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John Stevenson
03-08-2009, 07:33 PM
I mentioned in the 'Had a good day thread that I had an inverse rotor to repair.
They are quite common over here, don't know about the US?, used mainly for fan motors.
The stator on these is mounted on the fixed end plate and carries two bearings.
The rotor is then on the outside and carries the shaft that runs on the bearings and this whole assembly rotates.

Pic of the opposite end to the fixed end showing one bearing location.

http://www.stevenson-engineers.co.uk/files/inverserotor1.jpg

Pic of the opposite end showing the bearing location buried round down inside, plus the fixing pads

http://www.stevenson-engineers.co.uk/files/inverserotor2.jpg

As you can see no matter which end you need to bore and sleeve there is nothing to hold on.

Enter the El Stevo MKI expanding collet, custom made at great expense.

http://www.stevenson-engineers.co.uk/files/inverserotor3.jpg

Just a bar turned down to 32mm, the size of the bearing, drilled, tapped and counterbored to a diameter less than a cap screw.
4 slits down with a hacksaw by eye, nothing special and a cap screw with the head tapered.
Stuffed up the spout and tightened via an allen key it will grip tight enough to allow it to be spun in the lathe.

http://www.stevenson-engineers.co.uk/files/inverserotor4.jpg

Cables are held back with duct tape, that's what the white is on the stator as this one has already been sleeved one end.

This post isn't about doing an inverse rotor as chances are no one will ever see one, let alone having to work on one.

This post is about thinking outside the box and remembering ideas to be used on other projects.

.

lazlo
03-08-2009, 07:41 PM
Just a bar turned down to 32mm, the size of the bearing, drilled, tapped and counterbored to a diameter less than a cap screw.
4 slits down with a hacksaw by eye, nothing special and a cap screw with the head tapered. Stuffed up the spout and tightened via an allen key it will grip tight enough to allow it to be spun in the lathe.

But is it accurate to 2 microns? :p

Nice job John. I've made one-off expanding mandrels like that with a slitting saw and 1/8" male NPT tap for the expanding taper bit.

motorworks
03-08-2009, 07:42 PM
Great idea on the expanding collect.
Are you using soft jaws?

See many motors in my shop but not one like that yet...
Bet the next ship that comes here from Europe will have one :)

lazlo
03-08-2009, 07:48 PM
See many motors in my shop but not one like that yet...

We have them in the 'States too -- they're called "outrunner" motors. Outrunners have a rotating magnet-lined bell, spinning around a wire-wound fixed stator. They're generally used for low RPM high torque applications.

motorworks
03-08-2009, 08:01 PM
Most of the motors I see come from shrimp/crab processing type equipment.
Most are TIFC and we also see a lot at of "metric" motors .

Not to steal the post, but along the line of motors and repair
I find the motor that were made in Europe much easier to work on.
If you have to bore an end bell they are almost always very easy to do.
The chinese are the Shiqs to set up.
e

John Stevenson
03-08-2009, 08:03 PM
Yup, soft jaws, use them a lot, allows you to split microns to a thou or two :rolleyes:

I get a lot or weird stuff because the small run of the mill motors are cheaper to replace than repair.

A lot of my work is on DC motors and old slip ring AC motors as these are just too expensive or too hard to replace.

JCHannum
03-08-2009, 08:13 PM
Those soft jaws are not the usual top jaws, but are one piece. Are they also a Stevenson special? If so how did you machine the threads on the back side?

John Stevenson
03-08-2009, 08:33 PM
No just bought in items, we used to have a firm about 25 miles away that used to specialist in making soft jaws for all types of chucks.
A lot were two piece Kitagawa type for production machines but he also did standard types as well.

Quite cheap, unfortunately although the web page is still up it looks like they have ceased trading.

http://www.emnet.co.uk/mtm/softjaw.html

There have been a couple of articles in MEW about laying out the scroll on the backs of the jaws. Not as simple as it first sounds, if you look at a set from the rear not only are they crescent shaped they are also off centre.
Interesting article on why this is.

