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Author Topic: Odd earthing for Taycols....  (Read 2015 times)

dodgy geezer

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Odd earthing for Taycols....
« on: September 15, 2012, 05:47:44 PM »

I'm trying Action's reversing box with a set of Taycols. My test rig includes a 'blue-fin' Chinese ESC, because that's the only reversible ESC I had going.

Most of the Taycols needed inductors on the power lines to run smoothly, but once installed they were fine. But the big ones (Standard, Supermarine and Double) still kept glitching. So I tried earthing the frame to battery negative - no joy. However, when I earthed the frame to the ESC positive output they ran as sweet as nuts. Earthing to the ESC negative output didn't work...

Any interference ace out there with possible reasons? Note that we're talking about line-borne interference alone - I was using 2.4ghz ...
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Tug-Kenny

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Re: Odd earthing for Taycols....
« Reply #1 on: September 15, 2012, 05:53:15 PM »



The ESC has variable pulsed positive pulses to govern the speed of the motor.  I really wouldn't like to connect general earthing systems to it as it may be a wire 'Too Much'

Perhaps a capacitor might help to protect the Esc unit.   Just a thought Chaps.

regards

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dodgy geezer

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Re: Odd earthing for Taycols....
« Reply #2 on: September 15, 2012, 06:55:20 PM »

I surprised me. But all the wire-bound interference certainly stopped when I connected the frame to the positive motor terminal...

The ESC battery input appears to have a capacitor across it. Are you suggesting putting one across the ESC output? That would be the same as the capacitor across the brushes, wouldn't it?
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Tug-Kenny

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Re: Odd earthing for Taycols....
« Reply #3 on: September 15, 2012, 09:21:38 PM »



Nothing goes across the ESC  output leads otherwise it would affect the signal


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dodgy geezer

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Re: Odd earthing for Taycols....
« Reply #4 on: September 15, 2012, 09:43:22 PM »

There's frequently a capacitor across them at the motor end...?
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Tug-Kenny

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Re: Odd earthing for Taycols....
« Reply #5 on: September 15, 2012, 09:49:31 PM »



One in the Pico-farad range would be OK

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dodgy geezer

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Re: Odd earthing for Taycols....
« Reply #6 on: September 15, 2012, 09:58:41 PM »

Still leaves me wondering why earthing the +ve output should make the interference go away...
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Tug-Kenny

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Re: Odd earthing for Taycols....
« Reply #7 on: September 15, 2012, 10:38:55 PM »



You are technically not earthing it,  but actually making the motor shell Live.  Should any stray wires brush across the case it might be trip to Action's new headquarters.

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dodgy geezer

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Re: Odd earthing for Taycols....
« Reply #8 on: September 16, 2012, 09:53:38 AM »

Well, of course, there is no case on a Taycol, and much of the exposed body is paxolin anyway. And the normal practice of connecting -ve to earth would run into the same problem....

This isn't a proposal for actually installing the motors (yet.. %% ). I have the motors on a test rig, because I need to get a reliable understanding of what will work with modern electronics.

I suspect that this is so far removed from everyday experience that I'd better go away and bone up on field-wound motor theory...   {:-{
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malcolmfrary

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Re: Odd earthing for Taycols....
« Reply #9 on: September 16, 2012, 10:51:15 AM »

Interference, or getting rid of it, is a black art, and it should always be remembered that in theory, there is no difference between theory and practice, but in practice, there is.
It could be that the stray voltages, if injected into the local ground line, could affect the signal voltages "seen" by the ESC.  Shunting them into the "power" side of things, the voltage regulation can probably soak them up and lose them.  Earthing the frame direct to the battery -ve with a heavy enough wire should, in theory, work (but see the top line). 
An RF capacitor at the motor terminals is intended to soak up RF coming from the motor before it gets to the leads by providing a short circuit at RF.  Fitting one at the ESC output just changes the shape of the ESC output waveform, rarely a good idea.  ESCs often have either protection diodes built in that shunt out of voltage range spikes into the supply, or the output FETs, due to their construction, for such diodes.
Seeing as its an elderly motor, is the insulation still as good as it should be?  This might need testing with a high voltage insulation tester - high voltage back-EMFs could be breaking odd spots of insulation down and escaping.
Another thought - presumably the field winding is being fed via diodes from the ESC output - it could be that these are isolating the winding from the supply, and an extra set of diodes might be needed to shunt the spikes back into the supply, but to both + and -.  Or maybe a dustbin sized electrolytic across the field winding.  The voltage will always be the same direction, and it isn't necessarily RF that is the problem.
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roycv

