# Drill press motor swap

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MRA:

I'm definitely not the first to do this. I've been wanting to try this on something reasonably "safe", before biting the bullet and re-powering a lathe or mill. So far its' had its' ups and downs, but getting a more powerful motor in a smaller form factor with variable speed to boot... I think that so far my biggest gripe is that wile you CAN vary the speed, it's in 100rpm steps. When you consider that this thing was designed to power an industrial sewing machine, I guess that 100rpm steps was close enough. It's obviously close enough for lathe, mill, and sanding belt applications, as I've seen it used to re-power all those devices.

I took my foot pedal control apart last night and checked the signal voltages. My VEVOR servo voltages agree with the voltages listed in the Hobby Machinist thread link that I provided above and my "manual" matched his.
At 2.4V on the signal wire, my signal wire was yellow, the motor started running at the minimum speed setting.
At 4.2 volts the motor was running at the maximum speed setting.

If you want to know how I arrived at my resistor values, read the long-winded explanation below - if you're not interested I'll see you later.
We building a voltage divider circuit. Knowing the required voltage values at the various points in my voltage divider, I can now calculate the required resistor values. They probably WON'T match standard resistor values, so I'll need to get close then run the voltage calculations again. I need to be sure that the voltage at the wiper of the pot will be close to but still below 2.4V at the minimum setting, and close to but still above the 4.2V at the maximum setting. Then I need to find a standard sized resistor that will give me the 0.8V drop that I need between the 5.0V source voltage and the 4.2V needed at the pot. Eazee-peazee, a 1st year electrical engineering student can do it. The problem is that I haven't been one of those in about 40 years, so I need to remember how to do that - but I'll get it figured out.

What we are building is a voltage divider that has 3 resistors and we know that voltage values at each end of the resistor and we know the value of one of the resistors - the pot, mines 10K. If we play fast and loose with this, and assume and/or ignore a lot of stuff that the 1st year electrical engineering student wouldn't be allowed to do, we can get close enough without too much brain sweat.

We know that the voltage drop across the 10K pot is 1.8V, (4.2V-2.4V), that gives us a rough number of a 0.18V per 10K of resistor. We want a 2.4V drop after the pot, 2.4V/1.8V tells us that we need a 13.3K resistor. We can get a 13K or a 15K, I don't know what I've got in my box right now, let's go with a 13K as the will give us a little lower voltage and ensure that when the pot is turned to 0 that the speed is 0. On the other end we need a 0.8V drop above the pot. 0.8V/1.8V tells us we need a 4.4K resistor, the closest standard resistor valve is probably 4.7K. OK, let's look at this voltage divider using these resistor values and the 5.0V input power and see what our new high/low voltages are for the pot wiper. Using those resistor values we get an approximate voltage drop of 1.80V per 10K of resistance. Using this value we can do a sanity check to see if this thing will turn off at the minimum pot position. Our 13K resistor will give us a 2.34V drop, this is definitely below the measured 2.4 volts so it will turn off. What about our pot wiper voltages, what will it see? We know on the bottom end it will be at 2.34V, on the upper end it will be at 4.14V which is CLOSE to 4.2V, don't know if it's close enough though. I'll have to look through my resistor stash and see if I can bread-board this and see if it's CLOSE ENOUGH. Sometimes calculated values just DON'T work in the real world, but not often.

I am going to include the Run/Stop switch option, and the effects of this is one of those things that I'm going to ignore that the 1st year electrical engineering student couldn't. The resistor used for it is a parallel circuit and WILL affect the speed control side. I'm going to do the same thing the OP in the Hobby Machinist thread did, make it a large resistor. (10-20 times the resistance of the speed pot side should work. Like us electricity is lazy and seeks the path of least resistance.) That does 2 things for us, first we can effectively ignore the resistor in OUR calculations, and second it ensures the when the Run/Stop switch it turned off the voltage that the signal wire sees will definitely be below the 2.4V minimum speed voltage.

