Gun turret rotation using servos.

[Paul75Participant @paul75]

Hello Everyone.

I'm planning to install kit to make the gun turrets rotate on my HMS Duke of York. I'm aware of different mechanisms to do this but since I'm retrofitting an already almost complete model I think the easiest way for me to plumb this in will be to use (micro) servos.

I hope to use the proportional rotary switch (one rc channel) on my Futaba T7C Tx to control the servos to allow the turrets to travel 180 degrees from one broadside to the other.

I bought a Futaba S3114 micro servo but the end stops on this will only allow a maximum of about 160 degrees overall travel. I've read online that it is possible to modify a servo by trimming away the end stops on the output shaft and fitting resistors on the potentiometer but the thought of trying this fills me with dread!

I've seen servos used for robotics which rotate 360 degrees but I don't require this amount of travel and I'm not sure that I could control the movement of these with enough precision for my own requirements.

Rather having to resort somewhat to trial and error could anyone assist by recommending specific servos which allow proportional controlled travel up to a full 180 degrees please?

Many thanks,

Paul.

[Paul75Participant @paul75]

[Colin BishopModerator @colinbishop34627]

The ACTion Servomorph will extend travel to 180 degrees which may be sufficient.

**LINK**

No doubt our resident Guru Dave Milbourn will be able to give further information.

Colin

[Paul75Participant @paul75]

Thanks Colin.

I've bought one of these too but I don't think it can extend the servo travel beyond the mechanical end stop on the gear shaft.

All the best,

Paul.

[Amy jane SeptemberParticipant @amyjaneseptember49770]

Hi Paul.

If you disconnect the out put gear from the pot, and use a dab of glue to fix the pot out put tang in a central position, then the servo can be made to rotate continuously in either direction. The rotational speed will be proportional to how far you put the stick over. It should be no small matter to put a stop on the turret to control extremes. (just back the stick off a little and the end of throw, so the servo's not stalled)

Amy

[Dave MilbournParticipant @davemilbourn48782]

Microservos generally have a very small output arc [I'm surprised at this one moving 160°], and it's correct that you can't electronically over-ride the physical stops in a servo's gear train. You might consider fitting a 2:1 gear (or pulleys and a belt) to the output disc i.e. so that the gun rotates 180° when the servo rotates 90°, and using a P96 or similar to reduce the output arc of the servo to 90°. You can also use the ServoMorph to slow down the rotation speed. It's either that or put up with 160° – which is what I'd do!

Dave M

 

 

Edited By Dave Milbourn on 14/02/2015 23:14:16

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Hello Paul,

I obtained some servo controllers from modelradioworkshops and he sells a specific unit for turret control, as well as other units such as switchers and slowers etc.

Aye, Kim

[Dave MilbournParticipant @davemilbourn48782]

Kim/Paul

I'm familiar with Mike's stuff (and very good it is, too). Alan Bond designed a similar unit for Technobots but neither will enable a servo to turn beyond its physical stops. **LINK** **LINK**

Dave M

[Malcolm FraryParticipant @malcolmfrary95515]

The end stops in a servo are there to prevent the wipers in the position sensing pot from over-running thereby mangling themselves and converting the servo into a paperweight. The only time that the stops get disabled is when you are converting it to a multi turn winch, and that involves mechanically disconnecting the drive to the pot. The actual arc of travel of the servo ultimately depends on the transmitter, not all transmitters give the same results.

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Me again Paul,

you could always do what we are doing over here (some of us) and that's using the "Pollulu" chip systems and programming our own servo functions. My colleague displayed this at Warwick last year using the 4 servo board (retails at about £7) all you have to do is build it (solder) and then program it using free downloadable software compatible with Windows and Mac OX (and Linux). It's very simple, do not get put off by the phrase programmable chips! With the four servo unit he had a turret that turned, 3 guns that raised and lowered independently and noise and led flashes to resemble gun fire. And the unit once engaged continued with its movements free from the transmitter, for display purposes, or could be triggered to operate with the R/C when afloat if required.

As to increasing rotation, we have used piggy-backed servos. One hidden in the turret upside down, and its servo disc attached to another servo's disc, this one the right way up, or opposite the one above. The upper servo can travel say 60' each way, and it in turn can be rotated another 60' each way by the lower servo giving you 240' in total. Of course you need a bit of room, but turrets are light weight, so use mini/micro servos. The lower servo is slotted into a servo box very similar to that suggested by DM on another thread here last week.