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Re: Odd earthing for Taycols....
« Reply #10 on: September 16, 2012, 10:53:22 AM »

Hi D-G keep up the research, you are doing a grand job.  Have taken note of your findings.  I have had a project in mind to utilise a Robbe controllable pitch prop system.  It needs a servo to work the pitch and gives a smaller pitch in reverse.so is the equivalent of the esc.

I was going to use a Taycol standard with just an on / off switch or perhaps a series / parallel control.  My main concern is the interference to the receiver.

Did you make your own inductors?  Were they wound around a ferrite?  I would be interested to know.
Carry on the Taycol Torch,
regards Roy
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dodgy geezer

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Re: Odd earthing for Taycols....
« Reply #11 on: September 16, 2012, 02:35:50 PM »


Did you make your own inductors?  Were they wound around a ferrite?  I would be interested to know...
 


They are just ferrite coils pulled out of an old PC power supply - or maybe from an old TV board - I can't remember.  You can see them in this shot. This is what the spare bed looks like at the moment! The tissue is to stop the oil spreading all over the place..



I was running the motors initially without capacitors, because I wanted to get a feel for what the inductors were doing on their own, and I hit a funny.  Normally a Taycol will draw 3-5 Amp, much the same as a modern motor. But when I tried a little Comet on a 30Amp Turnigy ESC, the ESC switched off, as if it went into an overload. I connected up the Comet to a 6v SLA through an ammeter, and that registered variable amps - 15, 20, settling at around 35. What was going on?  Obviously 30A+ weren't going down the line - everything was quite cool. I put the capacitor back, and the drain then registered as 1.5A.  I was surprised to find that interference could have so similar an effect on both an ammeter and an ESC - making both think that the motor was drawing 20 times the current it was...


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NFMike

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Re: Odd earthing for Taycols....
« Reply #12 on: September 16, 2012, 04:10:03 PM »

Try putting the meter in the lead from the battery. The output of an esc is not pure dc and may be fooling your meter. It is also a pseudo ac so with all the inductors and capacitors in the circuit there could be some odd effects around that as well.

dodgy geezer

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Re: Odd earthing for Taycols....
« Reply #13 on: September 16, 2012, 05:27:19 PM »

Try putting the meter in the lead from the battery. The output of an esc is not pure dc and may be fooling your meter. It is also a pseudo ac so with all the inductors and capacitors in the circuit there could be some odd effects around that as well.

You're right, Mike - I should have thought of that earlier. But I think I have worked out what I have been doing first that so confused me. The oddity was the 'earth' connection - connecting one of the brushes to the ESC output resulting in completely glitch-free operation. But, of course, I wasn't 'earthing' it. Connecting the ESC output to the frame is the same as connecting one of the brushes to the frame...

I was only running with a capacitor across the brushes. I've been experimenting with that capacitor and a pair of inductors - what I've found out is that I really need the capacitors between brushes and frame as well. Effectively, when I was looking for an 'earth' point, I was actually putting in a junction between a brush and the motor frame. Not a capacitor - but that didn't matter so long as there was only one connection!

