Step 13: Fabrication Notes and Conclusion

That's it. I have just written 12 Instructable pages without actually telling you how to build anything. I think few can beat that...

This is only intended as a guide and primer on what you could do. I did not include directions on how to fabricate one specific motor because it assumes too much engineering knowledge to tell someone to follow my lead, at least in my opinion. In a future Instructable, I might go over the specifics of building RazEr's motor. But, in the interest of modularity, I elected to keep things separate this time.

Maybe you guys can take up my slack by talking about how you made your hub motor!

What I can do now, though, is put in a few fabrication notes for when you embark on your hub motor adventure.

� The "elevator pitch" in terms of motor design here is to stuff in the strongest magnets and the largest stator using as many turns of the largest wire running across the highest voltage battery you can get your hands on. Maximize ALL of N, R, L, i, and B. But wait, I thought earlier you said as few turns as possible was the best? Not necessarily: I said that just enough turns to get a workable Km contributes to lower motor resistance. There is no need to constrain yourself to low turn numbers. In fact, high turn numbers running at high voltages are almost always better than low turns and high current!

� Use a good high temperature 24+ hour epoxy to glue the magnets in. Cheap hardware store 5 minute epoxy has inadequate time to set, and the chemical crosslinks are not nearly as strong. Thin laminating epoxy (for fiberglass and carbon fiber layup) is recommended, with a microsphere filler. The filler shortens the working time of the epoxy, but causes it to be stronger and more tenacious.

� Speaking of gluing the magnets, you may notice that they have a tendency to snap towards eachother in your can. To avoid this, cut up some popsicle sticks into wedge shapes and push them into the gap to separate the magnets.

� GoBrushless' rotocalc also generates a magnet placement guide image. Print this out at full scale on a piece of paper and perform your magnet gluing over it.

� As long as you have machine access, make jigs and fixtures to help you glue the magnets. Try not to let them float as you're gluing.

� While on the subject of epoxy, sealing your motor windings with high temperature enamel or epoxy will keep them together (prevent unraveling or jiggling) and make them more heat resistant. Do this AFTER you make sure your motor works and winding is correct.

� Never wind wires on a naked stator. The metal edges will pierce the magnet wire's thin enamel coating and result in a phase short to the core. You are bound to make more than one, so the phaes will short to eachother!  

If you cannot avoid winding on a bare stator, liberally apply heatshrink or electrical tape to the inside corners of the stator, and wind carefully. If you create a short, you MUST rewind that phase.

� Pull your wires tight. Loose windings are more likely to be damaged, and they are longer than they need to be, so your motor has extra resistance.

� Insulate, insulate, insulate. You have wire running past high speed rotating surfaces which will abrade the insulation if allowed to rub.

� Use a good, flexible wire. Silicone high strand count (HSC) wire, including the popular "Wet Noodle" from W.S. Deans, are the best choice.

� Use high quality hardware. On Razer's motor, I made the mistake of using stainless steel screws because they were cheap and already at the hardware store (instead of ordering high quality socket head cap screws). Bad mistake - they sheared and stripped one by one, leaving the motor wrecked.

A Note on Motor Control

BLDC motors can either be sensored or sensorless

Sensored motors have Hall Effect sensors which react to magnetic fields. There are at least three of them inside your average sensored motor, and they function as a very crude position encoder. A sensored motor controller reads the state of these sensors and correlates them to the position of the motor through a lookup table. It then outputs the proper voltage levels to the motor according to this state table. This is called Space Vector Modulation.

Yours Truly has build a fully hardware (logic chips, op amps, no microcontrollers) SVM motor commutator for a class project. And it actually worked.

Sensorless motors are operated by controllers which sense back-EMF. Remember from the page about DC motors and their ability to be used as generators? Every time the brushless motor moves, it puts out a sinusoidal (or trapezoidal) waveform on its 3 connections. A smart controller can actually read these voltages and have an idea of which direction the motor is traveling. It can then sequence its output to "encourage" the motor to keep rotating, generating torque.

What is the difference? One has 3 more parts and the other doesn't?

Well yes, and...

Sensorless motors cannot operate from standstill unless the controller is very sophisticated. If the motor is not moving, the controller has no way of know where it is. There do exist controllers which can sense motor position based on the effect of the motor's magnets on the phase inductance. However, those are ungodly expensive and are a new industrial technology (which makes them even more expensive.

