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Author Topic: Gun turret rotation - servo or stepper motor?  (Read 13358 times)

C-3PO

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Re: Gun turret rotation - servo or stepper motor?
« Reply #25 on: January 09, 2016, 10:45:00 AM »

Hello Norman,


Sorry I may have added to the brain pain!



I'm sure you are right that eBay have the same item cheaper re geared motor  - just make sure it's shipped from UK (ideally).


Re turret rotation which is more important to you ability to vary/determine the speed of travel OR smoothness of travel at one set speed?


C-3PO
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ballastanksian

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Re: Gun turret rotation - servo or stepper motor?
« Reply #26 on: January 09, 2016, 11:48:29 AM »

Whatever you choose Norman, make sure to keep an eye in top weight when designing and building.

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Norman Castle

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Re: Gun turret rotation - servo or stepper motor?
« Reply #27 on: January 09, 2016, 01:00:29 PM »

Re turret rotation which is more important to you ability to vary/determine the speed of travel OR smoothness of travel at one set speed?

The former  :-)

Whatever you choose Norman, make sure to keep an eye in top weight when designing and building
 
No worries on that score, mister.  I'm red hot on keeping top weight (or whatever the technical term is) down!
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dreadnought72

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Re: Gun turret rotation - servo or stepper motor?
« Reply #28 on: January 09, 2016, 05:32:17 PM »

Best bet, IMO, is to go with the geared stepper listed above. Super cheap and smooooother than Smooth Radio quietly playing The Carpenters.  %) Mount the stepper securely to the hull, and the turret directly to the output shaft. If I ever get a day off work, I'll brew up some code and demonstrate jitterlessness by the Power of Video.   :-))

Andy
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Norman Castle

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Re: Gun turret rotation - servo or stepper motor?
« Reply #29 on: January 09, 2016, 05:43:24 PM »

Best bet, IMO, is to go with the geared stepper listed above.

Cheers Andy.  Sorry to be a (insert term of choice here), but which motor?
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dreadnought72

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Re: Gun turret rotation - servo or stepper motor?
« Reply #30 on: January 09, 2016, 06:41:43 PM »

The 28BYJ-48 stepper: five for eight quid. Here's an in-depth look into this model.

Andy
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plastic

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Re: Gun turret rotation - servo or stepper motor?
« Reply #31 on: January 09, 2016, 08:54:22 PM »

I don't get it.  :o

Are the turrets supposed to be traversing back & forth randomly? In real life, the guns would be stationary until battle and then they'd probably all point the same direction and stay trained on the target - what exactly is the end result that the op is expecting?

All of these solutions seem way too complcated compared to a simple geared dc motor under each turret and some rotation limit microswitches.  :-))
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dreadnought72

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Re: Gun turret rotation - servo or stepper motor?
« Reply #32 on: January 09, 2016, 09:28:26 PM »

Hi Plastic!


Here's why I get it: my plan (coming soon to this forum!) is to rotate five turrets via individual stepper motors to a designated target bearing. By tying in an Arduino to a six-axis gyro/accelerometer my turrets will 'track' a target no matter what course alterations the hull makes. Given that steppers allow rotations that are smooth, well below degree sensitivity, and indefinitely repeatable and accurate, I think this is the best solution to realistic gun control on a ship.


...We'll see.


Andy
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Re: Gun turret rotation - servo or stepper motor?
« Reply #33 on: January 09, 2016, 09:36:00 PM »

plastic,

I think the intention is to add some "animation" to the model. The position of the gun turret does not traverse back and forth randomly which I guess is what you would achieve with limit micro switches. The animation is only limited really by your imagination and programming ability!

The solution the guys are using is a pre-programmed sequence of movement/speed/delay before next movement with no human intervention.

e.g. a sequence can be as simple or complicated as you want to make it:
  • Move  to 40 degrees slow rotation speed wait 7 seconds
  • Move  to 50 degrees slow rotation speed wait 5 seconds
  • Move  to 45 degrees fast rotation speed wait 3 seconds
  • Move  to 110 degrees medium slow rotation speed wait 15 seconds
  • Move  to 30 degrees fast rotation speed wait 9 seconds
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Re: Gun turret rotation - servo or stepper motor?
« Reply #34 on: January 09, 2016, 09:37:09 PM »

wow Andy - I like your thinking....
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C-3PO

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Re: Gun turret rotation - servo or stepper motor?
« Reply #35 on: January 09, 2016, 09:46:24 PM »

Fresh eggs within arms reach :)

Andy - what a great idea - would love to see it working.

Could you use a compass reads (electronic). Get the compass bearing of the enemy, store the reading and then as the compass reading change compare to your stored reading and adjust guns with the plus/minus difference.

C-3PO
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dreadnought72

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Re: Gun turret rotation - servo or stepper motor?
« Reply #36 on: January 09, 2016, 10:08:13 PM »

I bought a solid-state compass for testing, but it's not at all ideal. There's a lot of 'dip' at our latitudes (the signal for 'dip' is more than the horizontal 'north') so any slight roll of the hull causes dramatically unusable figures to pour out of the compass.