.

lazlo
03-08-2009, 08:40 PM
Those soft jaws are not the usual top jaws, but are one piece. Are they also a Stevenson special? If so how did you machine the threads on the back side?

Jim, there's a brilliant article by Ivan Law in last month's Model Engineering Workshop about how to cut the weird off-center pinion teeth on the back of scroll chuck jaws.

Shoot me a PM if you're interested...

Dunc
03-08-2009, 08:41 PM
I really like that idea of the tapered cap screw. Any I have seen - chiefly in Model Engineers' Workshop - uses tapered pipe thread & suitable plug.

Never tried to machine one b4 (and I have not done a whole lot ofr machining) as I believe that they are hardened.

Would appreciate somne how to? Hss bit, carbide or?

Thanks

JCHannum
03-08-2009, 09:07 PM
Thanks Robert, no real desire to make any, just curious if John had undertaken to make them. I know there is a lot more to them than a casual look would indicate.

The heads of most SHCS are soft enough to machine with HSS. If not, you can put enough of a taper on them for this application by grinding on the bench grinder.

davidfe
03-09-2009, 05:39 PM
John,

I looked in google and did not really understand what the inversse rotor is.

Any pointers to other site would be appreciated.

TIA,

David



I mentioned in the 'Had a good day thread that I had an inverse rotor to repair.
They are quite common over here, don't know about the US?, used mainly for fan motors.
The stator on these is mounted on the fixed end plate and carries two bearings.
The rotor is then on the outside and carries the shaft that runs on the bearings and this whole assembly rotates.

Pic of the opposite end to the fixed end showing one bearing location.

http://www.stevenson-engineers.co.uk/files/inverserotor1.jpg

Pic of the opposite end showing the bearing location buried round down inside, plus the fixing pads

http://www.stevenson-engineers.co.uk/files/inverserotor2.jpg

As you can see no matter which end you need to bore and sleeve there is nothing to hold on.

Enter the El Stevo MKI expanding collet, custom made at great expense.

http://www.stevenson-engineers.co.uk/files/inverserotor3.jpg

Just a bar turned down to 32mm, the size of the bearing, drilled, tapped and counterbored to a diameter less than a cap screw.
4 slits down with a hacksaw by eye, nothing special and a cap screw with the head tapered.
Stuffed up the spout and tightened via an allen key it will grip tight enough to allow it to be spun in the lathe.

http://www.stevenson-engineers.co.uk/files/inverserotor4.jpg

Cables are held back with duct tape, that's what the white is on the stator as this one has already been sleeved one end.

This post isn't about doing an inverse rotor as chances are no one will ever see one, let alone having to work on one.

This post is about thinking outside the box and remembering ideas to be used on other projects.

.

oldtiffie
03-09-2009, 06:01 PM
Dunc.

They are readily machined - use your normal HSS or TC - what-ever. Just take it a bit slower, higher feed rates and cutting oil/fluid.

They are easily cut to length with a HSS or bi-metal (hand) hack-saw.

They are just another high-tensile bolt.

bob_s
03-09-2009, 07:48 PM
As in a lot of smaller size servo-motors.

lynnl
03-09-2009, 07:54 PM
John,

I looked in google and did not really understand what the inversse rotor is.


David

Sounds like an analogy would be an internal combustion engine where the crankshaft is held stationary while the engine block and heads, et al rotate around it.

I think some acft radial engines worked that way.

John Stevenson
03-09-2009, 08:38 PM
John,

I looked in google and did not really understand what the inversse rotor is.

Any pointers to other site would be appreciated.

TIA,

David

David.
See here:-

http://www.micronradiocontrol.co.uk/scorpion_about.html

.

TGTool
03-09-2009, 10:26 PM
Sounds like an analogy would be an internal combustion engine where the crankshaft is held stationary while the engine block and heads, et al rotate around it.

I think some acft radial engines worked that way.

That would be rotary aircraft engines in which the block and cylinders spun as distinct from radial engines in which the block is stationary and the crank turns.