Just for funzies we can determine the wattage our resistors need to handle. Watts=(V^2)/R, if V=5, and R=4.7K+10K+13K then Watts=25/27700=0.9mW, 1/4W or 1/8W resistors will work JUST fine.

Don

Old age MUST be creeping up on me, over 68 dontchaknow, I seem to have misplaced the small multi-compartment box containing MOST of my electronic parts. I could swear that I've seen that box within the last couple of weeks. But I've searched all of the likely places where it could/should be hiding, but with no joy. I may just have to BUY the parts I need. I did get the box that will hold the Run/Stop switch and the Speed Adjust Pot printed over the weekend, along with the bracket that mounts it to the servo drive.

I know. I know - No pictures so it didn't ACTUALLY happen. I'd say trust me, I was there it DID happen, but with the temporary loss of my electronic gizmo type stuff....
Who knows, maybe it didn't? I'll check when I get home, then I'll let you know.

Don

I bought one of those servo motors and controllers a while back and use it for test setups. I was curious about the actual torque output because there was conflicting info on the labels and the 2 page "manual".

I rigged up a friction prony brake to measure torque and rpm and current draw. I was impressed with the flatness of the torque curve. Makes the motor a lot more useable. If I were adapting this to a drill press I think I would a 2 to 1 speed step down (torque increase) in the belts and then just divide the rpm from the controller by 2 in my head.

Here is the link to the post and video.
https://www.homemodelenginemachinis...st-a-3-4-hp-sewing-machine-motor-video.34494/

Lloyd:

I read that that guy. Your investigation of the torque curve was one of the things that convinced me to give the sewing machine servo motor idea a try.

I'm going to try it with the rpm's at 1:1-ish first and see if it's got enough "ooomph" for my purposes. If it comes up lacking, then I'll go for the belt reduction and do the math in my head as you suggested.

Don

because there was conflicting info on the labels and the 2 page "manual".
Conflicting information in a Chinese "manual"? Surely you jest!

I have looked for my electronics parts and am not able to find them, so I ordered a resistor assortment kit. I'm pretty sure that my original parts will magically reappear about a day before the replacements arrive. I believe that Murphy had a corollary covering that probability.

I have looked for my electronics parts and am not able to find them, so I ordered a resistor assortment kit. I'm pretty sure that my original parts will magically reappear about a day before the replacements arrive. I believe that Murphy had a corollary covering that probability.

Good luck on finding that missing box, but admitting defeat and buying that replacement resistor assortment is the first step to a healthy recovery. I am dealing with a "missing box," too. (Boxes??) I am almost at the point where I will admit that it never really existed and must erase the entire event from my mind. It won't be the first time. It can be cathartic.

The resistor assortment arrived last Friday. Twenty of each from1 ohm to 1M ohm, that's a LOT of resistors. I found some LEGO parts boxes on-line that will do a bang-up job of keeping them separated - as long as I don't do something stupid like knock the boxes over when they're open, they showed up Monday. Transferring the resistors from their tapes in their little baggies into the boxes is going to take a while. I can only do about 100 resistors, then I start going Bonkers and have to do something else. (I wouldn't survive as an assembly-line worker.)

I tried a quick & dirty hook-up to the pot over the weekend, and it failed miserably. It failed mechanically, the leads broke, I never got to the point of testing the circuit to see if it would actually function. I went through my stash of perf-board, which I was actually able to find, and am currently working on building a small PC board that will contain all the connections. I didn't leave a LOT of room around the parts in my 3D printed box and I'm trying to fit the board into the box I already have printed. I think I came up with a workable solution last night. I kept screwing up my circuit board connections, forgetting which side of the board I was working from when drawing it. (Really SHOULD have done it in CAD instead of trying to just sketch it.)

