Cowboy Analog Servo Motor Modifications?

[BDAZ]

This is the servo motor I have on my 3200 and I believe it is the same as the one on the 4500 as well. I have running at around 60 stitches a minute maximum but to get there I just barely nudge the pot from it's zero position, I would like to get more control over the lower end of the range but the pot is way to sensitive and just a touch makes a huge difference in speed.

I have not seen the schematic of the motor but it sure seems the pot is wrong for this application. Has anyone replaced the pot on their servo? It seems that the pot is probably linear and should possibly be a log type pot.

Here is the motor:

Thanks!

Bob

Edited May 14, 2014 by BDAZ

[Wizcrafts]

My FS-550 motor has a multi-position rotary switch. I wish it could be converted to a log taper pot. Let me know if/how any mods work out for you.

[BDAZ]

THis shouldn't be rocket science. I spoke to Bob the younger, and they are not aware that there is an issue. I'll oopen it up when I have cleared my back log..Any chance of getting hold of a schematic?

Cya!

Bob

[Wizcrafts]

One big difference I see is that your motor has a large pulley. Mine has a 50mm (2") pulley, which gives more low speed torque and runability.

[Wizcrafts]

Aside from the pulley difference, when I opened up my motor, I looked at the switch and found that it is populated with small resistors. I'm not into electronics anymore (for 3 decades) and have no meters. But, I'm guessing that someone with the right equipment and good close-up eyesight could figure out how to replace the rotary switch with a suitable military grade, long life, log taper pot (or stacked concentric pots).

[BDAZ]

The pic s not my machine but one off the net. I assume I also have a 2" pulley. I'll try to take a look this afternoon.

Cya!

Bob

[BDAZ]

Found the problem! The pot is a 220K Ohm linear pot. The machine is off when there is zero resistance. When I crank it to the maximum that I would eve use, it's around 80K ohms. So that's the answer! Replace the 220K ohm pot with a $.99 log taper (for testing) 100K. If I get the range and speed curve I am interested in, I'll invest in a better pot. The pot is plugged into the board using a standard Molex connector, so one could conceivably have a 20K 60K and 100K and simply plug and play.

I have ordered a couple of pots and will install them when they arrive.

I have just ordered the pots and connectors and I'll give it a shot.

Cya!

Bob

Edited May 14, 2014 by BDAZ

[Chief31794]

I have the same motor on a 3200 and it has a full range of speed, using about 3/4 of the adjustment on the dial to go from 0 to as fast as I want to go, but the control isn't overly sensitive.

Chief

[BDAZ]

I'm not concerned about going fast. I want to max out at 60 spm and have the full range of the pot cover 0 to 60 ONLY.

Thanks!

Bob

[Random]

Just noticed this thread or I would have responded a lot sooner. I ordered a Servo from Toledo (Ordering and shipping was fast and flawless.) I discovered that low end speeds were almost impossible to get right. I am a DIY sort and since it was 10pm I didn't expect Toledo to be open. I grabbed an old dead computer gaming headset and ripped the volume control off of it (2K Ohm) and grabbed a pot from a computer Power supply fan (100k ohm). Spliced them in series and was able get the speed adjusted to my liking.

For ~60 SPM the reading is 18.3K Ohms and using the 2k Pot will adjust the speed up words to ~120 SPM. Its's no wonder everyone is having trouble getting it zeroed in at the right speed since at the low end a turn of just 3 degrees can result in a doubling of speed.

The other advantage with doing this mod is that I now have the speed control mounted near the reverse lever so I can quickly and easily adjust the speed.

I didn't even know there was an item called a Log/audio Pot, and apparently neither did the person who designed this Bob seems to be right on the money and if his test works as well as I expect it to I will grab a Log Pot and throw it in series.

Thanks for the info Bob.

