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Author Topic: T.A.R.G.E.T - Rotating Seven gun turrets?  (Read 47755 times)

C-3PO

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Re: Rotating seven gun turrets?
« Reply #175 on: January 01, 2017, 05:07:16 PM »

Martin,

Yes I am sure you could use micro switches - it just adds another level of complexity of both build and sensing - I think it could be tricky to get switches aligned so you get guns aligned in park position

Maybe a rotary encoder - but again more hassle!!

I am playing with driving "2 servo's as one"  -  2 standard servos attached to each other to get 360 degrees movement which gives the positional feedback

Could just use a 1.5 turn sail servo of course but I don't have any of those in my junk box...

Bob - I honestly think the "system split" between 2 hulls is something to assess at the end of the journey as who knows what the most elegant solution to that may be as the basics have yet to be defined and decisions now could easily change - all part of the fun.


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Colin Bishop

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Re: Rotating seven gun turrets?
« Reply #176 on: January 01, 2017, 05:26:47 PM »

I would agree that the split hull issue is peripheral to the generic solution. Bob. you are going to need physical connections to join the two halves of the hill together anyway. There are many multiway locking connectors on the market with reliable twist locks and other quick connect/release mechanisms so utillising perhaps a couple of these would not really add to the complexity of attaching and detaching the two hull halves and could make life a lot simpler.

With regard to jittery servos, if it is the servo itself that is the problem then more expensive servos may be the solution such as these: http://www.hyperion-world.com/en/p1005985-hp-ds20
A quick search online suggests that others have encountered this issue when trying to set up remotely controlled cameras which also need a very smooth action with no jitter.

Colin
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C-3PO

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Re: Rotating seven gun turrets?
« Reply #177 on: January 01, 2017, 05:54:53 PM »

Hi Colin,

Re jittery servo - the cause I believe is that I am simply telling it to frequenty to move little amounts - there are quite a few ideas yet to exhaust with this challenge

I am going to go back to basics and look at the signal supplied to make servo sweep smoothly and see if I can glean update rate etc from that and then simply duplicate what I find.

Re the 2 hull bit - my original suggestion was along the line of a Master and Slave unit - they could talk to each other through the bulkhead without any physical connection either by radio or by light/IR if a transparent "waterproof" window was created on both joining faces of the hull.

Or perhaps a magnetic multiway connector like the ones on the current MacBook's which are super clever

C-3PO
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Colin Bishop

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Re: Rotating seven gun turrets?
« Reply #178 on: January 01, 2017, 06:02:01 PM »

Yes, plenty of connection options I would have thought, your suggestions are interesting.

Just been looking around and there is a lot of stuff about smoothing servos such as this extract: http://forum.arduino.cc/index.php?topic=19367.0

I expect I am trying to teach you to suck eggs though and I take your point about sending too frequent signals to the servo. I suppose it is really a question of finding the right combination for the electronic and mechanical parts of the system to 'mesh' efficiently.

Keep up the good work.

Colin
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Re: Rotating seven gun turrets?
« Reply #179 on: January 01, 2017, 06:08:05 PM »

The stepper motor has no "position feedback" mechanism. It simply steps X steps in either direction as and when it's told to. So whilst you could manually align several steppers at the start it's possible they may drift in alignment over time.

But take this scenario - power disconnects from Arduino when they (steppers) are not in "park" position - how do you tell them to go back to park? they have no idea where they are at power on?

Andy - do you have a solution for this one? - Have I missed the obvious? - wouldn't be the first time :)

Does this simply mean that you would have to "calibrate" the system each time you "power on" so they know where home is?


Re: drift - they won't. They're driven by step counts, and if not stalled or 'over-clocked', they will continuously 'know' where they are.


Loss of power will leave the steppers pointing in random directions, and - short of a 'self diagnostic' reset requiring microswitches, which I think will over-complicate things, I'm aiming to use the 'thirty-second warm-up' period for the compass to allow the user to set the park position (by use of the target bearing pot and a switch) turret-by-turret.


Meanwhile, it's great to see posters coming up with the same potential issues that I'm working though. Nothing's lurking under the bed, so far!