� Hence, if you keep your motor sensorless, you may find yourself kick-starting your vehicle.

The vast majority of inexpensive R/C airplane motor controllers are sensorless.

� Sensored motors can operate from 0 speed, but require a controller that can read them. These tend to be more expensive than their sensorless brethren.

� Additionally, if you add sensors to your motor, you have to place them in the correct spots. Hall sensor placement is a quasi-nontrivial process that requires knowledge of the motor's electrical slot ratio.

Two popular Hall Sensor placements exist: 60 degrees and 120 degrees. I glean over this on my website, but the degrees refers to how many electrical degrees apart the sensors are.

To place Hall sensors properly in your motor, you have to know how many electrical degrees each slot (or tooth) occupies:

°elec = 360 * p / t

where p = number of pole pairs. For a LRK motor, this is 7. Likewise, t, the stator slot count, is 12.

For a LRK motor, the electrical degree of one slot is 210 degrees.

Now that you know the °elec of your motor, you can technically place the first sensor anywhere. Let's call this the "A" sensor. I  have just wedged it between the Aa winding of the first phase.

You must place the B sensor in a slot that is °elec ahead of sensor A. This may or may not actually end up in the middle of a slot, and it is an iterative process. Each slot is 210 electrical degrees, so start adding. Begin at 0 degrees, the position of sensor A. Keep track of the number of times you add, wrapping around 360 degrees for each result, until the result is equal to 120.

That is:

1) 0 + 210 = 210. No need to modulo 360. The number of additions is 1.

2) 210 + 210 = 420. Subtract 360. The result is 60. The number of additions is 2.

3) 60 + 210 = 270. No need to modulo 360. The number of additions is 3.

4) 270 + 210 = 480. Subtract 360. The result is 120. The number of additions is 4. You win.

Thus, sensor B should be 4 slots away from sensor A, and sensor C a further 4 slots away.

Conveniently enough, in a LRK motor, a 120 degree hall sensor placement actually results in the sensors being physically 120 degrees apart. Isn't that awesome? 

� Sensors complicate the wiring issue because you need at least five more wires: Logic power, ground, and the three outputs A, B, and C.

However, I believe that sensored motors (or the wacky inductive sensorless jiggymabob) are the best for small EVs. And EVs in general. They allow you to take full advantage of the massive torque capabilties of BLDC motors by using them at 0 speed!


DIY electric vehicles are fun and exciting, as well as a treasure trove of learning opportunities. Engineering your own motor is no small feat, especially one destined to be operated in a vehicle of your own design.

Here's hoping that future regulations over the nascent electric vehicle industry and laws over their operation grant amnesty to, or even encourage, DIY mechanics, hobbyists, and experimenters.

The virtually rendered motor seen in the opening page is a motor for my next crazy EV project: Deathblades. I'm aiming to do what alot of people have been peer pressuring me to do, and drop RazEr's technology into some foot trolleys of certain head trauma. See my Youtube page for a snazzy animation of how the hub motor goes together. If you've been confused by my thousand-word explanation, this should help clear it up!

If you've never seen RazEr in action, check out its test video here.

I'll be updating, editing, and changing things around as I go, so if you see any glaring omissions or errors, absolutely point them out to me!

And good luck. See the next page for a list of resources!

