Heat sinks are different enough, yes. But are they necessary?
I’d love to see a small eBoard with 4wd with all small motors. It’s definitely doable, I’m not sure how much free time you have but I’d absolutely be willing to help design a small motor setup with you if you’d like!
Things to keep in mind:
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Small motors require a small stator, if you want a low kV you’ll need it to have as much copper as you can get in there and usually in this case that means you’ll be accomplishing that with fairly thin wire. Thin wire doesn’t handle high voltage super well so I think your idea of using 6S could definitely work, but I think 8S would end up running them a bit cooler because you don’t need to throw as much current at the motor as you would need to with a 6S setup to achieve the same performance.
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The longboard axle is already 8mm, so fitting a stator over that and still accommodating room for the mounting screw will take up a lot of room so you’re going to likely need to make the motor fairly wide to make up for what it’s lacking in diameter. I don’t think it would be too ridiculous though with 4WD because the load is so well distributed. This could potentially be solved by using a permanent mounting solution or making a hard modification to the trucks for mounting with less space needed.
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This 4WD setup will likely more of a cruiser/light commuter setup and not a hill climbing monster.
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To meet the minimum order quantity of custom motors this size will cost somewhere between $2-5k depending on the manufacturer and material selection.
On a side note to chime in on the whole voltage vs current affecting brushless motors it boils down to kV * voltage=max rpm. The motor will run most efficiently near it’s top rpm, unfortunately this means at the lower end of it’s RPM range it’s efficiency is pretty low and that turns into heat. The reason why increasing your voltage allows you to run motors cooler is that you can achieve higher rpm using the same current. This is great because you can run motors at a higher voltage and actually decrease the necessary current to have the same performance you would have if you were running lower voltage and higher current. I used to spec out by eBoard to around 70A when I ran 6S(belt driven), and over time found like many others here that increasing my voltage gave me better startup torque and top speed and I could now spec my eBoard to 40A.
The heat generated from running at higher currents in hub motors is particularly noticeable because there is no gearing(generally) so the motor that usually runs happily at 6S at say 1000rpm is now only running at half or a third the speed it usually would run at in a belt driven setup. So as you accelerate from a stop on a hub motor you are spending significantly more time in the motors “inefficient” low rpm range, because at any given time on a belt system the motor is running 2-3x faster than on a hub so it gets up to it “happy” rpm much quicker. This is aside from the fact that the gearing in a belt system also minimizes the necessary current to get the motor spinning but is also a factor. edit: in addition this effect is another reason why unsensored belt driven systems tend to have pretty great braking, when the motor is running at a pretty high rpm even when you’re going slow the regen braking is more powerful, you run into an issue with unsensored hub motors that when you are coasting at a low speed and want to brake the motor is essentially reading a zero state with the ESC and can no longer be regen’d, this is why sensors in hubs are really great, you can apply active braking effectively with the addition of sensors and come to a complete stop instead of only having brakes down to 5 or so mph.
Ive yet to see evidence of higher voltage systems keeping a motor cooler. someone here did just such a test and the higher voltage system performed worse: at the same speed a higher voltage set-up is further from the no-load speed when at the same speed as the lower voltage system, as you describe as being inefficient.
i can brake down to 2mph without sensors
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Higher voltage isn’t always the answer, the best solution is one suited for the particular motor set up. With small motors they tend to not be able to handle higher voltage of 10-12s but also can’t handle a lot of current so there’s a sweet spot of 6-8S. I forget what the exact size of your motors are but I’d imagine 8-10S is probably ideal. This is where kV is pretty important. The higher your voltage goes the lower your kV needs to be so that the motor doesn’t heat up too fast as it’s accelerating and taking in massive amounts of power. The main problem you run into when you increase voltage is that heat can build up heat very quickly if the motor can’t keep up with the power your putting in. Because Watts = volts x amps, say you are running 40V at 40A = 1600 watts but you then compare that to a system that’s 24V at 40A = 960 watts. While technically there is more power available in the higher voltage setup that 1600W means there is a lot more heat that can be generated if the motor isn’t running efficiently because watts in the system essentially dictates how much heat can be generated in the system. So if your motor is struggling a bit at startup running the 24V setup at 40A might give it enough time to get spinning before it overheats, 640W less of power makes a huge difference when the bulk of the power is going into heat when you start unsensored. Personally I like 10S for hubs right now as with my setup i haven’t had any overheating issues, the 40V 40A figure was purely as an example figure.
The voltage a motor can take is only dictated by the magnet wire enamel and the rpm limit of the bearings
Energy in a battery isn’t necessarily power in a motor
I read that higher voltage wont increase anything necessarily other than the no-load speed. You can burn up your stuff just as quickly on 2s system. Voltage is the force pushing the amps but u can get just as many amps to the motor and just as much performance with any voltage
After lots of looking into this and coming at it assuming more volts equals more power… there is no reason to go to higher voltage unless u want more speed or to keep the esc cooler. Amps can get there just as fast. Just as fast acceleration possible with low voltage. More volts is more energy in practice.
