Custom Fighters - Custom Streetfighter Motorcycle Forum banner

Electronical gurus, please confirm I have a vague idea what I'm doing?

1K views 7 replies 4 participants last post by  SEBSPEED 
#1 ·
Not quite bike related, but I'm making a rotary positioner for welding round shit. Maybe making 2 of them.
Been wanting to for a while, and we just replaced a couple of the swiveling seat bases in one of the helicopters. I made the replacements, they're stout machined bits of 7075 and the bearing for the pivot is like 8" diameter, and the inner piece has a very convenient radial bolt pattern. Perfect for what I need. I'll make a big ring gear for it and stick a small gear on a motor to turn it.

Dug around in my shit bin and found an old Milwaukee M12 drill marked NFG. The battery connector broke on it... probably could have made it good as new with a bit of epoxy, but that's no fun. There's no useful label of any kind on the motor (has a Milwaukee part number which has no info associated with it), so I have no idea what the amperage draw on this thing is.
The trigger is some Chineseum company and marked for 24V/15A (the motor and battery are 12V). So... I'm guessing as long as my other components are rated for 15A I should be good, right?

I think the motor is PWM but I'm not sure how to tell, other than the fact that there's a big circuit board in there doing some kind of fancy bullshit. Hooking up my benchtop power source directly to the motor runs it fine, and changing the voltage changes the speed. Hooking power to the battery connector, though, kicks the motor on for a split second and then flashes the battery light on the board angrilly. The broken tab on the connector corresponds with a contact marked "T" on the M12 battery... I'm guessing some kind of thermal protection, but I don't know what kind of signal it would need to fool the board.


What I'd like to do is have the ability to run it off both an M12 battery or wall power, but if I have to pick one it would be the wall. To do this I'm thinking I can fix the connector from the drill and use the board from it, then immediately downstream from the board I'll link the wall power in, with diodes from both sources to keep things from flowing to the wrong places.

For the wall power, I'm thinking a 12V/15A power supply (this one looks ok I think).

As for the control, on the battery side I'd jump the trigger (can I even do this without making the board angry??) so it's effectively always on, and feed both sources into something like this PWM speed controller (do I even need PWM?)


My automotive electrical knowledge has come a long way in recent years, but I'm still catching up on the rest of it. Does this all make sense? Is there some big concept I'm missing that fucks it all up?


There's also an old DeWalt nicad drill in the shit bin. Guarantee there's no fancy computer bullshit in that one. Maybe better off reassembling (and maybe even fixing?!) the Milsuckee and using the DeWalt for the franken-spinner-thingy?
 
See less See more
#2 ·
Yeah fuck it I think I'll try and reassemble the Milwaukee and use the DeWalt guts... probably work on that tomorrow.
But I don't know if
A) The DeWalt motor works. May be the motor's burned out, won't know til I tear it apart.
B) I'll be able to reassemble the Mil. I took the gear reduction apart out of curiosity and it's a triple-stacked, dual-stage planetary set with no data sheet anywhere on the interwebs. I think I'll be able to put it back together off memory and logic but neither of those are my strongest qualities :D

In the event this route is successful, I'd still need a DC power source (of a different rating) but for the speed control I'd need... something. Either a potentiometer or a rheostat I think, but I'm actually not sure of the difference. Which one would be best suited?
 
#4 ·
Either a potentiometer or a rheostat I think, but I'm actually not sure of the difference. Which one would be best suited?
They are not identical, but pretty much the same thing. They both do the same job, but one has two contacts and the other had three. A rheostat is a variable sliding resistor + contacts sort of deal with two contacts, or terminals. Whereas a potentiometer just has an extra terminal where you can splice off voltage from the sliding resistor. I don't know what that 3rd terminal would be needed for, unless you wanted to have a readout of the voltage ?

I don't know if it's true or not, but I've always heard rheostats are more heavy duty, so that may be better for your project since it may see extended run times under a lot of resistance. But I can't swear that's true.

No clue on the rest of the stuff, but I can't see an battery drill pulling more than 15amps, so I think you'll be good there. Most battery drills can't hang with a legit corded drill, and we plug those in to 15amp wall circuits.
 
#3 ·
How about a second tig pedal to control the table speed? That's how the ones at my old job were set up. Right foot arc control, left foot table control, maximum brain effort lol
 
#6 ·
Sorry guys got a little sidetracked from this. Back at it now, still need to pick up some bleach to clean the blood off the helicopter bits.



Yeah that's something I was thinking about, and old sewing machine pedals are cheap.
Trying to decide between that and a finger control, like the sliding hand amptrols that velcro onto the torch. You have any thoughts on that?

They are not identical, but pretty much the same thing. They both do the same job, but one has two contacts and the other had three. A rheostat is a variable sliding resistor + contacts sort of deal with two contacts, or terminals. Whereas a potentiometer just has an extra terminal where you can splice off voltage from the sliding resistor. I don't know what that 3rd terminal would be needed for, unless you wanted to have a readout of the voltage ?

