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Sailboat electronics cutting out while running after changing servos

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Edward Hobbs 218/06/2022 14:02:26
1 forum posts

Hi Folks,

I'm experiencing a very frustrating issue with my Footy RC boat. I had originally set the boat up with two 9g servos - one for the rudder, one for the sheeting arm. This was using the "power arm" setup to give the 9g a fighting chance, and worked okay - it had some issues in stronger winds though so I wanted to update to a larger sail arm.

I replaced the 9g servo with an MG995 servo as it's capable of around twice the power, but whenever I try and sail with it my electronics will randomly cut out. Sometimes they will come back after i move the sticks a bit, sometimes they will die for good and i have to wait for the craft to drift back to shore.

I thought it may be a case of the servo drawing too much power in high winds (our local lake is VERY windy!) however the exact same problem happened this thursday when there was very little wind at all.

I thought it could be the fact that I'm using rechargeable batteries that are only rated at 1.2v and the receiver takes between 4.8-6v, 4 full batteries is ~5.5v. I tried 5 batteries in case the extra power would help and the receiver exploded so that's definitely not the solution!

I'm currently in the process of converting back to the 9g setup to rule out anything else, but given the only thing that changed was the servo I think it may be the culprit.

Have any of you ever seen this sort of behaviour and managed to fix it? Is it a case of cheap servos causing the receiver to fail? Any help would be most appreciated.

Thanks,
Ed

Richard Simpson19/06/2022 09:33:15
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1027 forum posts
256 photos

Firstly welcome to the forum. Just a couple of thoughts, firstly you said "...and the receiver exploded..." which I assume is not strictly what happened?

There are a couple of things that could happen with putting a new bigger servo in, one is are you sure that the servo arm is not interfering with any part of the model? Then the next thing to check is that you have enough slack in the sail cord to allow the movement of the servo arm. If there is not enough slack the servo will be over loaded. Check that the movement of the arm is the same with the cord connected and disconnected. Does the servo make any unusual noises as it operates?

As regards the batteries you do need to be sure they are fully charged or fresh so you will be supplying 4.8V with four rechargeables or 6V with four non rechargeables. That's why the receiver is designed to operate within that range.

If possible try a few different servos in the same set up and test them all. There is a possibility that a brand new servo might have a fault so you need to eliminate that. I have only just received a brand new speed controller, which simply doesn't work and is going back, so it happens.

John W E19/06/2022 18:19:11
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302 forum posts
284 photos

hi there

I had a quick look on line about the specs of this servo you are using - and - my first thoughts are - Is it a digital servo that you are using? on an analogue set?

If it was this - it could cause some of the problems.

But, if you read through some of the comments on the link I have put on (if it works) - that some people don't rate these servos very well and there seems to be a problem with them.

The other thing I notices is that in the advert for them they are a 180 degree turn servo - or - you can have a 360 degree turn servo.

**LINK**

John

gecon20/06/2022 07:56:07
676 forum posts
626 photos

Hi Edward, I am not an expert....but my thoughts are;

Most servos are produced to operate on 4.8v. A few accept up to max 6v. but they don't usually 'like' 6v. 5 X1.2v -fully charged cells deliver more than 6v for a while. This may cause damage to the circuitry.

I think the long 'power arm' on a small servo may overload it somewhat. Does it come with a long arm? or did you make it yourself? A long arm gives more sheet movement, but needs more battery capacity to move it -especially in a breeze!

Ray Wood 2 is a 'power arm' fan, maybe he can give some info?

The anologue/digital compatibility issue may also be a factor as John mentions. Digital servos require more battery capacity too... ie amps, not volts.

There may be a voltage drop in your setup which causes the whole show to shut down. ie. voltage drops to below 3.6v when sailing.

George

 

 

Edited By gecon on 20/06/2022 08:00:30

Edward Hobbs24/06/2022 21:12:54
11 forum posts

Hi All,

Thanks for the replies, sorry about the late response I'd got distracted by other things...

I wasn't exaggerating when I said exploded, i'm not sure what component specifically went but it did go with a bang, sparks smoke the whole 9 yards!

Since making this post i have finished rebuilding the boat with two 9g servos, and the same issue is still happening which is really very odd.

I'm not sure about the digital/analogue problem, it would make sense but I think the receiver uses the standard PWM signals so all should work fine? The 9g servos work fine on-shore then produce the same issue.

I should say that prior to trying with the larger servo the boat would sail absolutely beautifully, I spent a good 2-3 hours down at the lake pootling around with it and I only had to stop due to low transmitter power. I think my next port of call is to check if the transmitter is the one causing the issues? It's the only thing left to change as i've already tried:

- new receiver
- new batteries
- new servos both rudder and sail arm as the rudder servo also stopped working recently (but i think that's my fault for not waterproofing them at all)

Edward Hobbs24/06/2022 21:14:18
11 forum posts

The only other thing I think it could be is that previously, i was using 4xAAs for power but currently i am using 4xAAAs. I wouldn't expect that to cause issues especially with such small servos but maybe they aren't providing enough power?

Chris Fellows24/06/2022 22:47:16
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1196 forum posts
752 photos

Hi Ed

Pity you didn't mention that earlier!!!

And remember that old adage about only changing one thing at a time!

Anyway, that is more than likely where the problem lies. I can't think of anything else that I use other than tv remotes etc. that use AAA batteries and their power requirements are very low.

Why did you change to AAA? I suggest returning to AA and the original servos and if they work fine, then try the more powerful servo.

Chris

Ray Wood 225/06/2022 08:54:51
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2847 forum posts
993 photos

Hi Ed,

I'm afraid the size of the cells AAA or AA has nothing to do with your problems, receivers are happy with voltage between 4.8v & 6v actually most racers are using 5 cell packs to give the winch or servo a bit more umph !!

I fly with AAA 300mah on lightweight aeroplanes no problem.

With the cost of radio sets at £35 for a drycell set, throw your old set away

Regards Ray

Richard Simpson25/06/2022 09:37:43
avatar
1027 forum posts
256 photos

While the capacity can be limited on an AAA cell due to its physical size the important thing here is voltage and they are the same for AAA and AA, i.e. 1.2v for a rechargeable cell and 1.5v for a non rechargeable cell. The only thing you should notice is that the AAA set usually won't last as long.

I must admit I have never heard of a receiver going bang, something must have seriously gone wrong such as a huge over voltage or a failed internal component.

You haven't mentioned the radio or what you changed the failed receiver for but I'm going to suggest a complete clearing of the decks here. I have only just bought a radio set to operate a little tug boat for my great nephew, which was great value with a six channel 2.4G transmitter and included matched receiver for the grand sum of £40.00. Although the instructions do not tell you how you can convert the sticks to sail use.

Radio Link

I would buy one of those, get yourself a normal AA receiver pack holder and try it. I can't imagine your problems not being resolved.

Chris Fellows25/06/2022 10:58:46
avatar
1196 forum posts
752 photos

I stand corrected!

I was assuming, always a dangerous thing, that the lower capacity of the AAAs would soon be overcome by the work the sail servo was having to do, especially as it was working fine on the shore.

Chris

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