I cut the perf-board to fit, and now I just need to get it loaded and connected. The board is ELL shaped and about 17x25mm, with an 8x10mm chunk cut out of one corner to clear one of the cover's mounting posts. I've got PLENTY of room between the board and the body of the pot on the board's component side - maybe a whole 5mm? So the 1/4W resistors will have oodles of room to live there.

Don

Don or others,

Don't know if anyone else has an excess supply ... but I have found a use for my empty medicine (prescription) bottles (with labels removed, of course). They are perfect for for organizing small parts, ranging from resistors to m3 screws. I use a sharpie (permanent) marker to write the value or type - if I had a label maker, I would probably do that instead, but the marker works.

Hope this is a helpful idea for others, but of course, mileage will vary ...

Andy:

I used to do that, still do with some stuff, stored parts of my airbrush in one so I wouldn't lose it - now IT's gone walkabout.

I got the LEGO boxes because they had 28 compartments in each box. I will eventually get the resistors sorted by ranges, 1 to 82 ohms, 100 to 8.2K ohms, and 10K to 1M ohms. It was less than \$20 for the 1400+ resistor assortment. (Sorting them at 100 resistors per night, it should only take me a couple weeks to get it done.) What I'm going to do with twenty 1/4 watt 1 ohm resistors, I don't know - but I GOT'em.

Don

I hear you. My heirs are going to be sorting through boxes of 100 this and that and the other ... but it was a killer deal, and it got me the one part I needed at the time, and surely I'll need some of these others sooner or later!

I'll need some of these others sooner or later!
That's kinda' what I was thinking. But now I'm not so sure about the 1.0, 1.2, 1.5, 2.2, 3.3, 3.9, 4.7....etc., etc., ohm resistors. I've got a feeling that the lower end of 1-820 ohm resistor box won't get used very often.

But now that I think about it, they MIGHT be useful to get a voltage drop for a small load. I've been wondering how I could use an Arduino to sense when a small gearmotor application (N20 motor) was at the end of its' travel - without using limit switches when you have no room for the limits. Those motors have a stall current of about 0.6A and normally run in the mA range. Yup, that just might work, monitoring the voltage drop across that resistor might just be the way.

OK, last night I sorted enough resistors to be able to try putting together my perf-board comglomeration... It didn't work, the board that is, I wasn't getting ANY voltage from the wiper of the pot. That I think is due to a couple of problems, I think I screwed up the switch while trying to solder the leads onto it. My shaking hand couldn't apply the solder, kept missing, and I had the soldering iron on the switch WAY too long. I think I probably screwed up the perf-board connections too. I was working from a sketch, yeah - my drawing, barely legible. This perf-board is individual solder pads on both sides of the board and I think I confused which edge of the board I should have been counting pads from.

My neurologist and I disagree as to what's doing OK regarding my tremor. He's of the opinion that if I can still feed myself I'm doing OK. I set the bar a little higher, I'd like to be able to at least read my own writing - that can be a real challenge at times.

I did have an epiphany though last night while working on this, or maybe I was just channeling a Gibbs/DiNozzo moment? You know, where Tony gets smacked up-side the head? (With me being the smackee, not the smacker.) A tutorial on TIG welding from the Fabrication Series flashed through my head, and I remembered him harping on arm/wrist placement. That you need to get comfortable with your arms resting on something solid. I got to wondering if TIG techniques would apply to soldering... THEY DO, THEY DO!!!! I was able to make good looking joints on a perf-board with a 0.1" pitch, that's 2.54mm for you Imperially challenged folk. I WON"T be doing any surface mount PC building, but I CAN build a through-hole board. Even it it is only one joint per set-up, one joint at a time is better than none ever.

I started out the night trying to use one of the 3rd hand set-up, you know - the alligator clips on swivel joints. That didn't work for me, too high, and my hands kept shaking because my arms weren't steady enough. When I WAS able to make a joint it was crappy looking and had the heat on the joint WAY too long. I wound up working with the board at about a 45° angle, slightly above the workbench top, with my arms resting on the workbench. I've got to figure out a better way to hold the board. I was still using the 3rd hand to hold it and it was a ROYAL PITA to set up. (Plus, you know, alligator clips?)

