Servo problem

This topic has 30 replies, 5 voices, and was last updated 1 month ago by Tim Cooper.

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20 July 2026 at 11:14 #128434
Tim Cooper
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@timcooper90034
I have two identical servos in a model of a Russian OSA 1 boat. They are turning the gun turrets at the bow and stern. One works very smoothly, the other tends to ‘jitter’ . Both are controlled by the same channel on the transmitter. At present I have taken them both out to investigate.

The servos are the small SG 90 type.

Anyone have any suggestions. I think I will initially try a different servo but I think I have tried that before.

Tim
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20 July 2026 at 13:23 #128435
ashley needham
Participant
@ashleyneedham69188
Hmm…perhaps the run of the wiring is an issue…the jittery one gets too close to something?? Length of run??

Try a ferrite ring.

Er…er…

Ashley
20 July 2026 at 15:39 #128448
Tim Cooper
Participant
@timcooper90034
Thanks Ashley

Now I have them out of the boat I cant remember if it’s the bow or stern gun! It must be my age!

I’m sure I had Ferrite ring in a drawer somewhere.

Tim
20 July 2026 at 16:40 #128449
Colin Bishop
Moderator
@colinbishop34627
Tim

If you swap them over and the jittering stays with the same servo then it is likely the servo is at fault.

Colin
20 July 2026 at 17:52 #128455
Richard Simpson
Moderator
@richardsimpson88330
If you have two servos connected to the same channel and only one jitters it sounds almost certainly that it is the servo that is the problem. If it was anything to do with transmitter/receiver signal reliability etc. you would expect to see the same with both servos. The first thing I would do, as Colin suggests, would be to swap the servo plugs around and see if the fault moves or stays with the same servo.
20 July 2026 at 18:54 #128463
Tim Cooper
Participant
@timcooper90034
Thanks

I will (hopefully) have a look that tonight.

Tim
21 July 2026 at 16:49 #128486
Tim Cooper
Participant
@timcooper90034
It seems to be the servo on the stern gun.

I have managed to take out, so I will replace it with a new one and try again.

Tim
22 July 2026 at 06:07 #128513
Dodgy Geezer 1
Participant
@dodgygeezer1
I had a lot of trouble with a 9G servo on the Lark – worked fine but jittered like anything when the motor started up. I spent ages trying to suppress interference, but eventually swapped it for an identical other servo which had no ‘interference’ problems at all.

The impression I get is that these 9g servos are very variable, and may exhibit odd behaviour…
22 July 2026 at 13:44 #128514
Tim Cooper
Participant
@timcooper90034
I have tried a new servo on the bench, with the other original one. It seems to ok. They are on separate channels on the radio but both operated by one slider on the radio.

Tim
23 July 2026 at 12:06 #128529
Tim Cooper
Participant
@timcooper90034
I thought changing over the servo would be a quick fix, but the servo I took out was smaller than the SG90. Not sure where it came from but it fitted in the turret base. It also had a smaller knurled fitting on the top for the servo arms.

The SG90 needs a new connection to the turret and some work to secure it. It also protrudes into the deck, so will have to cut a larger hole in that.

Strange how what starts as a simple job always seem to get more complicated.

Off to look at my veg plot as something keeps coming to play at night and trying to eat my leek seedlings, parsnip and carrot tops and rhubarb leaves!

Tim
23 July 2026 at 12:18 #128530
Colin Bishop
Moderator
@colinbishop34627
Strange how what starts as a simple job always seem to get more complicated.

Not strange at all, seems to happen all the time to me!

Also, the longer it takes, the more likely it is that you’ll mess it up.

Colin
23 July 2026 at 13:32 #128531
Tim Cooper
Participant
@timcooper90034
Thanks Colin

Not sure I find that reassuring!

Tim
23 July 2026 at 14:50 #128532
Colin Bishop
Moderator
@colinbishop34627
Well, you know how it is Tim. You do some painting on the model and it all looks great, except for one small blemish or run. Should you just leave it or try to fix it? Of course, you try to fix it, it’s only a small area after all. Then it becomes a bigger area and your fix doesn’t quite blend in with the original. You fiddle with it some more, you look at it – and then you realise you have to start over….