The magnet wire enamel is insulating the wire from whatever voltage it’s rated for but if the magnet wire is heating up quickly this directly affects the efficiency of the whole motor so wire gauge can be really important, while thicker gauge wire technically has a lower resistance than thin gauge wire, there is something called the skin effect which says that the electricity primarily flows on the outside or “skin” of the wire so the inside of the thick wire isn’t really doing much. So to a point thin wires actually increase your surface area because you can fit more turns in and pack the stator much tighter.
My thoughts on the whole higher voltage vs higher current is that it all depends on how you’re planning to use the board and what ESC motor and batteries you can get your hands on. Voltage is really just one small part of the whole problem and having a properly setup system is really the goal instead of aiming for a set voltage or current. I agree that if your system is running well at a lower voltage and you’re not having any heat problems and you’re content with the top speed then you have a great setup for yourself and no need to change that. My points above mainly pertain to increasing the voltage as a means of fixing some part of the system that you’re not happy with, usually that is top speed for a lot of folks. This is all aside from the limits of the ESC and how higher voltage can cause significantly higher heat in the esc if not spec’d appropriately.
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Skin effect isn’t relevant at these frequencies.
From what I read heat in the esc, at least the vesc, and probably all of them, goes down with voltage not up
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So this is starting to reach the limit of my understanding of motor control but the Miller Effect increases the input capacitance in the gate driver(DRV8302) as the voltage goes up, so even though the current can remain basically the same to flip the gate there is a small increase in the current coming from the driver that when left constantly running like in an eBoard ends up turning into increased heat in the driver. Unfortunately I’m not an expert(not even close) in embedded systems or in circuit design so my knowledge on this is minimal. I think Vedder could probably give a much better answer to the question of increased heat due to higher voltage in the VESC but from what I’ve read the miller effect seems to be the main cause.
edit: I believe in the Vesc 6.0 vedder switched to the DRV8301(mainly due to the 8302 being phased out), and I think he separated the gate driver to be switching the mosfets indirectly so less power should run through it and make the DRV not so prone to failure.
from what I remember vedder said the higher the voltage the cooler the vesc will run. until you get too high of course and then SNAP!
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All these side tracks are fun but small wheel hub motors is the topic. I really am excited to get one done long! Same diameter. Yes!!! A single. Only need one and one vesc. A roller that goes on 10mm axle! I’m on it if u guys want it. I’ll get it done and charge u all cost plus very small cost for time. include motor (singular😀) and 2 tires that are made of epdm high heat rubber.
If ur into it.
I am.
I like the idea of the single sticking out the side asymmetrical. Fuck symmetry. Cheaper. Simpler. I can imagine not a single reason not to…other than maybe even a 10mm axle would bend or the glue won’t hold. Can easily be tested!! What’s the strongest way to connect.
I’ve always wanted the simplest cheapest thing. Maybe I’ll change my mind but I really like this idea now. Not (2) 4725 stators, but single 4760 or maybe even 4777. Hehe. Hoho.
Chhheeeeeeeep!! est build possible.
Do someone know what the number of teeth of a stator does to a motor specs? Is more teeth car bring more torque with same number of turns? What about heat?
I think if I remember it correctly more teeth will allow a smoother very slow movement but u can still only get a certain amount of copper and iron into the same volume regardless if u do a standard 12 tooth vs something else so similar power performance in that regard. I think the 12x14 that is pretty standard is one of the best combos for power but if u do a multiple of that, say 24x28 it’s the same power possible. 12x 14 is not the most efficient but most powerful. Power is what we all want…to be efficient.
What do u guys think of the motor I’m going to get prototypes made of? I’m still calling it a small wheel. Small and long. If any of u are interested in getting prototypes of it I’ll get them for u at cost. Get the price in a day or two. The redundancy of needing two hub motors if they’re small is silly. 2x as wide 3x the power and run one motor and esc.
I would take 2 motors if you make them.
Do you know maybe what stator size sk3 6374 is? would like immagine a comparisation with mine. I hate the tube sticking out on mine^^ but helps cooling and diy options are limited sometimes.
Thats the bell not the stator actually the bell is 59mm diameter even if the motors are named 63xx
I’m not sure if sk3 does it the same as most but that should have a 74mm long. But if I remember right it isn’t. Can u measure. It’d be interesting to know how u do with a single. It might be comprable. Maybe some math with ur bigger diameter wheel and bigger motor matching up with my smaller diameter wheel and smaller diameter motor at 47 instead of your 53
“6374” motor probably has ~5045 stator (-it is 86mm long overall)". And they’re 60mm overall as said so the actual stator…I think it’s almost always a cm less so a 50mm stator diameter
So I read
Rather have more motor than fan
I can measure them the next days, have them in my workshop.
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To custom motors makers, do you know good magnets suppliers?
Also how do you fix them to the rotor, glue?