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Sentry Gun Project

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Unread postAuthor: POLAND_SPUD » Sun Jan 24, 2010 4:31 pm

@kenbo
I guess its how you achieve your precision more so than the motor type itself
yes, but servos have a limited number of steps while step motors can be geared down so they can achieve sub MOA accuracy and they can still turn the turret full 360 deg

@jsr
fill your neighbour's greenhouse with holes
uhmm... actually the one I hit all the time is mine

I still think that it would be better to build one with a
stepper motor

maybe it would be a little bit more expensive and slightly more complicated than buying a ready made product


It would be cool if someone who has some experience in robotics or electronics would post in this thread
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 24, 2010 4:45 pm

POLAND_SPUD wrote:maybe it would be a little bit more expensive and slightly more complicated than buying a ready made product


This is my main issue, when it comes to the software and electronics I haven't the faintest clue. This package seems to be a reasonably priced unit where all the work has been done, and as far as I can see it's constantly being updated. The hardware portion of such a project is a challenge in itself so I'd prefer to concentrate on that.
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Unread postAuthor: kenbo0422 » Sun Jan 24, 2010 11:03 pm

Our servo motors were geared down to about 1200:1 and turned quite fast with the accuracy of about a micron. They weren't the hobby type, though and they worked like a regular motor. They were about 4 inches long and about 3/4 inches in diameter, planetary gears and all. Any motor can be geared down. It would more likely be the accuracy that you want to achieve between steps. With a stepper, you can achieve high precision without gearing it down by way of microstepping, which is having two coils energized at the same time but with different amperage. By shifting the amperage (usually digitally), you minutely change the position of the shaft. It retains the original torque, but with a higher degree of precision for those pinpoint targeting goals.

But, from the looks of the screenshots, I doubt you would need to go to that much trouble. The simple looking setup that was shown seemed to be quite adequate.
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Unread postAuthor: Ragnarok » Mon Jan 25, 2010 1:19 am

jackssmirkingrevenge wrote:Even without a functioning gun, it would be pretty cool to have it follow people around the living room especially as the default sounds for the program are the cute but creepy effects from the Portal sentry turrets...

Heck, I think you could make an effective area denial system with just the creepy voice.

"Are you there?"
*Trained soldiers run off screaming*
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 25, 2010 1:21 am

Ragnarok wrote:Heck, I think you could make an effective area denial system with just the creepy voice.


Quite. A fake gun barrel with maybe a laser coupled with that voice would be enough to make me bugger off :)
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Unread postAuthor: Demon » Mon Jan 25, 2010 7:49 am

Well, i have built a sentry turret :roll:

And learned everything to do it within 6 months while being in school and making spudguns...
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 25, 2010 8:42 am

Demon wrote:Well, I have built a sentry turret :roll:


And why isn't it in the showcase then? Go on, let's see it :)

Is it simply remote control or does it track moving targets automatically?
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Unread postAuthor: Demon » Mon Jan 25, 2010 11:51 am

And why isn't it in the showcase then? Go on, let's see it

Is it simply remote control or does it track moving targets automatically?


I dismantled it to take the pieces for my line following robot...

It was only tracking on horizontall and there needed to be nothing else then the target or else it would start to 'look' at a chair or anything else...It was pretty dumb and would never had supported the weight of an airgun...(It was my first project tough)

Keep in mind that the more accurate the sentry is, the slower it is.

The corean have made a fully operatable sentry turret with a machine gun mounted on it.

http://www.youtube.com/watch?v=v5YftEAbmMQ
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Unread postAuthor: dewey-1 » Mon Jan 25, 2010 12:45 pm

@JSR

Here is a Robotics site that I found to be quite interesting!

