Model Boat Mayhem

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: HELP - Servos for ship's gun turrents  (Read 584 times)

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
HELP - Servos for ship's gun turrents
« on: June 15, 2022, 08:14:30 am »

COULD anybody help me please i am attempting to get my gun turret turning which i have done an get the guns to elevate with a micro servo but to keep this simple the big servo that turns the turret works ok but the micro servo work ok when i turn the turret one way its fine an ok but when i turn the turret the other way the micro servo starts to jump an ends up in the revese postion an i have the servo both working off one channel through a  action servo morph SO CAN ANYBODY TELL ME WHY THE MICRO SERVO IS Doin THAT ? :embarrassed: <:(  an how to get it to go  right ? >>:-( <*<
chris
Logged

HMS Invisible

  • MICROGYROS.COM
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 389
  • Location: Paisley, Renfrewshire
    • Yes, it works!
Re: HELP
« Reply #1 on: June 15, 2022, 05:08:12 pm »

Decades-old rc electrics meant servos could be driven anywhere in the range 0.75 to 2.3 millisecond. That is why I put the same signal range limit on rc products driving a servo and why I also ensured that escs worked in the 0.75 to 2.3 millisecond range.

Beyond that range, I observed some servos exhibited the behaviour you see. It could be viewed as an electronic safety limit to prevent mechanical overdriving. That is why I have suggested increasing the span of a quarter turn servo by the addition of resistance either side of its position feedback potentiometer.

See https://www.google.com/search?q=servo+pwm&tbm=isch&source=iu&ictx=1
In short, without more information and testing, a likely cause is the servo is being driven beyond its timing range.


Modification is shown in the youtube video. https://www.youtube.com/watch?v=rU7LDKdKQH0
Logged
< All manner of contact methods over to the left.

Umi_Ryuzuki

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,268
  • Location: PDX, OR USA
    • Models and Miniatures
Re: HELP
« Reply #2 on: June 15, 2022, 05:39:17 pm »

Having absolutely no clue as to how your micro servo is connected...
My itty bitty brain, %) , says use a cam to elevate guns instead of a hard connection?

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #3 on: June 15, 2022, 06:10:18 pm »

Decades-old rc electrics meant servos could be driven anywhere in the range 0.75 to 2.3 millisecond. That is why I put the same signal range limit on rc products driving a servo and why I also ensured that escs worked in the 0.75 to 2.3 millisecond range.

Beyond that range, I observed some servos exhibited the behaviour you see. It could be viewed as an electronic safety limit to prevent mechanical overdriving. That is why I have suggested increasing the span of a quarter turn servo by the addition of resistance either side of its position feedback potentiometer.

See https://www.google.com/search?q=servo+pwm&tbm=isch&source=iu&ictx=1
In short, without more information and testing, a likely cause is the servo is being driven beyond its timing range.


Modification is shown in the youtube video. https://www.youtube.com/watch?v=rU7LDKdKQH0



HI thank for your reply
chris
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #4 on: June 15, 2022, 06:14:27 pm »

Having absolutely no clue as to how your micro servo is connected...
My itty bitty brain, %) , says use a cam to elevate guns instead of a hard connection?


AN HI also Umi WELL the micro servo is connected by a Y led from a servo morph an i have a sail winch servo on my main turret gear
hows that
chris
Logged

John W E

  • I see no ships !!
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 8,655
  • Location: South shields
Re: HELP
« Reply #5 on: June 15, 2022, 06:23:08 pm »

hi there,


So, have I pictured this correctly?   Your sail servo is rotating the gun from left to right - mid section centre - so therefore your mini servo inside the gun is, as you turn the gun to the port, the mini servo should begin to elevate the barrels  As you return back to centre position of your gun; the barrel elevation will go back to level.


But, when you turn to starboard, the mini servo will naturally start to try and de-elevate the gun, because this is how the signal is coming through the 'Y' lead.


The other thing that springs to mind is the feedback signal from your sail servo is of a slightly different frequency to your mini servo causing interference.  That is in layman's terms :-)   I had similar problems myself with the Exeter build and this was because of me using 'cheap' mini servos.    Also, I ended up using Forge Electronics for operating the guns, along with 2 separate channels on my transmitter and receiver - one channel is for rotating the guns, the other channel is used for elevating the barrels of the guns.


You will also need to try and fit in the servo reverse so that the stern guns turn in the opposite direction to the bow guns.


