Motor cycling between limits

John, Ken: Thanks; will have a crack at this soon.

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Terry Pinnell
Hobbyist, West Sussex, UK

In article , John Fields wrote: [...]

.. and here's another change. At start up, there could be a problem with both outputs going high on a glitch so lets hook the capacitors to +V like this:

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kensmith@rahul.net   forging knowledge

Here you go. Uses 2 DPDT relays. Choose your Rs & Cs for the delays you want.

Ed

+---------------------+ | Fwd Limit N/C | Reverse Limit N/C Vcc -+-o +-o \\ \\ o-----+ o-----+ | o--To MtrA | o--To MtrB o---- o---- ^ ^ | Reverse | Forward +---o relay N/C(1) o---+ relay N/C(1) | | +--------+ +--------+ | | | | [R] [FwdRelay] [R] [RevRelay] | | | | | /c | /c +---+------| +---+------| | | \\e | | \\e [r] [C] | [r] [C] | | | | | | | Gnd+---+-------+---------+---+--------+ | | | o--To MtrB | o-- To MtrA o---- o---- RevRelay N/O(2) FwdRelay N/O(2)

And here is how to use the CMOS properly relative to those huge pause times: View in a fixed-width font such as Courier.

. . . Vdd . | CD4093 . [10K] . | ___ U:1 ___ U:4 . +----|- \\ ___ +---------|- \\ _____ . | | ||_o---+-|- \\ | | ||_o---A_DIR . |o +-|___/ | | ||_o--+--[Rb]-+-|___/ . -+ | +----|___/ | | . A_STOP |o | | | U:3| === . | +--------------------+ C | . gnd | | gnd . | | . | | . Vdd | | . | | | . [10K] | | . | | | ___ U:2 . +----------+ +--------|- \\ _____ . | | | ||_o--------------B_DIR . |o +-[Ra]-+-|___/ . -+ | . B_STOP |o === . | C | . gnd gnd . . . . 0.7RaC pause on A_STOP . . 0.7RbC pause on B_STOP .

You have a helluva a surge through that 2200u. It would be better to do microswitch to GND- to trigger 555 monostable- to transistor base.

View in a fixed-width font such as Courier.

5V | | | +---------------+ | | NC | | | | | | o--------------+ | | | | +------+--------COM o | | | + | | | --- | | o | MOTOR --- | | | |2200u | | NO | | | | | | | | | | | | | +------------ /\\/\\ -------+ | | | | | | | | | +---------------+ | | | | | | +------|-------------------------| ----+ | | | | | --- | | /// | +---------------|---+ | | | | +------+---------+-----|

Excellent, thanks. I'll probably try that relay-based solution before the Ken/John circuit, as it will be faster to implement, incorporating the driver section as it does.

However, I now have serious doubts about the practicality of the intended application itself! My automatic car pump (cigar-socket supplied) broke the other day. So for fun I thought I'd try to 'motorise' my standard foot-pump. I want to emulate the normal action, and envisage standing by idly while it pumps away, switching off when the meter-displayed pressure reaches the required level.

To experiment, I used this simple circuit:

To its credit, it worked reasonably well for a while. But, although it wasn't actually connected to a tyre, so was hardly a fair test, after

5 mins the gallant little ex-screwdriver motor got so hot I switched it off.

So I next tried a much more rugged affair, using an ex-windscreen wiper motor. But that doesn't 'freely reverse' when switched off, so it would need the circuit I've been asking for help with.

However...I've since found that the downward stroke isn't quite fast enough. It seems a critical speed is needed to get any air compression, and this doesn't cut the mustard.

I'm now tentatively considering improvising a lash-up with an old mains-powered drill. This is well up to the power required from initial tests, when driven via a basic triac-based speed control circuit to slow it down. But the snag is that it's non-reversible. So I'm think I could dispense with further electronics and use some sort of large cam affair. This would pull down the pump (fast) then releases it to snap up again under its own springing, then catches it again, etc. Should make a hell of a racket .