Sometimes you are lucky, My Silver Mist has a few blemishes which would be difficult to remedy, but I have literally been able to cover them up by adding a bit of extra detail. Sometimes low cunning comes to the rescue.

Colin
24 July 2026 at 10:09 #128537
Tim Cooper
Participant
@timcooper90034
Colin

You were right.

New servo in and secure but it now deeper than the turret so had to cut a hole in the deck piece it sits on!

I now need to look at the way the turret deck pieces are secured!

Tim
24 July 2026 at 14:57 #128538
Tim Cooper
Participant
@timcooper90034
Looked at pictures on a new trail camera and although I hadn’t set it up completely I did get some pictures! Me watering the garden. Our dog watering the garden and two foxes playing with my carrots and leeks. They did leave me an old rubber ball and a black work glove .

Tim
24 July 2026 at 17:13 #128539
Colin Bishop
Moderator
@colinbishop34627
Made two on deck dining tables for Silver Mist. The first one wasn’t too good and then I noticed that the mahogany sheet tabletop surface had a dividing line down the centre crosswise with one side darker then the other. Matt varnish made it even worse so I ended up makinga second one which looks much better.

I must say the Bob Smith odourless cyano has been a Godsend in making and fitting the detail. It is useful having both varieties. The thin stuff soaks into the joint whilw the + thicker variety will sit on the surface and takes slightly longer to go off.

You’d better check that the foxes didn’t leave you with something smellier over your veggies making them a bit more organic than you intended!

Heat has been building up again today steadily…. Still, things are very much worse on the Continent.

Colin
25 July 2026 at 14:21 #128559
Tim Cooper
Participant
@timcooper90034
Hopefully I will sort out the rear turret this afternoon. The bow turret is making better contact with a magnet but may near another.

My trail camera caught two young foxes playing in veg plot at between 4 and 5 this morning.

They didn’t like the more substantial cage I had built around my leek seedlings. Do they play vat jumping over the carrots and parsnips.

Tim
26 July 2026 at 17:08 #128562
Dodgy Geezer 1
Participant
@dodgygeezer1
You know, I never thought of making the turrets turn, though I had both radar aerials turning on my prototype. I think I will design a Mk.2 AK-230 with a servo mount. Do you place yours under the base?
26 July 2026 at 17:43 #128563
Richard Simpson
Moderator
@richardsimpson88330
As regards one job leading to another. I’m just finishing a very old Japanese plastic kit of the QE2 and decided a little rigging around the mast would lift it a little. I fitted a fine handrail to tie the running rigging ends to and was just putting a spot of cyano onto a knot when the drop fell off the toothpick and landed slap bang in the middle of the penthouse roof. Now I have to paint over that again and try to hide the mess!
26 July 2026 at 18:58 #128579
Dodgy Geezer 1
Participant
@dodgygeezer1
And further, my son, by these words be admonished: of making many boats there is no end, and much modelling is a weariness to the flesh.

What Ecclesiastes 12:12 should have said…
26 July 2026 at 19:58 #128583
Tim Cooper
Participant
@timcooper90034
Dodgy

The front turret has the servo under a small piece of deck, the rear was inside the turret but now protrudes slightly beneath the deck, as I have now changed the servo.

The top of the turret has a brass rod which connects to a polystyrene tube which fits to the servo.

Tim
26 July 2026 at 21:30 #128584
Dodgy Geezer 1
Participant
@dodgygeezer1
Ah – can the gun barrels still move up and down?
26 July 2026 at 22:00 #128585
Tim Cooper
Participant
@timcooper90034
Dodgy

No the dome of the gun is made from a plasticard framework and the car body filler. So the gun barrels are fixed .

Tim
27 July 2026 at 09:16 #128591
Dodgy Geezer 1
Participant
@dodgygeezer1
This is my turret Mk 2, using a 9g servo. The green connector lets the barrels elevate manually. I suppose a redesign using nano servos might allow control of elevation and slewing…
27 July 2026 at 15:06 #128602
Tim Cooper
Participant
@timcooper90034
Dodgy a few pics of my turrets.

The bow gun servo has to go into the hull. The stern one just needed a hole in the deck. The styrene tube is made up of several diameters so it has a tight fit to top of servo and to some brass rod at base of the turret.

The extra bit on the lead (yellow blob) is supposed to increase the servo rotation to 180 degrees.

Tim
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