John

Logged
Knowledge begins with respect
But fools hate wisdom and discipline

HMS Invisible

  • MICROGYROS.COM
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 389
  • Location: Paisley, Renfrewshire
    • Yes, it works!
Re: HELP
« Reply #6 on: June 15, 2022, 06:32:42 pm »


AN HI also Umi WELL the micro servo is connected by a Y led from a servo morph an i have a sail winch servo on my main turret gear
hows that
chris
Even before John W E's reply I could see that you can test for (or eliminate) a power supply problem by unhooking the main servo.

Without a scope or digital readout you can comparitively measure PWM input to a servo with a voltmeter on the non power wire with respect to 0volt.
Pulse height and frequency affects the measurement this way.
Logged
< All manner of contact methods over to the left.

RST

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,012
  • Location: UK
Re: HELP
« Reply #7 on: June 15, 2022, 07:58:40 pm »

Hi Chris,


My first bet is you might have extended the servo throw past the limits of that small blue servo on your build thread.  If it's a cheapo $3 import jobby with plastic gears they don't take kindly to overloading in my experience.  The one on my printer failed of its own accord and started jumping and clicking (fine one way, not the other).


...otherwise it sounds about right from what we deduce, left on the sail winch and up on the micro servo and right down etc?


When troubleshooting I find it easier to eliminate things from the circuit.  Test things separately, start plugging things in one at a time and note when the first time you combine things that you run into a trouble.  No need for oscilloscopes etc until the basics have been checked.


Happy to be proven wrong but hopefully you can work through logically.


Rich
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #8 on: June 15, 2022, 10:56:25 pm »

hi there,


So, have I pictured this correctly?   Your sail servo is rotating the gun from left to right - mid section centre - so therefore your mini servo inside the gun is, as you turn the gun to the port, the mini servo should begin to elevate the barrels  As you return back to centre position of your gun; the barrel elevation will go back to level.


But, when you turn to starboard, the mini servo will naturally start to try and de-elevate the gun, because this is how the signal is coming through the 'Y' lead.


The other thing that springs to mind is the feedback signal from your sail servo is of a slightly different frequency to your mini servo causing interference.  That is in layman's terms :-)   I had similar problems myself with the Exeter build and this was because of me using 'cheap' mini servos.    Also, I ended up using Forge Electronics for operating the guns, along with 2 separate channels on my transmitter and receiver - one channel is for rotating the guns, the other channel is used for elevating the barrels of the guns.


You will also need to try and fit in the servo reverse so that the stern guns turn in the opposite direction to the bow guns. tiger refit
John


hi John you hit the nail on the head correct in what you say as thats what the layout is but i havnt got any back gun only two turrets on the bow as my ship is a helicopter carrier hms tiger refit
chers for your reply
chris  :-))
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #9 on: June 15, 2022, 10:59:18 pm »

Even before John W E's reply I could see that you can test for (or eliminate) a power supply problem by unhooking the main servo.

Without a scope or digital readout you can comparitively measure PWM input to a servo with a voltmeter on the non power wire with respect to 0volt.
Pulse height and frequency affects the measurement this way.


ok i'll give it a try if i can understand what u r sayin as im not that good on eletrics
cheers for the info
chris
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #10 on: June 15, 2022, 11:05:24 pm »

Hi Chris,


My first bet is you might have extended the servo throw past the limits of that small blue servo on your build thread.  If it's a cheapo $3 import jobby with plastic gears they don't take kindly to overloading in my experience.  The one on my printer failed of its own accord and started jumping and clicking (fine one way, not the other).


...otherwise it sounds about right from what we deduce, left on the sail winch and up on the micro servo and right down etc?


When troubleshooting I find it easier to eliminate things from the circuit.  Test things separately, start plugging things in one at a time and note when the first time you combine things that you run into a trouble.  No need for oscilloscopes etc until the basics have been checked.


Happy to be proven wrong but hopefully you can work through logically.


Rich


HI RICH yes u r right there as ive done all this testing an yes it is a cheap servo one of the little blue ones so what i'll do tomorrow is try a normal size futtaba  servo on it an see what happens
an cheers for your reply rich thanks  :-))
chris
Logged

RST

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,012
  • Location: UK
Re: HELP
« Reply #11 on: June 16, 2022, 12:16:09 am »

Hi Chris, yes try that.  I may be very wrong.  Also it might be  as others alluded to that cheap electronics in the servo don't like the butchered signal from the servomorph.  The model railway guys love cheap mini servos but not a jerky slow movement on their points or signals.




...I was reading the specs on component shop before and thought it rather interesting two servomorphs could be daisy chained together. That means one servo moves before the next.  OR you fit a microswitch on your slew ring at a point the turret moves to (either side) and the second servo moves to it , presumably either way with 2 microswitches.  Rather neat I thought.


