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Model Electric Motors?

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Brian H08/11/2018 10:59:17
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Many thanks Jason, I can feel a Christmas or birthday present idea coming on!

Brian

Ian S C08/11/2018 11:55:56
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The first year of Model Engineer 1898 had drawings for a number of electric motors/generators, and this continued for many years.

I'v got a couple of books, "Small Electric Motor Construction" by J. Gordon Hall, a Percival Marshall publication, and "Small Dynamos and how to make them" Mechanic & Work Handbook, written by experts. Those books date back to the 1920s. Then a more modern book, "Practical Design of Small Motors and Transformers" by E. Molloy, first published in 1940, with 6 editions to 1947.

The only thing I find difficult to make is the commutator. Some of the materials used just arn't around any more.

Ian S C

JasonB09/11/2018 07:55:38
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As I said while looking around the net for these early electric motors I came across an image of a toy electric engine from 1908 and then found a video which says it dates from 1908 and would have cost $1.25 from the likes of Sears or Roebuck. It is not the same principal but looks like it will make a fun project.

electric.jpg

lecky1.jpg

After a bit of sketching last night with Alibre it seems to work, well at least on the screen it does! By moving the reversing lever one of the two spring wire contacts will touch the conrod and complete the circuit which draws the rocker towards the magnets. Time to start winding some wiresmiley

 

Edited By JasonB on 09/11/2018 07:56:19

JasonB09/11/2018 08:16:10
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A quick question for the more electronically minded members.

I plan to use a bobbin to wind the wire around and use the core to retain that to the vertical plate that sticks up from the base. Question is can I screw the core straight into the plate or should I insulate the hole and retain with an insulated washer and nut on the far side? The base does become part of the circuit.

lecky3.jpg

Thanks, Jason

Ron Laden09/11/2018 08:36:59
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Jason, since looking at old motors on youtube I keep getting links, take a look at this video, its the very type you are looking at. Crude crankshaft but it runs, wait until he speeds it up, runs quite well.

https://www.youtube.com/watch?v=8aWobDU0Cm0

Ron

Ian P09/11/2018 08:49:17
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Jason

Do you mean insulation for the electrical or the magnetic circuit?

The core of the electro magnet does not need to be electrically isolated as presumably the coils will be wound on bobbins made from an insulating material.

Magnetically your design is a slightly iffy. The force provided by the moving armature will be very non-linear and only over a very short distance just where the gap is near minimum. Your crank therefore will need to have a very short throw (maybe less than 1 or 2 mm and the shaft will have to have very little bearing drag. You will get the greatest force from the electromagnets (as you have drawn them) if the base plate material is ferrous so with the moving armature plate forms a complete magnetic circuit.

Ian P

e only significant amount is produced when the

JasonB09/11/2018 09:31:31
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Electrical will be insulated I just wondered if the magnetic force would be stronger if the cores were insulated from the rest of the engine. All the dark parts of the engine will be fabricated from steel.

This is the video that I found which has a similar crank throw to what I have drawn and seems to go like stink.

Thanks Ron, I had seen that one too.
Ron Laden09/11/2018 09:41:46
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That does get a move on, I didnt imagine they would run that fast. Fascinating little thing, its easy to forget how well a lot of the old stuff ran and though it seems simple now it would have been quite ingenious in its day.

Ian P09/11/2018 10:12:19
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Definitely the attraction produced by the magnetism from the coils is maximised if the magnetic structure forms a nearly closed loop so its best not to introduce any insulation or gaps other than the deliberate one where the armature is attracted.

I think I mistook the CAD cursor as the position for the crank pin which gave me the impression that the stroke was longer than it actually is.

Ian P

Ron Laden09/11/2018 13:18:00
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Jason, are you going to improve on the crankshaft or keep all as per the original, it obviously works well enough on the original.

JasonB09/11/2018 13:56:58
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If I can bend it OK it will be like the original.

Ian P09/11/2018 14:19:44
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What will you use to stop the connecting rod from slipping sideways off its location on the shaft, a couple of circlips would work but would weaken the shaft.

Ian P

Ron Laden09/11/2018 16:21:10
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I would have thought that the bends in the crankshaft would keep it centred, plus the original doesnt appear to have any form of location or retainers but I could be wrong.

SillyOldDuffer09/11/2018 16:55:20
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Posted by JasonB on 09/11/2018 09:31:31:

... I just wondered if the magnetic force would be stronger if the cores were insulated from the rest of the engine. All the dark parts of the engine will be fabricated from steel.

...

Good question! I don't know.

Best practice is to make the 'U' from a stack of thin steel laminations to discourage eddy current losses. Also, the metal should be a high permeability steel or soft-iron. Ideally the magnetic field should build up and disappear in line with the current with low losses.

Ordinary steel tends to magnetise permanently and being solid will also suffer from eddy currents. Both effects will reduce the motor's efficiency, though it will still work. No matter - the original motor isn't 'best practice' - it's an interesting novelty.

I guess insulating the core from the plate, or not, won't make any difference because the design is already compromised. Insulation would reduce eddy currents (hurrah) but also the magnetic flux (boo). Not insulating is the opposite case - it would increase eddy currents (bad) while increasing the flux (good).

Although I think the negatives and positives will cancel each other out there may be a lesser of two evils. Could you try both fixings and let us know how adding insulation affects the motors RPM?

Dave

Ron Laden10/11/2018 10:59:36
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Jason, I dont know if you intend to post progress or not but I for one would like to see the build as it goes along, I think it will be an interesting project and it would be good to see it develop.

Ron

JasonB10/11/2018 13:13:21
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Crankshaft is successfully bent and if it runs I will do a build thread with drawings.

Also made 13 parts for it last night, just the small simple turning jobs.

I don't think the conrod will move far sideways as it won't be able to pass the bends unless it is tilted sideways and the fork in the rocker will prevent that. I do need to do a bit more work on the crankshaft pivots as the way it is shown at the moment you can't put the crank in place, original looks to have a screw and cup arrangement so will go with that.

Ron Laden10/11/2018 13:48:42
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Sounds good Jason, out of interest what material did you use for the crankshaft.?

JasonB10/11/2018 20:21:44
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Ron, I just used a bit of Bright Mild Steel EN1A, don't think a little toy like this needs anything exotic or the need to work to 10ths

Sam Stones10/11/2018 21:17:38
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These animated projects really fascinate me.

Therefore, (as Devil's advocate), does the back EMF work 'for' or 'against' the solenoid motor's performance?

Or, does it produce lots of radio interference and burnt out contacts?

Just curious.

Regards,

Sam smile d

Would adding a diode across the coils/contacts have any benefit?

Ron Laden10/11/2018 21:35:13
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That base looks really good, a pleasing shape, boy you dont hang around do you, only 24 hours ago you were thinking of making it, its now drawn, base made, turned parts done. I would need at least a week to think how I was going to tackle it.

Ron

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