Do you mean http://www.pololu.com/catalog/product/1182 for the second of those links ("less expensive driver")?

Yeah I did.

An LN293 is not suitable for this motor, because it reaches its maximum current at such a low voltage. This sort of motor requires a regulating (or chopping) driver that not only controls the sequence but also the current. You can set the current to be anything you want it to be and there is no need to run the motor at it's maximum current.

Here's an example as Mike describes, or if you can handle sticking to 2A you can try this less expensive driver at Pololu. Both drivers use the same step/direction/enable interface.

If you read the documentation for these drivers you can see that the controller's voltage (5V) is independent of the voltage the motor is running at  and you will want to use a higher motor voltage (typically 12V to 40V) to gain more speed with the stepper. If the motor gets too hot to press a finger on it then you need to lower the amperage.

Beyond that, the FETs in the servo will run less efficiently when at slower speeds; does it seem to get warmer when run slowly?

Are you sure of this?
Do you know what the mechanism of this is?
I can't think why this should be.

Why wouldn't you expect the FETs to run hotter (less efficiently) under the PWM or linear mode that would be required for the slower speed?

Amperage is based on how much torque the servo is providing and that is the most likely reason, especially given the high gearing in the servo which is a major use of the available power. Beyond that, the FETs in the servo will run less efficiently when at slower speeds; does it seem to get warmer when run slowly?

How much of this welder is missing? The amperage control and wire feed? Are you trying to build a spool gun or do you have the original gun?

In your code you might want to verify what value you're analogReading. Pots can get scratchy and that might be the cause of your jerky motor. It would also be a good idea to use some smoothing; something like:

Code:

void loop()
{
  if (analogRead(analogPin) > val && val < 1024) {
    val += 1;
  } else if (analogRead(analogPin < val && val > 0) {
    val -= 1;
  }

  analogWrite(ledPin, val / 4);  // analogRead values go from 0 to 1023, analogWrite values from 0 to 255

  delay(10); // creates a smoother ramp up/down
}

Coding it this way, if your analogRead() values are jumping around (due to interference or such) then that won't be reflected in the motor.

I'm struggling to imagine any situation where I'd want a home made welder instead of a decent quality production one.

That situation would be immediately following seeing the price of a 290A welder.

This is a generic error. The kernel is simply saying it looks like you plugged in a device that isn't communicating like a USB device should.

Found it:

http://mayhewlabs.com/products/go-between-shield

Can you post a picture of your board?

The "Battleswitch" is very expensive ($25) for what you're doing. By comparison a Seeedstudio Grove Relay is $2.90. Both require the same wiring but with the relay you'll just do a "digitalWrite(PIN, HIGH)" instead of using the Servo library attach/write/etc. with the Battleswitch.

Connecting your 110V motor should be possible with the nature of your wiring however this is not something I'd be comfortable describing without the ability to see exactly how your electrical circuit is wired. Your picture shows what is needed for the wiring; take that picture to a professional electrician -- or even a knowledgable sales clerk at a store that sells electrical supplies --  and ask for advice. Note that per your hydraulic diagram you need counterclockwise rotation (bottom half of the picture).

Your hydraulic diagrams (the last two pictures you posted) are not related to single phase or three phase operation. Those are the paths for the hydraulic fluid in the system. The only difference is that the second shows a piston and some kind of pressure control valve in the circuit.

Out of curiosity, what are you building?

mingki you need to tell us what country you're in so that we can understand the nature of your home electricity.

Yes, "those things" are the start and run (if there are two) capacitors.

I think he's referring to the load being on the collector side of the transistor (common emitter) vs. on the emitter side (common collector). That answer is available here (gotta read a few paragraphs forward).

A heavy duty R/C ESC, with a meaty heatsink?

A Radio Control type won't be easy to find. It'd need to be a brushed controller which is getting to be a rarity and the few I've found require 2-3 LiPo cells which is 7.4 to 11.1V input range.

As far as determining how many amps you'll need all you can do right now is guess. When you take the plunge and get it in your house you can tear it up a bit and stick a multimeter on it but that's not helpful now of course. One thing you can do is look at the battery it has in it; a sealed lead acid battery usually has specified limits for current draw so knowing the voltage and amp hour (Ah) rating of the battery can start you off on a search for a similar size battery that has that current spec defined.

You can solder two rows of pin headers to a prototyping board and make your solder connections on that board. That will make it a sort of plug that you can easily remove or cheaply replace.

When servos are powered off they are still quite difficult to turn because of the high gear ratio. Granted chickens are pretty tough and they have a lot of leverage pushing open the door; you might want to use a second servo to control the latch if you're concerned.

You're on target with the servo you have linked. Notably the metal gear types are preferred. The 15kg rating refers to the force at 1cm from axis of rotation. That same seller also sells devices that will handle your 12V to 5V conversion for the servo -- an Arduino alone can't supply enough amperage and is also less efficient.

With respect to using "two stiff rods" I assume you're thinking of a setup like this. Logically though you only need one rod (push/pull) or two strings/cables (pull/pull) like in the picture. I'd recommend using a stiff wire (like piano wire) though -- if something breaks you want it to be something cheap to replace.