<p>this is one of the absolute best instructables I've ever read : mainly because it is actually instructive !!</p><p>great work</p><p>for my part I'm interested in the topic because I'd like to make an electric skateboard with hub motors : options are cheap Chinese ones I'm afraid to waste money on, custom made ones that are quite expensive (250$ apiece+shipping) and now I think it might be worth going the DIY way if I can get my hands on an acceptable stator...</p><p>in fact I think the best would probably be to make 2 with lower power to make them easier to wind and especially to heat less...</p><p>thanks again for the inspiration</p>
<p>Hey there I just recently found this instructable and first I want to say, nice work! I did want to <br>point out that in step 2 Kv and Km are inversely proportional. I.E. Km has units <br>[V/(rad/s)] and Kv should be [(rad/s)/V], which means when you multiply <br>Kv by your battery voltage you get a rough estimate for top speed. What you calculated by substituting your equations is that the back-emf constant Ke is equal to the torque constant Kt, which is true. You refer to both of those as Km.</p>
<p>End-Turn also contributes to Torque. Anything that increases magnetic flux desity in the cores also increases the torque.<br></p>
<p>Hi</p><p>I wanna make an hub motor inside an longboard wheel.</p><p>How should I build it?</p>
<p>great write up, thank you!</p>
<p>great job</p><p>can i control this motor using arduino ? and if i can do that how could i do it ?</p>
<p>Hi, great job.</p><p>what if regenerative braking concept. in the sense do we get back emf in BLDC motor.</p><p>if yes what if you harness the power from it</p>
<p>I am not good in electricity, but you explain very well, thanks!</p>
<p>I learned something A=heat that's why ev are high voltage.</p>
<p>This looks so cool, but after I read the why not to build list it got a little stale. </p>
<p>how large a motor would I have to build to power a bike light consisting of approx 50 led lights?</p>
<p>Could you just clarify for me the &quot;AC&quot; part of this whole thing.</p><p>Does the controller simply emulate the commutator of a DC motor, energizing the coils in such a way as to create a rotating magnetic field or are you saying it also converts the supplied DC to a true alternating current which it distributes to the coils in such a way as to produce a rotating AC field?</p><p>Thanks</p><p>Doug</p>
hi. i'm from tunisia. good job man !. can you contact me on jakefouly@gmail.com i need some help. thank you
<p>hello guys. i am new member. hope to could find good things for better future for succeses. tx all</p>
<p>Issues with your formula:</p><p>You pick Mevey's 2.30 equation:</p><p><strong>T = 2 * N * B * Y * i * D/2</strong></p><p>Where N is the number of turns per pahse, and '2' is the number of active phases. Then you redefine N as the number of turns per tooth, and define m number of teeth per phase. So (previous definition of N) = (new definition of N) * m. The result equation:</p><p><strong>T = 2 * </strong><strong>m * </strong><strong>N * B * Y * i * D/2</strong></p><p>Not four but two!!!</p><p>Next, in Mevey's 2.30 equation D is the diameter of the coil centers. Not stator's outer diameter, but diameter of the coil centers which is obviously smaller than stator's outer diameter.</p><p>P.S. Thanks for the article anyway. It is really motivating!</p>
<p>the most in depth view about brushless motors awesome saving this page for future guidence cheers</p>
<p>Hi, </p><p>good math derivation, T = 4 * m * N * B0 * (t / (t + g)) * L * R * i, <br>but this is exactly the double the torque you calculate using what reported on <br>LRK Motor Analysis Worksheet<br><a href="http://www.femm.info/examples/lrk40/lrk-bldc.pdf" rel="nofollow">http://www.femm.info/examples/lrk40/lrk-bldc.pdf<br></a>T = 4 * (rr+rs)/(rs-rr) * Br * N * L * t * ( I - I0)</p><p>where this formula is calculated taking into account that just two phase current are active on a trapezioidal drive, and that the current to be used should be just the active current (total current less free running current).</p><p>Which formula is the correct one???</p>
Torque should definitely depend on current. So, it should be T = 4 * m * N * B0 * (t / t + g) * L * R * i instead of T = 4 * m * N * B0 * (t / t + g) * L * R
<p>Or better, using correct parenthesis position:<br>T = 4 * m * N * B0 * (t / (t + g)) * L * R * i<br>but furthermore:<br>- for &quot;i&quot; you have use the useful portion of total current, i.e. &quot;i&quot; - free running i zero (taking into account the eddy current and friction losses);<br>- for &quot;R&quot; you have to intend the medium radius between stator and rotor (where the magnetic force act) which is in the middle of (t+g)=magnet thickness + air gap zone.</p>
