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16 V AC POINT MOTOR? Answered

Hi there, I would like to say hi to the instructables members for a start.


I have always enjoyed reading from this site and I see that there is a lot of help in the topics posted here.
I am a Computer Technician that now wants to play in the hardware game (Are you all enjoying Windows 10?).

So I'm starting small with an arduino and the raspberry pi, (not side by side yet,) a few motors, servo's, 7" color crystal display, and other things that I have salvaged from stuff or found cheap. I have a few of these CD drive eject motors with lil' knobs

I was reading this post about how to make an electric magnet as I am trying to manually make my own point motor for my model train set. 

For those in and not in the know, here is some information about what I am trying to do.

Create 2 electric magnet coils that pull or repel a nail or metal bar where an upright pin ~2-4 mm is able to travel a distance of ~6-8mm (oo Gauge) in order to change a track piece from one position of a "junction point" to the other, allowing the train to change track or take another route.

I would like to try and do this myself as I have plenty of different types of gauge wire, dpdt's (for pole switch?), nails or metal bars(to act as middle pin maybe and bar to be pulled back and forth), diodes (for bridge rectifier) , resistors (to calm the voltage down if I have to as I think it will get rather warm else), a constant power supply (16V ac admittedly)  and plenty of BABY BABY small yet rather strong.. magnets..etc.. ( BTW These were taken from a motor that was inside some water speakers, for perfect reasons the motor had a spin disc attached to it with 3 very small magnets, then in the water compartment there is a spin disc with more magnets attached and a wirly-gig to create the siphon to jettison the water up when the music is played so I now own 60 of the little blighters, (that's if i need them at all to be honest I'm a little lost in this idea)) 

So please take me as a n00b and please help me in going about this. Yes I could go buy one, but what does that achieve, when I believe I have everything I need at my fingertips and I wish to learn.

I presume I will need to deal with the constant AC in order to be able to make a switch to change the polarity of the two coils in order to pull or repel the magnet or nail in either direction to then move the tracks junction from one line to another.

I'm going to try and make some coils, in some rather thin wire that is insulated. 

Thanks again for any replies.



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Jack A Lopez
Jack A Lopez

5 years ago

I think this phrase "point motor" is jargon specific to model railroad builders.

I mean when I ask Google Images to show me pictures of "point motor", almost all of the pictures are of model railroads.

However, to me, this thing you call a "point motor" looks like two solenoids aranged back to back so they share the same armature.

A more general word is "actuator".
That's a machine that produces motion in response to an electrical signal.

Although sometimes the word gets super generalized to electrically driven events besides motion, so an electrically driven light, heater, or chemical injector, could also be called an "actuator" in this sense.

But usually an actuator is something that moves.

This might seem pedantic, me explaining the words for these things, but I think part of the reason why there have been so few replies to your query, is because a "point motor" is something only model railroad builders know about. However, your actual goal here ( I am guessing) is to build a machine that makes something move, i.e. an actuator of some kind.

Back the subject of electromechanical solenoid. A solenoid is probably one of the cheapest, easiest to build, actuators there is. Although rolling your own solenoids is kind of labor intensive, both in terms of mental and physical labor.

I mean first you have to find, or make, a spool to wind the magnet wire.

Then it helps to have a machine that can wind wire onto the spool, and count turns as it winds. Although, you can wind manually and count mentally, it is kind of time-intensive, boring, work.

As an alternative to actually counting the number of turns, you might be able to estimate it based on the dimensions of the spool. Essentially it is a volume-filling problem. A long piece of wire occupies volume, its length multiplied by its cross-section, and it occupies the same volume when wound onto the spool. Although I think it is helpful to actually count turns, if you can, because a lot of equations for magnetic properties of the solenoid, depend on N, the number of turns, e.g. magnetizing field H is proportional to N, self inductance L is proportional to N squared, etc.

The length of a piece of magnet wire can be measured directly with a tape measure, or similar, or it can be measured indirectly using an ohmmeter, since its DC-resistance is proportional to its length.

Because building solenoids from scratch is somewhat challenging, it might be easier, preferable, to modify some existing solenoids, if you could find a source for small, cheap, solenoids, that are roughly matched to the voltage supply you want to use, and to the amount of force, and work, you need them to deliver.

You can find solenoid actuators, as parts, as components, from the usual places that sell electronic components, e.g. factory new, from places like Jameco, and Digikey, e.g. surplus, from places like Electronic Goldmine, and BGMicro. Those are all sellers based in my home country, the FUS. Although I think the best prices are going to be found via the direct-from-China sellers on eBay. e.g.


5 years ago

Go to your favourite scrap yard and open some old laser printers / copy machines.
They use several pull magnet coils to move parts.
Some might be even the size you need but if not they will show you how to make one of your dimensions.
If they would fit all you need is figure out how much wire and what gauge you need for proper operation with load.