DTC - https://en.wikipedia.org/wiki/Direct_torque_control
FOC - https://en.wikipedia.org/wiki/Vector_control_(motor)
FOC is a subdomain of DTC. In Industry if you drive motor with square wave (lot of loss and noisy) you call it DTC, if you drive motor with nicely modulated voltage wave (that mostly looks like a sine) you call it FOC.
I don’t think that would happen. It’s too late since we are so used to it due to BLDC tool, I mean just look at what we get to choose from BLDC of FOC…there is no “DTC” option. Your attempt at correction is like how people say bullet instead of ammo or clip instead of magazine. I get it.
Maybe we can update bldc tool to have a proper naming ? maybe people will follow ?
there you go 
Sorted.
(well, not quite … vedder has to merge it, but it’s a different story)
Any option for good torque on the 107mm but will still get up to 35mph plus?
I feel like it’s always going to be a trade off. FYI I’m used to dual 6374 belt drive on 107mm…
The XL Drives will give you 38.553705 MPH on 12S setup with 107 wheels … in theory. It mostly depends how good is you battery pack if voltage sags to only 3V when you drain 140 A (2x 70A fo max power) you can make it. If you use 3 parallel 18650 you can forget getting anywhere near that.
For anybody considering a torque of motor, it’s pretty simple:
This describes max torque motor can give: T (torque) = I max (max motor current) / Kv
This describes how much power motor gives. P (power) = I (amps) * V (voltage)
This desribes repation between power, torque and rpm: P (power) = T (torque) * RPM.
It’s common in the bussines to limit torque at the beginning because you could rip motor out of it’s mounts of damage prop shaft or differential … So at the begining you will see torque being limited to let’s say 800 N/m and then you will see it dropping of due to power limit (torque to rpm relation) - which is caused by battery limit most of the time (sometimes heat rejection of motor) https://qph.ec.quoracdn.net/main-qimg-97419c138fce4fa430e0f557be936df3 https://qph.ec.quoracdn.net/main-qimg-fd1a400759e06f006620d4d75789bd0b
So from what I’ve seen arround most of motors are pretty good, and vesc is pretty good as well but people cheap out on batteries and end up with power clamp from physical battery performance (or they set voltage limits for battery to low and damage battery resulting in 10 charge cycles to death or resulting in fire)
I asked Jerry and he told me they got it up to 35mphs and still had a little more to go and it was on 90mm wheels , and I believe weight is a factor
3.6V x 12 = 43.2V 43.2V x 85kV = 3672 RPM 3672 RPM x 107mm / 25.4mm/in * 3.14 = 48572in/min
48572in/min * 60 min/h / 63360 in/mile = 46mph
46mph under no load theoretical limit.
Where did you get 38mph limit from? 140A? You’re assuming that you need 6kW to reach 35mph? Where did you get that from?
To properly characterize the motor limits we would also need Io and internal resistance which we don’t have.
Probably his preference of nominal voltage. 36V would get you 38 mph.
Under what load you will have 3.6V per cell ? If you put skate on your desk and drive it without a load than maybe yes …
Check voltage curves under load for more or less the best high current cell on the market that people use for vaping.
(edit, forgot the link)
%2040A%202015/AWT%20IMR18650%203000mAh%20(Red)%2040A%202015-Capacity.png)
@PXSS tell me what cells you will use and how you will configure the pack and I will tell you what voltage you will get …
No, for calculating max power out of the pack for e-skate I take 3V for computing the speed - this is where you will get at 50% for most of packs that guys are using here.
I’m not going to make assumptions here like 4.2V, wind behind a driver, driving down the hill and out right lie to people, if they can get better result - great! if not I don’t want people to come back saying “ohh you said XYZ and it’s far slower”
AWT are shiity rebranded cells. If you want a reference cell, use Samsung 30Qs or Sony VTC6.
0.2A 15A and 30A per cell curves for AWT vs VTC6:
Henrik also started incorporating temperature limits in his testing later on. Which is why you see the VTC6 discharge cycle stopped early for 30A
Either way, 3.0V/cell seems reasonable, I personally use 2.5V/cell as that is the lowest voltage I allow on my systems. I just didn’t get what you meant the first time you said “battery pack if voltage sags to only 3V” and assumed it was a typo or something. I usually say 3V/cell or 36V battery voltage.