Hi mate I'm making a hub motor for a skateboard, 100kv 15turns in wye dlark with 6 strands 0.34mm wire (this is all I can fit)<br>80mm diameter wheel, 50mm diameter motor, 40.7mm x30mm stator 12t 14p, with 40SH magnets 30x7x3, air gap between 0.5-0.7 depending on tolorance.<br>Will be using 29v batterys 8ah 30c.<br><br>I want to get up a hill of about 10-15% grade at about 20km/h<br>70-90kg. How much power do I need, is my wire cross section ok?<br>Iv been struggling with the math, and worried about the new winding not having the current capabilities I need, but it's hard to fit the copper inside of the stator, but maybe I'm just not good at it!<br>I'm also using hall sensors or optical sensors soon to get better start up as I seem to get a lot of cogging! From even a small push!<br><br>Each skateboard is using 2 motors on the rear.<br><br>I really need help!<br>My email is jacob.bloy(at)gmail.com<br><br>My build page.<br>http://endless-sphere.com/forums/viewtopic.php?f=31&amp;t=65636&amp;sid=32c74875705d1d55d0801eeae1381c11
<p>So I have a question about the equation to measure the theoretical torque. T = 4 * N * B * L * R * i in my case would be 10 turns per phase, 52 for the neodymium magnet and assuming you measure things using the imperial system the length of the stator would be 19.8 inches and the stator radius 3 inches. Putting through 42 amps would theoretically give me 5189184.0 torque. Now this can't be accurate because at 1500 RPM that would give me 1.4821e+6 horse-powers just to put things into perspective, which is a insane amount of horsepower.<br>t = 4 * 10 * 52 * 19.8 * 3 * 42 - Where did I go wrong in the equation?</p>
<p>If we rewire series connection of coils to parallel i.a.w. <a href="http://www.thebackshed.com/windmill/FPRewire.asp" rel="nofollow">http://www.thebackshed.com/windmill/FPRewire.asp</a> without changing position of hall sensors, does it influence on steering algorithm? How to include this wiring difference in one equation(e.g. torque equation)?</p>
<p>Excellent instructable! Thanks for taking the time to document and share your work. I need clarification on (at least) one topic. In the section discussing Magnet Length the author states:</p><p>&quot;Optimally, the magnet length is equal to the stator length (<em>L</em>).&quot;</p><p>In the same section, magnet width is mentioned. Would someone clarify for me the magnet dimensions that should be used for a given stator? Specifically, what is the stator length (L)? A diagram would be especially useful.</p><p>Thank you.</p>
<p>Jah mahn, danke mahn, huge, this is monster info bro.</p><p>Thanks you!</p>
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<p>You mention that you used 2 x 22AWG wires instead of 1 x 18AWG wire because it was hard to wrap and bend for 25turns. You said &quot;Use the wire gauge table to compare diameters!&quot;, now 22 AWG wire is 0.644mm in diameter and 18AWG wire is 1.024mm in diameter. So 2 x 0.644mm is 1.288mm and thats well over the diameter of the 18AWG wire. Now 24AWG wire is 0.511mm in diameter, and 2 x 0.511mm is 1.022mm which is a lot closer to 18AWG. I don't want to be annoying i'm just confused. If we compare the surface areas though 18AWG wire is 0.823mm^2 and the closest pair that would measure similar is a pair of 21AWG wires, at 0.411mm^2 x 2 = 0.822mm^2, BUT neither of those are the wire you said you were using. Should the diameter of the multiple strands not add up to close to the diameter of the single wire? Thanks for any help, just confused.</p>
<p>Hi, I thought I'd jump in here and clarify a few things for you: When doing anything with electrical wire, especially when said wire is going to be carrying a significant percentage of its maximum safe current, you should be aware that the determining factor in current capacity is the cross-sectional area of the conductor, not the outside diameter. Since the area increases faster than the diameter or circumference, a wire of half the diameter will have one fourth the cross-section and thus one fourth the current capacity. A wire 1.024mm in diameter has a section of 0.82 mm^2, where a wire of 0.511mm diameter has a section of only 0.20mm^2. A 0.644mm wire has a section of 0.32, which means a pair are up to 0.64, close to the original 0.82. If I were doing this, I'd use three strands of 22, for a section of 0.96, better than the 18 gauge.</p><p>TL;DR don't go by diameter, go by cross section. They don't equate directly.</p>
<p>Thanks for the formulas to make my motor, but your math was off by .01 on 3.66/(4*4*10.9*0.03 *0.035)=19.98.</p><p>it is really 19.99 (19.986)</p>
<br> I really love your <br> write-ups guys continue the good work. <br><p>http://www.zapelectricianbrisbane.com.au/</p>
<p>Being one of the last electrical and electronic engineering graduates from my school, before they dropped the &quot;electrical&quot; part, electric machines have always been a favourite subject of mine. This 'ible is one of the best I've ever read. Excellent work. </p><p>Incidentally, you can get tyres made by the guys who can retread forklift truck wheels. They vulcanise the tyre onto your own hub. </p>