Random

Edited May 16, 2014 by Random

[BDAZ]

I don't get what the 2K pot in series is doing for you. unless you are using that as a fine adjustment once you have the 100K set to an approximate speed. I did a very crude test and figured on my system (remember it's also about pulley sizes) 60 SPM equates to around 60K Ohms. I like the idea of moving the pots off the motor and accessible without sticking one's hands past the belts and pulleys.

For those who are analog challenged here's a chart:

When I have the log pot installed I should get 50% of the knob rotation controlling the first 10 ohms, so I doubt the second pot is necessary. It would be with a linear pot.

Such a simple fix for a significant issue.

Cya!

Bob

[JoMama]

The problem is not with the multi position switch and there is no potentiometer on this motor.

The Speed is controlled by a linear hall sensor that varies the control voltage based on the strength of the magnetic field from the magnet in the black plastic arm. The problem is, the way the magnet is position in the arm, the field strength goes from zero to 100% with only a small movement of the arm.

Here's how you fix it.

1. Remove the left end cover and the screws that hold the electronics box under to motor. (let it hang on the wires)

2. Remove the screw (5mm hex key) and nut from the arm that holds the brake pad. (Brake pad already removed in picture)

3. Release the spring from the tab just below the brake pad.

4. Pry the arm off the shaft with an open end wrench or small cressent wrench that can stradle the shaft and spring. You may want to wedge a flat head screw driver into the slot and pry it open a bit, but too much force can break it, since it is only cast aluminum.

5. Remove the black plastic arm with the shaft and square magnet pressed in.

6. Use a Sharpie to mark the side of the magnet that faces out.

7. Either pry the magnet out with a small sharp screwdriver or drill a small hole through the plastic behind the magnet and push it out.

8. Using a Dremel or small sharp wood chisel, angle the bottom of the magent pocket down as shown in the picture.

9. Reinstall the magnet and glue in if necessary.

10. Reassemble, in reverse order paying attention to the clocking between the plastic arm and the brake arm.

I removed the brake pad completely, since I never run it that fast and like to be able to turn it by hand without stepping on the pedal. There is a stop tab that prevents the brake arm from contacting the wheel when no pad is installed. The control will now have more range of movement and be more linear. To get even more control, move the pedal linkage from that little tab that bolts to the top edge of the pedal to the side of the actual pedal. (you'll need to drill a hole) The closer it is to the pivot, the more control you will have. With the brake pad removed, you will have to preload the linkage when you tighten the clamp, or there will be a lot of deadband before it starts to spin.

Edited May 24, 2014 by JoMama

[BDAZ]

The speed control IS a 220K linear pot and changing the value to a 100K log pot WILL achieve the desired effect but your system may enhance the effect assuming there is a magnetic sensor on the motor.

Cya!

Bob

[JoMama]

Maybe it is has different electronics.

The knob on the front (circled in blue) is the speed LIMIT and only sets the maximum speed. On mine it is a multi-position rotary switch with detented positions, but it could just as well be a potentiometer which would be smooth, while turning.

The speed CONTROL comes form the linear hall sensor circeld in red and it varies the speed between zero and the maximum set by the knob, in relation to how far the foot pedal is pushed down.

Modifying the magnet angle increases the range of motion that the arm travels between zero and maximum (set by the knob) and makes it more controlable.

[BDAZ]

On mine it is a 220K pot connected to a connector on the board. The initial problem was setting the maximum speed more accurately since only a few degrees of rotation of the pot results in the full range of required top speed. So both mods should result in much better control of the motor.

Thanks!

Bob

[JoMama]

The magnet modification made the biggest difference on my machine. With the knob set to the maximum speed, I can still control the foot pedal to get anything between about 50spm to 1500spm. The only problen with that long, skinny, 2 pole motor design is that is does not as have much torque when run in the bottom 5-10% of its range. It is a motor designed to run at 3400 rpm and anything less than 340 RPM, they don't like and it can oherheat the windings, which is why I have a speed reducer on the way. That should take it down to 17-500spm of controlable speed.

