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>> Home > Forum > Electrical Related > Servos & motor having a wobbly
Servos & motor having a wobbly
(839 views)
Author Message
EricMB
(Lieutenant)





Forum Posts: 16
3rd Jul 2017 13:17  
>> Permalink
mdlbt.com/30869

Hi all, I'm working on a small boat with an outboard motor, that seems to have developed a judder when powering up. I'm running a 7.2 volt battery pack, Mtroniks Micro/Loco (marine) 10amp reversible ESC, flysky FS-R6B 6CH 2.4Ghz RX and Flysky FS-T6 TX. I've video'd it having a wobbly, any helpful suggestions gratefully received! I did wonder if the motor has got wet and is shorting out as it's in the outboard under water, but not sure. Thanks.. here's the link (too big to attach!)
https://youtu.be/t-oJtdGMyYw

Dave M
(Fleet Admiral!)





Forum Posts: 1399
3rd Jul 2017 17:32  
>> Permalink
mdlbt.com/30876

Hi EricMB
There is certainly interference as the Rx light is flashing almost constantly.

The rudder servo looks like a small type that I have had problems with (twice) on my RG65 yacht used as the rudder servo. Initially try disconnecting this and see if the symptoms disappear.
If not reconnect and disconnect the leads from the ESC to the motor and see if the problem disappears.
It could also be a faulty battery connection so check the leads and try moving (twist and pull) them whilst switched on.
Let me know how this goes as there are other things you can do to solve the issue
Dave


Live long and prosper

Dave
RNinMunich
(Fleet Admiral!)





Forum Posts: 1086
3rd Jul 2017 18:17  
>> Permalink
mdlbt.com/30877

Interference!! 😡 Is the motor suppressed???


"The brain is not intended to store facts. It is for thinking, and for knowing where to find the facts !" Albert Einstein. 😉 cheers Doug
EricMB
(Lieutenant)





Forum Posts: 16
3rd Jul 2017 19:03  
>> Permalink
mdlbt.com/30878

Thanks Dave, that's good advice, I'll try a different servo. I'm hoping it's not this as there isn't much space for a bigger one, but I guess a more expensive one may not cause the same probs?😜

EricMB
(Lieutenant)





Forum Posts: 16
3rd Jul 2017 19:04  
>> Permalink
mdlbt.com/30879

Thanks too Doug, I'm guessing the motor isn't supressed, as it's sealed inside the plastic housing for the outboard and directly connected to the prop. The reason I know this is that I took the last one apart to check it and it now leaks!!!! I've ordered another one.. is there any way to supress it without connecting the capacitor directly to the motor body?

Dave M
(Fleet Admiral!)





Forum Posts: 1399
3rd Jul 2017 19:09  
>> Permalink
mdlbt.com/30880

No need to change the servo. Just disconnect and see if the problem goes. If not disconnect the motor from the esc and see if it's the motor causing the problem, as you suspected. If you have a rx battery you could just disconnect the ESC.
Regarding those minature servos in my experience they are all the same and driving a big lump of motor will be a heavy load. Looking again it seems there may be two rudder servos and either could have failed.
Dave


Live long and prosper

Dave
RNinMunich
(Fleet Admiral!)





Forum Posts: 1086
3rd Jul 2017 21:24  
>> Permalink
mdlbt.com/30890

Hi Eric, yes there is - put two chokes with ferrite cores in the leads to the motor. Mount them as close to the motor as possible with a 0.47 uF capacitor across the output ends (closest to the motor).
See attached pics of such installed in my Type IIA submarine.
Not quite as good as direct on the motor can but , 'better than a slap in the face with a frozen haddock' 😉
Your local model shop (or Maplins? etc) should be able to supply the chokes. They are also used in the auto industry to suppress ignition interference on car radios etc. Cheers Doug 😎


Attached Files - Click To View Large


"The brain is not intended to store facts. It is for thinking, and for knowing where to find the facts !" Albert Einstein. 😉 cheers Doug
EricMB
(Lieutenant)





Forum Posts: 16
5th Jul 2017 10:15  
>> Permalink
mdlbt.com/30960

Hi Doug, that looks very impressive! I'm not sure my electronics are up to your level, is the circuit board available with the chokes already built-in, or did you manufacture it? Cheers, Eric

RNinMunich
(Fleet Admiral!)





Forum Posts: 1086
5th Jul 2017 11:35  
>> Permalink
mdlbt.com/30961

Hi Eric, No rocket science involved! 😉
In my case I was lucky, many many moons ago I worked for Rank Telecoms in Brentford where I ran the Test Dpt for mobile radios. These little boards were part of the installation kit for a 25W VHF car mobile.
But Veroboard would be just as good. You only need 4 holes for the chokes and 4 for the input / output wires. Maplin or similar should be able to supply the parts. Maybe even complete boards as part of CB or Amateur radio installation kits? Good luck, Doug 😎
PS I may still have 1 or 2 boards knocking around😉 If I find one during my current workshop / cellar sort out / make room to work exercise I'll send you one. 👍


"The brain is not intended to store facts. It is for thinking, and for knowing where to find the facts !" Albert Einstein. 😉 cheers Doug
Dave M
(Fleet Admiral!)





Forum Posts: 1399
5th Jul 2017 12:32  
>> Permalink
mdlbt.com/30966

Hi Eric
Have you eliminated the servo as the problem?
Doug, won't your choke interfere with the high frequency pulses used in modern ESC's? and is there a max current capacity for the chokes?
Dave


Live long and prosper

Dave
RNinMunich
(Fleet Admiral!)





