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NDS
08-12-2008, 11:39 PM
OK, here's the deal. Ive got this big air cannon near completion and I thought a great first project would be to automate it with pan/tilt, on board camera, and elevation sensors.
The thing that has be stumped is what kind of motors to use for the pan/tilt. See, this thing is freakin heavy, so any normal sevo or geared motor would just give way to its 10lb+ girth. IS there any...uber-servo that could support this not-so-balanced beast?
thanks

4mem8
08-13-2008, 12:03 AM
It"s not so much the strength of the servo you use, it's the type of gearing you have in place, For instance if you had a 100:1 large base gear on a ball race to take the load and the 1 gear ratio on the servo that would take your load. There are many combinations here that would work.It depends on a few factors, Weight, and Speed of the pan/tilt you want.

NDS
08-13-2008, 12:17 AM
OK, but say I use a dc motor I have laying around. Is there any way to keep the weight of the cannon from just spinning the motor back into resting position?

Adrenalynn
08-13-2008, 01:00 AM
There are big honkin' servos out there. Very expensive. ($400+) - Vantec makes one.

As far as keeping it where it belongs with a DC motor, worm-gears are generally used. I have one telescope that's ~120lbs + 10lbs of camera gear, 6+feet long, and one of my mounts swings it around at 22deg/sec with reasonable accuracy, dropping down to fractions of a degree/sec when it "gets close". It uses a DC motor (12v) with a worm-gear box. My other telescope is 2.5ft long, 34lbs, and it performs similarly, a bit less than 20deg/sec.

Did you get the bottle off the gun? How else can you lighten the load? Hopper/ammo supply off the gun and fed externally? Why isn't it balanced?

NDS
08-13-2008, 01:08 AM
Did you get the bottle off the gun? How else can you lighten the load? Hopper/ammo supply off the gun and fed externally? Why isn't it balanced?
It's unbalanced because I would much rather mount it by the chamber, and the thing is like 5' long. The gas bottle/compressor is externally mounted, but I have to have the mag beneath the barrel for simplicities' sake. Alright, looks like I'm just going to have to get my hands on some big ass worm gears, oh how i long for simple sprocket/chain.:rolleyes:
EDIT-completely forgot about the tremendous recoil and diminishing ammo weight issue. I might even have to add shock springs in the back so it doesn't blow itself over.

Alex
08-13-2008, 09:33 AM
I'm no math guy by any means, and these maybe waay underpowered for your needs, but Robotis is coming out with an a ridiculously strong servo called the EX-106:

http://www.robotis.com/html/sub.php?sub=2&menu=2

(if it's in Korean click on English at the top)

ScuD
08-13-2008, 10:58 AM
I'm no math guy by any means, and these maybe waay underpowered for your needs, but Robotis is coming out with an a ridiculously strong servo called the EX-106:

http://www.robotis.com/html/sub.php?sub=2&menu=2

(if it's in Korean click on English at the top)

Djeez.. hobby robotics have come a long way since my first beam walker.

Electricity
08-13-2008, 11:15 AM
I may be wrong, but this isn't for an airsoft or paintball gun is it? Are you making some sort of magazine fed nerf/spud machine gun?

Adrenalynn
08-13-2008, 11:54 AM
If you have that much recoil, I wouldn't recommend a direct link to a servo no matter how strong it was. That's the kinda stuff that shatters gears. Even worm-gears probably shouldn't be in direct line with that recoil.

Electricity
08-13-2008, 11:58 AM
If your doing what I think your doing, which I think you are, doing what I think your doing that is, then you might want to consider having a separate dump chamber that vents out the back. It will greatly reduce recoil.

NDS
08-13-2008, 12:01 PM
I may be wrong, but this isn't for an airsoft or paintball gun is it? Are you making some sort of magazine fed nerf/spud machine gun?
1.78 bore 200psi pneumatic golfball gun.

@lynn, I know. I was thinking maybe some howitzer-style recoil absorbers before the gearing/motor.
Anyway, dont expect this to be done anytime soon. I have an extremely limited budget and school soon.

Adrenalynn
08-13-2008, 12:03 PM
I think that's a good plan - or start shopping for unobtanium wormgears. ;)

Electricity
08-13-2008, 12:04 PM
1.78 bore 200psi pneumatic golfball gun.