Once I understood what I had been doing, I put capacitors back onto the little Comet, and the measured Amps at the brushes went down to a stable 1.2A - which it what it would have shown the first time if I had taken Mikes advice and put the meter in the proper place!  :embarrassed: 

All seems sorted now - except that I probably have to rewrite the interference suppression web page...
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kiwimodeller

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Re: Odd earthing for Taycols....
« Reply #14 on: September 17, 2012, 11:26:58 AM »

Hi Dodgy, I remember when I was first corresponding on the forum with various people about running my Taycol with modern radio gear I was directed to an article on a web page of a shop in Canada - Model ?? of Canada - the oldtimers has kicked in but it will come back to me. Anyway among the reccomendations in their article were to loop all power leads at least twice through Ferrite beads and also to put a small resistor in series with each of the capacitors , both across the brushes and from brushes to frame. Both of these mods helped considerably. Cheers, Ian.
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dodgy geezer

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Re: Odd earthing for Taycols....
« Reply #15 on: September 17, 2012, 12:02:57 PM »

Thanks, KM! The resistor idea is something I hadn't tried. I must add that into my arsenal...

There are quite a lot of clever interference suppression devices around nowadays. I am looking at some little things called Bi-Directional Transient Suppressor Diodes, which look as if they could have an effect...

I am now able to suppress all of my Taycols, including the really poor sparky ones, sufficiently well to run a PIC processor on the same line, which means that the Action P105 can be operated happily. Of course, there is always the option of running the receiver off a separate set of batteries. The trick seems to be to use ALL the available suppression techniques...!!
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NFMike

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Re: Odd earthing for Taycols....
« Reply #16 on: September 17, 2012, 05:32:51 PM »

I have a few suppressors for reducing arcing on mains (230VAC) switches, such as those with a fluorescent light load. They are 0.1F in series with 100Ω in a single package.
While messing with my boat motor suppression I tried subbing one of these for a plain 0.22F capacitor but it seemed to make no noticeable difference (these were in addition to the little disc ceramics).

dodgy geezer

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Re: Odd earthing for Taycols....
« Reply #17 on: September 17, 2012, 06:19:25 PM »

I have a few suppressors for reducing arcing on mains (230VAC) switches, such as those with a fluorescent light load. They are 0.1F in series with 100Ω in a single package.
While messing with my boat motor suppression I tried subbing one of these for a plain 0.22F capacitor but it seemed to make no noticeable difference (these were in addition to the little disc ceramics).

I've found that adding things on the same path doesn't help.

A 0.1F will short out high frequency spikes from the brushes - I think they tend to suppress the RF stuff. You can attack the lower frequencies by using a 220uF in parallel - or do what I'm experimenting with and put a ferrite bead in each power line. That has cut a lot of the very messy stuff coming out of a Taycol.

Earthing is also a good idea, and I'm just about to experiment with some 'Transient Voltage Suppressors', once they're delivered. These sound really useful - a diode device which has a fixed voltage it will allow to pass by, and any spike above that level is clamped down. If they work as advertised, they might be all the suppression that's needed - though capacitors are so cheap I guess they will always be used...
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NFMike

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Re: Odd earthing for Taycols....
« Reply #18 on: September 18, 2012, 12:42:40 AM »

The action is different.
Voltage suppressors chop the top off an offending pulse, but the lower part is still active and can cause interference. Their effectiveness will partly depend on how close the cut-off is to the line voltage.
Capacitors tend to short out any sharply rising waveform, regardless of voltage.

So the 'best' protection is likely to be both - as you say capacitors are cheap.

Earthing is a bit of a misnomer in this situation. I think bonding (with a bit of screening perhaps) is what we are practising.

kiwimodeller

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Re: Odd earthing for Taycols....
« Reply #19 on: September 18, 2012, 10:51:35 AM »

The article I was thinking of is at http://modelsolutions.ca/articles.htm . I dont pretend to understand all the permutations of suppression but this article made it fairly clear and apparently the resistors in series with the capacitors slows down the rate of change in voltage caused by spikes. Cheers, Ian.
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NFMike

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Re: Odd earthing for Taycols....
« Reply #20 on: September 18, 2012, 11:42:42 AM »

The article I was thinking of ...

Interesting. I shall try some of that in due course.
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