Rich
Logged

Akira

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 472
  • Model Boat Mayhem is Great!
  • Location: Hope, Maine USA
Re: HELP
« Reply #12 on: June 16, 2022, 01:47:39 am »

Am I correct to understand that both the turret rotation and the gun elvation run through the same ServoMorph? if so, that is your issue. When your turret rotates in one direction, and the guns elevate, the servos are sharing the signal in one dection from neutral. When they return to center line the servos return to neutral. when you then command rotation in the opposite direction, you get the correct rotation because the train svervo can do so, BUT the elevation servo, having been at neutral is now attempting to move your gun elevation in the opposite(down) direction. What needs to happen is that the elevation servo needs to move from neutral to up, regardless of the turret's rotation direction. Unless you have a digital radio that will alow you to write script, I do not think you can do it, at least not through a shared ServoMorph.
If I am not mistaken, the ServoMorph will allow modification of the servo speed and the limit of travel. But unless it will reverse an output, selectively, you are stuck.If you have a spare channel available, you could out elevation on it separately, or go with a digital radio, like a FrSky that allows scripting. Or, as Umi suggested, use a cam.
Logged

Umi_Ryuzuki

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,268
  • Location: PDX, OR USA
    • Models and Miniatures
Re: HELP
« Reply #13 on: June 16, 2022, 03:35:53 am »

With a oval cam, it doesn't matter which way the servo rotates, the cam will
rotate to a high lobe, and push your actuator forward, and elevate the gun barrels.
And then return to low level at center or neutral stick.  :-)

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #14 on: June 16, 2022, 08:08:53 am »

Hi Chris, yes try that.  I may be very wrong.  Also it might be  as others alluded to that cheap electronics in the servo don't like the butchered signal from the servomorph.  The model railway guys love cheap mini servos but not a jerky slow movement on their points or signals.




...I was reading the specs on component shop before and thought it rather interesting two servomorphs could be daisy chained together. That means one servo moves before the next.  OR you fit a microswitch on your slew ring at a point the turret moves to (either side) and the second servo moves to it , presumably either way with 2 microswitches.  Rather neat I thought.


Rich


CHEERS Rich for info but i think i will try a big servo on it an turn down on the servo morph on how far it causes the servo to travel an try that if not work then im goin to try Umi idea of a cam which is a very good idea an easy to do an see how that works out
THANKS
Chris
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #15 on: June 16, 2022, 08:13:53 am »

Am I correct to understand that both the turret rotation and the gun elvation run through the same ServoMorph? if so, that is your issue. When your turret rotates in one direction, and the guns elevate, the servos are sharing the signal in one dection from neutral. When they return to center line the servos return to neutral. when you then command rotation in the opposite direction, you get the correct rotation because the train svervo can do so, BUT the elevation servo, having been at neutral is now attempting to move your gun elevation in the opposite(down) direction. What needs to happen is that the elevation servo needs to move from neutral to up, regardless of the turret's rotation direction. Unless you have a digital radio that will alow you to write script, I do not think you can do it, at least not through a shared ServoMorph.
If I am not mistaken, the ServoMorph will allow modification of the servo speed and the limit of travel. But unless it will reverse an output, selectively, you are stuck.If you have a spare channel available, you could out elevation on it separately, or go with a digital radio, like a FrSky that allows scripting. Or, as Umi suggested, use a cam.


AN HI akira yes you are correct an as said i think i'll try what i said to RST rich firstly an then if not no go then Umi idea of a cam
thanks for your help
chris
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #16 on: June 16, 2022, 08:35:43 am »

With a oval cam, it doesn't matter which way the servo rotates, the cam will
rotate to a high lobe, and push your actuator forward, and elevate the gun barrels.
And then return to low level at center or neutral stick.  :-)


Umi thanks very much for takin the time on my problem with your drawing an very helpfull so thats your good deed done for the day as i will just try a quick try with what i said below an then if no go which i dont think it will then i'll go with your cam idea as that is brilliant idea very WELL DONE an im very pleased as i was goin with a cam idea but nothing like your idea an this  was how i did it on an old ship yrs ago an that was have a cam edge fitted to the main deck an risein up to a high point pushin the guns to elevate an yes it worked but so complex compared to your idea which is far easyier an the one i will go with MANY THANKS
Umi for your time an im very pleased  :-)) an i will mention your idea in my HMS TIGER thread if you dont mind as you deserve the credit for solvin my prob if you do mind then i wont mention you ?
THANK YOU Umi
ATB to you
chris
Logged

