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Solenoids

Postby BJG145 » Tue Dec 03, 2013 1:37 pm

I want to pick up a solenoid so I can start building roboticised drums like Metheny and Jazari.

http://www.youtube.com/watch?v=rMrk-pZ4RBk
http://www.youtube.com/watch?v=9VymAn8QJNQ

The solenoid listings on ebay seem geared more towards car mechanics than avant-garde drummers though. Any suggestions for a suitable part...? Will anything do...?
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Re: Solenoids

Postby MarkOne » Tue Dec 03, 2013 2:18 pm

somewhere like this?

Robot Shop Solenoids
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Re: Solenoids

Postby The Elf » Tue Dec 03, 2013 2:33 pm

There's a guy I'm helping out here in Sheffield with his recording rig who's doing a robotics degree - and I've seen some of the stuff he's built himself.

I'll have a chat with him when I next meet him and see what light he can throw on the subject.

I have to admit that this is something that fascinates me - the idea of building a real version of some of the Animusic machines...
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Re: Solenoids

Postby BJG145 » Tue Dec 03, 2013 3:35 pm

Cheers Elf. He's on the right track...robotics is the future. And I've just staked my claim in it with Amazon's finest (OK, cheapest)...

http://www.amazon.co.uk/dp/B00EK6JQFK/ref=pe_385721_37986871_TE_item

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Re: Solenoids

Postby The Elf » Tue Dec 03, 2013 7:45 pm

Really pleased to see one of the SOS regulars trying this out. I have a dream of a Black Beauty snare with a couple of tasty mic's around it and the ability for me to program the thing! :D

Keep us posted on progress, man!
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Re: Solenoids

Postby Folderol » Tue Dec 03, 2013 8:51 pm

Possibly you know already, but always fit a reverse diode (typically 1N4002) across solenoids and relays, for back EMF suppression. Within reason the higher the voltage solenoid you use the better, so you don't end up with massive currents swirling around.

If you get into this in a big way and start to use a fair quantity, contact Magnet-Shultz. They are the makers for a lot of the ones you see, and may give you a better deal. Also, there are customisation options on most of the ranges. At work we use one of the big daddies in a heavy carton kicker - you don't get your finger in the way! :roll:
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Re: Solenoids

Postby BJG145 » Tue Dec 03, 2013 8:56 pm

Folderol, where did you get your electronics know-how?

I once worked on a kibbutz factory line producing female depilatory products, but what do I know.

http://www.epilady.co.il/eng/htmls/home.aspx
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Re: Solenoids

Postby Folderol » Tue Dec 03, 2013 9:49 pm

BJG145 wrote:Folderol, where did you get your electronics know-how?

I once worked on a kibbutz factory line producing female depilatory products, but what do I know.

http://www.epilady.co.il/eng/htmls/home.aspx
Short version:
Everywhere!

Longer version:
I picked up my first soldering iron when I was 8 - it had to be heated on a primus stove, and the flux was separate from the solder. In short order I was hooked. It helped that I was always a voracious reader. My parents gave up trying to stop me when I was about 14 and actually knew enough to repair TVs... safely :roll:

In the middle 60s I saved up my paper-round money to buy two transistors to experiment with - I'd already learned to re-use just about everything, right down to nuts and bolts.

I swapped jobs a lot until the middle 70s but stayed in the domestic repair industries until the market collapsed due to cheap reliable Japanese kit, then moved to industrial electronics.