Rotary engines developed well up to a point, cooling air was pretty much guaranteed, but the gyroscopic effect became problematic in larger sizes. Imagine trying to turn the craft with a huge horizontally mounted gyroscope mounted to the nose. Strange motions start to happen.

TGTool
03-09-2009, 10:32 PM
John,

I looked in google and did not really understand what the inversse rotor is.

Any pointers to other site would be appreciated.

TIA,

David


MEW also had an article describing how they worked and showing how to contruct them yourself. It's a multi phase motor that uses electronic sensing and control to change polarity among the phase coils as the magnets rotate. Pretty clever I thought.

Evan
03-09-2009, 11:07 PM
As in a lot of smaller size servo-motors.


They are actually very common. Hard drive and floppy drive motors are rotating magnet as are most brushless motors. The hard drive motors are almost all three phase and require a special drive controller although I have been able to run them from a simple ring oscillator with three stages. Incidentally, hard drive motors and related parts are made to micron level accuracy. Microns are really big compared to the accuracy required of optical components. I have been tempted for a long time to build a scanning atomic force microscope. The X and Y axis travel on such a device is only a few microns at most. It would be pretty cool to see what a mirror finish looks like at the atomic level.

Circlip
03-10-2009, 08:03 AM
All that glisters don't HAVE to have permanent magnet in it. This type of motor has been used for years in the Aircon industries.

http://www.axair-fans.co.uk/manufacturer.php4?manu=ecofit

The ones I used to rescue from the external re-cycling container have two sealed ballraces and a ground shaft.

Machining Allen screws, machines BEAUTIFULLY with HSS. Used to buy M16 capheads with enough shank length to be able to cut the thread off and re-machine a L/H M16 thread on it for the Looooooooooong delivery replacement blade retaining bolts that the animals on the shop floor used to bu**er at regular intervals.

Advised many toy ingineers to use 8.8 bolts for crankshafts, that is about the same material and with SHARP HSS gives a superb finish.

Regards Ian.

Evan
03-10-2009, 09:02 AM
Hex head cap screws do machine very nicely. I have used the same trick as John to expand internal fitting adapters or even to lock a small caliber shaft to a gear or pulley. It produces a very secure and concentric hold. No fussing with lands for set screws or drilling for pins. Just poke some threads in the end and split the shaft for half an inch. When you loosen it the pulley slides right off as the OD of the shaft is unmarred. Works well for low power transmission.

John Stevenson
03-10-2009, 09:31 AM
Another advantage over using tapered pipe threads is that the smallest common pipe size is 1/8" gas but that's bore, the OD is a tad over 3/8"
Next is 1/4" gas at just under 1/2" then it starts getting big.

Using a cap screw means it fits any size, any thread.

.

tony ennis
03-10-2009, 09:32 AM
Rotary engines developed well up to a point, cooling air was pretty much guaranteed

The Fokker DR.I among many others used rotary engines. They'd kill a careless pilot. I wonder if two counter-rotating rotary engines would work or if you'd still get weird torque-y things happening. I am thinking the latter.

Evan
03-10-2009, 10:06 AM
Two equal counter-rotating gyros on the same shaft null each other so there is no gyro effect.

[edit] They also null if they are in the same plane or the same axis.

lazlo
03-10-2009, 11:49 AM
Two equal counter-rotating gyros on the same shaft null each other so there is no gyro effect.

That's how torpedoes are driven.

JCHannum
03-10-2009, 12:14 PM
I keep a few 1/16" NPT pipe plugs on hand for smaller mandrels, they are not uncommon, and allow for smaller mandrels than the 1/8" plugs.

These are expanding mandrels for use in work pieces with blind bores. They are detailed in an article in the current HSM submitted by YVT. They are the same idea, but the expansion plug comes in from the rear.

http://i320.photobucket.com/albums/nn351/jchannum/P1060573.jpg

davidfe
03-10-2009, 12:22 PM
Thanks to all for the replies.

Now I have more to read and study.