By the time I got done and got the board installed on the drill press it was about 10:00 PM. So when it didn't work I didn't do much trouble-shooting, just took a few voltage readings. I've got 5V coming into the board, and 5V on one side of the switch - Nada on the other side, in either switch position. I've got 0V on the signal lead, that could be me screwing up the board connections when going from solder side of the board to component side. I don't remember checking to see if I had any voltage on the wiper of the pot, I'll have to check that tonight.

So, a couple of steps forward, and at least one step back.

Don

I remember many years ago when I took the one and only class I've ever had in welding (community college, continuing education type class) - it was incredible to understand how much of the struggles I had been having could be solved simply by making sure I had a way to support my arm. Good insight to apply this to soldering - I will go and do likewise!

I remember many years ago when I took the one and only class I've ever had in welding (community college, continuing education type class) - it was incredible to understand how much of the struggles I had been having could be solved simply by making sure I had a way to support my arm. Good insight to apply this to soldering - I will go and do likewise!

Was introduced to the concept when I was taking a pressure welding class.
Don't always use it but when I really want those nice clean welds - - - - it sure does help.
Am keeping the encouragement in mind as the 'not getting younger' seems to be accelerating - - - - argh!!!!

Thanks to both Misters DDMCKEE54 and Awake for a very appropriate reminder!

My neurologist and I disagree as to what's doing OK regarding my tremor. He's of the opinion that if I can still feed myself I'm doing OK. I set the bar a little higher, I'd like to be able to at least read my own writing - that can be a real challenge at times.

snip

So, a couple of steps forward, and at least one step back.

Don

For electronics soldering - - - not so much - - - - for welding - - - I've seen welds done by a guy who also just couldn't hold his hands still (a number of years ago and I wasn't smart enough to ask any questions then) but he just used the hand tremors to actually get a great weld puddle - - - - with outstanding results.

(Not trying to make light of your affliction - - hopefully giving a little bit of hope. I have found that if I push the specialist that some of them will come up with interesting options - - - that really help and are worth doing - - - - then there are those who shovel everything under the rug - - - - argh (those I think everyone could do without!).)

Not speaking as an expert - - - - would it help if you used a higher heat for a shorter time in the soldering?

(I'm remembering something like that its a combination of time and heat - - - dunno - - - - electronics specialists please advise!!!)

Hang in there - - - - you will get 'er done!!!!!

Soldering PC boards is kind of a balancing act. You want enough heat to be to get the joint to temperature quickly enough that you don't damage the electronic components, but you don't want so much heat that you cause the copper foil to delaminate from the board. My soldering pencil is adjustable from 16W to 30W, I've got it set in the 20-25W range.

I some did some careful examining of the PC board Friday night and discovered a couple of things:
1) One of the tabs on the pot, the wiper tab, had shifted when soldered. This shift created a small gap that LOOKS like the joint is OK, but it ain't. I was NEVER getting the speed signal to the outside world. I remedied that problem and VIOLA, it ran... at minimum speed. Only at minimum speed, no matter where the speed pot was set, or where the run/stop switch was set. (That switch DOES work by the way - I checked it with a meter.)
2) More careful examination of the board reveled that the 100K resistor was connected between +5V, and the WIPER of the pot. That's NOT where it should have been. You know those parallel resistance calculations that I ASSUMED I didn't need to make? I wound up doing them last night. I haven't had to do anything like that in 30 years. I wound up having to look up how to do it on the interwebb, just to be sure. Turns out that damned 100K resistor was causing the minimum speed problem. Me, myself, and I were having a discussion, and we decided that it's true. When you ASSUME something, it really does make an ASS out of U and ME.

