servo motor startup speed

[Uwe]

Depending on your expertise in electronics and programming, you can also build your own motor and controller that does exactly what you want. I did that once using a stepper motor and Arduino controller, just as a demo project for a thumb controller retrofit. The stepper motor I had on hand for testing was not suitable for actual sewing, it was super noisy.

Here’s the demo video I made of that experiment. Aside from the thumb controller, you can also see the super slow ramp-up speed I got with the foot pedal.

 

Using a modern servo motor like the Clearpath line made by Teknic  you could build a usable system that truly ramps up as slowly as you want with no jump from zero to some minimum starting speed. Cost would be around $700-$900 for the parts, I imagine. 

Edited September 22, 2023 by Uwe

[fibersport]

Uwe - great information and really am impressed with your home built unit.  As for the Efka - way too rich for my blood.  The Teknik would be a very interesting way to put together a great system but right now I already have way too many projects!

Kgg - good information, thanks, I'll put it all in my memory bank as I continue my quest.

[GerryR]

You might want to consider a 3-phase AC motor with a variable frequency drive (VFD).  They are at rest (0 rpm) and go to whatever frequency in their max spec.  Under line frequency (60 hz) they are in constant torque mode and above line frequency, they are in constant horse power mode.  A simple pot varies the speed (think TIG welder's foot pedal).  I used one for an old singer 153W103 machine that I had.  The 3-phase controller runs off 1-phase power (does the 3-phase conversion internally) and was less than $200.00 at the time.  I had the 3-phase motor from an automation project I was involved with; It was 1 hp, way overkill for the sewing machine, but the price was right.  You can get fractional hp 3-phase motors reasonble priced, so I would expect you could do what you want for way less than $500.00 and make the ramp-up speed whatever your foot can control.  Just another approach you might want to consider.

Here's an example for $151.00 for a unit that will handle up to a 1 hp motor off of 120VAC 1-ph input.  Many options available.

https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/micro_vfds/gs11n-11p0?gclid=CjwKCAjwmbqoBhAgEiwACIjzEPTZASfk6Z5gjXMFhUpfdFMd8IOdoPKZY2FSaUI4c0NeXNRC6rN19xoCR9AQAvD_BwE

Edited September 23, 2023 by GerryR
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[Gump]

I can run the needle slow enough to thread it on the way down. Ramp up is as slow as you can ease the pedal down. Slowing down is a little more abrupt, but that is because of so little resistance from the pedal.

[fibersport]

Gump - that's what I'm looking for, however my eye's aren't that good, I would probably sew through my finger!  Your comment reminded me of a video I once saw of someone changing a fan belt on an old VW beetle with a screwdriver when it was running.  I've been doing some reading up on the Sailrite Workhorse, they too say that you can basically go stitch by stitch when starting up or in intricate areas.  Any idea what the minimum speed might be of your motor, I can only find range and a maximum but not a minimum.  Maybe because you can't really measure the minimum as it's ramp speed is variable so they just say it starts out at 0?

Edited September 25, 2023 by fibersport

[GerryR]

17 hours ago, Gump said:

I can run the needle slow enough to thread it on the way down. Ramp up is as slow as you can ease the pedal down. Slowing down is a little more abrupt, but that is because of so little resistance from the pedal.

The same would be true with the VFD and 3-ph motor.  I used a 5:1 gear reduction motor giving a max output speed of 345 rpm, so you could vary the top speed down from there through the VFD setup.  As you stated, ramp up is as slow as you can ease the pedal down.  (I wouldn't try threading a needle while it was moving!  )

[fibersport]

GerryR - as they say (not that I would), many ways to skin a cat.  I think your method would be great for a system that is run full time as it sounds very robust, it sounds like it would be at home in an industrial environment.  Right now, I don't have the time to devote to yet another project putting everything together for the drive system - I like to tinker but I'm more mechanical than electronic, but still I like your approach.

[Gump]

At dead slow, you can pretty much feel the fields of the motor as it almost bumps from one to the next. With a needle positioner you get 1 stitch for one tap of the pedal.

[GerryR]

1 hour ago, Gump said:

At dead slow, you can pretty much feel the fields of the motor as it almost bumps from one to the next. With a needle positioner you get 1 stitch for one tap of the pedal.

Being a DC motor, you would get that effect.  With a VFD you would not.  One thing I didn't mention about using a 3-ph motor with a VFD is that the motor has to be an "inverter duty" motor to tolerate the slow speeds (low frequencies)  They are more robust and can handle the extra heat generated not having the cooling fan running at full speed.  I expect that using a needle positioner / sensor would have the same effect, one stitch per tap of the pedal.  The advantage of the DC servo over the AC system would probably be in the motor size.  DC motors generally get more power in a smaller package size.  The AC system is just another option to think about.

[fibersport]

Has anyone installed a smaller drive pulley on a digital servo motor and if so, were there any issues?