Akira

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 472
  • Model Boat Mayhem is Great!
  • Location: Hope, Maine USA
Re: HELP
« Reply #17 on: June 16, 2022, 12:53:55 pm »

I had a thought, watch out. Not knowing what you have for a radio system, you may be able to accomplish what you want by mixing to channels together. Slaving the elevation channel into the train channel. The key will be to ensure that you use only one half of the servo throw for the evelvation, as I mentioned in my earlier post. This should be fairly easy to accomplish if you have any sort of digital radio. It might save the cam work, although Umi's idea is an old time classic approach and not one to be dismissed.
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #18 on: June 16, 2022, 12:55:49 pm »

HI ALL WELL i exsperimented with a big servo an then a micro servo an found that i just alterd the servo morph on the servo throw an cut it back a bit an all servo work how they should do so MANY THANKS TO YOU ALL FOR THE INFO BUT Imi i keep your cam idea in my head in case i do need it cheers
ALL
Chris  :-))
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #19 on: June 16, 2022, 01:01:42 pm »

I had a thought, watch out. Not knowing what you have for a radio system, you may be able to accomplish what you want by mixing to channels together. Slaving the elevation channel into the train channel. The key will be to ensure that you use only one half of the servo throw for the evelvation, as I mentioned in my earlier post. This should be fairly easy to accomplish if you have any sort of digital radio. It might save the cam work, although Umi's idea is an old time classic approach and not one to be dismissed.


HI Akira its now sorted thanks if you read the below post an a linkpic to my T/X an such as its a 14 cha T/X carsons
Chris
https://ibb.co/qCf0s8T


AN SORRY ALL I SHOULD HAVE POSTED THIS PIC AT THE START BUT I COULD NOT GET ONTO IMGBB SITE WHERE PIC IS STORED AS I THINK IT WOULD HAVE SAVED SOME TIME
Logged

Akira

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 472
  • Model Boat Mayhem is Great!
  • Location: Hope, Maine USA
Re: HELP
« Reply #20 on: June 16, 2022, 01:42:41 pm »

Great Chris!! Whatever it takes.   Carry on :}
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #21 on: June 16, 2022, 04:19:29 pm »

Great Chris!! Whatever it takes.   Carry on :}


CHEERS Akira now thats sorted i can carry on with building the 6inch  gun turret  an  get  all the wirein in an the knockon switches to work the gunfire an gun flash unit that ive sent for an just as well ive got plenty of wires goin up to this gun turret just got to hope there are enough of them an i must admit this is the most complex ship ive ever built as its even more complex than my big nimitz aircraft carrier an a lot of my boaty m8's said that was complex enough but i love wirein up things an getting them to work but all you guys who have helped me on this MANY THANKS TO YOU ALL
ATB all
chris  :-))
Logged

frogman3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,894
  • Model Boat Mayhem is Great!
  • Location: norfolk england
Re: HELP
« Reply #22 on: June 17, 2022, 03:50:18 pm »

hi there,


So, have I pictured this correctly?   Your sail servo is rotating the gun from left to right - mid section centre - so therefore your mini servo inside the gun is, as you turn the gun to the port, the mini servo should begin to elevate the barrels  As you return back to centre position of your gun; the barrel elevation will go back to level.


But, when you turn to starboard, the mini servo will naturally start to try and de-elevate the gun, because this is how the signal is coming through the 'Y' lead.


The other thing that springs to mind is the feedback signal from your sail servo is of a slightly different frequency to your mini servo causing interference.  That is in layman's terms :-)   I had similar problems myself with the Exeter build and this was because of me using 'cheap' mini servos.    Also, I ended up using Forge Electronics for operating the guns, along with 2 separate channels on my transmitter and receiver - one channel is for rotating the guns, the other channel is used for elevating the barrels of the guns.


You will also need to try and fit in the servo reverse so that the stern guns turn in the opposite direction to the bow guns.


John


HI John just lookin at your gun turret could you tell me what build this is an where on here as i would love to see how your ship turned out  please
chris
Logged

John W E

  • I see no ships !!
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 8,655
  • Location: South shields
Re: HELP - Servos for ship's gun turrents
« Reply #23 on: June 17, 2022, 03:56:28 pm »

Hi Chris


it is HMS Exeter which I built in about 2011 -  been in the water once or twice - bit of a handful for the size - so God help you with yours  %% %%


Here's a link to my build :-)


John


HMS EXETER BUILD 1939 (modelboatmayhem.co.uk)

Logged
Knowledge begins with respect
But fools hate wisdom and discipline
Pages: [1]   Go Up