Cowboy Analog Servo Motor Modifications?

[BDAZ]

Bob, I would liken this to adding a better sound system or maybe a GPS to a new car. It's not about looking different but about optimizing the performance of the motor for low speed operation. Once we determine what the optimum value for the potentiometer is, you could request the motor with a potentiometer (The speed control knob) with the appropriate value for leather work. The correct value should allow the speed control to go from minimum to maximum (the fastest speed a leather worker would want) with the complete turn of the dial. On my new 3200, from newbie slow to a controllable speed for belts was about 10% of the dial.

The magnet mod is a bit more problematic and would take some retooling for the manufacturer but the change in values on the speed control is a no cost , no brainer.

Cya!

Bob.

[JoMama]

To your knowledge, will your pot mod substitute for the rotary switch currently installed in my FS-550s? I already have great slow speed control, especially with the 3:1 reducer in the chain.

With a 3:1 reducer, I still use the stock multi-position switch and just leave it set a couple clicks below the fastest speed. Before the magnet mod and rod repositioning on the pedal, the motor would go from zero to full speed using only 10-15% in the middle of the pedal range. After the mods, the first 10% of the pedal movement is dead-band (intentional) and the last 90% is variable. When I say pedal range, I mean hard-stop to hard-stop on the pedal, as if the control rod was disconnected, not the stops on the motor arm limiting the pedal movement. I'm typically only doing 30-90 spm, but when I want to go faster (300+), I don't have to turn the knob to a faster setting, I just floor it, because the control is soooo much better.

I see no reason to change my switch for a lower resistance pot.

[BDAZ]

JoMamma, My motor has a 220K pot and not the multi resistor switch. Do you know what the value of yours is? It may be a lower value than mine?

Thanks!

Bob

[pcox]

I have 5 machines with the motors Bob sells and have installed many more with no control problems. If what you are after is more pedal travel, that is a function of the ratio between the point of connection of the rod or chain on the servo motor lever and the foot pedal. closer to the pivot on the foot pedal/longest point or even extend the lever on the servo will give you more pedal travel/less sensitivity. All of my leather stitchers have speed reducers.

Edited June 10, 2014 by pcox

[BDAZ]

This is about more accurate maximum speed control.

CYa!
Bob

[JoMama]

JoMamma, My motor has a 220K pot and not the multi resistor switch. Do you know what the value of yours is? It may be a lower value than mine?

Thanks!

Bob

I never checked it, since I did not see the speed LIMIT as the problem. The issue I had was a lack of range of motion on the motor control arm between zero and full speed. When I was first looking at it, I noticed that adjusting the speed slower, just increased the dead-band before the motor started to spin and did nothing to increase the arm's range of motion from zero to full speed. This motor controller does not adjust the travel range when you when you adjust the pot as you would hope. My guess is that the pot just provides an offset voltage to suppress the voltage from the linear hall sensor, limiting the speed by decreasing the effective output of the hall. Hench the decreasing resistance on the pot to limit the speed.

I have used the same linear hall sensors in numerous other applications, and typically, you want the magnet to approach the sensor axially to its face, so the magnetic field extending from the face of the magnet gradually presents to the sensor. On this motor setup, the magnet approaches laterally, where the magnetic field lines are closer together and the transition from zero to full field strength happens with a shorter motion and is less linear.

I have my FS-550 motor RPM set at 2830 RPM (two clicks below the fastest speed, 3450rpm) and it is easy to control the speed between 15 and 60 stitch/min, but it will also spin up to 300+ when I want it to, also totally controllable.

I'd suggest you go back to the stock pot, set it between 75% and 100%, do the magnet mod, drill a line of holes in the side of your pedal and attach your pedal rod or chain to those, to see which position you like the best. The closer to the pivot you attach the rod or chain, the better your control will be. That can also limit the speed by not having the pedal movement that allows the motor control arm to travel into the faster region.

edit: As pcox mentioned, you could increase the controllability by just moving the rod or chain closer to the pedal pivot, but the magnet mod changes the speed curve to have more linear speed control.

Edited June 10, 2014 by JoMama

[BDAZ]

First off I have already done the pot mod and replaced it with a 100K pot. I generally work on intricate pieces with some straight sewing and I like to work at 30 SPM for the intricate stuff and 80 SPM for straight line stitching, no faster. I want to be able to set my maximum speed for a piece leave it there, consequently the pedal is less important to me than the speed setting. Prior to the mod, only a fraction of a turn would take me from 0 to 80. Now it's half a revolution of the knob and the speed increase is gradual and repeatable.

I have done the magnet mod and I suspect it may be problematic, reducing the amount of travel that triggers the transducer. Maybe my magnet is angled a bit too much but it ts definitely an improvement and could be incorporated in the manufacture of the arm, with a longer angled or tapered magnet since the transducer works on the strength of the flux.

Cya!

Bob

[JoMama]

Just a note on the magnetic field, the strength of the field is an inverse cube relation to distance. By biasing the voltage from the hall sensor with the pot/switch to limit speed, you miss out on the long gradual taper of the sensors voltage curve, which improves the slow speed control, while still leaving plenty of top speed.

Now if you are setting a speed limit and then running the machine at that limit for a bunch of pieces, that's completely different from what I'm looking for, which is to easy slow speed control via the pedal along the curves and tight corners and then still be able to open it up on the straights without stopping to adjust a dial. My speed limit is my foot.

Cheers,

Jo

[catskin]

Thanks all for your input. I am NOT an electronics person 99% of this stuff goes right over my head, but now I sort of understand what you are all getting at.

[BDAZ]

I just received my 20K pot and wired it in series with a 100K pot and discovered that my threshold resistance (The minimum amount of resistance in the circuit that is required to start the motor) is 14 ohms. I think that a 100K Log pot with a 10K resistor in series is just what the doctor ordered. The 10K will allow the pot to kick in at the ideal part of the log curve for a gradual speed increase.

I have extended the jumper to an identical jumper mounted on the back of the motor housing so I can test various components without removing the motor housing.

Cya!

Bob