They also have a forum. Note the MechWar secion.

http://forums.trossenrobotics.com/

This looks like the controller.
http://www.pololu.com/catalog/product/727/resources

JSR may soon become an electronics nerd!

edit; added another source
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Last edited by dewey-1 on Mon Jan 25, 2010 4:09 pm, edited 1 time in total.
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Unread postAuthor: JeffSinger » Mon Jan 25, 2010 2:08 pm

POLAND_SPUD wrote:@kenbo
I guess its how you achieve your precision more so than the motor type itself
yes, but servos have a limited number of steps while step motors can be geared down so they can achieve sub MOA accuracy and they can still turn the turret full 360 deg

@jsr
fill your neighbour's greenhouse with holes
uhmm... actually the one I hit all the time is mine

I still think that it would be better to build one with a
stepper motor

maybe it would be a little bit more expensive and slightly more complicated than buying a ready made product


It would be cool if someone who has some experience in robotics or electronics would post in this thread
you still think steppers would work? then answer/solve the problem in my previous reply.

steppers are stupid. they don't have potentiometers. you can't tell them to go to an angular position without having software try to calculate where they currently are. servos know where they are at all times, whether they loose power or not. steppers are stupid and you only need 40-60 degrees of travel due to the field of view on the camera. There's a damn good reason the automated turrets out there use servos and the dumb/simple remote control one use steppers.
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Unread postAuthor: kenbo0422 » Mon Jan 25, 2010 2:40 pm

A stepper would need a reference point, a simple switch that would open/close and tell a separate microprocessor that it has reached a zero point, or home position (like an XY stage on a homemade CNC router). From there, the stepper can move to any position. The backside of this is there is no feedback. If a stepper misses a pulse, you wouldn't know it. If you install a code wheel on a stepper for feedback, you eliminate this problem and the processor can adjust. Hobby servos usually go to their home position on startup, and that position can be tweaked. Once it is set properly, the processor can move the servo with great reliability. Otherwise my electric racing cars would be more of a PITA than a source of fun.
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Unread postAuthor: USGF » Mon Jan 25, 2010 3:38 pm

JSR,

We'd get a small pan tilt web or security camera. Remove the existing motors. Likely to be miniature stepper motors. Build a small interface board to drive larger stepper motors. Transfer the camera and weapon onto the newly built gun mount. As you note, software is available everywhere. There are people that will write custom code for a low cost if not.

BTW, the confusion in this thread seems to be guys are mixing up Radio Control servos with dc servo motors with encoders attached. They loosely do the same thing but obviously are set up differently.

For lowest cost, go stepper. Open loop and not as fast. The servo can be faster and thus more accurate but will likely cost more.

USGF
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Unread postAuthor: POLAND_SPUD » Mon Jan 25, 2010 3:59 pm

@JeffSinger
I've already mentioned using encoders...

@ USGF
yeah I know that step motors with encoders are, technically, servos

but the software offered by that guy has to be used with RC servos

and I think that when people used the word 'servos' here, they meant RC servos
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Unread postAuthor: Ragnarok » Mon Jan 25, 2010 9:49 pm

Demon wrote:The corean have made a fully operatable sentry turret with a machine gun mounted on it.
http://www.youtube.com/watch?v=v5YftEAbmMQ

Already linked - that's the Samsung SGR-A1 mentioned before.

Bloody weird video though. It starts out with your normal "triumphant music played on an electric keyboard using the brass band setting" that you get on ALL weapon demonstration videos, then switches to the Pirates of the Caribbean theme.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 26, 2010 2:13 am

dewey-1 wrote:JSR may soon become an electronics nerd!


That looks like the one :) but I doubt I would actually go into such detail, in the same way that I would prefer to buy ready made PVC barrels than cast them out of epoxy, if the technology's there, why reinvent the wheel?

I think the whole stepper motor vs servo discussion is a bit moot, the guy at paintballsentry.com seems to be getting fantastic results from R/C servos so why overcomplicate the issue? I'd much rather have a prebuilt solution so I can concentrate on the hardware portion of making a reliable high pressure BBMG turret ;)
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