Then I discovered the joys of combination gyro/accelerometers. I'm only using the gyros in one (mathematical!) plane, since slight roll, and even less pitch, has little noticeable effect - it's that old cos(little-theta) thing - but I have been astounded by the accuracy.


Indeed, I thought the chip was faulty first time I plugged it in. It drifted by 0.01 degrees every couple of seconds.


...It's measuring the rotation of the Earth.  :o


Andy
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C-3PO

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Re: Gun turret rotation - servo or stepper motor?
« Reply #37 on: January 09, 2016, 10:35:49 PM »

Great project - look forward to your updates.

All understood (I think) re compass not being an option.

I had a quick look at the spec for a gizmo (appreciate you may be using a different board but I'm sure it also has lots of hieroglyphics in it's spec I have never heard this word before "quaternion") and I could feel my brain hurt as I read the specification - best of luck!
  • I2C Digital-output of 6 or 9-axis MotionFusion data in rotation matrix, quaternion, Euler Angle, or raw data format
  • Input Voltage: 2.3 - 3.4V
  • Selectable Solder Jumpers on CLK, FSYNC and AD0
  • Tri-Axis angular rate sensor (gyro) with a sensitivity up to 131 LSBs/dps and a full-scale range of ±250, ±500, ±1000, and ±2000dps
  • Tri-Axis accelerometer with a programmable full scale range of ±2g, ±4g, ±8g and ±16g
  • Digital Motion Processing™ (DMP™) engine offloads complex MotionFusion, sensor timing synchronization and gesture detection
  • Embedded algorithms for run-time bias and compass calibration. No user intervention required

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derekwarner

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Re: Gun turret rotation - servo or stepper motor?
« Reply #38 on: January 09, 2016, 11:22:23 PM »

Guys......this is all a step up in technology :o, however we need a defined time period for what is being considered to understand prototypical armament movement

If we are talking five turrets, are we are looking at vessels between WWI  to WWII?.......the low speed movement of turrets in these latter years was radar controlled

Turrets of these generations did not perform an SHM [random simple harmonic mode ] in both train and elevation awaiting confirmation from the FCC [fire control computer] to determine all variables.....[& yes O0  in earlier days FCMC 'fire control mechanical computers' were used]

I am sure the system components offered below by dreadnought72 and  C-3PO would work very realistically with ultra modern missile launchers, and to a latter extent modern small bore & low calibre high fire rate gun turrets [British 3'' or the Italian Otto-Malera 76mm], however collectively be wasted on model vessels based on designs between WWI  to WWII

Further even with all of this technology controlling a vessel turrets train and elevation of a warship in heavy seas does need human intervention  :P as the target still must be defined........... Derek

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Norman Castle

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Re: Gun turret rotation - servo or stepper motor?
« Reply #39 on: January 10, 2016, 07:58:50 AM »


I don't get it.  :o

Are the turrets supposed to be traversing back & forth randomly?

Only apparently.  Perhaps I should have explained that I'm not after lifelike turret rotation.  I'm actually trying out various ideas for the next build, the general theme of which is perhaps best described as watered-down Steampunk with overtones of Burning Man ...  8)


The 28BYJ-48 stepper: five for eight quid. Here's an in-depth look into this model.

Thanks for that Andy.
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The Old Fart

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Re: Gun turret rotation - servo or stepper motor?
« Reply #40 on: January 10, 2016, 07:59:44 AM »

I have stepper motors controlling the crane swing and lift, on my Dusseldorf.
When checking the current drawn, I realised that the stepper were still drawing current when stationary.
Reprogramming the 'picaxe' controller now switches off all outputs when not required.
saves around 1/2amp drain on the battery.

dreadnought72

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Re: Gun turret rotation - servo or stepper motor?
« Reply #41 on: January 10, 2016, 10:12:41 AM »

Sounds like the spec for the one I'm using - it's an MPU-6050 mounted on a breakout board and it requires IC2 comms to chat to it.

Andy
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derekwarner

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Re: Gun turret rotation - servo or stepper motor?
« Reply #42 on: January 10, 2016, 10:24:57 AM »

So Mr Castle finally says ......'perhaps I should have explained that I'm not after lifelike turret rotation'..... :o

Well ..who are the fools here?  >>:-(...the members who I also suppose who could have expended less constructive thought & comment on a hypothetical with a  %% poster? 

But after all we did learn a little on the potential of stepper motors & controllers :-)) .... we live & learn..... Derek
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Colin Bishop

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Re: Gun turret rotation - servo or stepper motor?
« Reply #43 on: January 10, 2016, 10:59:18 AM »

Steampunk?

