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[John W E]

Hi all,

This is one for the electrical lads.   Can someone answer me why the capacitive suppression must be soldered to the motor?   Could the capacitors not be soldered further back in the wiring from the electronic speed controller to the motor?

The reason I ask is that I had a hell of a time trying to solder the capacitor to the metal case of the electric motor - I was frightened I put too much heat into the motor casing and also onto the capacitor.

aye
john
bluebird

[DickyD]

You need it hot to solder to the motor John. Hot and flux.

Richard

[FullLeatherJacket]

John
You won't do too much damage to the motor with that crummy old iron of yours, even with the gas-ring turned up full............ Just make sure you first give the motor case a good scrub with a file or fine emery to remove any coating where you want to solder. I've found it easiest to tin the case first; then solder the caps to the brush contacts and finally to the case. As regards why the caps should be soldered directly to the case, I haven't a clue..........but I know several men who do!
Suit yourself, sir. It works for me.
FLJ

[wombat]

Hi John,

The reason you have to have the caps as close as possible to the motor is because they are to suppress the high frequencies generated by the motor turning - these are the spikes caused by the brushes moving from one commutator segment ot the next. They can cause interference with the electronics - both the control and RF stages. If you separate the caps from the motor by a length of lead, those spikes of current will flow down the lead and radiate from the wire into the rest of the system. Also, the inductance of the leads can interact with the caps and cause other problems.

The capacitors also have to be the right type - they need to be decent ceramic capacitors.

Wom

[OMK]

Geordie lad, that's a damn fine question. But how to answer without recourse to an itsy-bitsy bit of techo' isn't easy. So hang in there for a minute...

The reason for the capacitors in the first place, as you know already, is to clip (suppress) any high-voltage spikes from getting into your RC system. Those unwanted spikes usually originate from an inductive source (in this case, the motor) and can manifest itself in the form of unwanted servo jitter (among a myriad other nasties).
Agreed so far?
So in order to counter those effects, designers of radio equipment, digital equipment, etc., usually locate the capacitors as close to the source of interference as mechanically possible. In effect, any unwanted voltage spikes are suppressed before they can travel along the motor wires and get into the radio system. Leastways, that's the theory.
But, like you, I too have had concern on several occassions where I've been a tad worried of soldering the caps' directly to the motor body. I'm no engineer, so I'm not sure just how much heat those motors will handle before causing irrepairabe damage. And some of 'em need a LOT of heat before the body gets hot enough to allow you to make a sound solder connection. Spooky.
So here's the deal...
In most cases those capacitors can indeed be located away from the motor. If you have room inside your ESC, stick 'em there. Or you could even solder them directly across the wires feeding the motor - at any position along their length.
But this is where my vocabulary (or lack of) lets me down. I'm useless at explaining these things. A picture speaks more words, so maybe this sketch might help.

Just for the record, I have been known to install motors without ANY capacitors... without the slightest hitch, glitch, burp or fart. But don't let that fool you into a false sense of security. In other words, its best to keep those caps' there. But don't put too much emphasis on sticking them on the motor. As long as you stick them SOMEWHERE in the wiring, then, 99% of the time, you can rest assured that you're system is well suppressed.

PS...
Was just about to hit 'send' when Wombat's reply came in, which pretty much says it all. But don't forget to take into account the voltage rating of the caps. Your chaps over at ESR have what you need.

[OMK]

By the by, amigo... Wombat is indeed correct when he mentioned inductance to you. Even a small, straight length of wire will exhibit a certain amount of inductance - albeit tinyl. But mixing inductance with capacitance is the sure-fire way to make your RC system sing and resonate throughout the galaxy. This is what you DON'T want. But it can - and does - happen.
Theroetically, the motor wires will radiate all sorts of rubbish -- more so if the caps' are located away from the source of interference. And when that happens is when you start getting into all kinds of problems. But a lot of modellers resort to all sorts of counter-active tricks, such as bonding the propshaft, grounding all metalwork, blah, blah. In practice, however, the chances are that you won't notice the difference where the caps' are situated.
Bog-standard ceramic caps' are usually the norm. But those wee 'mono'-type caps (monolythics) are equally as good.

[BobF]

Hi BlueBird,

I will just add two more things to the above.

Use a big/High wattage iron to solder the motor case. The bigger the iron, the quicker the local area will heat up, withought transferring heat to the rest of the motor. ( Just like a spot weld)
Secondly if you clip a small crocodile clip or similar to the wire before it gets to the cap, the heat will transfer away, and the wire will stay cold. I have had several motors get hot enough during use to unsolder the battery wire, but with no problems caused to the motor after.

Bob

[OMK]

Nice suggestions! The crocodile clip is neat way of directing the heat from the capacitor. I normally use a spring-loaded aluminium heatsink for such jobs, but the croc. clip idea is equally effective. Simple and sweet, too.
Maybe we ought to invest in bigger irons... or spot welders(!).

While you're there, Rob... Tried PM'ing you earlier. No reply. Bung your address my way again. (I thought I had it on the harddrive, but must have erased it or something). The diesel is packed, parcelled and ready to go.

[sweeper]

Some good suggestions there. May I add a couple of bits of info to them.

