Reddit mentions of uxcell DC 12V 1000RPM Micro Speed Reduction Motor Mini Gear Box with 2 Terminals for RC Car Robot Model DIY Engine Toy

> Geneva drive

Cool mechanism, but bulky and complex, lots of things can go wrong while making that, and it's a lot of work to make.
Consider just direct driving it with a simple servo, or stepper motor.
Both let you specify exactly how far you want the device to rotate, and omitting the Geneva mechanism oughta make the blaster much simpler.
Simpler means easier to build, faster to build, and generally more reliable.

For a stepper or DC gearmotor, you probably want a simple cycle switch to depress whenever the device is rotated so that a cylinder is in position, just so it knows when to stop if steps gets skipped. Lots of servos are position aware and don't need this.

If you do stick with the Geneva drive, you should look into either a stepper motor to power it, or search for a DC gearmotor. You can use the TT arduino gearbox, but run it at 2S voltages + with the stock motor so that it doesn't blow itself apart in a jam. I'd recommend an n20 gearmotor over it. If you do the geneva drive, that'll def give you style points + cool factor as well.


Perhaps this device would be adjusted/resized to be of use.

UCF gives you access to a pretty nice 3d printer, not sure if that's the limited access you mentioned.

That's all I can think of for now, if you come into any other questions, feel free to ask.

One last note.

n20 micro gearmotors are nice, and have a surprising amount of torque for their size. More than a lot of larger gear motors.

• See
  
• Torque the motor has
  
• Higher geared version of what I used in the ecto-ii, it's massive and the above n20 actually has more torque some how.
  
  • However, note the difference in gear ratios. Despite having more torque, the n20 gear motor will be slower to start up/stop as it has to get to much higher speeds.
    
• I want the motor to rip the blaster apart if something gets stalled tier. the 282 RPM version of that has 60kg/cm, so that motor probably has something like 120kg/cm when stalled.
  
  
  Personally, I'd probably try using a servo first, one that has 180 degrees rotation, then stepper, then that n20 gear motor if I didn't like the former two.
  The size of that n20 is super convenient, and it's prime shipping.
  
  Edit:
  One advantage of the geneva drive I just realized.
  The servo and stepper both have the ability to hold the cylinder in place in a direct drive, and make it quite difficult to move it.
  The servo will even return to it's specified position if you do manage to move it.
  But in both these cases, constant amount of power is required, and that'll drain a battery pretty quick if you always leave it on.
  
  In that case, you could either
  
  
• Use a cycle switch, keep checking the cycle switch with the micro controller, and if the cycle switch ever gets released, turn power on and deal with it. For the servo that's easy, just let the servo return to it's spot. For the stepper, unless you know what direction the stepper moved in, you'll have to get more creative.
  
• Perhaps use another servo (or a solenoid) as a locking mechanism?
  
  • EX, servo has an arm, cylinder has grooves that when no rotating, the servo puts that arm into to hold it still. Something along those lines.
    
    Edit Edit:
    In case you find a 180 degree servo limits your turret cylinder selection too much....
    
    
• https://www.adafruit.com/product/3614 (Provides a mechanism to get position, but doesn't automatically hold a position, you have to write code for it to.)
  
• https://www.servocity.com/hs-785hb-servo
  
• https://hobbyking.com/en_us/sail-winch-servo-13kg-0-7sec-360deg-55g.html
  Basically any non continuous, full turn/multi turn (often called winch) servo is ideal.
  
  And one last idea. You can always just add a potentiometer yourself to the turret cylinder. Then any old stepper/dc gear motor will be position aware, and you can direct drive it and return the turret to it's former rotation when an external force forcibly rotates it.