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g6swj

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Re: Gun turret rotation - servo or stepper motor?
« Reply #44 on: January 10, 2016, 11:07:29 AM »

There are no fools here! There are hobbyists exploring what's possible. And the answer is simple - you can make the movement do exactly what you want and using these methods (some sort of microprocessor) it will be more lifelike than almost all other solutions. I don't recall anybody specifying type or period of model - just an exploration of what could be achieved and how.

Guys......this is all a step up in technology :o, however we need a defined time period for what is being considered to understand prototypical armament movement

Why do we need a defined period when any movement could be simulated?

Mr Castle - or Norman to most of us, has already achieved quite a lot in a short period of time and is simply wanting to refine the concept - specifically the smoothness of movement.

Lighten up guys - it's supposed to be fun! - and if Norman ends up with a gun turret spinning like he wants but nothing like the real thing does it matter?
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Norman Castle

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Re: Gun turret rotation - servo or stepper motor?
« Reply #45 on: January 10, 2016, 02:26:22 PM »


Steampunk?

Sort of, Colin.  The original inspiration was this picture which I found on the internets.  I just thought "Ooooh look - a Steampunk Springer"...



Then it occurred to me that it might be fun to try to combine elements of Burning Man "art cars" with that approach, which naturally led me to thoughts of moving elements, and before you know it I'm knee deep in turret rotation and the Arduino, thanks to the help I've received via this forum. 

It's a hell of a learning curve for me, but it's all great fun  :-)

(PS  The gun and the turret itself's been the easy bit - one aerosol cap, one curry sauce jar lid, two bits from The Lady Wife's dead garden sprayer, some plasticard and some plastic filler)
 
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Re: Gun turret rotation - servo or stepper motor?
« Reply #46 on: January 10, 2016, 07:05:22 PM »

This dead garden sprayer - got to ask - was it dead before or after it lost these two bits?


While a bit of notchiness might not be noticeable out on the lake, things like this tend to get attention ashore, so smooth is better.  Harping back to turntables, in use, the real thing needed to have the engine being turned as balanced as possible to turn more easily.  Extrapolating this, a turret needs a lack of contact with its hull other than its bearing.  That way, smoothness comes down to the motor and gearing.
If going steampunk, it will need a very good steam maker in order to really look like something from the late Victorian era in the other trouser leg of time.
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Norman Castle

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Re: Gun turret rotation - servo or stepper motor?
« Reply #47 on: January 11, 2016, 06:04:49 PM »

Oh believe me, Malcolm, the sprayer was definitely way past its best-before.  There's only so much you can do with one of those with epoxy and gaffer tape, and besides, The Lady Wife's birthday was approaching  %)

I'd love to make a proper job of a Steampunk boat, but alas (a) I have neither the facilities or the skill necessary to do it justice and (b) in any case I'd be worried about it being top-heavy.  So this one is simply a Springer influenced by some elements of Steampunk, some elements of Burning Man art cars, and the biker chappie from Postman Pat ...

Getting back to turret rotation, in this particular application there's actually no contact anywhere 'twixt turret and deck, but I have established that the bloomin' servo I need to use is a little bit jittery even when plugged into my servo tester and set to the neutral position!   It's not a problem as such though - I'm just keen to understand as much as I can about this whole turret rotation / servo control / stepper motor / Arduino lark.  It's all new to me and it seems to have endless possibilities  :-)
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malcolmfrary

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Re: Gun turret rotation - servo or stepper motor?
« Reply #48 on: January 11, 2016, 08:53:27 PM »

If it is jittery on the tester, first check the tester batteries (been there got the tee shirt) and/or another servo to compare.  A perfectly testing servo means that not only is the servo a good'un, but so is the tester, the battery and all the bits of wire between them.  Jitter could have its source anywhere in the chain.  And there ain't no rule saying that there is only one source at a time other than in Haynes manuals.
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Re: Gun turret rotation - servo or stepper motor?
« Reply #49 on: January 13, 2016, 02:31:54 PM »

I've quickly done a video on a gun turret project I'm working on, so you can see how slowly and smoothly a stepper can operate. I've made the speed of traverse proportional to joystick displacement which may or may not be a good idea? The video also shows the maximum traverse speed possible with this particular motor which (after a 64:1 gearbox) does 4096 steps / rev. The stepper is just under £4 (including a driver board) at Technobots or considerably cheaper if you're prepared to wait for a Chinese eBay supplier to deliver. I dispensed with the driver board and just used its chip on my breadboard. Technobots also do the same motor with a 16:1 gearbox if you need a bit more speed, but that's almost £5 and *without* the driver board. By step counting I can limit the angle of rotation - pot adjustable from zero to 360 degrees with "detents" at 90, 180 and 270 indicated by the LED in a setup routine - or there is the option for continuous rotation which can be needed for smaller guns.

Now working on a second channel to "fire" the gun - storing the "bang" as a sound sample in the Arduino - incidently I'm fresh out of Arduino Nanos which I'd be using so the video shows me using the much larger UNO during the development process.

https://youtu.be/eNhRwx8Gp_c
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