Gun Turret for Disabled Hunter

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bwwnav
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Gun Turret for Disabled Hunter

Post by bwwnav » Fri Nov 07, 2008 3:14 pm

I am trying to build a gun rest for a disabled hunter. I need it to pan up/down/left/right. The rest is pictured below. For the elevation, I thought maybe some king of linear actuator (maybe with a 0.1"/sec rate) on the front end to raise and lower. Rotating is another issue. The rest will be made from tube aluminum and pipe because it has to be stout and take the recoil. I'd like to place the controls on a joystick (wired or wireless). I'm not familiar with robotics, but will take the time to learn, any recommended reading would be helpful, as well as any suggestions and design help. Powering and wiring will be another hurdle. Any hints, steps in the right direction will be much appreciated.
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Chupa
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Post by Chupa » Fri Nov 07, 2008 3:53 pm

interesting project...

I guess the first step is figuring out what the hunter will actually be doing. Is this just a rig to hold the rifle and take the recoil? Or are you looking for sort of SWAT robot type thing where the hunter will adjust all movement via remote (joystick).

I have never worked with linear actuators before but my first thought was to use a ball screw with appropriate shaft. I think some linear actuators operate on this principle so maybe they have already done the hard work for you.

Stepper motors will be your friend for this project. I don't think servos with enough power to move this weight exist. A sprocket around the rotating base with a chain to a gear on a stepper will give you the ability to rotate along with some "play" to take the recoil of the rifle.

For the pitch I guess you would have to do the same thing. A little stub with a sprocket comming off with chain to a stepper.

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philba
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Post by philba » Sat Nov 08, 2008 7:42 am

I wonder if Steve Hawking is taking up hunting now that he's retired. Sorry, couldn't resist.

I'd go look at pan and tilt platforms. There are a number for cameras. Use them for ideas and build to the forces you will encounter (both recoil and resistance/weight). There are robotic fire platforms - some done by hobbyists. You can find them through google. The ones I've seen are pretty lightweight. I suspect a fair number more are highly classified though...

I agree with chupa - use steppers. Nema23 at the least, maybe bigger.
What kind of power will be available? There are industrial servos used for welding bots and such that probably would work. Waaaay pricey, though. Basically, you'd be building a specialized servo.

Is repeatability an important requirement? recoil is likely to disrupt that.

What kind of feedback mechanism are you thinking?

Is this for a specific disabled person or in general? Since disabilities run a wide range it would be helpful to understand what you are designing to.

bwwnav
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Post by bwwnav » Sun Nov 09, 2008 2:45 pm

Thanks for your replies. To answer the above:

1. The platform is targeted to shooters with no ability to wield a gun. The operations (up/down/left/right) will be done with a joystick.
2. Rapid fire repeatability is not important, more like fire-aim-fire.
3. I'm not exactly what you mean by 'feedback mechanism'. There will be a scope on top that is hooked to an LCD display to view and aim.

I'm not familiar with robotics/motors etc. I want to maybe try a few experiments to learn. Are there any books you would recommend? Like I'm not sure, with a step motor, how to activate or power it. Does the motor plug directly to a power source, then operations would be through a controller chip, and the controller tied to an input device like a joystick? I wasn't able to find much about joystick options online. If possible, is there anything I should read/research first to be more versed? I hate to take up your time replying to the basic ideas when I could do the work and ask more pointed and technical questions here after I've put in the time learning.

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philba
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Post by philba » Sun Nov 09, 2008 3:48 pm

Feedback in this case means some sort of closed loop positioning but since there is a camera attached, it probably isn't an issue.

There is a really good book called "Building Robotic Drive Trains" by Clark and Owings. It discusses the drive electronics and mechanical aspects.

You might want to also look into CNC stuff as they deal with heavier duty motors and steppers in more depth than the robotics crowd. There are several online forums for that. CNCZone is a pretty good one

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jwax
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Post by jwax » Sun Nov 09, 2008 4:19 pm

Unless you're doing a career change to learn and design with servos/steppers, I'd agree with philba and use an existing pan/tilt head.
For one, recoil from a deer rifle is a show-stopping design criteria vs a .22 cal squirrel gun. Huge difference in designing the platform to handle recoil.
There's a number of "Internet Hunting" sites whereby a subscriber controls a distant gun to hunt with. See what they use.

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