Stepper? Servo? What is this?

KAS · Post by **KAS** » Fri Mar 13, 2015 8:04 pm

I tried this a few years ago on the EEVblog and wasn't that successful. But I have more pictures now and it's either this or clean out the garage.

Our unit was tasked with reclaiming the warheads (MK84/BLU109 bomb bodies) from AGM-130's. This weapon system has been retired and sent to our location for reclamation. That's boring the back story, now the good stuff.

In the seeker section of the guidance unit both the IR and TV version have camera gimbals that are controlled by mystery motors of some sort. Boeing sent me the drawing of what they had, although it doesn't tell "me" much. Each side has a motor with four wires ( red, Black, Yellow, Green) with the opposite side having a "torque motor" with two wires (red, Black). When you apply voltage to both torque motors it basically creates an electromagnetic field and centers camera on the gimbal. I believe this is for stabilization during flight. When the weapon is powered up the cameras auto center. Without power the camera falls instantly to the bottom.

The Pickoff motors, I have no clue. Originally my goal was to create a joystick to move the camera around inside the seeker. Basically a static display to play with at work.

Oh, look up the part numbers to see how much this crap cost ... What a joke.
http://www.dlis.dla.mil/webflis/pub/pub_search.aspx" onclick="window.open(this.href);return false;

[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150313_105050.jpg[/img]
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150313_105134.jpg[/img]

[img]http://i482.photobucket.com/albums/rr189/Onuxis/data.jpg[/img]

Mac The Knife · Post by **Mac The Knife** » Fri Mar 13, 2015 9:25 pm

I vote servo motor. with "pick off" meaning "encoder" in the civilian world.

Nylocke · Post by **Nylocke** » Sat Mar 14, 2015 1:45 am

Looking at what pins it goes into I also vote Servo. It says +10V, -10V, IN, and GND. Steppers have a + and - for each coil (generally on stepper drivers they are known as A+/- and B+/- I think). You got a way for the motor to go forwards and backwards with the + and - 10VDC, a signal pin for the encoder, and GND. The second motor is probably slaved to the first in some manner.

Generic Default · Post by **Generic Default** » Sat Mar 14, 2015 2:30 am

I don't think steppers are used much in high performance stuff like this, steppers vibrate too much and are too slow. The sensor gimbal needs to be able to center extremely quickly and smoothly with no lost steps.

The 4 wires are the rotary encoder, the 2 wires are the motor power wires. At least I think.

EDIT:

The encoders are actually laser gyros, those things are worth >$10,000 each. The motors are DC. You should take a lot of pictures and do a dis-assembly thread!

http://www.google.co.in/patents/US4520973" onclick="window.open(this.href);return false;

barry99705 · Post by **barry99705** » Sat Mar 14, 2015 10:20 am

Agm130's were really cool. Used to load them on f15e's. Watched 4 of them go through the same hole on a target when they were dropped several miles away. Don't know why we use explosives to kill tanks. A 2000 pound laser or TV guided rock will turn one inside out.

KAS · Post by **KAS** » Sat Mar 14, 2015 1:34 pm

Thanks for the inputs so far. Servo seems promising if that's the case, hopefully it wouldn't take much to control it.

This is the government cost for one torque motor, this seeker uses two of them http://www.dlis.dla.mil/webflis/pub/pub ... &newpage=1" onclick="window.open(this.href);return false;

Few more pics.

[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150313_111159.jpg[/img]

Penny in the photo to show the size of the components.
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150313_105557_1.jpg[/img]
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150313_105516.jpg[/img]
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150313_105510.jpg[/img]
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150313_105041.jpg[/img]
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150313_105012.jpg[/img]

Polygonhell · Post by **Polygonhell** » Sat Mar 14, 2015 1:44 pm

Cost doesn't surprise me, in the early 90's there were no SS gyros and laser gyros were stupid money. I worked in aerospace for a short time In the late 80's on both military and commercial projects and costs for anything we produced was more about development cost and projected unit sales than actual manufacturing cost.
On the military stuff everything was also incredibly low tech for the time largely because anything only a few years old was rarely available in a mil-spec version. And of course those versions were usually 10x the cost of the standard component.

Generic Default · Post by **Generic Default** » Sat Mar 14, 2015 4:10 pm

It looks like the control boards are coated in some kind of epoxy for weather/waterproofing.

All of the functionality of that thing (minus the explosive part) can now be done for a few hundred dollars with hobbyist RC parts. The accelerometers, gyros, magnetometers, motors, controllers, batteries, ect. can all fit in a space the size of your hand.

The optics haven't exactly come down in cost yet, but visible light cameras like those on the Raspberry Pi could be substituted.

The gimbal could be printed, it would probably work fine with cheap skateboard bearings as inserts.

I'm tempted to make one of these.