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Terry Pinnell
Hobbyist, West Sussex, UK

Thanks, I'll have a play with that - although as you probably gathered, that simplish circuit depends on a motor which is not only powerful, fast and robust enough, but also 'freely reverses'. My ex-screwdriver motor qualified on speed and reversal, marginally qualified on power, but failed miserably on robustness!

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Terry Pinnell
Hobbyist, West Sussex, UK

Might as well mention that I left the diodes across the relay coils out - I figure you'd put them in anyway.

BUT - I like the cam idea. No electronics needed. To get electronics back into it, you could devise an opto circuit that would use light reflected off the PSI meter needle to shut the thing off automagically when the tire is full... :-)

Ed

Why not just put 10 ohms in series with it in his original schematic?

Ed

Yep - sort of second nature now.

I'm on the case .

On reflection I reckon a 'cam' approach might be unnecessarily complicated. Instead I'm thinking of simply 'cranking' a spindle fixed through the top front of the pump pedal, with sufficient play to allow it to operate freely through full rotation.

I'll get some electronics back into it one way or another! Your opto-detection might prove too much of a challenge, so maybe I'll just resort to R/C on/off. Or maybe an automatic power cut-out if signs of disintegration are detected .

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Terry, West Sussex, UK

I read in sci.electronics.design that Terry Pinnell wrote (in ) about 'Motor cycling between limits', on Tue, 23 Aug 2005:

A crank is just a cam on a diet. (;-)

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Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Wanna see pictures of your tire exploder ... er... pump disintegrator ... er , ah, ... mechanism when it's done. :-) I loved the drape opener/closer. Ed

One of these days you are going to have to order a PICkit from microchip... For these one-off kinds of things, software is really hard to beat.

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Regards,
  Bob Monsen

If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
                                  Thomas Henry Huxley, 1877

I've been wondering. Why not a stepper motor? X steps CW, pause, then X steps CCW. Can steppers respond as quickly as you need?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I've got the kit but never yet had time to complete the learning process .

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Terry Pinnell
Hobbyist, West Sussex, UK

He didn't say, "no microswitches". He said, "NO microswitches", which means "Normally Open." :-)

Cheers! Rich

On Sun, 21 Aug 2005 18:37:14 +0100, Terry Pinnell wrote: ...

Just use the windscreen motor as is - either keep the wiper crank, and couple its action to the pedal, or put a crank on the plain old motor with a connecting rod to the pump. You shouldn't have to reverse a motor, if all you want is up-and-down.

Good Luck! Rich

I have a few surplus steppers (such as salvaged from old printer, etc) but I'd guess they're nowhere near powerful enough. Astonishing how much force you typically exert when depressing a connected foot pump. In fact, I'm beginning to doubt I have *any* motor (DC or mains) which will cut the mustard.

Abandoned cam/crank' uni-directional mains motor idea for time being, for several reasons. Currently returned to experiment with reversible ex-windscreen motor, but I'm not optimistic!

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Terry Pinnell
Hobbyist, West Sussex, UK

Thanks, we got into some discussion up-thread about cams/cranks. And in my reply to JT I mentioned I'd temporarily abandoned it, for 'various reasons'. One is that coupling it (while maintaining adequate force throughout the movement) seems difficult. I'll get around to googling the subject one day, but maybe someone here can tell me the 'rules' for the geometry please? Specifically, with a pedal edge making an arc of 30 degrees over about 20 cm, how would you deliver that movement from a continuously rotating motor?

On the alternative of using the original in-built bi-directional facility of the motor: I lost my notes on this particular surplus motor, and so far haven't re-discovered the magic combination that restores that action! I have 4 wires to the motor. Two are presently carrying the 12V supply and giving constant rotation (reversible by changing polarity, of course). Difficult to tell whether the speed is 'regular' or 'fast' - I suspect it would have had both options? The other two wires, currently unused, either provide that speed option or maybe the automatic reversal. The only test I've done so far was to connect them while the motor was running, and that made no difference.

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Terry Pinnell
Hobbyist, West Sussex, UK