Now I'm almost {mmffty} {mmff} and working reduced hours I can play again :bouncy:

P.S.
They look very nice but I really don't think I want to be removing hair these days :)
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Re: Solenoids

Postby grab » Tue Dec 10, 2013 2:15 pm

For bonus points, a reasonable-sized resistor in series with the diode can be a good idea if you're talking serious magnetics. It's a safer way of dissipating the stored energy, compared to the diode which essentially becomes a short-circuit. Try not to use a wirewound resistor for it, for reasons which should be obvious when you realise that the only difference between an inductor and a wire-wound resistor is whether it's sold with the inductance or resistance as a quoted figure with a tolerance. :)
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Re: Solenoids

Postby ef37a » Tue Dec 10, 2013 2:56 pm

grab wrote:For bonus points, a reasonable-sized resistor in series with the diode can be a good idea if you're talking serious magnetics. It's a safer way of dissipating the stored energy, compared to the diode which essentially becomes a short-circuit. Try not to use a wirewound resistor for it, for reasons which should be obvious when you realise that the only difference between an inductor and a wire-wound resistor is whether it's sold with the inductance or resistance as a quoted figure with a tolerance. :)

Hmm, the purpose of the diode (as I am sure you know Grab) is to protect the drive transistor (say) from a large reverse voltage when it turns off and the field in the coil collapses. Transistors do not like this up 'em! Even a very wee relay will pop a quite butch transistor sans diode. If you insert any resistance in the diode circuit you could leave enough reverse volts to still bugger things. My view would be, as you use bigger ass'ed coils, use bigger ass'ed diodes! Them's cheap enough!

OP:If you have any Olde Worlde telly repair shops about you try them for some old line output and video op transistors. MJE340, BUX... sort of thing. Also use a liberal sprinkling of LEDs to show you what is working.

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Re: Solenoids

Postby Folderol » Tue Dec 10, 2013 3:00 pm

grab wrote:For bonus points, a reasonable-sized resistor in series with the diode can be a good idea if you're talking serious magnetics. It's a safer way of dissipating the stored energy, compared to the diode which essentially becomes a short-circuit.
Ha! Memories of the development of the valve TV line output and boost circuit... just add a capacitor :)

Sorry. I'll get back in my rocking chair :blush:
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Re: Solenoids

Postby dmills » Tue Dec 10, 2013 7:46 pm

Actually the resistor is a sane thing to do.

Consider say 1A flowing in a inductor, now open the circuit....

That amp will (initially) continue to flow, with the voltage across the switch rising until something gives, now a diode across the coil will clamp the voltage to supply + about 0.7V, which is fine if you can tolerate the time taken for the field to decay, if you need it faster then adding say 22 ohms in series with the diode will cause the voltage to peak at supply + 1A * 22 ohms = say 35V with a 12V rail which is well within the capabilities of most small switching parts, the current will now collapse much faster then in the initial case.

Another good trick for things like the snare case is to actually use a low voltage solenoid with a series resistor to speed the turn on (For real speed strap the junction to ground with a bloody great electrolytic). This causes the current to rise much more quickly, making for a snapper drum hit.

Regards, Dan.
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Re: Solenoids

Postby ef37a » Tue Dec 10, 2013 8:38 pm

dmills wrote:Actually the resistor is a sane thing to do.

Consider say 1A flowing in a inductor, now open the circuit....

That amp will (initially) continue to flow, with the voltage across the switch rising until something gives, now a diode across the coil will clamp the voltage to supply + about 0.7V, which is fine if you can tolerate the time taken for the field to decay, if you need it faster then adding say 22 ohms in series with the diode will cause the voltage to peak at supply + 1A * 22 ohms = say 35V with a 12V rail which is well within the capabilities of most small switching parts, the current will now collapse much faster then in the initial case.

Another good trick for things like the snare case is to actually use a low voltage solenoid with a series resistor to speed the turn on (For real speed strap the junction to ground with a bloody great electrolytic). This causes the current to rise much more quickly, making for a snapper drum hit.

Regards, Dan.

Sorry Dan.
Not often I have the temerity but!
The voltage produced when the field collapses is going to be way more than 35V. Have you never got a hand across a 6volt bell contact?
I see the discharge time as being LR where R is the coil's DC resistance plus a bit for the diode. Putting any more resistance in the circuit can only make the time longer?

As for power dissipation, by definition the coil resistance will cope with that.
If the OP wants to fit a series CR snubber as well, fine.