Andy
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malcolmfrary

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Re: Rotating seven gun turrets?
« Reply #180 on: January 01, 2017, 06:50:14 PM »


Re: drift - they won't. They're driven by step counts, and if not stalled or 'over-clocked', they will continuously 'know' where they are.


Loss of power will leave the steppers pointing in random directions, and - short of a 'self diagnostic' reset requiring microswitches, which I think will over-complicate things, I'm aiming to use the 'thirty-second warm-up' period for the compass to allow the user to set the park position (by use of the target bearing pot and a switch) turret-by-turret.
Printers are usually driven by steppers these days, and on a "just in case" basis have switches to sense the end of travel to avoid that horible noise that they make when they try to drive through the end. 
Servos, or a stepper driving a position sensing pot, and incidentally a turret, could automate the process.  The pot position could be read via an ADC, I assume that such things are available for Arduinos?  Effectively, re-inventing the servo, but with an Arduino providing the control electronics.
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C-3PO

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Re: Rotating seven gun turrets?
« Reply #181 on: January 01, 2017, 07:26:06 PM »

The pot position could be read via an ADC, I assume that such things are available for Arduinos?  Effectively, re-inventing the servo, but with an Arduino providing the control electronics.

Malcolm,

Arduino Uno has 5 dedicated Analogue ADC/DAC pins which can be configured as either input "read" or "output...

Most pots unless you spend lots only have a maximum travel of 300 degrees or so - hence rotary encoders would work better ...

Whilst I am a complete advocate of Arduino's they are not multi taskers and every additional thing they are doing is asking more of the little beast.

However if more umphh required could use Arduino Mega or my favourite the Arduino Due or Teensy running Arduino code ( Teensy v3.6 features a 32 bit 180 MHz ARM Cortex-M4) or indeed switch to ARM Cortex M4 development boards - and you would be cooking on gas in a multi-tasking environment - puts the poor Arduino Uno 16mhz version into context ...

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Re: Rotating seven gun turrets?
« Reply #182 on: January 01, 2017, 08:28:35 PM »

...Effectively, re-inventing the servo, but with an Arduino providing the control electronics.


 :-))


I've thought about this for home-brewed, industrial-strength sail winches. A stepper motor driving a worm gear (meaning any force on the output can't easily force the stepper) with a rotary pot being 'read' for position info. It could be compact and capable, and no problem to code for differing requirements.


Andy
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Allnightin

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Re: Rotating seven gun turrets?
« Reply #183 on: January 01, 2017, 08:31:26 PM »

I had a go at a similar system almost 20 years ago as a final project for a HNC course.  The main concept was to have a 8 bit binary register that counted up and down from a preset starting count which represented the forward facing turrets pointing forward.  Moving the control stick resulted in the counter going up or down.  The counter was linked to a Digital to Analogue converter so that a change in count became a change in voltage output.  This was input to an Op amp circuit that  drove a small motor via a simple worm drive to move a small potentiometer (ie a DIY DC servo).  The advantage of this was that the servoes were small, light and cheap and could easily be made to cover whatever arc of movement that was required by using a different gear reduction ratio.  Training limits were controlled by having seperate Op amp comparators (2 for each servo channel) also taking the DC signal and their output arranged to override (via a multiplex circuit) the main signal and take the servo to a park position or just freeze it until the counter came back within the limit of free movement. 

A seperate 8 bit counter with a different preset starting count is linked to the same RC channel input so it counts up and down in coordination with the first one but maintaining a fixed difference in output.  This allows the aft facing turrets to move smoothly through the right astern position while the forward facing turrets are in park or freeze positions.

This system meant the turrets were actually stepping at about 1.4 degree intervals and the full 360 degree circle would be covered in about 5 seconds if the training command was continuosly applied in one direction.  This was OK for a demo but it would be simple enough to increase to 10 bit counting to give about 0.4 degree resolution and 20 seconds for 360 degrees.

