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FAQ
Re-winding and building motors, tips and tricks, checks and tests
Please don't ask general questions or help/assistance in this thread, just add your tips and tricks. I move information from posts to opening posts, that way the information is presented in a logical (work)order.Use translate.google.com for automatic online translation. All you have to do is enter a link there.
Start a new thread when you have questions or when you start a fresh motor/wind project , in order to keep this a lean and mean FAQ/tips/tricks/checks/tests/manuals thread. Once/twice a year I try to clean up this FAQ. But don't worry, I will ask you to start a new thread anyway. 1 - Tips, tricks, manuals, checks & tests 2 - Efficiency governs power/weight ratio 3 - Popular motor misconceptions 1 - Tips, tricks, manuals, checks & tests
2 - Efficiency governs power/weight ratio Higher efficiency does not only mean that the motor makes better use of the batteries' power, it also means the motor is able to handle a higher power input before hitting its maximum temperature mark, i.e. a the power/weight ratio will be higher. An example Say the motor has an efficiency η = 0.700 and it can handle 500watt input. That means it can get rid off (1 - 0.7 ) × 500watt = 150watt excess heat. Now, by cramming in thicker wire (and/or using better stator-iron, segmented magnets), efficiency increases to 0.75. The motor's ability to loose those 150watt has not changed (by radiation, convection and conduction). This means the motor now can handle 600watt before it hits the 150watt (0.25 × 600watt) losses mark. So, going from 70 to 75% efficiency gives an increase in power of 20%, factor 1.2. That's why efficiency plays such an important role, in any motor design: efficiency governs maximum power. The motors weight may have increased a bit due to more copper. All of this assuming the iron will not saturate magnetically. A rather extreme example, just for calculation's sake/fun: going from 80% to 90% efficiency would increase the input power the motor can handle by a factor two (a.k.a. 2)  Going from 90 to 95% efficiency would increase power again by factor 2 Dream on boy  General case Going from efficiency ηold to efficiency ηnew would give an increase in maximum power motor can handle by factor N N = (1 - ηold) / (1 - ηnew) = ιold / ιnewCopper as thick as possible for ...
3 - Popular motor misconceptions
Kv is about matching battery voltage and prop rpm.Vriendelijke groeten Ron• Without a watt-meter you are in the dark, until something starts to glow • • e-flight calculators • watt-meters • diy motor tips • Cumulus MFC • |
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Last edited by Ron van Sommeren; Nov 22, 2018 at 02:55 PM.
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Speaking of Dremels
On some small cdroms i use small pieces of card between the magnets to stop them jumping together,when im happy with the placement i put a drop of Loctite Black max on each end of every magnet then chuck it in the Dremel hold it inside a toilet roll tube and spin it for a min' or 2,this forces the locktite to even out and mantain ballance as well as fill behind mags'. When cured trim any excess card flush with mag's with scapel then clean up with cotton bud lightly dipped in laquer thinner. It will surprise you how well this works, just check what is spun out inside the tube .
 Black max is good to 100c by the way. Good thread starter too Ron .cheers all.
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Want a tight fit?
Try going through your collection of shafts with a micrometer and select the smallest diameter,carefully grind a radius on the end then with a dremel grinder grind across halfway up just past the radius,you will have what is known as a D bit,it acts like a cross between a drill and a reamer,of course you will have to drill a pilot hole first before using the D bit use slow speed and metho' as a coolant lubricator.and so long as you dont keep it spinning in the hole to long you should have a press fit.
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Last edited by olmod; Dec 07, 2006 at 03:24 PM.
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Before fitting your bell
Use a black marker pen and blacken the inner face of the end bell and the face of each stator end allow to dry,then gently fit and rotate a couple of times,take apart and examine blackened areas for any signs of rubbing,its not unusual to have a group of stator ends rubbing just either file down or dremel sand the high spots but not the whole lot.if end bell rubs ,add small washers onto shaft till you have clearance.
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Usefull small cdrom data
Drum sizes for different magnet configurations.
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Want to extend your bell??
You can line the existing bell with old transformer ( i ) lamination iron..a guilloutine helps in cutting the strip width to the depth of bell required, cut longer than needed, hand roll around something wich is about 4 mm smaller to allow for spring back, then start trimming the ends off as they will have a flat on them,when you get close to the inner diameter of your bell,lay on a flat metal surface,take fine flat file one with a smooth edge to go down on the metal surface,squeeze the ring together so you file both ends together on the draw back stroke.by trying you can get a push fit and a perfect butt join.I use a little loc tite black max to glue them in and spin them with a drill in a toilet roll tube to even out and get rid of excess loc tite. I place the first magnet over the but join, when finished placing the magnets,i place a single drop on each end of magnet and use the same spin technique.when fitting stator i use the black marker to show witness to any rubbing and grind accordingly. so i might not be able to use max' thickness magnets but the lamination iron flux ring helps too.
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Quote:
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In example in twice longer stator you can get twice more MF at the same saturation level but at the same time you can use longer magnets in the twice longer rotor. So the force will be 4 times stronger. How it translates to power? At the same number of turns you can run twice more current before stator is saturated (this is the part of twice stonger MF from stator). So the power at the given voltage is just twice bigger than in single. But wait, the torque is 4 times stronger, so it must be lower rpm. Yes. Kv of that motor will be 2 times lower. So how to bring it back to the original Kv (and original rpm)? Use twice less turns. But wait again - you need again twice more amps to get the the saturation level. So now we have motor that is twice longer with twice longer magnets, with half of original turns (and probably thicker wire) and drawing 4 times more current. It runs the same rpm and delivers 4 times higher torque. Isn't it slick? RysiuM |
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Thread OP
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Remove original CD-ROM motor magnet ring by letting it soak overnight in acetone.
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Last edited by Ron van Sommeren; Sep 22, 2015 at 06:32 PM.
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Quote:
This sounds like just what I need. Does a D bit look like this? |
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Last edited by bz1mcr; Jun 22, 2004 at 07:40 AM.
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Kurt |
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Last edited by Fishnut; Jun 22, 2004 at 10:36 AM.
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To help prevent windings from rubbing the inside face of the bell, put the wound stator between two hardwood blocks place in vise or heavy C clamp and squeeze for all you're worth. This "flattens" the windings a few thousandths and may be the difference between rubbing and running freely.
JT |
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If you have problems with windings rubbing on a GB kit, it may be that the plastic retainer ring has been pushed too close to the inside face of the bell. Using a drill press or arbor press, "push" the shaft back into the bell a tiny bit. Because the bearing holder/stator is locked on the shaft by the plastic retainer, moving the shaft back also moves the stator back and provides the clearance needed. Unless there is severe rubbing, just 3-5 thousandths is usually enough to free things up.
JT |
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Fishnut
It will certainly be better than other adhesives,why i say that is because i have read and i did post somewhere a couple of links to the csiro wich have a couple of papers on materials made of compounds i suspect are similar and are useing and testing for manufacture of stators ect, the main thing is not to have any between the magnets as this is detrimental so ive been informed by a manufacturer here in melbourne. imagine moulded stators if you are interested try checking my past posts.
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2. To hold a stock can on the shaft use a prop adapter (or even a collar) that fits tight on the shaft and it's glued to the front of the bell. Any good glue for metal will do (Locite, plasti-zap, JBWeld). RysiuM |
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Last edited by rysium; Jun 22, 2004 at 01:08 PM.
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