With you with all the other tricks to get a fast response.

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Re: Solenoids

Postby Folderol » Tue Dec 10, 2013 9:18 pm

While there are some good points here, I think we are in great danger of overcomplicating things for the O/P !

However...
In the industrial world, for relays and contactors I have never seen anything more than a simple diode clamp, and only seen controlled decay on solenoids for specialist applications.

Capacitor discharge systems have to be handled with caution. Too high a capacitor value and the coil will overcurrent. Same if the resistor is too low, or starting voltage is too high. Also, if the CR time constant is too high for the firing rate, the cap. won't have charged sufficiently for a second strike. Magnet-Schultz quote power v duty cycle in their spec sheets. This gives a guide, as well as absolute maximum voltage - another reason we like doing business with them.

Some years ago my employer got a contract to refurb a cardboard stitcher. This is a machine that cuts, forms and sets those honking great staples you see on large corrugated cardboard boxes. It had multiple timed electromagnetic clutches. We found the timing was so critical we had to dispense with electrolytics completely and use 5% 'dry' caps. Clamping resistors didn't give a decent characteristic and we ended up using 500V rated transistors with about 100V zenners.

The whole thing took a lot of effort and cost many transistors as well as a couple of clutches. When the machine is running at full speed it makes one heck of a racket and those clutches get far too hot to touch. The caps get quite warm too!
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Re: Solenoids

Postby Daniel Davis » Tue Dec 10, 2013 9:40 pm

I've had mine removed.
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Re: Solenoids

Postby dmills » Tue Dec 10, 2013 9:42 pm

The voltage produced by the collapsing field will be exactly that which results in the current being a continuous function!

If the current is 1A at switch opening than into an (effectively open circuit) you get a big voltage, into a 10 ohm shunt you get 10V and into a 100 ohm shunt you get 100V, the voltage is simply given by ohms law applying the coil current and the resistance of the shunt resistor, nothing magic.

I encountered this stuff trying to get a vacuum relay to toggle fast enough to do full break in CW.

Regards, Dan.
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Re: Solenoids

Postby ef37a » Tue Dec 10, 2013 10:16 pm

dmills wrote:The voltage produced by the collapsing field will be exactly that which results in the current being a continuous function!

If the current is 1A at switch opening than into an (effectively open circuit) you get a big voltage, into a 10 ohm shunt you get 10V and into a 100 ohm shunt you get 100V, the voltage is simply given by ohms law applying the coil current and the resistance of the shunt resistor, nothing magic.

I encountered this stuff trying to get a vacuum relay to toggle fast enough to do full break in CW.

Regards, Dan.

So what is the voltage without the diode when the transistor turns off and the coil is O/C?

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Re: Solenoids

Postby dmills » Tue Dec 10, 2013 10:23 pm

High and limited by either the effective capacitance of the coil (It forms a resonant circuit damped by the resistance of the coil) or by the breakdown of some component in the system.

It is something of an edge case most of the time, but consider a flyback converter (Or Kettering ignition system, more or less the same thing), which works by storing energy in the primary then opening the switch and letting the voltage at the switch node shoot up until load current in the secondary starts to flow.

Regards, Dan.
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Re: Solenoids

Postby ef37a » Tue Dec 10, 2013 11:17 pm

Ok Dan,
so we need the diode. The current in it will be limited by the coil's resistance and even wee diodes can of course stand many times their rated current for very short periods so I don't see the need for an extra series resistor? And as Will says, you don't see them anyway.

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Re: Solenoids

Postby dmills » Tue Dec 10, 2013 11:31 pm

Actually the current is not limited by the coil resistance so much as is at peak equal to the running current at the moment of switch off, and the total energy to be dissipated is 0.5 * LI^2 in the obvious manner (Split between the diode and the coil resistance).

You don't need the resistor UNLESS you are trying for very fast operation, where the resistor can significantly speed up the switch off (In which case you do indeed see them).

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