Forum Posts: 1086
5th Jul 2017 12:53  
>> Permalink
mdlbt.com/30969

Hi Dave, interesting thought with the pulses! 🤔
My sub is working fine with a 40MHz RX Pico receiver and Graupner Micro Speed 10 ESC. Could test it with my Viper Marine 10 I suppose!?
Otherwise Eric may have to go back to a 'simpler' ESC if he can't suppress the outboard at source.

Current capacity depends of course on the wire gauge used for the choke.
The ones shown in my sub were designed to handle at least 15A as far as I can remember! Eric's outboard can't be that thirsty.
Cheers Doug 😎


"The brain is not intended to store facts. It is for thinking, and for knowing where to find the facts !" Albert Einstein. 😉 cheers Doug
Dave M
(Fleet Admiral!)





Forum Posts: 1399
5th Jul 2017 16:37  
>> Permalink
mdlbt.com/30977

Hi Doug
I well remember these chokes and that capacitor. I do believe modern thinking is to wrap the low current wires to the ESC round a circular choke, there are never any chokes in the supplied ESCs motor leads. I do recall advice on one of the forums regarding not putting any inductance in the motor leads, not sure if it was Electronize or Mtronic who gave the advice. They both adopted high frequency pulses for control a few years ago and there was lots of discussion as people upgraded their old ESC to a new one. Chokes were quite common in the past but the technology was vastly different to that used by modern ESCs.
Are you sure the interference is from the motor? I had a very similar symptom with a faulty servo, very similar to that Eric is using. I have asked him to unplug the servo and see if the problem goes away. So far I have not had a reply so can only guess what might be the problem.
Cheers
Dave


Live long and prosper

Dave
RNinMunich
(Fleet Admiral!)





Forum Posts: 1086
6th Jul 2017 08:06  
>> Permalink
mdlbt.com/30993

Hi Dave, I guess you're right! I obviously have more catching up to do than I thought 🤔
Re your question - if you mean my sub it has no interference problem; RX is in the bow, motors and suppression boards in the stern as in my pics. Two big 4AH 'lumps of lead' in between!
I simply wondered if Eric's problem was due to interference from a cheap motor in the outboard. I have taken a couple of these apart (from inflatable boats) and the motors are pretty basic with little or no suppression. But if he's using a hi freq. ESC then chokes are probably not the solution. I that case I might go back to a simpler ESC myself!
Cheers Doug 😎


"The brain is not intended to store facts. It is for thinking, and for knowing where to find the facts !" Albert Einstein. 😉 cheers Doug
Dave M
(Fleet Admiral!)





Forum Posts: 1399
6th Jul 2017 09:53  
>> Permalink
mdlbt.com/30997

Hi Doug
Progress especially with anything electronic moves at lightening speed and our PCs are almost obsolete as soon as we buy them.
I suspect your sub like many of mine has kit sourced from an earlier period and I can well remember all kinds of suppression aids we used to have to use especially with our cars to suppress the interference from the ignition!
I suspect it is only the modern high frequency ESCs that will have a problem, earlier kit used discrete chips that used much lower frequencies for the pulses. The original chips used became unavailable so manufacturers had to adapt to what was available.
If your sub works OK I would leave well alone.
Eric's problem could well be motor related but could also be from a faulty servo, my suggestion to unplug the rudder servo would eliminate this from the equation, but I am awaiting a response
Sun's back but thunderstorms promised for tonight!
Happy days
Dave


Live long and prosper

Dave
RNinMunich
(Fleet Admiral!)





Forum Posts: 1086
6th Jul 2017 10:27  
>> Permalink
mdlbt.com/30999

Hi Dave, Exactly, If it ain't broke - don't fix it! 👍😉
Will get some experience of current kit on my Sea Scout upgrade - A Quantum leap from Taycol to Brushless 🤔
Weather same here, ca 30°C 😎 with intermittent thunderstorms expected from tomorrow 😡 Cheers Doug 😎
PS The sub outruns many 'speed' boats, long and thin with plenty of Oomph! 😁


"The brain is not intended to store facts. It is for thinking, and for knowing where to find the facts !" Albert Einstein. 😉 cheers Doug
EricMB
(Lieutenant)





Forum Posts: 16
7th Jul 2017 09:50  
>> Permalink
mdlbt.com/31027

Hi Doug and Dave, very sorry for the radio silence, day job getting in the way! Really appreciate the input, interesting to hear about your experience with the progress of technology, I guess in using digital RX and TX setups there are different issues that arise! So, to your kind advice - I unplugged the servo Dave, and no difference, which made me think it was the motor. I disconnected the ESC (and hence the power), added a battery input to the RX and all was ok! That made me realise that the power section was the problem, confirmed by a suggestion a fellow model
Boater made about checking the battery - instead of chucking out 7.2v, it was giving about 5.3v! Recharged and hey presto - problem solved! Flat battery giving out interference!! Here's the system now behaving as it it should; https://youtu.be/VbGxC0VIo3A
Thanks again for all the help and advice - very much appreciated.
Regards,
Eric

RNinMunich
(Fleet Admiral!)





Forum Posts: 1086
7th Jul 2017 12:18  
>> Permalink
mdlbt.com/31035

Hi Eric,
guess we kinda assumed the battery had been checked / charged! 🤔
Main thing is you're up and running 👍👍
Cheers Doug 😎


"The brain is not intended to store facts. It is for thinking, and for knowing where to find the facts !" Albert Einstein. 😉 cheers Doug