KAS · Post by **KAS** » Sat Mar 14, 2015 5:58 pm

It's a conformal coating although if that gets wet, something has already gone wrong. It sits inside a sealed section that's never meant to be opened and pressurized with argon. While hobbyist RC electronics could definitely handle the basics. They would require specialized parts or modifications to work with the aircraft's 400hz power or the encrypted GPS signals the military uses not to mention the various odds and ends. But you're right... The technology has improved drastically over the last 20 years and so has our weapons. That's main reason we decommissioned this system.

Small Diameter Bomb or GBU-39 are becoming the weapon of choice right now. We can pretty much mount them on anything because of the size.

You're looking at the "last" AGM-130 in US inventory
[img]http://i482.photobucket.com/albums/rr189/Onuxis/11156717794_74ed8ce952_o.jpg[/img]

Eric · Post by **Eric** » Sat Mar 14, 2015 6:25 pm

What happens to all the parts after disarming, other than the few examples that end up in military museums? I'm guessing they remain sensitive and aren't trashed like dessicant? I'd be willing to help figure it out for you, if you sent me one.

KAS · Post by **KAS** » Sat Mar 14, 2015 7:46 pm

Eric wrote:What happens to all the parts after disarming, other than the few examples that end up in military museums? I'm guessing they remain sensitive and aren't trashed like dessicant? I'd be willing to help figure it out for you, if you sent me one.

Each item has a reclamation code that dictates the way it's disposed of. Everything here in the giant aluminium containers was shipped to Indiana and shredded for scrap. Trashed desiccant is one thing, but I'm a year out from retiring and I wont take any chances with that

[img]http://i482.photobucket.com/albums/rr189/Onuxis/11156597915_1cda79f425_o.jpg[/img]

In the distance top right you'll see the containers filled with guidance sections and seekers
[img]http://i482.photobucket.com/albums/rr189/Onuxis/11156659446_60d980b162_o.jpg[/img]

Rocket motors are ignited with a linear shape cutting charge in a demo pit
[img]http://i482.photobucket.com/albums/rr189/Onuxis/11156633106_14e12e57e7_o.jpg[/img]

Generic Default · Post by **Generic Default** » Sun Mar 15, 2015 2:16 am

Tax money well spent. I guess it's better than blowing people up, right?

KAS · Post by **KAS** » Sun Mar 15, 2015 9:02 am

Generic Default wrote:Tax money well spent. I guess it's better than blowing people up, right?

We're the low man on the totem pole doing the grunt work saying the exact same thing( minus the blowing people up

). This operation to reclaim something so insignificant in value, had to be done at a loss. Only feasible explanation we were told was the program management team for this weapon was shutting down and we had to make sure all assets world wide have been accounted for and dismantled.

Our unit handles depot level maintenance and works with a lot of contractors testing new systems and procedures. We're use to getting off the wall operations that most other units wont ever see.

Anyways, this is getting off topic and my fault. I'll grab more photos of the motors on Monday. The two Torque motors only have the black and red wire going to the motor it's self. the cable bundle that runs through the center is for the camera.

Same for the Pitch/ Yaw motor, 4 wires to the motor only with a hollow center for pass through wiring.

[img]http://i482.photobucket.com/albums/rr189/Onuxis/img0324gx.jpg[/img]

barry99705 · Post by **barry99705** » Sun Mar 15, 2015 12:34 pm

Generic Default wrote:It looks like the control boards are coated in some kind of epoxy for weather/waterproofing.

All of the functionality of that thing (minus the explosive part) can now be done for a few hundred dollars with hobbyist RC parts. The accelerometers, gyros, magnetometers, motors, controllers, batteries, ect. can all fit in a space the size of your hand.

The optics haven't exactly come down in cost yet, but visible light cameras like those on the Raspberry Pi could be substituted.

The gimbal could be printed, it would probably work fine with cheap skateboard bearings as inserts.

I'm tempted to make one of these.

It would have to survive the drop though. Bombs don't just fall off. They are shoved away from the bomb rack explosively. There have been examples of pilots bombing themselves due to the bomb not getting enough distance from the plane, then the slipstream pulling it back in.

Eric · Post by **Eric** » Sun Mar 15, 2015 6:16 pm

Anyway, to achieve your stated goal of moving the assembly with a joystick, I suspect the pick-off assemblies can be ignored. Just use the torque motors with visual feedback, which is all a static display needs. With only two wires, they're presumably DC motors, so just a matter of finding the right voltage to run them at.

rpress · Post by **rpress** » Mon Mar 16, 2015 6:04 pm

Here's my take. The pickoff is a feedback device, so it's a servo system. The +/-10V are power supplies to the feedback devices, note they are the same for each axis. Once powered up the PO IN will change voltage depending on the angle of movement. The torque motors are electromagnets.

Hook up a joystick to a RasPi with a Pololu DRV8835, and write a Python script to do the servo loops.

teoman · Post by **teoman** » Mon Mar 16, 2015 6:36 pm

What kind of power supply does that thing have? Battery powered or derives power by means of a generator from the engine?

