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Originally posted by Rotwang:
Clock wise, as for revs in this application dont know.

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The air con clutch on my S13 use to kick in at ~7000rpm with no problems. that's assuming that the aircon was geared 1:1 with the motor though.
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Most air con compressors spin quicker than the engine.

There is probably an upper limit imposed by the internals of the compressor not the clutch.

My concern is turning the clutch off in a hurry.

If the flipper misses its opponent it’s going to hit the stops hard.

I have a suspicion that the clutch will be quicker to grip than release.
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Cool, should be fun to play with. I could have the clutch disengage @ half or full throw or something or timed.

How many ribs has the small pulley got? So I can get a small belt on its way.. cheers.
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Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.
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I posted it Thursday morning so it shouldn’t be far off,

I think it was a 4.

Yes I would experiment with a test rig rather than try to build a real bot first off.

Too many unknowns but that goes with the territory when you are trying to be original.
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Satisfaction is proportional to effort and results.

Yeah thanks mate. I was thinking further about the disengage issue you brought up, do you see that as a mechanical issue or electrical or a bit of both? If it was a issue and it was mechanical I could get my head around that but if it was electrical like the magnetic field wouldn't switch off instantly I might need some tips from ppl.

The misses had the pulley, I got it now. Four groves very nice, thx heaps Gary.
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Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.
Albert Einstein.

Electrical is my feeling, while the field is collapsing as battery power is disconnected the collapsing field tries to keep a current circulating in the coil.
This tends to weld contacts as they open. A diode stops the relay contacts welding but lets the current keep flowing so the field collapses slower.

Some sort of switch that open circuits the coil and stops the current circulating the quickest would I think cause the clutch to release cleanly.

Some sort of solid-state switch or a circuit breaker type switch made to cope with high voltage that can go high resistance would I think be desirable.
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Satisfaction is proportional to effort and results.

Possibly just using a suitable oscillator/capacitor combination to fire a timed pulse through the coil at hi voltage to get the field on and of nice and quick and minimum slip would be better than just switching a low voltage battery supply to it.
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Satisfaction is proportional to effort and results.

With switches, we have found that they generally weld on.
At start up (ie when the switch closes) a big coil will suck heaps of amps to charge its magnetic field. That causes like a spot weld effect holding the switch/relay on.
Arcing when the switch opens happens as Garry said. Its usually less of a problem but it can cause the contactor to become pitted or to have high spots, which makes it far easier for it to weld when the contact closes the next time.

As for a pulse of HV, it would work but it'd probably be prohibitive to develop on the bot. (think farads of capacitance). Some coils (like fuel injectors) are wound such that the "keep on" or holding voltage is much less than the supply voltage. On those they connect full battery power for a short period of time then PWM the output so they don't fry the coil. You *might* be able to re-wind a coil of this type but its probably not worth it, give the thing a try first and see what happens.
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Mechanical engineers build weapons, civil engineers build targets

http://www.jaycar.com.au/productView.asp?ID=SY4086&CATID=&keywords=solid+state+relay&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=

What about one of them. What sort of voltages would be safe to use with this 12V coil? Is there any benefit in higher voltages?

Thanks, guys.
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Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.
Albert Einstein.

I think the SSR would still just have a diode in it.

I was thinking about it today and it occurred to me an electronic ignition module from a car ignition system might work.

The primary current in an ignition coil must be turned off suddenly so the magnetic field collapses causing the high voltage in the secondary.

These modules can cope with the clutch coil current and can switch very fast and cope with very high voltage spikes.

You might need help from one of our electronic people with the circuit to trigger it but the common Bosch module used in 80’s magners/holdens/fords would be a good starting point.

I will mention it to Brett, If he is not to busy I could give him one to experiment on.
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Satisfaction is proportional to effort and results.

SSR should handle the draw for a coil fine.
I'd like to see a datasheet on one of those things, i'm fairly sure they have a diode built in.
As to what voltage its safe to run the coil at continuously basically it comes down to heat. See how fast it heats up and that will tell you how much you can run it at (at a guess 16 or so should be ok, you might make it 18 for 3 minutes)
If your keen and your running 24v as your battery voltage you could give it a shot of that then PWM it down.

All the voltage boost things come down to energy. You need to store enough energy in the coil to make a difference with regards moving the actual clutch. I have a feeling its probably not going to be worth it. 24V is going to be something like 16x more power than at 12v (or something) it should give you the oomph you want. I'd suggest trying that first then adding fragile electronicsy bits if you need them. (dealing with collapsing coils and the like sucks ass electronically speaking)
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Mechanical engineers build weapons, civil engineers build targets

Well if the rotor is doing 10000 RPM and he only wants the clutch to turn on long enough for the hub to turn through 90degrees of one turn that isn’t long.
My concern is once the power is turned on and the field builds it will take longer to decay if a diode is letting current circulate.

Better to switch it with something that can go from conducting to high resistance as quickly as possible.

To tackle it mechanically attaching the flipper arm through a gear reduction so the rotor can do at least a few revolutions would make life easier on the clutch as far as how quickly it would need to grip and release.

With my original flywheel driven hammer idea I set the hammer up so it can spin 360 without hitting the bot as in Fragmentor.

Perhaps a crank and con rod connection to the flipper would allow the clutch to be a bit slow releasing.
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Satisfaction is proportional to effort and results.

Going on Andrew's idea for his Sproing-esque flywheel flipper bot. gear it down heavily after the clutch, used a crank system to allow to it to over shoot if needed.
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ahh i get you now.
If you put something of a high resistance in the current path its just going to drive the voltage up until it can get rid of the energy stored in the coil.
You need to conduct that energy away and dissipate it.
I saw a PDF on it a while ago but i can't remember off the top of my head what the best method was. I believe it was putting a zener diode across the motor such that it will short and dissipate any voltage over battery voltage. But it will "waste" any voltage produced over that as heat which causes it to shut down faster. There is also some magic ratio where you put a resistor of a certain size in there as well and use it to dissipate more power.
If you really wanted to get fancy you might be able to use some kind of super dooper switch (uber fast mosfet style) and disconnect vbat and then connect the motor to some kind of current sink. A discharged cap and resistor perhaps?

You might be able to allow the coil to punch up to around 100 volts and dump that through the resistor, that would get you the best current flow into the resistor without having to worry too much about arcing through your windings and the like.
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Mechanical engineers build weapons, civil engineers build targets