Try and ovoid belt and gear drives, they need aligning carefully and will always let you down at some time.

Aye, Kim

[Glynn GuestParticipant @glynnguest59245]

Is there something wrong with using a 180 degree rotation servo?

Ref Model Boats Feb 2014 page 10.

Glynn Guest

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Hi Glynn,

absolutely nought wrong with 180' at all, it's just not normally found, but re-reading your article I've made a note, and I'd forgotten the adding a resistor trick to extend rotation too.

I think turrets look better being able to point aft of midships, right around to the other side, but any rotation must be better than a static look.

The trick with stacked mini servos is to use a transmitter that has mixing capability, so not suitable for the cheap end of the market, then the second servo can be operated via the first servo channel in the mixer. Using the pollulu servo controller no channel is required, the operator sets his own time dwells when programming, and speeds etc.

Aye, Kim

[Dave MilbournParticipant @davemilbourn48782]

I can't find that issue in my collection, Glynn. The answer to your question is, of course, no – but you first have to find a servo which actually does rotate a full 180°. Apart from undercarriage retract servos I don't know of one – maybe you could help?

Dave M

[Paul75Participant @paul75]

Hello Everyone.

Thank you all for your replies – they have given me valuable food for thought. Sorry about the delayed response from me – I haven't had a chance to get onto the computer for a couple of days.

If anyone knows of a particular servo that would allow controlled movement over a 180 degrees range (perhaps a bit more too) that would be great. I've had a play with an old Digifleet servo I have and the mechanical end stops allow perhaps 185 degrees of travel. Given the popularity of RC model warships I think it's a shame that servos tailored for gun turret rotaion aren't readily available – or perhaps I've not been looking in the right place!

Thanks again,

Paul.

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

DM and Paul,

here's what Glynn was talking about, still same price too. Tower Pro MG 995 180 degree rotation.

**LINK**

Aye, Kim

[CookieOldParticipant @cookieold]

Hi Paul , If you look at my gallery i simply converted a standard servo to rotate continuous and made a cam arrangement works fine and rotates 170 degrees both ways on a RC switch.

Regards Dave

[Paul75Participant @paul75]

Hello Everyone.

I've just trimmed away the output gear end stop on inside of the top case of my Futaba S3114 micro servo and, using the modification from the Action Electronics Servomorph, the servo happily rotates to nigh on 90 degrees either side of centre. Now for the slight headache of removing the turrets, excavating the servo housings and plumbing everything in……

Thanks again for all your advice,

Paul.

[Max CormickParticipant @maxcormick]

questions:

1.Tower Pro MG 995 180: does turn 180° both sides?

and

2. does the Turret Servo Controller, if works with a standard servo 60-0-60, change it for instance to 120-0-120 ?

may be I did understand: if we have a phisical stop in the servo….it is impossible

I would like to turn my 6 turrets in my fletcher too…..

regards

[Malcolm FraryParticipant @malcolmfrary95515]

All servos use a fairly standard rotary potentiometer as their sensing device. These have a track covering 270 degrees, and unless there is an extra gearbox (or a non-standard multi turn pot), that is the maximum for a normal servo. The stops prevent it doing further damage to itself.

A normal servo will cover about 90 degrees in total, depending on the electronics in the servo and the signal put out by the transmitter. This is a safety feature among other things that allows pretty much any servo to work with any transmitter without much chance of self damage.

Multi turn servos (e.g. winches) have gears to use the same pot but have the output turn several times. If a high degree servo does not have extra gearing, it will always be at risk of over-running the pot travel. which is not good. If the signal working a servo is doctored to send it beyond the point where it physically cannot go, something will break, but for any individual servo, it all depends on whether the extra travel is achieved mechanically or electronically.

[Max CormickParticipant @maxcormick]

Pls:

questions:

1.Tower Pro MG 995 180: does it  turn 180°both sides? : I mean: 180-0-180 or it is only 90-0-90?

if it turns 180-0-180 solve all for turret's turn

regards

Edited By Max Cormick on 02/03/2016 14:49:59

Edited By Max Cormick on 02/03/2016 14:50:32

[John RigbyParticipant @johnrigby89710]

I know this is a bit late but, if you still want to make your turrets rotate? Check out the warships underway web site. Go to their "how to" page. I think you will find what you are looking for there.

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