couple of Momentary Push Buttons Te He :P . The 2 Power Diodes Prevent either PWM Controller Reverse Powering each other. I've tested it. it's very "Old School" but it actually works a real treat. I know the Clever Boys and Girls out there Interweb Land would achieve the same Outcome/Results, Probably with an Arduino, a PIC Controller and some Fancy Pants bits of Coding, but I'm too Long in the Tooth to Start that Coding Mularkey, to me Coding is a Strange and Mysterious Black Art. and Akin to Witchcraft!!
:wink: :P :D Soulbear
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rsimms3
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Re: Variable speed motor for lpi?

Post: # 42789Unread post rsimms3
Sat May 28, 2016 8:25 am

Soulbear - Just so I make sure I'm reading this correctly, your tests are open loop and without a comparable lathe/feedscrew application? I see tests on consistent speed over a period of time and amount of torque, but not at the same time to account for loss of speed over time under load. Everything I have heard reading Markrob's posts and talking to others about DC motors is that they aren't consistent under load without a feedback loop, even with high torque. Maybe I'm not reading your posts correctly, but any loss of consistent RPM at any point in use with a feedscrew could result in overcut given the type of tolerances we are considering for the application.

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markrob
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Re: Variable speed motor for lpi?

Post: # 42790Unread post markrob
Sat May 28, 2016 8:55 am

Hi,

Running a higher voltage supply rail will not cause an increase in low duty cycle torque with a given motor. All you'll end up doing is running a shorter duty cycle to apply the same effective voltage to the motor. Open loop PWM is just a more efficient way to apply power to the motor as opposed to a variable analog DC supply. If you intend to run open loop, you will have to vastly over spec the motor rating so that its is less affected by shaft load.

In a DC permanent magnet motor, torque is directly proportional to motor current. At very low drive voltages, you can't force enough current into the motor to produce the needed torque. If you close the loop, the servo will track to the correct voltage to maintain speed as the load changes. There are some open loop drives that do IR compensation. These provide some degree of speed regulation by sensing the motor current and commanded speed and then compensate for the drop in across the motor internal winding resistance.

You really want to scale the shaft RPM of your motor such that it is running in a more reasonable voltage range during cutting. That would be in the range of 100-250 LPI, for example ( a 2.5:1 speed range). If you are running a 12 Vdc motor, you would want to scale the shaft speed speed so that at 12 Vdc, you are running at the 100 LPI rate. That would put you in the 4.8 Vdc range at 250 LPI. The problem is that you will need to overdrive the motor too much to make 5 LPI or so for the leadin/leadout (about 20:1 above the nominal voltage rating). That's why you need some sort of gear shift or dual motor, or high performance servo drive to handle the wide speed range. If you give up on doing high speed leadin/lead out, you should be able scale an open loop PWM to work for cutting if you size the motor correctly.

The stepper motor idea is a good one but, the mechanical noise it generates might be too much to bear. There was somebody here that has tried using the stepper as a 2 phase brushless motor with good reported results. Microstepping starts to approach this mode and if fine enough, might work. This could be a poor man's solution, but by the time you go there, a standard 3 phase BLDC might make more sense.

Mark

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Soulbear
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Re: Variable speed motor for lpi?