<p>Being one of the last electrical and electronic engineering graduates from my school, before they dropped the &quot;electrical&quot; part, electric machines have always been a favourite subject of mine. This 'ible is one of the best I've ever read. Excellent work. </p>
<p>Oh my, that's a lot of work and thanks for putting it all up here.</p><p>I was looking for a motor I could pass my leg though instead of using a ring gear and a small motor to rotate it off to one side. The open motors would be used to rotate segments of a leg roughly depicted here: </p><p><a href="http://youtu.be/RV9fvg3C_fo" rel="nofollow">http://youtu.be/RV9fvg3C_fo</a></p><p>I'm still working out how many segments and at what angle and speed each segment should rotate at for the maximum comfort of the rider while still providing a good, natural leg motion. Seems making the motor would be beyond my capabilities and I'll have to settle on the ring gear driving by a motor or the like.</p>
very interesting very ( ty iv bine tring to find info on moters like this )( o and I Quote &quot; Their large outrunner motors are inexpensive enough to consider cannibalizing for stators. &quot; <br>well LOL!!! ) thank you for this it was very help full. :)
Can the stator core be plastic? Does it need to still be magnetic at all? I dont' understand why you wouldn't build it out of something completely non-magnetic
No not plastic. The material has to have a high permeability to concentrate the magnetic fields and at the same time reduce Eddy Currents.
I wonder if a motorcycle stator from the magneto would make a nice stator for a brushless motor? Used they are not too expensive.
Is it possible to melt down many cores in a foundry and then cast my own core? The core I need is huge and would cost a lot of money to have it machined and cast by a specialized group. Especially when I will need at least 3.
Stators are not cast. If you look at one, you'd notice they are many thin and fine layers. Each of those actually are insulated from each other. <br><br>A cast stator would basically be a big magnetic brake and would be extremely inefficient and heat up quickly due to eddy currents. I think you should look into motorcycle alternators and washing machines for large-ish (5&quot; - 6&quot; - 12&quot;) stators.
Where can we buy one of these motors (not the wheel) as a kit to put together and learn? It's easy to get the wire, but not the pieces the wires get wrapped around :-(
it looks to me that the torque should be proportional to the square of the radius. At constant magnet induction and current density the force per unit circumference length would be constant so the torque would be proportional to the radius and the length of the circumference, in turn proportional to the radius , hence the radius square.
Im an electrician, and house wiring is done in 14, 12 and 10 gauges mostly. Winding a motor in 18 gauge must be a chore! But im sure chris farley would say, &quot; It builds dexterity!&quot;
That's a lot to read but I read it anyway I can't make one of these. Because I don't have the tools nor the supplys to build it but awesome job
very nice and educative. learned a lot from this.
So there is probably something stupidly wrong with what I am about to write, but I am tired and can not get this idea out of my head, so on with it. <br> <br>What is to stop you from taking a standard dc motor, like the ones used in toy scooters, and reinforcing the !#$@% out of it, namely in the (casing? or is it a shell?) itself and the axel, welding a rim to the (reinforced) casing of the motor and using that as a hub motor with the motors axel acting like the axel of a bike wheel, with everything revolving around it? <br> <br>Would the motor just plain not have enough torque?, or is there some other blatantly obvious issue that I can't think of?
here is a mild example of your concept and a solotiuon using a standard dc brushed motor as an axle or pivot point. and having to add a gear reduction to it to get it to move. <br> <br>https://www.instructables.com/id/6-AXIS-ROBOTIC-ARM/ <br> <br>check it out. <br> <br>and vote for me <br>
You would not have enough torque, even on scooters with small diameter wheels the motor is usually geared down at least one to five, on a bike you will need a gearing of at least four times that! I hope this helps.
Sort of like this, or this.

About This Instructable




Bio: lol robots
More by teamtestbot:How to Build your Everything Really Really Fast Chibikart: Rapid-Prototyping a Subminiature Electric Go-Kart Using Digital Fabrication and Hobby Components The New and Improved Brushless Electric Scooter Power System Guide 
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