[msdeluca]

Bdaz,

I'd be interested in a tutorial when you have this figured out to your liking.

Mike

[Constabulary]

Very interesting thread!

So no matter which servo motor you have it seems a speed reducer in addition is always your friend.

[BDAZ]

I am still waiting for my pots and connectors to arrive. The pot mod is mostly about controlling speed between 0 and 60 SPM. I have ordered connectors, leads and pots from China so I can test various components and produce a "plug and play" configuration.

I'm hoping to get my components this week.

Bob

[Trox]

Please let me know when the Chinese manage to make an modern sewing machine motor that actually works as it should.

For those who cannot afford a Efka or a Ho Sing; Try a 3 phase clutch with a Frequency converter (and a speed reducer if its a heavy stitcher). Thats the system with the worlds best low speed control; for sure. Its the cheapest options also, normally you get those old 3 phase clutch motors thrown after you. Its easy to find a used frequency control on EBay too. The wiring its easy, all you need then is a sewing machine and a single phase outlet.

Good luck

Tor

By the way nice topic!

Edited May 26, 2014 by Trox

[JoMama]

....Try a 3 phase clutch with a Frequency converter...

Cheap 3 phase motors do not do well with VFDs at low speed. They heat up and the voltage spikes can breakdown the insulation. Inverter duty motors can be run down below 10% of the normal speed, but cheap 3 phase clutch motors probably would not last long running below 25% of rated speed. The "servo" motor being discussed in this thread is a two pole DC motor with PWM driver, not really a servo.

[Trox]

Like I said I have expensive Efka`s and Chinese Eco motors, but the 3 phase clutch with freq. converter works almost better than the expensive ones (part from the needle position that is). I even used such converter on a 3 Ph Efka varistop with no problems (only on the motor part, single current direct to the control box). It has worked for ten years no with out any problems, with out any extra heat from the motors. I only uses the same as they do in all modern industry today; Ac motor with a frequency controller. I currently have three setups that has worked flawless for many years. I am sorry for the off topic, this is for all the others looking for motor alternatives.

Thanks

Tor

[Wishful]

I have the same problem as stated above. The speed at the low end cannot be adjusted just a bit, it jumps to too fast from zero so a speed reducer is next.

[Constabulary]

Like I said I have expensive Efka`s and Chinese Eco motors, but the 3 phase clutch with freq. converter works almost better than the expensive ones (part from the needle position that is). I even used such converter on a 3 Ph Efka varistop with no problems (only on the motor part, single current direct to the control box). It has worked for ten years no with out any problems, with out any extra heat from the motors. I only uses the same as they do in all modern industry today; Ac motor with a frequency controller. I currently have three setups that has worked flawless for many years. I am sorry for the off topic, this is for all the others looking for motor alternatives.

Thanks

Tor

I have no clue what the frequeze converter does and how it works with a clutch motor...

Does it slow fown the speed and how can you control it? Can someone explain it to me in plain english?

Trox - can you post pictures of your setup?

[Trox]

It coverts to normal single house hold current in to 3 phase current; to run the motor. And lets you control all the motors parameters, such as speed, torque, start time, stop time...... you name it. You can set the max speed as low as you want and let the motor have maximum torque at that speed. Like one stitch a minute if you want to. You can also attach a pot meter to regulate the speed, like a pedal just as you like. (otherwise you got to use the buttons and the display to control it).

I do not have 3 phase current in my workshop so I use this systems on my 3 phase motors. You loose a couple % of the power this way, not much. Sometimes the motor makes some noise (wrong frequency), just change the speed a bit and its gone. You need one that can handle the amps rating on your motor. Its easy to connect; single in on the top (on this one) then the four motor cables out underneath. Earth to earth and just change the other three around until your motor turns the right way. You got to download the pdf to find out how to program it, its not very difficult. Every electricians know how to do it. Or send me an PM and I tell you how to do it. Thats it

Tor