@lynn, I know. I was thinking maybe some howitzer-style recoil absorbers before the gearing/motor.
Anyway, dont expect this to be done anytime soon. I have an extremely limited budget and school soon.
What are you using for tubing? Also, how have you tested your barrel? 5' sounds a bit long.. And finally, your not planing on shooting this at people are you?
Just have to make sure lol.


Edit:
I think that's a good plan - or start shopping for unobtanium wormgears. ;)

BOOOOO!!! :p

Matt
08-13-2008, 12:08 PM
What about rigging up some hinges with linear actuators? That would be really strong, just not fast.
http://www.trossenrobotics.com/linear-actuators.aspx

NDS
08-13-2008, 12:10 PM
@ elec, Stainless/galvanized steel for the pressure vessel, and abs for barrel (lightweight). The barrel is actually like 3.5' long. The entire gun is 5'.
I would never, ever, ever even think of shooting people. Getting hit by a 500fps nerf is bad enough.

lol, unobtainium

EDIT- missed matt. I never even thought of those. bit pricey for me though, as i can get a nice big hammerdrill motor for 7:50 at the local junk bin. how would those actuators handle repeated shock?

EDIT EDIT- could I use those with somthing like a servo controller? In the end this should be laptop controlled.

EDIT EDIT EDIT- Elec, what is it you think im doing? I need the exhaust air for the gas operated breech though.

Matt
08-13-2008, 12:16 PM
how would those actuators handle repeated shock?

That's a "try it & experiment" kind of area. No specs on that sort of thing. I'd check the data sheet, but I doubt there's a line for "gun recoil max" LOL

Adrenalynn
08-13-2008, 12:59 PM
I'd think about shooting people with it, but I *probably* wouldn't. Not today anyway... ;)

A screw and nut's ability to handle shock is easily derivable. They can handle tremendous shock in-line, but the moment you have any angle on that shock they like to (literally) explode. High-carbon-steel shrapnel is not a pretty thing [unless you enjoy what Discovery Network has done with their "science" shows this season, and you have a blast-shield handy].

Other than decoupling or building a "recoiless rifle", I can't think of a safe way to directly couple the forces of recoil to the system. The downside to recoil is that it posseses a character of extreamly high instantaneous G forces for very short periods of time. I can push straight down on even a steel nut with thousands of pounds of continuous force and it will laugh at me, but rap it with a ball-pean once and it doesn't think things are so funny anymore... ;)

The best decoupling of the shock that I've seen is done with moderately viscous fluids. I shoot a .50 in competition, and have two rifles. One of them has oil-damped shock absorbing, the other doesn't. One I can shoot three or four times and I have to ice my shoulder for a couple hours and then get in the hot tub. The other I can fire until I run out of money [or the barrel melts] with the last round being within fractions of the very first.

Electricity
08-13-2008, 02:00 PM
Wait wait wait wait wait wait... Jodi, you own a 50? Marry me? (and my fiance, I can't just leave her behind..).

Adrenalynn
08-13-2008, 02:40 PM
Nope. Two of 'em. :tongue: An AR-50 with custom stock, and an M99.

LinuxGuy
08-13-2008, 02:57 PM
I think that's a good plan - or start shopping for unobtanium wormgears. ;)
Things would have to get a bit hot for those to work.. :p

8-Dale

Adrenalynn
08-13-2008, 03:05 PM
Sorry - I don't get the reference?

I use it here in the context of the aerospace industry.

Electricity
08-13-2008, 03:49 PM
One line joke into seventeen line break down..

sam
08-13-2008, 03:50 PM
Ok, I just read the thread, but there are a couple things that I don't understand.

You have a big penumatic gun out of balance and you want to have a pan and tilt system for it to move? Right so far?

The problem is that there is a lot of recoil when you shoot the gun? Couldn't you just put the whole pan and tilt platform on a kind slide? Like have a slide on the pan system so when the gun shoots, it can recoil. Then you can tilt the gun too.

Adrenalynn
08-13-2008, 04:03 PM
You could also decouple with a chain drive out of axis on a stepper for tilt and use a rotating plate (like a lazy susan) for rotation, chain-driven on stepper.

