Solenoid Pendulum Problems

THE_RB

Joined Feb 11, 2008
5,438
...
The current pendulum now actually runs on 24 volts at 1.4 amps any less and it stops, the solenoid is rated between from 12 to 36 volts, i am using bench supply. How would i power it for exhibition or do you know way i can reduce the power consumption? ...
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I would like to see a close up photo of the solenoid, especially at the point of the swing where it affects the pendulum.

Solenoids are most efficient when the solenoid armature (moving piston part) is almost fully drawn in. The further out that armature gets, the weaker the pull force it exerts. It can be a delicate balance between getting the solenoid armature travel in a very short distance (for max force) vs the leverage to move the load (as leverage is reduced with a short travel distance).

A way to cheat is to put a tension spring (or rubber link) between the solenoid and the load, this makes it quieter and more efficient. That is because the solenoid can draw fully in, where it makes the most force, and stretches the spring. Then the energy stored in the stretched spring continues to be released into the slow moving load (the pendulum) as the spring contracts over time. :)
 

atferrari

Joined Jan 6, 2004
4,764
Why do you need such a large boost to swing your pendulum?
a) I strongly suspect that pushig the pendulum (by just repelling a magnet) at any end of the swing path (as you normally do with hammocks) would require a smaller pushing force and with the due sensing plus more electronics, you could forget the reed relay.

Up there, that small lever arm (see his diagram) seems to require more force for an equivalent effect.

b) The optimal condition would be to push the "bob" of this pendulum exactly on its center of gravity (again, as you do with hammocks). (The tricky parts is to find out where it is, but you can get a decent approach to it).

What seems to be closer to the above concept (and MUCH more common approach) is shown here

A different animal, a clock motor (and more complicate for me) is shown here.
 

wayneh

Joined Sep 9, 2010
17,496
I suggest trying an experiment. Remove the solenoid and use your finger to provide the energy. You'll see you need very little force if it's applied at the right time, and it works with the natural motion and not against it.

But hey, if you like the current sound, you're done.

For power, do you require battery operation, or are you looking for a plugin?
 

Thread Starter

Derek Ogbourne

Joined Sep 20, 2013
151
Atferrari... thanks for your links some new ones i haven't seen before. I did make the coil type pendulum before the solenoid one and it worked well but only had a short and swift swing. it had to be uber light to work, it was silent and therefore elegant though. I needed something a little more meaty that could swing a heavy weight ago a good hight...
 

Thread Starter

Derek Ogbourne

Joined Sep 20, 2013
151
The_RB ....

I have attached some close ups for you in one photo. today it worked for 7 hours until i turned it off, it did get rather warm, i just wonder how it would fair after a month?
 

Thread Starter

Derek Ogbourne

Joined Sep 20, 2013
151
Wayneh... i know, yes , it takes very little energy to push the paddle , See close up photos above. I used a rubber disk to give the paddle extra energy. I do need a plugin power source, it is to run all day, every day for up to 3 months.

Best

Derek
 

THE_RB

Joined Feb 11, 2008
5,438
It's not bad really. :)

You have good angles, and a rubber cush there. And solenoid armature travel seems fairly optimal. You may get slight efficiency improvement changing the rubber cush to a small compression spring.

What kind of "bearings" does your pendulum use? You mentioned oiling? Seeing that it is fairly heavy I think the majority of your load losses will be bearing losses.

You could switch to tiny ball bearings like 605 (14mm OD, 5 mm width, 5mm hole) which are cheap and common on ebay. They will easily take that pendulum weight and be extremely low loss compared to a stick in an oily hole;

 

Thread Starter

Derek Ogbourne

Joined Sep 20, 2013
151
Thanks RB

I don't know what bearings i used, got them ages ago from a specialist supper, they are sealed type ones. the added compression spring is a good idea.may give that a go if i have problems. It ran for 7 hours yesterday

My main enquiry now is how i am going to power it seeing that it only seems to work at 27 volts at 1.4 amp, i am using my bench supply and i want a plugin in main source.
 

inwo

Joined Nov 7, 2013
2,419
I would try it at lower power, manually triggering the solenoid. (longer weaker pulse)

Stretching the pulse from the switch might be needed.

Although an old HP printer brick I found, ~31V ~3A might be a candidate.
 

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Thread Starter

Derek Ogbourne

Joined Sep 20, 2013
151
I tried lowering the power step by step but it just likes to work at 27 v. How would i stretch the pulse simply ;)

I think your HP 'brick' would do the job!!!


..but boy can it swing on its perch!!!
 

inwo

Joined Nov 7, 2013
2,419
Lots of simple ways to stretch the pulse.

It seems to swing slow enough that you could try it manually first. Just to see if it works.

One way is a second switch. One on and one off.
Another is a timer.

It just seems there should be a way to make it swing with very little input power.

I have no idea how.:confused:

It could be that you have the sweet spot now. Giving it a very short pulse!

Wish you were in States. The PS is in my junk bin.
Could be a much smaller (amps) supply would work with a large buss capacitor.
 

Bernard

Joined Aug 7, 2008
5,784
First a question- how heavy is the bob?
I saw a pend. drive once - a curved brass rod with a iron ball on the end was attached to pend. An open solenoid was suepended ai center of travel. The ball could be hit twice per swing, comming and going. Position sensing with Gray code segmented encoder. Digital comparator would select proper timing. If decoded from Gray to 16 line, a line of LEDs could follow the pend. Another dig. comparator could detect amplitude and inhibit power if amplitude were too high. You could always know where the pend. was for whatever purpose.
Any outline available for future projects?
 

Thread Starter

Derek Ogbourne

Joined Sep 20, 2013
151
I think i should should stick with the set up the way it is because it works. Look around for a power source and get on with my next piece which involves a motor winching ups heavy weight then dis-engaging via another solenoid from the drive enabling a heavy weight to fall about a metre...then engaging again and winching up. this has to work all day like the pendulum. I will draw a diagram and attach a photo of the mechanism later this evening. Not sure whether to start another thread for that one?
 

wayneh

Joined Sep 9, 2010
17,496
I think i should should stick with the set up the way it is because it works. Look around for a power source ...
A 20-24V AC wall wart (or transformer, if you have to make your own) would work. I believe household HVAC systems run on 24V AC, so I think it would be easy to find a transformer for that.

That AC voltage would rectify to over 27V. You would also add a large capacitor across the DC poles of the rectifier. This would smooth the DC and store a good chunk of the power required to fire the solenoid.

Your solenoid is not constantly firing at 1A, it is only intermittent, so I believe the wall wart could be rated well below 1A. Of course a higher rating is fine, but I'd guesstimate that a 0.5A one would be fine.

If you find that you need finer control over the voltage, you can add an LM317 voltage regulator to the scheme above. This would allow you to dial in the exact voltage. If you search for a LM317 power supply schematic, you'll get a billion hits.
 
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