This was all implimented in dedicated specialist function ICs and I spent a lot of time getting the interface between different parts to work reliably and ran out of time to iron out a few anomalies before I had to present the system as it was.  I meant to return to it and convert to a more computer based version (probably using PICs) but got sidelined by the 1/32nd Type 42 record attempt so never took it any further.  I do know that the DC servo bit worked well and can pass on details if anyone wants to follow that aspect up.  The specialist ICs used for the counter are almost certainly out of production so I would doubt that side is worth considering but perhaps the overall concept of two registers with a fixed relationship would be a good starting point for implimenting via Arduino(s) or similar?
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unbuiltnautilus

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Re: Rotating seven gun turrets?
« Reply #184 on: January 01, 2017, 11:54:44 PM »

As promised, turret rotation mechanics from some of our models. These are built heavily, as they have to operate quite hefty pyrotechnic effects. They are also very 'old school' compared to systems being discussed here. However, they may provide some ideas for the basics of the mechanics.
The first unit uses microswitches and diodes to drive to a pre-selected position, then stop when that position is reached. This system allowed the selection of any of six positions plus fore and aft rest positions. If a particular turret had no microswitch on a selected bearing, it would not respond. Only moving when a valid position was selected. The electrical system used to select, command and stop the turrets was based on the electrical circuit used to select floors when you use a lift!
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unbuiltnautilus

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Re: Rotating seven gun turrets?
« Reply #185 on: January 02, 2017, 12:06:24 AM »

The second design was simplified so that more members could build them. It uses a geared motor to directly rotate the upper plate. It only has two limit switches fitted, equipped with diodes to stop the turret if it attempts to drive beyond it's stops. The turret can be stopped at any position, as well as at it's end stops. The offset gearbox casing in red, provides the cam effect which engages the microswitches.
The limitation of this system, as previously discussed, is that on any angle of traverse that is not 90 degrees to port or starboard, the fore and aft turrets are pointing in different directions.
We also have a variation on this version driven by 1/4 scale servos. These have had to be fitted with a rubber shock absorber in the drive train, otherwise we run the risk of stripping the gears when using the pyrotechnic effects. These were built before Actions Servo Morph was introduced. We have yet to marry up the servo driven units to some of these, so cannot comment on their suitability.
As I said previously, these units are not the latest tech, but hopefully something in their design may help with the hardware side of this project.
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Bob K

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Re: Rotating seven gun turrets?
« Reply #186 on: January 02, 2017, 07:55:09 AM »

When the words Portsmouth and Pyrotechnics are combined I assume that these are from ships taking part in the wonderfully realistic battle displays we all admire at numerous Shows.  Really interesting to see how it is actually done inside.  Thank you.
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Martin [Admin]

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Re: Rotating seven gun turrets?
« Reply #187 on: January 02, 2017, 09:42:06 AM »


As there are now two topics covering roughly the same topic,
 I'm therefore moving this top into same area as other topic so we can follow both topics with avid interest!  :-))

 

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C-3PO

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Re: Rotating seven gun turrets?
« Reply #188 on: January 06, 2017, 01:36:20 PM »

Hi,

If you were interested in this thread and thought things had gone very quiet.... well going back to work slowed things down a little - however lots of activity behind the scenes.

Coming soon my concept of a solution - also Andy now has a seperate thread where he will be posting his updates http://www.modelboatmayhem.co.uk/forum/index.php/topic,56884.msg591153.html#msg591153

C-3PO
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RAAArtyGunner

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Re: Rotating seven gun turrets?
« Reply #189 on: January 07, 2017, 03:40:57 AM »

Yes,

It was getting suspenseful, O0 O0
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C-3PO

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Re: Rotating seven gun turrets?
« Reply #190 on: January 09, 2017, 10:03:08 PM »

Video shows movement of 7 turrets being controlled by a sensor connected to an Arduino

https://youtu.be/dfrxhtwXMoQ

Fine tuning required......

Regards
C-3PO
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Colin Bishop

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Re: Rotating seven gun turrets?
« Reply #191 on: January 09, 2017, 10:12:52 PM »

Impressive!

Colin
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Bob K

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Re: Rotating seven gun turrets?
« Reply #192 on: January 09, 2017, 10:20:40 PM »

Now that looks to have real potential.  :-))
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C-3PO

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Re: Rotating seven gun turrets?
« Reply #193 on: January 09, 2017, 10:30:41 PM »

I have learnt quite a lot in a short time!

