@FullMetal_Machinist you do realise that by building this enertion can no longer call there board the most “powerful direct drive skateboard”
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Yea… for starters my battery alone is more expensive than their entire board Top speed 49 kph… i can go faster on level road on inline skates…
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Sick build man!
ESC is now tested at reduced voltage, servo motor was used as i have not completed hub motors. One small mistake was found as one via did not connect to ground plane, fixed with 0,5mm drop of solder. Value of few resistors was adjusted. It runs in sensored mode in bldc and foc without problems. I did not have motor with high enough KV to go above 30k erpm for now. For sensorless i can say for certain that it wont run with a very small unloaded motor, as noise in current sense is now at 0,4 A (about 5-6 ADC steps). If big enough motor is used, it should run sensorless as well, to be tested.
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Nice job getting the controller working. Sounds like you really need those hub motors finished to properly test it. Hows the progress on the motors?
Way back in your earlier posts you were talking about how this machine is going to be capable of breaking traction on all 4 wheels with go-Kart slicks for tires. I’m thinking you’d be more likely to do wheel stands instead. How low does your center of gravity need to be to not do a wheel stand?
I am glueing magnets to rotor right now. Brought home from work two spools of magnet wire 0,15 and 0,2mm diameter and will be doing winding with 450-something stranded Litz wire made from those those on friday/saturday. Friend of mine lets me borrow very fast 4-ch digital oscilloscope for a week. Hope to have it fully tested and adjusted in a week or two. When i am certain voltage spikes are within reasonable values i will switch to 20S, as main battery is ready. As for center of gravity it needs to stay below line easliest described as 60% incline starting at contact point of back wheels, what translates to 60 cm high over front wheels. In my opinion 100% doable. However keeping stable position at 1,6G of acceleration is something that has to be learned by experience. For now tales of the future. Looked over https://www.electric-skateboard.builders/t/indoor-esk8-event-nl-5feb/80847 and figured that some practice on karting track would be good, luckily in Warsaw several karting tracks are present. Hopefully some of them will let me in during empty hours. It really looks like a good blast. Back to glueing magnets.
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That will make for easy winding using such fine magnet wire. But do you think that the performance of your motors might suffer from doing it this way? What I mean is that using 450 strands of fine wire, you pay the price of the enamel insulation thickness 450 times. Whereas if you use less strands of larger diameter wire, you have less insulation cross sectional area ‘waste’, leaving more cross section area for copper. I would have thought that optimising your motors for lower phase resistance would be more beneficial than optimising to lower skin effect? Of course you will have considered this already, what are your thoughts?
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With thinner wire fill rate is much better, so net amount of copper is greater. With thick wire it is hard to compact winding inside the triangular slot. Also depends on which wires you use - if single insulated to 500 volts are used it is better, however if double-indulated to 1000volts were used then insulation would have consumed too much space without giving any benefit. Especially for ESC with very fast switching times it is good to use litz wires, wew dozen watts at full power can be saved compared to same awg but single thick wire. On idle or small load difference is so small it is hard to measure.
On the material choice, silver was looked at, it’s expensive but swissboards are going to use it
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Not a choice for me as i would have to use at least 8 strands of that in pararel, winding length per phase is about 4 feet, so i would need total of 96 feet per motor, which means $1800 per motor in winding wire alone. And i am not certain everything is ok at the moment so i will pass. If everything is tested at full capacity and i happen to grab a spool of silver wire then why not? Winding alone weighs about 10oz per motor, at silver scrap price it would be $160 per motor.
https://www.hopea.eu/drut-srebrny-ag999/druty-srebrne-ag999-okr/srednica-0-40mm-miekki-drut-okragly-ag-999.html I could buy silver wire here at close to market price but insulating it myself would be an issue. Proper enamel is not easy to make. For total of 1,5 kg needed (silver weighs more than copper) i would have to pay about 1000$. Might look into it when everythin else is done.
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Ouch, understandably avoidable
Every motor rewinding I’ve ever read about has shown an improvement with thicker wire as apposed to thin mutistrand with a reduction in electrical resistance and likely better cooling ability.
From what I read the skin effect, which litz wire is designed for, occurs at higher frequencies than we use. https://www.rcgroups.com/forums/showthread.php?2318019-Skin-effect-within-the-windings-of-a-BLDC-motor
I’ll be surprised if they use solid silver wire in their motors. Crazy expensive and rare. Ive seen silver coated wire which is touted as better because of…skin effect. But in motors that didn’t get to a frequency it would occur
I though the motor’s pwm current would be largely smoothened by the inductance anyway and there isn’t an ac frequency in the motor
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Today i have tested how much coppper i can fit using different wires. Using only 0,2mm 520 wires can be fit, which is over 16mm2. With mixed 0,15 and 0,20 360 pairs can be fit, which is 17,7 mm2. With 1,2mm wire only 12/13 can be fit reasonably, which is 13,6mm2 per slot. Nothing thicker than 1,2 is possible bencause this is the width of slot opening. Result is clear. This is result of slot geometry and length of the stator - the longer the harder it is to fill completely, at 40mm it is hardcore. Litz wires are easy to compact using a piece of wood or bakelite, then slot cover slides in to protect the winding from sticking out, exactly as big industrial motors are wound (done that myself). At single enamel there is not much difference in slot fill due to only wire diameter. Mixing two different diameters is what does the trick. Also look here: http://eprints.whiterose.ac.uk/9077/1/Zhu_Influence.pdf?origin=publication_detail It is proven that skin loss is greater than extra loss from longer strands in 10KW motor. In my case, with much faster switching and faster current rise it will be even more pronounced, as they tested at 10kHz and i will run at 40kHz.
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This is a point the I still didn’t understand perfectly
What switching frequency we have to take in account? In my minds is obviously that it’s not the MOSFETS switching frequency since the inductance of the motor smooths it out
Isn’t the electrical rotational frequency we should consider? Them what @Hummie said makes perfect sense, in a book I’m studying about BLDC motor design I remember the author saying the same but the wording was not clear enough to be sure
In this case running at 60k ERPM we would be just at 1 kHz and the skin effect would be much lower
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its not the speed that kills
…its the sudden stop
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Or in our case the board suddenly becoming stationary and we keep going
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Again fine, until we become stationary too
while this is a late reply and this is really an extremely dangerous battery, it will probably not kill you.
I know from experience unfortunatelly. I designed and built a 96S battery for a motorcycle. I was really careful but the fucking balance wires still managed to jolt me arm to arm at ~330VDC… like 5 times. It is not pleasant and you get some adrenaline, but you will live. Or I am a mutant of some sort.
edited because its late and i suck and the good people pointed it out
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What sort of ESCs exist that can handle voltage and current that high?
Some extremely expensive one that is custom made I suppose. Our company was just subcontracted for the battery with a bms and a case, so I have no clue 
Edit: sorry for slight thread hijack, wont happen more