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Old Dec 02, 2004, 01:49 AM
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Impact of Manufacturer Tolerances on

I've posted a new thread, taking the discussion of the impact of tolerances on motor design/fabrication to another venue. What was a simple tip to acquire and take tolerances into account in calculations and fabrication, looks like it requires a separate thread.

"Impact of Manufacturer/Other Tolerances on Motor Design/Fabrication"

http://www.rcgroups.com/forums/showthread.php?t=305341

This thread kicks off by demonstrating calculations that show significant Stator/Magnet interference issues for common motor parts (22.7mm stators and cans, and 5mm Wide magnets, of 2mm and 1mm Thicknesses).

How one might calculate a perfectly viable motor using the nominal part dimensions, but discover significant problems when the part dimensions begin to change, but remain within commonly specified limits.

escudo
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Last edited by escudo; Dec 02, 2004 at 02:38 AM. Reason: clarification
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Old Dec 02, 2004, 06:53 PM
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Planning/Assembly To Reduce Chance of Assembly/Operational Failures

Planning/Assembly To Reduce Chance of Assembly/Operational Failures

Here are some practical ideas on how to help reduce the chance of stator/magnet obstruction and some other tolerance-affected problems during assembly and during operation of the motor.

There is a practical way to help reduce some of the impact of manufacturing and asssembly tolerances in the magnet/stator obstruction situation. However, you need a micrometer, you will likely need more than just the minimum number of magnets to assemble a motor (a motor using 12 magnets might require 20 or more from which to measure and select, so unless you want to wait for a second order of magnets and are willing to trust in luck, order more magnets the first time around), and you may need chemicals/tools to modify your stator.

1) Measure your can/rotor Inside Diameter in several separated locations. If any measured ID is LESS than what you planned for, either correct the rotor/can or use another.
2) Measure the orthogonality of the shaft to the rotor. Verify that it is perpendicular to the rotor. (One way to do this is to measure the distance from the shaft to the inside surface of the rotor/can near the shaft/rotor press-fit joint, and again near the "back" end of the rotor/can. Take into measurement consideration any changes in ID caused by rotor design.) Take several measurements. Correct as needed or use another rotor/shaft assembly if you cannot achieve values to maintain the AirGap calculation in the MRC.
3) Measure your stator Outside Diameter in several separated locations. If any measured OD is MORE than what you planned for, either correct the stator or use another. Realize that modifying the stator can seriously impact assembly and motor operation.
4) Measure each and every magnet you plan to use (measure each magnet dimension). If a magnet dimension exceeds the value you have used in your calculations, do not use it in your current assembly. Do not attempt to modify the magnet.
5) Avoid designs in which the magnets will end up touching each other on their sides. While some people have successfully assembled motors with touching magnets, it is risky (see caution2 note below)
6) Select only magnets that according to the "Motor Rotor Calculator" (MRC) will produce Air and Magnet gaps you know you can assemble.
7) Examine your stator for any design or assembly elements that extend beyond the "face" of the stator. Modify, remove, or compensate in the MRC for any extensions as needed. Remeasure your stator if needed. Realize that modifying or removing this sleeve may have other considerations.
8) Factor into your calculations that adding glue,epoxy,paint, protective stator sleeves, or other factors into your assembly will change some dimensions after assembly.

Caution1: I've got one stator that has a plastic protector "sleeve" on the top and bottom laminates. This sleeve INCREASES the OD of the stator beyond the OD of the metal stator "arms", but this extension is NOT very wide...it's more like a tiny peg extension, 0.08mm long...I almost missed it. It is not flush with the face of the stator arm, and forms a channel into which the magnets slot. If I hadn't seen this, was able to assemble my motor, and were to use magnets that did not fit totally within the space formed by this sleeve (with adequate clearance as the stator shifts along the axis), I might eventually have a situation in which the sleeve contacted a magnet(s)...most probably while the motor was running. I'd soon have a small broken pile o' parts or a seized motor. This sleeve was clearly designed for custom magnets, in a custom manufacturing assembly, and trying to use generic magnets and a hand-made assembly with more "slop" is inviting trouble. The solution? Modify or remove the protective sleeve. If you do that however, realize you may have to deal with wiring issues and be extra careful about stator-wiring shorts..

Caution2: thermal expansion during operation will cause the stator arms to lengthen, and magnet height, width and thicknesses to all increase. If you rely on assembly variations on the order of a few hundredths of a milli-meter (0.001 inches), this may cause problems. As the stator warms up from heating caused by the wires, the Air-Gap will be reduced.* If youíve provided too little clearance between the magnets and the stator faces, you will end up with stator/magnet obstruction. The magnets also heat up and expand as the motor runs. This also reduces the Air-Gap by some degree. It adds another factor to consider during assembly. If you have assembled the motor such that the magnets are too close or press against each other when cold, then once they heat up this could contribute to adhesive failure, warping of the rotor/flux-ring (due to mechanical stress caused by the heated magnetsÖnot thermal stress), or buckling of the magnets. Any of these factors could contribute to motor failure while running.

