Motorhead?

What??

Just got these motor-gearbox thingies from Amazon, along with some PWM drivers for brushed DC motors.

Nothing special. They have interchangeable gears, providing a wide range of reduction ratios. 

This one is 6rpm (one rev every 10 seconds) and the larger one with the black motor is 10rpm The PWM drivers are good for operation off 12V 

Being a nosey b4stard, The Stupid Fat Bloke took the smaller one apart and managed to drop the guts on the bench by opening it upside down. There's a load of different gears and spacers that have to be assembled in the correct positions before the lid will go back on, so I had to figure that all out for him.

What's going on now, Fatty?

10 years ago, I made this little powered trolley thingy. Little stepper motor with (high temperature!) O-rings and a small stepper motor.

The stepper is driven by an MSP430 eval board aka "Launchpad", fitted with an "Easydriver" stepper driver board. 

The Linbin is simply a means of avoiding accidental short circuits and blowing the thing up.

The Schmalzhaus stepper driver is an Allegro A3967 that takes a step/dir signal and drives the motor. The MSP430 is simply being used as a pulse generator. I don't recall why I went this route but certainly there are simpler means of generating pulses and ideally it would be possible to change the frequency (speed) of the drive.

Then there's also this thing:

Inside there's a PP3 9V battery and a brushed DC motor driver.

After 10 years, the battery still has some electrons to spare, although not enough to actually turn the motor.

This DC motor driver seems to be from Canakit. This is a very simple PWM generator with a FET and flywheel diode, driven by a 555 timer. Hardly the height of sophistication.

It simply drives the large wheel (also sporting a high temperature O-ring)

What's the point of all this?

Perhaps this will help. 

Yes, it's a motorised head for driving a MIG welding torch. It was originally aimed at helping me to weld exhaust pipes, where consistent welding conditions are critical if you want to avoid blowthroughs. 

It was showing some promise when I had to pack it all away (something to do with moving the workshop, house and family back to the UK from Canada). It was showing promise:

And the bits I just acquired are intended to be another attempt at making one of these.

There are a couple of other bits and pieces I bought back then of varying appropriateness, including this thing. The least said the better...

Another escapade with Chinese connectors:

Yes, I'm thinking how I might make a useable version of the above, with a view to integrating it with the MIG welder.

How would I get the welder and the motorised head to operate together? Ideally the motor would come on when the torch trigger is pressed - and would be powered by the welder.

Battery power is all very well but the MIG has a connector on the front for powering the spool gun, so it makes sense to see if I could use that to power any such device. Here's the plug on the spool gun - China's finest:

It looks like this one. It seems to be described as another "aero connector", although I'd be concerned if any aircraft I travelled on sported these things. Either way, here's the socket on the front of the MIG machine:

And here's what's shown in the manual. No voltage specified:

This is what turned up from Amazon. Close - but no cigar. Can you see the problem?

Yes, the welder has female contacts and the Amazon product also has female contacts. Doh.

I bought 2 sets of these male/female connectors, so I can butcher one of them if necessary. Obvs I'd rather not but at £4 each, it wouldn't be the end of the world if I can come out of it with only one surviving connector that mates with the welder.

The central body is a slight rattle fit in the outer body and the rear has a larger diameter than the front, so clearly it's been push fitted in from the back with some form of ramp / latch to retain it. 

Sure enough, it's a simple matter to press the central body back out of the outer housing.

I was then able to push the alternative central guts back into the outer body.

Bottom line- yes, it works.

I now have 2 sets of connectors of each polarity. I can swap the remaining pair over if I find I need a second set.

How does the spool gun operate with the MIG welder?

The trigger switch on the spool gun operates a NO switch which energises the welding power to the torch. If the spool gun mode is selected from the front panel, the main feed motor is disabled and instead, the power for the feed motor is diverted to that 4 position connector (pins 1 and 2). The voltage measures as 22Vdc with no load connected. That's pretty much as you might expect.

So if you wanted to power a torch motor (to move the torch along the weld line), you might want to use that front connector - but unfortunately it will only work when the spool gun is being sued ie no use when you are using the main wire feed.

I guess I could modify the main unit so that 22V is fed to the 2 spare pins on the connector - or use a battery. Not what I would consider ideal.

What's the plan then, Fatty?

Looking at the various artefacts and having a play with them, I've concluded the following:

• "One wheel drive" on a 4 wheeled bogie isn't a great concept. Unless you apply constant pressure to the one driven wheel, the "cart" version doesn't have any traction.
• The "square tube with the big wheel" thingy isn't a serious option, apart from being obviously fragile in its current state. I quite like the idea of a single wheel adjacent to the torch head but to begin with I feel more interested in pursuing the 4 wheeler concept. I might come back to this later.
• The 4 wheeled bogie would be greatly improved if both wheels on each side were driven. This could be achieved by fitting a longer o-ring (drive belt) that goes around the motor and both wheels. I might refer to this as the "tracked" concept.
• Changing to a "dual shaft" motor (where the output shaft comes out both ends of the motor) would allow both sides to be driven.
• Trying to use the tracked concept on an inside corner might be tricky. I could imagine it being possible but TBH, this isn't really the target application, which is more sheet metal and thin pipe.

So, if I implemented this scheme on both sides of the motor, using a dual/double shaft motor, I'd achieve a sort of "all wheel drive" scheme, almost akin to a tracked vehicle. It would also be suited to running around the outside of a pipe.

The o-ring would ideally be rated for a fairly high temperature. Viton (FKM or "fluorinated") is suitable over 200C, whereas the default nitrile isn't much use above 120C or so. FFKM is rated even higher but is much more expensive - I can always get some later if / when I conclude this concept has legs. Silicone rubber would survive high temps but it's far too elastic (soft) to work as a traction element.

This motor is 42x42x34mm ie same size as previous but with dual shafts. At a tenner each plus postage, that doesn't seem like a bad deal, assuming they are a genuine outfit.

How to interface with the welder?

Unlike the old CEA MIG I have just jettisoned, the Arc Captain MIG200 doesn't have a pulsed "stitch" welding mode. It has a "spot welding" mode which energises the arc for a fixed on time after the trigger is pressed.

I'm thinking that I'd probably use an Arduino Nano to drive the Schmalzhaus stepper motor shield (or similar). It could also control the distance between "spots" (aka "dimes" to the Youtube warriors), independent of the speed of the torch. The number of step pulses to the motor and the distance between spots would be ratiometrically fixed - so I'd have one pot for speed and another for spot distance. The welder would be triggered by the Arduino to produce each spot weld.