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Author Topic: U-47 Electronics Issues Servo Fluttering  (Read 2844 times)

irishcarguy

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U-47 Electronics Issues Servo Fluttering
« on: February 11, 2012, 06:15:31 PM »

Need a Little advice.
I'm having fluttering  on my rudders and dive planes when I activate the Engel 824EA using the Engel UNI

Prior to adding the UNI and Piston Tank all three servos and ESC worked perfectly Since this is my first R/C I was patting myself on my back, but alas too soon, I guess?

Here's what I'm using Rx Futaba R168DF (75mhz in US), Rokraft 120uP, Engal EA825-6 Channels. Rx Channels  1+2 Rudder and Rear Dive Plane, Channel 3 ESC, Channel 4 Front Dive Plane, Channel 5 the Engal Piston Tank. I disconnected the center lead (White) from the RX to the ESC. During my testing I'm using a battery pack for  Rx power but will be using a BEC.

Does anyone have an idea of what's causing the servos to flutter when the Piston Tank is activated? Per Engel the Motor has built in noise suppression. I have added noise suppression on the two motors
Thanks John
 {:-{
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Mick B.

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #1 on: February 11, 2012, 06:23:01 PM »

Have you disconnected the ESC red wires, else the BEC's will be feeding into the RX bus. Try disconnecting the ESC's altogether, and see if the flutter disappears on the servos when operating the tank. Could be a clash between the ESC's and the Unipro.

Also have you got a wire running from the piston tank motor can back to the negative terminal on your main battery, to provide a ground for the suppression caps?

irishcarguy

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #2 on: February 11, 2012, 08:07:13 PM »

I had already disconnected the RED center wire to the ESC. I did try completely disconnecting the ESC then I did not get any fluttering . However from what you say I should run a wire from the negative post of the piston motor to the negative of the battery to act as a ground, is that correct? According to the Engel wiring diagram it doesn't show to do that any chance I could damage something?
Thanks for your help
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Mick B.

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #3 on: February 11, 2012, 08:42:17 PM »

No, from the can of the motor back to the negative terminal of the battery, not the negative terminal of the motor, that would create a short circuit condition.

In your original post it said you'd disconnected the white wire from the ESC, which is the control pulse not the red wire.

So no servo fluttering with the ESC disconnected, even when operating the piston tank. Also no fluttering either when the Unipro is disconnected and the ESC is hooked up. What happens if you hook everything up with the ESC's BEC powering things? e.g. no external pack.

It sounds like some sort of clash between the ESC and the Unipro board. These kind of faults can be tricky to nail down to be honest.  I had a problem with two speed controllers of different manufacturers that were fitted in a submarine. One controlled the pump for the ballast system, the other the drive motor. Intermittently the signal failsafe would kick-in for the pump ESC, leaving me with a boat that either wouldn't submerge or surface. I tried every trick in the book, in the end I replaced one of the ESC's so they were both the same- end of problem.

sub john

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #4 on: February 12, 2012, 01:52:59 PM »

HI John
This sounds like you have a ground loop problem, back emf from piston tank motor from what you said the problem only happens when you plug that part of the circuit in to RX, one thing i would try is the wires coming off motor on piston tank try and make the wires a little longer and twist them together tight put the twisted wires around a ferrite ring about 8 times and then take back to control board. Do the same thing with wires coming from control board for piston tank that plugs in to RX  I know that you said you have put sirpression on motor on piston tank trouble is caps needs  to be worked out for the frequency you are using to control the sub, you could always put across the motor a bipolar cap that they use in speakers i have seen this work quite well. What Subculture said about taking earth wire from metal can of motor back to neg on battery was spot on that is the right thing to do, all neg wires should go back to the same point neg on main  battery. Little tip on using BEC a lot of BEC,S regs work by switching high frequency at about 300 KHZ i have seen people loss about half of there range with the radio try and go for a linear reg i have been playing about with one that will give about 5AMPS

What is a good thing to do is twist all power cables  together as what you are doing by doing this is forming capacitance down the wires and will take out high frequency noise
    Hope that helps Sub John
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Subculture

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #5 on: February 12, 2012, 06:46:59 PM »

I have used switchmode BEC's in a couple of models and haven't experienced any issue with range, although perhaps I'm not exactly pushing things. They do come in handy if you're running higher voltages and don't want the extra bulk of a separate battery pack. I don't have the equipment beyond simple range checks to see what they're doing to attenuate the signal.

What about ESC's though? They switch the current to the motor when running other than flat-out, or is the lower switching frequency less of an issue?