NDS
08-13-2008, 04:17 PM
Ok, I just read the thread, but there are a couple things that I don't understand.

You have a big penumatic gun out of balance and you want to have a pan and tilt system for it to move? Right so far?

The problem is that there is a lot of recoil when you shoot the gun? Couldn't you just put the whole pan and tilt platform on a kind slide? Like have a slide on the pan system so when the gun shoots, it can recoil. Then you can tilt the gun too.

Yes
Yes again, but I would have the recoil plate mounted on the tilt system so the motor/actuator/sevo wouldn't have to take all of the shock.

Adrenalynn
08-13-2008, 04:35 PM
http://servocity.com/html/ball_bearing_turntables.html

The bearings on the turn-tables would take the force, the stepper would freeze the chain's movement, the stepper wouldn't be in the "line of fire"...

sam
08-13-2008, 04:49 PM
A stepper for the pan would be a good idea. But it couldn't handle the tilt. So you don't know what to use for the tilt? Since you system is already penumatic you could use air muscles, give good contraction and a lot of force (50 pounds or so). The problem would be controlling the muscles. You would have to have a 3 way valve to give tiny bursts of air untill your at the right level. It could probably give 50 burst a sec, so the movement would be somewhat fluid I beleive.

Are you going to use a powerfull string for the recoil? Just a quick question : How many pounds of force is exerted (aprox) when a shot is fired?

Adrenalynn
08-13-2008, 04:51 PM
"But it couldn't handle the tilt"

Says who? I have a stepper here that will handle several hundred pounds without gearing. I can make a finger-nail sized stepper handle five trillion tons, albiet very slowly.

It's common place to find steppers handling over a thousand pounds industrially.

Adrenalynn
08-13-2008, 04:58 PM
http://www.anaheimautomation.com/42Y65_Series_IP65_Sealed_High_Torque_Stepper_Motor s_Splash_Proof.htm

4000+ oz-in - that's 250 pounds for an inch

sam
08-13-2008, 05:03 PM
*Whistles*

That's one stepper motor! :robotsurprised: Ok, so it could handle it. It weights 25 pounds about thought. But the most important : How much does it cost? Can't seem to find a price tag. :confused:

I imagine it's a pretty expensive.

sam
08-13-2008, 05:07 PM
I can make a finger-nail sized stepper handle five trillion tons, albiet very slowly.

It's common place to find steppers handling over a thousand pounds industrially.

Well, of course, but I think we can agree that we don't want to wait 90 seconds before the tilt is from maximum to minimum.

Yeah, but those steppers are licly to be very expensive. I should have added a price limit when I said it couldn't handle it... :veryhappy:

Adrenalynn
08-13-2008, 08:32 PM
$280 - About 2/3 of what a similarly torqued servo would cost.

Yes, it only weighs 25lbs. About 1/10th the weight of a compressor that would be capable of continuously driving a couple of "air muscles" capable of handling the weight? And, what, 1/20th the size? And how many cycles will stretched tubing handle versus motors that frequently have 10+ year warranties? Oh - and the air compressor is more expensive too.

A-Bot
08-13-2008, 09:08 PM
Does anyone know how the military actuates their robotic gun turrets?

sam
08-14-2008, 07:03 AM
Well, for the life expectensy, no one knows, probably much less than 10 years. For the price, he already said 125 was too much. (Maybe he's willing for this stepper tought since it's a beast)

He already has some compressed air onboard (I guess), so he could just augment the size of the compressor or the tank he has. If the air gun needs 200 PSI, I guess the tank is at least 1000 PSI, wich means he will have way enough to move the muscles for a while at 60 PSI. And I also think that he has a way of filling it, since he has the gun??

About 1/10th the weight of a compressor that would be capable of continuously driving a couple of "air muscles" capable of handling the weight?

No, a cheap compressor of about 25 pounds can supply plenty of air for more than 2 muscles. So I don't think that's the problem.

And, what, 1/20th the size?

He already has some compressed air for the gun, no need for a second compressor.

Oh - and the air compressor is more expensive too.

A compressor for 125$ could handle them, continuously. It doesn't need 100% duty, just need like 3 gallons.