The crocodile clips are much more effective as heat shunts if you fit a small piece of copper inside the "jaws" and make them dedicated heat shunts.
Re the rubbish radiated from motor supply cables, try running both cables (positive and negative) close together (in effect fasten them together). The larger the motor and hence the current, the larger any radiated effect will be. Running the cables in this way tends to null the radiated effects.
Regards.

[BobF]

Hi PMK,
No messages received.
I am sending you a PM with my addy as soon as I have posted this.

Many thanks AGAIN Bob

[OMK]

Dammit, Bluebird - I wish I'd thought to say what Sweeper has said. He is, of course, dead right. Placing the motor wires close together, or even twisting them together, will, in effect, cancel out a lot of that unwanted RF hash. And now that he's mentioned it has reminded me of another possible quick-fix that might help. Take a butcher's at the attachment.
What you see here are commonly known as toroids (donuts?). They come in a variety of flavours. Threading the motor wires through the toroid a couple times should tame that unwanted hash also.
ESR don't stock them but I got a few here if you want to experiment.

PM heading your way, Bob.......................

[sweeper]

Sorry for stealing your thunder PMK.
Just having a bit contemplation on the toroid idea, may be a goer. I'm not hot on RF stuff, power supply and motors (the heavy current side of life) are more to my taste. I've got a feeling that there may be a catch in the way that you wind the cables onto them. I've only used toroids in protection and detection circuits (and a means of demonstrating the basic principles of induction & the simple transformer).
Will have a peaceful thunk on that one over the weekend.
Beats watching the cr*p that passes for television these days.
Regards.

[John W E]

Oo yee Sir Full Leather Jacket purchased at South Shields Market  how dare you complain about my soldering implements.  As you can see from the picture here, there is nowt wrong with them.  Just a wee bit dusty.  Just wait until I get me hands on an ACTion Kit and send it back to be repaired.

On a serious note I think part of the problem was I was using this God forbidden lead free solder, courtesy of our EEC friends.  Also, I purchased the motors from EBay via Taiwan and I think the casings on the motors could have been made from melted down BMWs or worse still Saab's    Cos I did as Mr FLJ suggested and it didn't make any difference, even when I put the 25watt soldering iron on to it.

As for you Mr Dorset Button, yes and the rest of you who have chipped in with kind answers - its shed a lot of light in a grey area, thank you for the replies.

I should imagine its enlightened a lot of us.

aye
John e
bluebird

[BobF]

Hi BlueBird,

I use an 80 watt iron with a solid tip. (not a screw driver style end)
to solder to the motor case.

Bob

[John W E]

I am thinking I might have to invest in a bigger soldering iron.

aye
john e
bluebird

[omra85]

Bluebird - that soldering iron is PRISTINE.  It should at least have a few chips in it where you've knocked in the odd screw
I find that with any steel, if you gently touch a Dremel grinder to it to take off the surface, then apply the solder and pull it into a peak, when you come to attach lead, etc, you only have to remelt the top portion of the base solder to get a join.
Course I am using that new fangled alectrocity.
Danny
 

[DickyD]

Soldering with a cold chisel John. Different. ::)

Is this a north of Watford thing ?? ???

Richard

[OMK]

I'd not heard that expression before. Stealing thunder is a neat way of putting it.
No worries, though. You're not stealing anyone's thunder. Matter of fact, I'm intrigued. I'm getting the idea that you're talking along the lines of single, or 3-phase, AC supplies? I wonder if the inductance formula still holds true there as it does at RF. Perhaps we could could get together over a couple PM's and chat some more.

On a different note...
How come Geordies know their way around every longitude, and every latitude, yet if you stick 'em on a Roman road they wouldn't know Somerset from Dorset?
Wye-aye, lad. Close enough, though. Must say, that's a classy piece you got there.  Last time I seen something looking equally as lethal was 1976 - school metalwork room. Ernie Vearncombe stuffed it in the furnace, got it nice and hot, then jabbed it on Tommy Cairns's butt.
Now let me ask you one...
When you use that plank-on-frame method, how do get all the strips that they all join together neatly? Do you have to hold each piece until the glue sets? The cruiser you built from your Dad's oldie-timey magazine, you used that plank-on-frame method. Where it gets a bit tricky around the bow, do you have to cut and shape each and every individual piece?
On second thoughts, perhaps this is the wrong place to be asking.
Could you put up a new thread, with a few photos and a few words, that shows and explains how you do that?

[wombat]

Hi PMK,

Yup the formula do hold the up the same at RF as at mains frequency - only difference is that unless you are wanting to deal with higher frequencies in the system (10KHz to 1MHz region) the effect of parasitic capacitance is less.....though not negligable as we found with a capacitive voltage divider on a 600kV system once. The effects are very similar to RF though some of the magnitudes are much higher. If you get enough current, you can even see the skin effect.

If it is three phase then things get more complicated, especially when you get onto some of the more exotic windings - such as 3phase to 12 phase conversion transformers.

Sweeper, the way you wind the toroids depends on what you are trying to suppress - if it is common mode IIRC you wind both windings in the same way, if it is differential mode you wind them opposite ways. You also need to take into account the toroid and the amount of current that will be shoved through it, otherwise the core will saturate and do no good at all.

Wom