Got any tips on how we go about calculating correct capacitance values for different radio frequencies? The advice I've seen always gives an arbitrary value, so it would be useful to know what is optimum for say 40 and 27mhz which are the frequencies most model submariners use in this country.

sub john

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #6 on: February 12, 2012, 09:06:01 PM »

HI Subculture
   Some of the switch mode BEC'S do not work to bad but some of them are rubbish its just like carrying a in built jamming device to knock out your radio. One of the problems is as you load the out put on a switch mode BEC the noise that it produces RF interference will travel up and down the RF band's as you load the out put  a lot of these you will not notice because with sub's you are not very far away from TX but what happen's is as the sub travels out of RF range of TX the  switch mode BEC will start to swamp RX in put in side of sub in my opinion you are better off using a linear reg as they do not produce noise, but  by saying that all out puts on linear Reg's should be decoupled with tant caps on the  in put and out put of reg  to take out RF noise

Speed controllers, when you select what frequency you won't the fet's to switch at 5 KHZ or 10 KHZ or what ever as you start to apply throttle the 5KHZ burst to the gates on the fet's is only switched on for a very short time and as you apply more throttle that on time gets longer so as you go to full speed it does not just switch the fet's hard on it just hit's them with a 5 KHZ burst all the time by doing this you get more talk in the motor

Suppression of motors some where i have got it all written down will look in my folder's and find info. One of the thing's i did with my big sub was to use transient voltage suppressors the one's i used on motors where AXIAL BIDIRECTIONAL these device's are very fast at clamping high voltage spike's and they do a good job but you have to select the right voltage type
     SUB JOHN
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Subculture

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #7 on: February 13, 2012, 04:27:09 PM »

I've seen those mentioned before in this article-

http://modelsolutions.ca/articles/DavidsOriginalArticles/RFIArticleMarch2006.pdf

I was once advised against putting sensitive electronics inside aluminium cases. The reason given was that aluminium behaves rather oddly in relation to magnetic fields, and that it's best to stick to ferrous metals for shielding.

sub john

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #8 on: February 13, 2012, 09:30:58 PM »

HI Subculture
   Had a look at site you posted up hadn't seen that before but there is some good info on there i noticed about putting receiver in aluminium box if you was to do that probably the best thing to do is put band pass filter on end of receiver in box and then put preamp front end but i suppose it is how far you won't to take it.

If you was to use aluminium to make a screen box just say put receiver in it and if it was next to a electric motor you would not just have to worry about RF interference one other big problem would be the motor making a magnetic flux next to the receiver and would end up detuning the receiver because of the magnetic flux coming off the motor, and if it was pulling high current it would get worse. What i do a lot of the time if i won't to make a screen box is take a piece of single sided PCB board cut it up to form a box all of copper can be soldered on in side of box and can be made any size you won't , i use the same idea to make custom boxes for test gear if you take your time it comes out quite well

One thing you can do on end of motor where you fit caps, you can parallel different values of caps to stop different bands of interference. Other thing is if you just put ferrite beads on the end of wires if you just put one or two it would not do a great deal on motor wires you would have to fit a lot of them much better off using a ferrite ring and passing wires through it many times

                                              sub john
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irishcarguy

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #9 on: March 04, 2012, 05:58:10 PM »

Just an update I took Sub John's advise made the wires longer, twisted them and ran them though ferrite rings. One thing I had to do was use two ferrite rings to get the wrap around 8 times as Sub John suggested. It seems to work great I do get on slight flutter on one servo when I start the pump in only one direction. I have still to add the ferrite ring on the lead from the UNI to the RX but I do believe I'm on the right track

So Thanks to everyone who replied

No my next big hurdle will be if the WTC is water tight. As soon as I figure out how to add pictures to my post I'll be adding them. It keep rejecting them.

Again thanks John
 :-))
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Mick B.

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #10 on: March 07, 2012, 07:01:10 PM »

REPLY#9
Glad to hear some of your interference has gone ferrite ring do a good job i use them a lot on all sorts of electronics, thought i would give you some thing to try across brushes on all your motors in your PM you said that your sub ran on 6volts you could fit some of these across the brushes they are 1500w BIDIRECTIONAL SUPPRESSION DIODES  you can get them from FARNELL IN THE UK stock number is 446-567 but do not use these if you are running over 6 volts. Don't know what battery you are using but if you are using a jel type cell fully charged it will be 6.9 volts when took off charging or should be hope information helps
    SUB JOHN
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irishcarguy

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #11 on: March 13, 2012, 10:29:47 PM »

John, I looked at Farnell at the diode you recommended for the PM but it's been discontinued and replace by this which as i read it's 12 V.
http://uk.farnell.com/stmicroelectronics/1-5ke12ca/diode-tvs-12v-1500w/dp/9801081?whydiditmatch=rel_3&matchedProduct=446567&matchedProduct=446567&whydiditmatch=rel_3

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irishcarguy

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #12 on: March 13, 2012, 10:32:32 PM »

Sorry hit return by mistake also you asked about what battery I'm using 7.2 V NiMh ( 6- Sub "C") after charging it shows just under 8V ( 7.8V -7.9V)

John
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Mick B.

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Re: U-47 Electronics Issues Servo Fluttering
« Reply #13 on: March 24, 2012, 07:10:23 PM »

REPLY#11
   Sorry for long delay in getting back to you had a problem getting back on to mayhem after it went down seems to work fine now.  The replacement diodes should work fine they will work OK with battery voltage that you stated .

    When i said to you about whyding wires around a ferrite ring if you won't to cut down on space if you get some copper enamel wire say 18SWG gauge you can wrap it around the ferrite ring more times but what i would recommend you do is the copper wire cover it in heat shrink sleeving after you have shrunk it round the wire then  wrap it round the ferrite ring as it will give it a lot more insulation plus by doing this it does not matter it the two wires touch if you won't you can wined them side by side hope it helps
John
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