*The rotor shell will also expand with heating, which could help reduce the severity of this problem. However, because of itís greater distance from the heat source, its greater ability to dissipate heat, and itís less significant contribution to radial movement, itís contribution is likely not as significant in affecting stator/magnet obstruction during operation.
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Last edited by escudo; Dec 02, 2004 at 07:07 PM.
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Old Dec 03, 2004, 12:14 PM
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United States, OH, New Franklin
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Stator Winder Construction Details

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Old Dec 08, 2004, 04:20 AM
homo ludens modellisticus
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The Netherlands, GE, Nijmegen
Joined Feb 2001
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DIY magnetic flux/strength meter:
http://www.rcgroups.com/forums/showthread.php?t=307133
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Last edited by Ron van Sommeren; Dec 08, 2004 at 05:47 AM.
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Old Dec 20, 2004, 11:02 PM
Model Bender
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Australia, NSW, Newcastle
Joined Jun 2004
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Old VCR's and printers are a great source of pre-ground shafts,circlips & bearings to use in homemade cdrom motors. I have lots of 3mm shafts with circlip grooves accurately cut in them already (some with splines as well!)
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Old Dec 27, 2004, 04:51 PM
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ni'ihau
Joined Nov 2003
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tape a neo-dym magnet to the wire of your soldering pencil so it will stick to the arms of your flex light to get it out of the way if you need to use both hands for a second. Much better than laying it on the bench when you realize the holder for the pencil is covered up with meltables.
jimbo
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Old Dec 27, 2004, 11:00 PM
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Interesting tip on, "proper proping," of cd rom motors, (as well as other motors,) from Astro Bob.
http://www.rcgroups.com/forums/showp...7&postcount=30
This can really help with choosing the right winding per volt when building these cdrom motors.
I'll delete it if it doesn't belong here.
Bill
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Last edited by Bilbobaker; Dec 27, 2004 at 11:03 PM.
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Old Dec 30, 2004, 12:10 AM
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Bearing holder

I made this bearing holder from an aluminum archery insert for Carbon arrows. The outside diameter is 8mm. Used a 15/64 drill bit to ream out the inside. The result is a press fit for the bearings. This would probably work best using a drill press to get the proper alignment. YMMV... Cost, 0.25

Ken
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Old Jan 20, 2005, 10:42 PM
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United States, MI, Houghton Lake
Joined Dec 2002
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CDROM Mounts

The Firewall mount sold by StrongRCMotors fits all 8 mm bearing tubes. Like those on Lens motors and even GoBrushless carbon tubes.
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Old Jan 21, 2005, 02:17 AM
Master of the Wind
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TEXAS
Joined Jun 2001
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Here is a simple method for wiring up those 25mm 12pole stators ..use heat shrink.. allow to over lap the tooth .. once your done winding you can use a sharp razorblade and knock off the excess.. I like the heat shrink that leaves a hard plastic finish once your done heating up the tooth..

enjoy the pics guys and go wind a LRK or a simple ABCX4coils per phase for a real boost in power!

I used a 3stator stack of GB 25mm stators in the photos..
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Old Jan 21, 2005, 06:55 AM
Good Better Best quest.
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Australia, VIC, Cranbourne East
Joined Apr 2004
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Flux rings

When using solid bar stock this may save a bit of time
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Old Jan 21, 2005, 03:58 PM
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Maine USA
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Stainless steel tweezers are a must for magnet placement. As you know stainless steel is non-magnetic.

Also before you attempt a tricky cascaded magnet arrangement NNSSNNSS with curved magnets for 100% coverage.. first try a NSNS configuration to see if they even fit!! Once in an while an out-of spec magnet will prevent them from fitting.

Welcome Frogger, better to post GBv questions on a gobrushless discussion thread

Charlye
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Old Jan 22, 2005, 09:14 AM
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United States, MI, Houghton Lake
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Quote:
Originally Posted by Charlye
Stainless steel tweezers are a must for magnet placement. As you know stainless steel is non-magnetic.

Also before you attempt a tricky cascaded magnet arrangement NNSSNNSS with curved magnets for 100% coverage.. first try a NSNS configuration to see if they even fit!! Once in an while an out-of spec magnet will prevent them from fitting.
Charlye
Not all stainless steel is non magnetic. Less than half in my experience.

Attempts at 100% magnet coverage usually end up not fitting or with one space. Thats why I us 25 degree segments and use a magnet spacer to end up with even spacing all around. Also some have concluded magnets interfere with each other if too close together.
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Old Jan 22, 2005, 12:05 PM
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300 series stainless is non magnetic while 400 series IS magnetic. If it doesn't stick to a magnet....you know the rest.
Rick
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Old Jan 31, 2005, 03:21 AM
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Joined Sep 2004
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When winding a CCW-CW-CCW motor (eg for a 9 tooth stator and an 8 magnet can), be aware that counting turns of wire on the teeth will give you a bad wind. Depending on which side you are looking at, you will have to put on, or leave off an extra turn of wire on the middle (CW) tooth. The attached figure will hopefully clarify this.

The figure shows 3 teeth, each with one full turn of wire. Looking at the teeth from the front you count 2-1-2 winds on each tooth, looking at the teeth from the back you count 1-2-1 winds on each tooth.
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Last edited by wnreynolds; Jan 31, 2005 at 03:32 AM. Reason: typos/clarification
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