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Option D : 3-Phase AC Gearmotor with VFD See the parent article: Choosing a Motor The lesser known of motor options is the 3-phase AC Gearmotor with VFD (variable frequency drive). This option gives excellent driveability (does what you ask with no surprises) but requires a fair amount of setup. 1. Interesting Posts about 3-Phase AC Gearmotors with VFD The search bar on the forum does not support three letter words like “awl” or “VFD”. So you will have to use an external search engine to find posts on VFD. Try this search for example: https://www.google.com/search?q=vfd+site%3Aleatherworker.net Here are some forum posts to get you started: GerryR: Description of his VFD setup Tigweldor: How to build a portable VFD GerryR: Adapting a 3-phase clutch motor for use with VFD GerryR: How to get started with VFD TinkerTailor: "The sewing world has not embraced vfd like the machinist world it seems, though in theory it is likely the best way to go for a slow moving leather stitcher." friquant: Introduction to Gearmotors and VFD 2. What is an AC Motor Specifically, we’re talking about AC induction motors. Think table saw, bench grinder, garbage disposal, air conditioner fan. In typical use, an AC motor runs at a constant speed. For example, when you turn on the table saw or bench grinder you hear the motor goes WhOOOOSH for a couple seconds as it gets up to speed. Once at speed, it stays at about that same speed. (A little less under load than with no load). AC induction motors can be single phase or 3-phase. (We want 3-phase for use with a VFD.) The speed the motor turns depends on the frequency of the power source and on how many electromagnetic poles the motor has. As an example, a four-pole AC induction motor typically has a speed around 1400 rpm when fed 60Hz power from the wall. 3. What is a Gearmotor A gearmotor means a motor with a gear reducer added at the end. It looks more or less like a single unit. The gear reduction can be a little bit (like 3:1, which can also be written “3k”) or it can be a lot (like 200:1, which can also be written as “200k”). 2.1 Shopping for an AC Gearmotor Choose a motor size that is suitable. 100W (1/8 horsepower) to 400W (½ horsepower) is probably adequate Make sure your AC gearmotor is 3-phase Make sure your AC gearmotor can run on 220V power. (Some can run on either 220V or 380V) Choose a gear reduction that is suitable. (3:1, 5:1, 10:1 are probably the most suitable) Get one that mounts horizontally (sometimes called a “foot mount”) 4. What is a VFD (Variable Frequency Drive) A VFD (Variable Frequency Drive) is an electrical device that outputs 3-phase power (in the range of 220V) at whatever frequency you choose. (0Hz - 100Hz is typical). 4.1 Why do we want a VFD The speed of an AC induction motor is proportional to the frequency of the power source. The VFD allows us to send whatever frequency we want to the motor, between 0Hz and 100Hz, and the motor speed will change accordingly. 4.2 Shopping for a VFD When shopping for a VFD, make sure you get one that accepts as input power whatever power you have conveniently available. (110V single phase input is a common option.) Note VFDs will usually have a cooling fan that turns on when the VFD is engaged. Mine is louder than I would prefer. I may look for another one with a quieter fan. 4.3 Setting up your VFD When you first get your VFD you can test it out with your motor by using the knob on the front of the VFD to control the frequency. The motor will not move at all when the knob is set to 0Hz, but the hand wheel will still turn freely. Once you move the knob above 0Hz, around 1Hz you will start to see very slow movement in the motor. Turn the knob up high and it will go full speed. For actual use with a sewing machine, you will want an external potentiometer to tell the VFD how fast to go. Buying a TIG pedal is a cost-effective way to get a pedal with two potentiometers and an inline switch so that you can both engage the VFD and drive at whatever speed you want. Here is the TIG pedal I bought. Digging into the user manual for your VFD you will be able to find options for setting the minimum speed, maximum speed, and for limiting the acceleration. 5. Is a 3-Phase AC Gearmotor with VFD Right for Me Choose a 3-Phase AC Gearmotor if: You want the absolute best in terms of driveability. (Does what you want with no surprises) If you want the consistency of the needle always penetrating the fabric, without need to “get a run at it” You want full configurability of how fast your motor goes, and when. (Very slow start available!) You are comfortable wiring electrical equipment You understand basic electronic components such as potentiometers and switches You are comfortable reading technical manuals (The VFD will come with a manual) You are comfortable configuring electronic devices through their menus You want gear reduction without needing extra belts You are willing to buy a pulley separately that fits the gearmotor output shaft and your belt of choice You are willing to mount the motor yourself and come up with your own belt tensioning system