There hasn’t been a thread dedicated for discussing this so I thought I’d start one despite being a total motor theory noob.
What we want is a direct drive motor for ~6" AT size wheels.
Pros:
easy setup compared to belts/gears
easier to clean out mud compared to belts
no belt snapping
light weight compared to belts/gears
Easy to swap wheels compared to belts/gears
more clearance for motors cans compared to 100-120mm urethane wheels
???
Cons:
Can’t easily change gear ratios like belts/gears unless you have different sized wheels
less peak power than dual 6574 motors (to be discussed further down)
More stress on the motors? (Depends on the design)
less clearance for true off-roading. (tree roots, mud, rocks, etc)
???
Currently in the market, we have:
58kv elofty direct drives. But 58kv is slightly too high to be optimal with a 6" wheel. link
75/90kv torqueboards direct drives. Although more powerful motors, the kv is also too high. link
Hub motor AT such as backfire ranger x2. But its fairly weak (~500w-1000w per motor?) link
Design ideas:
A 6" wheel gives more clearance, so we can use a low KV 8080/10080 motor similar style to the elofty drives. But It’ll be more difficult to swap back to 100-120mm PU wheels
A more powerful backfire style motor from scratch. (I don’t even know where to begin in terms of motor design from scratch)
re-utilizing a bike/scooter hub motor and design a custom hub that bolts into the hub motor mounts. But most of these are pretty big and heavy for 250w-500w of power. like this.or this pre-existing design kinda.or this. We would also need to make a custom truck to attach these motors onto. (But all the options need custom trucks made)
And I don’t understand how ebike hub motors are so big and heavy, yet have pretty low power ratings (~500w) compared to our typical 6374 motors ~3000w?
Just got into escooter and ordered one from China to keep the frame and change electronics. It’s true that the hub you see used there or in ebike are low rated. The reason to me is simple because they use all the same bldc controller rated for low current. It’s the optimal power to run the motor over time and cooler. They are not looking for performance but to give a nice riding experience and avoid customers to send an email one month after claiming another motor.
Same reason why the classic 350watt mptr from meepo I used at 60A at 12s. Watt is just related to volt and Amp. Once I got the scooter I will put a new controller. Hope from @shaman or @jeffwuneo ESC to get to at least 14s and push the Amp into the motors. Mine are dual rated at 1000watt each. They are big. Pretty sure you can push much more out of them.
For DD for AT application, the best would be to use planetary hub motor (geared) so that you can use decent Kv (easy for internal resistance) and get the ratio to gain torque. Are already use in electric MTB or some scooter too.
Simply because it’s all marketing bullshit, first, motors are rated for torque, not power, or saying better, should be
Most electric motors are heat limited, and heat losses on our small motors are almost perfectly proportional to torque
But if we are talking about power, and running at 10S, our motor couldn’t do 300 W continuous, and most ebike motors are rated somewhat more realistic, not because they are honest, but because of legal limits, even if it can handle more they print 500 W or 250 W on it so it can be used everywhere legally
For direct drives the only solution is a bigger motor, lowering Kv doesn’t matter
One big advantage of electric motors is that they are really scalable, and the torque they can produce is proportional to diameter squared and length
So let’s say you have a board with 8” tires, geared and running 6355 motors, if you want the same performance, with the same efficiency and consequently no overheating motors, you would need a motor size around 120100
If you guys want I can share the math behind this result
What surprises me is that we don’t make use of any forced air cooling that is attached to the shaft and powered by the shaft? It’s used my many larger DC motors such as those in electric vehicles, and its totally possible to get 40mm fans. I don’t see any issues with implementing such a thing, albeit on a smaller scale
At the speeds we run we already have plenty of air flowing in the motor, specially on the more open designs
And for hub and DD motors it makes no sense to cool the outer shell when the biggest thermal resistance is the air gap, the steel laminations and the thin aluminum cross section that is in the center, that’s why I say Statorade is the answer, but again, if you are heating up a lot, it’s means you are running it very inefficient, for example, take a Raptor 2 and put Statorade, it may help on the cooling department, but it wouldn’t make a big difference in the ridiculously consumption, just a bit due to lower windings temperature means lower resistance
Well the idea of the thread was to make a new drive and wanted to look like hub or DD. Gear drives are fine but I wouldn’t call it elegant. Between the outrunner motor and the gear they take out a lot of space. They work out nice but give limitation as well. Based on trucks and decks you will need to mount them with motor facing inside or outside.
I am making a new gear drive now and found all these limitation to the design, that’s why I am saying it.
If you go to bike or scooter applications then geared drive are not elegant at all. This just to say that there is a lot of room for improvements.
For instance some geared hub have the ability to disengaged the gear portion at a certain speed. That will allow to reduce the ration towards a 1:1 configuration and get higher top speed. So same motor great torque and automatic gear changing for top speed.
So I am stalking your discussion because I have 2 builds but i want the result of what comes from what you guys are talking about.
My 2 builds are Carvon XL’s with the Janux quattro wheels 4.5in hubs 6.5in wheels.
The challange I find is when I hit hills the board doesn’t have the power to just keep motoring up without hesitation.
When I stop at a light i still push so that it isnt under high torque demand at start.
My question is some of you who have the history with Carvon do you know the Kv of the Xl?
How would these compare to the elofty 58?
Or a lower TB DD ? Like the TB 60kv DD that out there.
When thinking on the system as a whole, the Kv should be as high a needed to achieve the top speed you want at the voltage you are using, more than that you will need to increase the motor current to keep the same torque, and that increase the loses on the esc and wiring
But from the motor perspective it doesn’t matter. That is why Kv is not a measure of motor performance
What is a measurement of performance is motor constant, Km, it represents how much loses happen for a given torque produced, and it’s completely independent of the Kv, how the motor is wound doesn’t change it, be it a lot of turns with a thin wire for a low Kv or few turns with thick for a high Kv, but again no one publish it because it would make a lot of motors look bad, and to be honest I doubt that any manufacturer has it calculated, but if we know Kv and phase resistance it’s pretty easy to find it
The best we can do is compare winding resistance. For two motors of the same size and same Kv, the one with lower resistance will always be better because that means it has a higher Km
but if you use a low kv, that means you need to use lower current to achieve top speed. wouldn’t that mean a cooler motor/more efficient motor because of the less amps used?