One thing that I think will work really well relates to the alignment issue of using stepper motors.

As you have no physical position feedback mechanism with a stepper motor an alignment process is required at the start up of the system.

This could be a very complex set of controls to "electronically" move steppers into a calibrated position.

My solution currently involves drinking straws cut down and pushed onto the stepper motor shaft. There is enough friction that they hold their position but you can very simply manually move them to line up with each other (place in "park" position at start up) by just moving them with your fingers.

There is an added benefit to this - in event of a system failure (perhaps a wire came off) then should the motor continue to rotate as soon as the gun barrel touches any part of the super structure it would stop and allow the motor shaft to rotate without causing any damage (stepper motors have got some serious grunt!) - I would suggest this "friction fit" solution is a very elegant, fast solution to the alignment process.

I am sure there something better than just the humble straw to achieve this....

Regards
C-3PO
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g6swj

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Re: Rotating seven gun turrets?
« Reply #194 on: January 10, 2017, 09:18:00 AM »

This video has some interesting info - it also has a really neat 3D printed "connector" for the 28BYJ stepper shaft.

https://www.youtube.com/watch?v=0TNBxt5hF-g


Looks like you can download 3D print file for this type of wheel from various sources https://www.thingiverse.com/thing:1115947
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Re: Rotating seven gun turrets?
« Reply #195 on: January 10, 2017, 10:14:22 AM »

Forgot to post - Stepper motor supply - hundreds of places to buy steppers but often not UK stock

Not the cheapest but if you have Amazon Prime then these are a good deal - I ordered some - they arrived next day

6 x 28BYJ steppers (including driver board) 12.99 or 2.17 each!

https://www.amazon.co.uk/gp/product/B01HEQY760/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

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Re: Rotating seven gun turrets?
« Reply #196 on: January 10, 2017, 09:18:39 PM »

The smooth movement of the stepper motors and the delay in reacting to the directors instructions are very realistic. There would be an appreciable delay when and if the director was ordered to change target quickly and the turret controller had to move the mechanism to regain a match with the dial.

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Martin [Admin]

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Re: Rotating seven gun turrets?
« Reply #197 on: January 10, 2017, 10:56:58 PM »

This video has some interesting info - it also has a really neat 3D printed "connector" for the 28BYJ stepper shaft.

https://www.youtube.com/watch?v=0TNBxt5hF-g


Excellent find!   :-))
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C-3PO

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Re: Rotating seven gun turrets?
« Reply #198 on: January 11, 2017, 10:02:25 AM »

Starter for 10...

I want to configure the turret rotation limits and non-fire zones based on HMS Agincourt.

I want to stress that these will be changeable by the user and I don't want to start a massive debabte as to what's right and what's wrong - I just want a sensible starting place and do not have that knowledge.

So Bob / Colin would you perhaps be able to give it your best shot ( excuse the pun!)

As per my image below - for guns marked A,B,C,D,E,F,G could you suggest for all guns (assume ship is heading due North):

  • Rotation stop point from "park" to Port and Starboard
  • Non firing zone within the arc of travel
So example Gun A might be

  • Port rotation stop point 80 degrees ( compass point 280)
  • Starboard rotation stoip point 70 degrees (compass point 70)
  • Non fire zone Port 10 to Starboard 10 ( 350 - 10 compass point)
Re reading my post - the text is a bit clumsy but I think you will get what I am after...

Thank you in advance

C-3PO
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Martin [Admin]

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Re: Rotating seven gun turrets?
« Reply #199 on: January 11, 2017, 11:16:23 AM »

 
( NB: Interesting read about Sultan Osman I / HMS Agincourt  on Wikipedia - https://en.wikipedia.org/wiki/HMS_Agincourt_(1913)  )

The rate of fire of these guns was 1.5 rounds per minute. When a full broadside was fired, "the resulting sheet of flame was big enough to create the impression that a battle cruiser had blown up; it was awe inspiring." No damage was done to the ship when firing full broadsides, despite the common idea that doing so would break the ship in half, but much of the ship's tableware and glassware did shatter when Agincourt fired her first broadside.    :o
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