Post: # 42791Unread post Soulbear
Sat May 28, 2016 10:21 am

Hi There Rsimms3,
Yes, I wouldn't dream of calling into question the Expert and Erudite Analysis Of Closed Loop Systems described in depth both here, and elswhere on the Forum by Markrob, and I concur, that would be the way to go if you are looking for the Nth degree of Precision and Control. I can neither measure, or even reasonably estimate, what Variance/Drag there may be on the Loading of the Leadscrew at any given Radius on a Disc or Amplitude of Audio Delivered to the Cutterhead. Whatever measure is used whether it be Amps, Milliamps,Watts, Milliwatts, Foot-Pounds, Ounce-Inches, Newton-Metres, Millinewton-Millimeter or a Star Trek Type Graviometricspondulycations. Then of course one would have to examine, how much this Variance in the Load Changes, translated into Variance within the Cut Groove. Nor am I suggesting there aren't plentiful drawbacks on using this system. If your'e looking to find faults with this Set-up then you surely will. I'm not advocating it's use or suggesting that this is the only way to go, but I'm merely sharing the results with Sameal (The one who Originally asked the Question) and Michaela, and anyone else interested enough to read the post, of my own Efforts and Observations into the Examination of this Issue. The drawbacks are quite numerous, and I'm completely aware of most of them. I would ask you what happens with Platter Driven Overheads, Presto's, Rek O Kuts and the like? Notwithstanding the "Inertial Flywheel" of the Platter, I'm sure if if you wanted to "Split Hairs" you maybe could find faults if you examined in detail, Variance in the LPI, caused by Load Changes when using a machine such as this too. Given that the Gear Reduction of these Little Gearmotor Models vary Between 200 and 300:1, I think any concerns about Hypothetical Load Changes on a Leadscrew and the Resultant Effects whilst probably measurable, is also "Nit-Picking" in the Extreme, or to Para-phrase my late-lamented Granny "Utter and Total Bollocks" No, I'm fully aware this is not a High-Tech approach I grant you, if I wanted one of those, I'd visit Flokason in Switzerland and buy a Great System from Florian Kaufmann. This approach to driving a Leadscrew though, might just be OK to those of us who are Budget Conscious, and not looking to own a Neumann, nor trying to make a Livelihood, from what to many of us, is simply a stimulating Hobby or Pastime
:wink: :P :D Soulbear

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Ciuens
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Re: Variable speed motor for lpi?

Post: # 42792Unread post Ciuens
Sat May 28, 2016 10:32 am

I use a small stepper motor with internal reduction. Apparently seems weak, but with incredible 800g of torque,low vibration, extreme precision.
28byj-48 is the model.
with this little giant, I can reach 0.2RPM to the maximum 30rpm, using 96 half steep, veeeeery smoth.
Look at my videos, all using this stepper motor.
The price? US $ 5 + US $ 5 for the small arduino, a bargain, right?

Cheers

Ciuens Silva

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mischmerz
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Re: Variable speed motor for lpi?

Post: # 42793Unread post mischmerz
Sat May 28, 2016 10:39 am

@Ciuens yes - that seems to be a viable solutions for smaller overheads. But maybe not enough torque to drive bigger rigs. I was wondering, how low 3 phase BLDC motors can be throttled? I was looking at some motors, they are rated something like 24V 3000rpm - could those be throttled down to .. say 2rpm and provide enough torque?

m.

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Soulbear
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Re: Variable speed motor for lpi?

Post: # 42794Unread post Soulbear
Sat May 28, 2016 10:43 am

Hi Ciuens,
Soulbear wrote:I know the Clever Boys and Girls out there in Interweb Land would achieve the same Outcome/Results, Probably with an Arduino, a PIC Controller and some Fancy Pants bits of Coding, but I'm too Long in the Tooth to Start that Coding Mularkey,
Ciuens wrote:The price? US $ 5 + US $ 5 for the small arduino, a bargain, right?
Nuff Said Te He!
:wink: :P :D Soulbear

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Ciuens
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Re: Variable speed motor for lpi?

Post: # 42795Unread post Ciuens
Sat May 28, 2016 10:45 am

mischmerz wrote:@Ciuens yes - that seems to be a viable solutions for smaller overheads. But maybe not enough torque to drive bigger rigs. I was wondering, how low 3 phase BLDC motors can be throttled? I was looking at some motors, they are rated something like 24V 3000rpm - could those be throttled down to .. say 2rpm and provide enough torque?

m.

800g of torque is a lot. remember that this torque is to rotate the shaft, not to pull the weight. If any lathe need more than that to move, certainly has problems.
do the test, after all, U$ 10 is nothing. :D

Ciuens

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