Those results got me to wondering about all the rest of my choices. Back to the interwebb to see what I could find on the Hall effect sensor that started this trip down the rabbit hole.

I found out that they had used a 49E sensor. By process elimination it was in a TO-92 package, the other configuration was surface mount. This sensor works on magnetic field strength, from -1000 Gauss to +1000 Gauss. The output voltage specification shows a fairly linear response with a 0V output at -1000 Gauss. At 0 Gauss the output voltage should be approximately 1/2 the supply voltage, that corresponds to the measured 2.4V at minimum speed.(One half of the +5V supply voltage.) At +1000 Gauss the output voltage should be approximately 4V, this also matches the measured values. I re-did the calculations, no assumptions this time, and.... IF I hook it up CORRECTLY this time, it should work.

I found a piece of a different style of perf-board that was left over from some other project. It will work much better and still fit the space available. I'll check the new design at LEAST one more time tomorrow, BEFORE I start to build it.

Don

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I built that board 2 times yesterday.

The 1st time using the board that I thought would work better - it didn't. As long as you didn't modify the traces on the board it was OK, the traces were arranged in parallel strips with 5 holes in each section. I needed to split 2 of the traces into 2 hole, and 3 hole sections. The traces were EXTREMELY thin. They seemed more like electroplating than copper foil. When I tried soldering those sections, where I had split the traces the copper would peel away from the board. I wound up with little halos of copper wrapped around the component leads. (Many bad words were definitely uttered.)

The 2nd attempt was made using the original style perf-board with the plated through holes, and VERY careful construction - making sure that Tab A actually went into Slot B. I plugged everything back into the servo controller and it ran - at minimum speed. (More bad words.)

I got out the meter and started verifying the circuit again, just to be really-really sure the components were installed in the proper locations - they were. Then I did something I hadn't done yet up to this point, I measured the total resistance through the circuit from the +5V side to the 0V side. And I came up short, about 3K short.

My 4.7K resistor measured 4.6K, which is within the tolerance. My 12K resistor measured 11.8K, which is still OK. My 10K pot measured about 8.1K - which is most assuredly NOT OK. My pots, the ones labeled 10K, are actually 8.2K pots? That's not good, but it still doesn't explain why I'm only getting minimum speed.

Up to this point I have been assuming, there's that word again, that the 49E Hall Effect sensor had only been supplying a reference voltage. Are they driving some type of load with the sensor output inside the controller? Looking at the speed control circuits that actually WORK with this servo controller the one thing they all have in common is they all use 1K pots, and they have a current flow in the range of 1.4-1.8mA. The current in my circuit is calculated at 0.17mA. When I try increasing the speed beyond minimum it actually stops the motor, maybe I just can't drive anything more than minimum speed with my circuit?

EBAY just told me that my 1K pots will be here by the end of the week. This time they WILL get measured to be sure I got 1K pots. Then we'll try with a fresh circuit and see what happens.

Houston... We no longer have a problem.

I got my 1K pot, and it actually was a 1K pot. I built a fresh board using the circuit with the run stop switch from the hobby machinist link that I sorta provided. It works as advertised, I've now got a variable speed motor that I can set the speed in 100rpm increments from my minimum to maximum speed using a speed pot. When I turn off the Run/Stop switch the motor will stop, then resume the same speed when I tell it to run. Since I adjusted the braking intensity to 0, from the default of 1, the motor will coast to the minimum speed and then stop.

There's 2 things that I wish I could change:
1) I'd REALLY like to be able to set the servo up to coast to a stop, not just coast to minimum speed. But I haven't been able to find any likely suspects in the available parameters yet.
2) That 100rpm increment just bugs the crap outta me. I don't have a tach so I don't know if the motor speed only changes in 100rpm increments, or if they are only displaying 100's of rpm. Either way, I've got no clue why they didn't just use a 2 digit display and say it's rpm x 100. (Maybe they had like a bazillion 4 digit displays left-over that they needed to use up?)

Don

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