Model Electric Motors?

[Ron LadenParticipant @ronladen17547]

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.

Ron

[Ian PParticipant @ianp]

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

[JasonBModerator @jasonb]

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 LadenParticipant @ronladen17547]

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 PParticipant @ianp]

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 LadenParticipant @ronladen17547]

Jason, are you going to improve on the crankshaft or keep all as per the original, it obviously works well enough on the original.

[JasonBModerator @jasonb]

If I can bend it OK it will be like the original.

[Ian PParticipant @ianp]

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 LadenParticipant @ronladen17547]

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.

[SillyOldDufferModerator @sillyoldduffer]

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 LadenParticipant @ronladen17547]

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

[JasonBModerator @jasonb]

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 LadenParticipant @ronladen17547]

Sounds good Jason, out of interest what material did you use for the crankshaft.?

[JasonBModerator @jasonb]

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 StonesParticipant @samstones42903]

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

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

[Ron LadenParticipant @ronladen17547]

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

[JasonBModerator @jasonb]

I'm just going to be keeping it simple like the original no fancy modern electronics hidden under the base. Should work on a single AA cell so won't be that much going through it to burn out contacts and that one in the video seems not to have suffered in 110yrs.

Ron, part of the drawing and designing also includes the thinking of how it will be constructed, no use drawing something you can't make.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Sam Stones on 10/11/2018 21:17:38:

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

Indeed, if Jason was building it for resale he would have to ensure that it complies with" EMC recast Directive 2014/30/EU"

Russell

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Russell Eberhardt on 11/11/2018 09:43:08:

 

… "EMC recast Directive 2014/30/EU"

.

^^^ possibly the reason why the classic 'clapper' doorbell is difficult to find these days.

MichaelG.

.

https://www.explainthatstuff.com/how-electric-doorbells-work.html

Edited By Michael Gilligan on 11/11/2018 10:28:11

[Neil WyattModerator @neilwyatt]

I once made a cardboard one:

[Ian PParticipant @ianp]

I know Jason will get his motor to run but I think it will be quite a challenge with only a single AA cell. This is just a gut feeling and whilst I have no idea what the 100 year old one used, I suspect a motor the same basic design and size will consume something like 5 to 10 watts.

Neil's cardboard model presumably uses a hollow solenoid with the 'piston' having a relatively long stroke especially compared to the flat plate drawn towards the poles of the 'doorbell' or relay type electromagnets.

Going back to the magnetic circuit of Jason's design and whether to magnetically insulate the cores from the frame. I originally assumed that the magnetic circuit went through the whole steel structure creating a roughly rectangular loop, (two horizontal and two vertical limbs) On reflection the loop only needs to include the part of the frame holding the two cores so that the loop is now rectangular-ish in the horizontal plane only. The two electromagnets could operate in (magnetic) series and the loop length would contain less metal and be a lot shorter.

Just my 2p

Ian P

[Michael GilliganParticipant @michaelgilligan61133]

Another good video [motor running on one D cell] : **LINK**

MichaelG.

[Ian PParticipant @ianp]

I'm quite impressed with that (you find some amazing things Michael!) and it is quite a good video. Interesting that towards the end it seemed to lose power, whether that is the battery expiring or something else is not clear.

The con rod big-end looks to keep itself centered on the crank journal without anything to restrain it, I'm sure if I tried to copy that mine wouldn't work.

Ian P

[JasonBModerator @jasonb]

Thank's Michael, I had seen that one too but liked the look of the one I'm trying to recreate more. There are also quite a few of the "piston" type solenoid designs about both old and new so wanted something I had not seen modeled before.

Frame is all silver soldered together and the copper wire and bobbin materials should arrive today.

[JasonBModerator @jasonb]

Things are looking promising. The Reel of 0.5 copper wire arrived and I thought I would see how good a magnet I could get from it so just poked an offcut of 10mm steel up the hole in the reel, dangled a length of 4mm rod vertically above and about 25mm from the end of the 10mm bar and connected up a 6V battery that was on the bench. The 4mm bar swung straight over to the core so the principal is right.

Bobbins are turned and I finished up last night with the flywheel from 60mm ERW tube and scraps.

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