I don't know if it's true or not, but I've always heard rheostats are more heavy duty, so that may be better for your project since it may see extended run times under a lot of resistance. But I can't swear that's true.

No clue on the rest of the stuff, but I can't see an battery drill pulling more than 15amps, so I think you'll be good there. Most battery drills can't hang with a legit corded drill, and we plug those in to 15amp wall circuits.
Voltage readout would be cool... an analog needle type would give me room to make my own dial with RPM markings on it. Might lean toward potentiometer then if I go this route.


Those are likely DC brushed motors and you'll want to keep the board or run it off a variable bench supply that can keep up with the current at lower voltages. Fake the temp input for the one that works with a pot, it's probably 10k to ground or so and if you wire the wiper pin back to one side of the pot you can adjust it until the temp sense circuit is happy, it simulates an NTC thermistor in a good temp. Or just measure the thermistor in the battery pack and add that resistor value to the input/ground.

The trigger is probably just a variable resistance, measure it with a DVM to make sure. If it is then you can wire pretty much whatever you want to it as long as the impedance is close. Personally I'd just make a little box with a trimmer and a knob that sits near your jig, and if you need to adjust it it's right there assuming you aren't feeding filler. A tig pedal works too if you can get the resistance right, they are usually multi turn pots on a mechanism that pulls a string or similar if I remember right.

15 amps sounds pretty reasonable for full load and full speed. Remember its 15 amps at 12vdc, not 15 amps at 120vac. Wattage is very different between those two. If it's easy to spin the rig then you wont need as much current. Current draw is proportional to load.

If your wiring in an external power supply to the board as a parallel power input, be careful if the batteries are lithium. They dont respond well to overvoltage (fire/explosion) and you should use a diode to isolate the battery pack when on external power.

Can any DC motor be ran off a PWM controller? Or is there a difference between motors designed for PWM and those intended for voltage modulation? Haven't been able to find a clear answer on google.

Diodes will definitely be used.
 
#5 ·
Those are likely DC brushed motors and you'll want to keep the board or run it off a variable bench supply that can keep up with the current at lower voltages. Fake the temp input for the one that works with a pot, it's probably 10k to ground or so and if you wire the wiper pin back to one side of the pot you can adjust it until the temp sense circuit is happy, it simulates an NTC thermistor in a good temp. Or just measure the thermistor in the battery pack and add that resistor value to the input/ground.

The trigger is probably just a variable resistance, measure it with a DVM to make sure. If it is then you can wire pretty much whatever you want to it as long as the impedance is close. Personally I'd just make a little box with a trimmer and a knob that sits near your jig, and if you need to adjust it it's right there assuming you aren't feeding filler. A tig pedal works too if you can get the resistance right, they are usually multi turn pots on a mechanism that pulls a string or similar if I remember right.

15 amps sounds pretty reasonable for full load and full speed. Remember its 15 amps at 12vdc, not 15 amps at 120vac. Wattage is very different between those two. If it's easy to spin the rig then you wont need as much current. Current draw is proportional to load.

If your wiring in an external power supply to the board as a parallel power input, be careful if the batteries are lithium. They dont respond well to overvoltage (fire/explosion) and you should use a diode to isolate the battery pack when on external power.
 
#7 ·
Was able to get the Milwaukee back together with only the bare minimum of extra pieces leftover :D

Then I used it to crack open the DeWalt.




Motor tested out ok.




It's marked for 9.6V but the manufacturer's data sheet lists it as 6-20V with nominal voltage of 18.... so I think I'll try and find an 18V power source.





Having trouble with the gearing... which is to say I think I'm gonna need more of it than originally planned. The motor's data sheet lists maximum efficiency at 15,680 RPM. Even if I run it an appreciable percentage below that, it's still stupid fast.
One idea is to make a vertically stacked gearbox underneath the rotating platform... basically a stack of large gears (8"+) on a central shaft (not locked to it though) with small (<1") gears connecting each large gear to the one above it. Would still need a stack of 6-8 probably to step the platform down to a reasonable RPM.
Another idea is to use the planetary gearbox from the drill to step down to whatever it's reduction is initially. That would double the length of the motor assembly, but I could cannibalize a right-angle gearbox from my pile of dead die grinders and have the motor assy oriented horizontally instead of vertically as I'd been planning.
Might need to do both and have the planetary run into the stack. 15k is pretty fast.

Will pick up bleach this weekend and after an overnight soak I can actually measure the parts and figure out how to fit what into where.


Need to pin down whether or not a PWM controller will work with this motor. If it will then that bit's solved and I can order one up on Amazon. Also need to find an ~18V 15A power supply that isn't too massive.
 
#8 ·
I'm not a fan of the torch mounted amptrol, prefer foot pedal. I'd prefer to manage one function per appendage lol

It may sound crude but what would be so bad about just strapping the drill to the base of the turntable and running wires to the power and trigger wires for speed function?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top