+-10V is an awkward voltage.

Captain Starfish · Post by **Captain Starfish** » Mon Mar 16, 2015 6:49 pm

Awkward maybe but pretty standard in the world of op-amps and it makes sense when the thing could be moving bidirectionally.

Note that, if it's using laser rings, your output is likely going to be a rate-of-turn rather than a position.

If it centres as soon as you put X volts across the wire pair, try varying the voltage - does it change position?

KAS · Post by **KAS** » Mon Mar 16, 2015 7:10 pm

3-Phase 115VAC 400Hz when running off the aircraft, upon weapon release 20vdc is fed into into this chemical activated battery that produces 28VDC/30A for 40 minuets. This powers an internal converter that brings back aircraft power 3-phase 115VAC 400Hz for the remaining flight. Over engineered I guess, I mean it worked but damn....

[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150316_185856.jpg[/img]

KAS · Post by **KAS** » Mon Mar 16, 2015 7:28 pm

I'm not seeing anything looking like a diode or laser. The center hub mounted on a bearing and has one contact that spins while touching the outer black wall. The Black and Red wire have a trace that appears to pickup that contact when it passes by. The Yellow has two contacts always touching the center hub. The Green is a mystery, it has a trace that goes towards the edge but it's not visible on the wall like the others. Unless it connects the wall itself somehow.

The torque motor is definitely a electromagnetic device of some sorts. The metal wings are magnetized. The black ring is magnetized when you hook up a 9v battery to it. Then it aligns to match the correct poles.

[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150316_183942.jpg[/img]
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150316_184012.jpg[/img]
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150316_184633.jpg[/img]
[img]http://i482.photobucket.com/albums/rr189/Onuxis/20150316_185049.jpg[/img]

rpress · Post by **rpress** » Mon Mar 16, 2015 7:37 pm

The pickoff is a potentiometer of some sort? Is the green wire attached to the metal body? Some resistance measurements would be interesting.

The black/red might be for limit switches.

When I look at the wiper contacts I think that they won't wear very long. But then again the powered on lifetime is measured in minutes!

McSlappy · Post by **McSlappy** » Mon Mar 16, 2015 7:57 pm

This is fascinating.

You're not planning on trying to rebuild one are you? I would advise against it on this public forum

KAS · Post by **KAS** » Mon Mar 16, 2015 7:59 pm

McSlappy wrote:This is fascinating.

You're not planning on trying to rebuild one are you? I would advise against it on this public forum

haha, I wouldn't have to rebuild it. The two in the above image are sitting in my office

KAS · Post by **KAS** » Mon Mar 16, 2015 8:01 pm

rpress wrote:The pickoff is a potentiometer of some sort? Is the green wire attached to the metal body? Some resistance measurements would be interesting.

The black/red might be for limit switches.

When I look at the wiper contacts I think that they won't wear very long. But then again the powered on lifetime is measured in minutes!

Rotating shaft clockwise only and measuring with a Fluke 1587 on auto range.

black - red constant 10.64k ohms
black - yellow starts 1.0 ohms to 15.49k ohms, starts 1.0, climbs to 15.49k then restarts at 1.0
black - green 2.823k to 5.453k, it starts 2.823k climbs to 5.453k then lowers back to starting 2.823 (like a sine wave)

green to yellow 9.62 to 18.90k, hits 18.90 then resets to 9.62
green to red constant 5.471k

red to yellow 1.0 to 24.02k, starts 1.0, climbs to 24.02 then restarts at 1.0

rpress · Post by **rpress** » Mon Mar 16, 2015 8:14 pm

KAS wrote:
rpress wrote:The pickoff is a potentiometer of some sort? Is the green wire attached to the metal body? Some resistance measurements would be interesting.

The black/red might be for limit switches.

When I look at the wiper contacts I think that they won't wear very long. But then again the powered on lifetime is measured in minutes!

Rotating shaft clockwise only and measuring with a Fluke 1587 on auto range.

black - red constant 10.64k ohms
black - yellow starts 1.0 ohms to 15.49k ohms, starts 1.0, climbs to 15.49k then restarts at 1.0
black - green 2.823k to 5.453k, it starts 2.823k climbs to 5.453k then lowers back to starting 2.823 (like a sine wave)

green to yellow 9.62 to 18.90k, hits 18.90 then resets to 9.62
green to red constant 5.471k

red to yellow 1.0 to 24.02k, starts 1.0, climbs to 24.02 then restarts at 1.0

Ah yes it is a potentiometer. The red and black are the outer terminals and the yellow is the wiper. So it makes sense to apply +/-10V to red and black. The resistive part is the outer ring and not the inner one. Not sure what's going on with the green wire, it's some kind of reference.

You could hook that up to the ADC on an Arduino/whatever pretty easily, and you can use the voltages to make the ADC happy, like 0-5V. The Pi has no ADC so you'll need to rig something up for that (like an I2C one).

What's the motor resistance?

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