Motor cycling between limits

Gee, I thought motor cycling would be Harleys or Hondas.

Since the three time values you mention are all multiples of 100 mS, how about the solver of all problems, the 555 set to 100 mS and a counter/decoder to get the on/off/delay times?

GG

Why? What are the consequences of continuing to power the motor when it is up against an end? I'd expect that there would be several consquences, perhaps including a destructive one or two.

And while we're asking questions, "How?" How do you know where the limit is so you know when to delay and reverse?

If you really don't want to use any kind of sensors (like if you are in a pit full of sewerage or something :-), you could monitor the motor current and stop/reverse the motor when it reaches something approaching stall current. That scheme has the added benefit of protecting it from other faults as well.

The more modern method of doing this is to use an "H-bridge" with four power transistors (bipolar or FET).

You may need more than a single bistable. Logically, you need a "quadstable": 1 = forward, 2 = R-delay, 3 = reverse,

Vcc ! o / ! ---- +----------! \\ ---- ! ! NOR >-+---+-----------! \\ / ---! / ! ! ! NOR >--- To power device \\ ! ---- ! ---/\\/\\/-+-! / / ! ! ! ---- \\ \\ ------- --- ! \\ / --- GND / ! / \\ GND Vcc / \\ ! ! ------- o ! ---- ! / ---! \\ ! ---- ! ! NOR >--+---+-----------! \\ +----------! / ! ! NOR >---To power device ! ---- ---/\\/\\/-+-! / / ! ---- \\ --- / --- \\ ! ! GND GND

Indeed. I have worked on projects where it was undesirable (or impossible) to use microswitches to sense the endpoints. I thought this was one of those projects. Duh!

Yeah - didn't notice that ambiguity until this morning .

Well, yes, a 555 could contribute, but that still leaves a lot you haven't mentioned! And anyway I'm hoping that simple RC sections could form the timing elements, without resorting to the complexity of monos or counters. No precision is necessary, as I hoped I'd implied.

Not sure what you're talking about here. Obviously, by 'pause', I mean STOP. No motor power.

I don't think you can have read my post properly. MICROSWITCHES are the sensors. I suppose sensitive current limiting might be a feasible example, but why not use the obvious choice?

Yes, I can do it with enough logic gates, but I'd hoped for some more elegant and simple solution. Maybe just one SPDT relay, 2 microswitches, two crude RC filters ... and some inspired logic!

Many thanks, that looks highly promising - I'll have a play with it and report back.

But could you first clarify what you have in mind for the driver circuitry please? Clearly it cannot be the single DPDT change-over relay used for the 'simple' case. That wouldn't accommodate any stops. Do you propose a second 'On/Off' relay? Or an H-bridge? Or...?

Easy microcontroller job. Drive the motor through an H bridge, or two relays if you think they will last long enough. The rest is software.

Paul Burke

I read in sci.electronics.design that Terry Pinnell wrote (in ) about 'Motor cycling between limits', on Sat, 20 Aug 2005:

'NO microswitches' doesn't mean 'no microswitches'.

What with 'motor cycles', it must be Ambiguity Week at Pinnell Towers. (;-)

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:-)

-- John Fields Professional Circuit Designer

Guilty as charged for 'motor cycles', your Honour. But innocent on the lesser charge of 'NO microswitches', on the grounds that its context made my meaning obvious.

But thanks, I see now where Richard was coming from .

"Terry Pinnell" a écrit dans le message de news: snipped-for-privacy@4ax.com...

Some high tech solution:

add some play between the motor/actuator and its load so that once the motor has just reversed the load starts moving 200ms later. Then adjust your microswitches positions one to +50ms, the other to -50ms.

You could adjust the motor speed so that the 200ms corresponds to 555 (um).

In article , Terry Pinnell wrote: [...]

A full H bridge would be the way to go in this case.

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

Transpose to NOR gates and you get the "high = run" polarity with just one package.

This is a good job for CD4000 logic. They make enough swing to drive power MOSFETS.

Thanks, John, looks good. Are you assuming an H-Bridge driver section, rather than relays?

But his delays are 100's ms, it is not a good idea to use RC like that. His circuit is good with 4093's on those outputs, and the delays are not critical.