Still, you are assuming it takes 5kW to get to said speed. I’m not sure that assumption is correct. I do not have an alternative though as I’ve never been that fast.
I know how to use discharge cycle charts, thanks! 
To keep the conversation going, if I were to build a high speed board using Carvon SD XLs, I would use a 12S6P Samsung 30Q pack. They are about half the price of VTC6s and dont give up performance that much.
Henrik didn’t test 30Qs at 30A so you cant use his graphs. Closest performing cell is VTC6. Either way, they can both provide 30A with roughly 0.6-0.7V drop per cell. (I have tested both cells and have my own set of curves for them)
@PXSS How about I’ll take the tone down of the conversation - I’m sorry I did not see your “under no load”. AWT are better under temp, but yes they are rebrands. (I see you keep editing your post and it just see edits happening :X) Anyway, I would stick with the Henrik opinion that there are no true >20A 18650.
Anyway I see that you get it as well. Peace!
ps. rule of thumb is for aredynamics from our experience is: over 30mph aerodynamics are horrible and you spend 2x power per every 10mph. You can kneel down etc, but there is another problem - at high rpm in permament magnet machines magnetic flux eats heavily in your power - so most manufacturers cut off RPM when you start loosing 10% of power, vesc doesn’t seem to have that limit so will whack as much rpm as it can … so when motor peaks out you can loose a LOT of power.
pss. If you look up on you tube some of vaders videos - early implementation of vesc he had while at full speed was draining 50A and limit was set to 50A. With more recent developments stuff I’ve seen around has limits of 70A so here is my assumption of 140A in 2WD setup while at full blast.
@PXSS How about different angle, when I assume 140A max current I personally would be not comfortable with putting more than 20A per cell (connectors, welds, internal wiring of cell in my mind is just asking for it) - so setup would require 12s7p setup. That’s 84 cells. Given the lowest price I’ve seen around to those been 5£ people will shell out 420£ for a pack that can give 140A and has 21Ah … considering some good ordering channels but still buying in small quantity I can drop price to 2.8£ but that’s still small quantity (and I don’t see purpose of using good favours for that type of stuff) that’s still 235.2£
for 200£ I can get as many lipo’s as I want, get twice the Ah if not more … from your experience do you see any other reason to go for 18650 here rather than just inherent lack of safety of lipos ?
Yep, sorry about that. I’ll usually write something up in 5 minutes and keep editing it for completeness over the next 10 or so minutes while I think “Oh! I should have included this!”
Drag = 0.5 * rho * v^2 * cd * A cd = roughly 1.2-1.3 for a standing up human. A = frontal area of rider. rho = air density.
If I remember I’ll look it up in my aero book at home. I have a research paper in there on the drag force of humans, (clothed and naked…) from wind tunnel data.
That is based on the temperature of the machine isn’t it? That is where I don’t have much knowledge. Magnets are fucking black magic to me.
It does have a temp and power limit. I’m sure a foldback algorithm could be implemented as the temperature of the machine gets too high, since that by itself is an indication of a higher loss of efficiency, whether it comes from the magnets or the the ir of the coils.
Yep. I haven’t seen that. I think there are at the very least a few people here that go that fast with bluetooth connectors and logger apps. I’ll probably look around tonight if I can find recorded data on that.
Is that a single drive or dual drive? A dual drive would not consume twice the power as a single for the same power condition. In fact I would say it would be more efficient since you are splitting the load.
Can anyone recommend 10mm bearings for the XL ? The XL do require 10mm bearings right ? Can anyone confirm, i know what it says on Carvons site, just want to hear it from folks who know for sure.
I have built packs with VTC6 cells that draw up to 30A per cell continuously. We do have very good airflow to keep the cells under 60C.
I have a VTC6 pack in 6P config that I have tested in lab at 130A continuously with no airflow. I think we managed 5 minutes with cells at 65C at the end of the test with no airflow (just sitting on a bench / not insulated though). The cells are of course welded to .02in thick copper plates like the ones below with 8 AWG wire on them.
Check nkon.nl, they have the best prices in europe. I can personally get 30Q cells delivered to me for less $3.3 a cell. 72 cells at that price = $238. I’d definitely spend that much on a 18Ah pack.
I thought so too earlier today, but not quite… 4S 16Ah batteries run at about $230, 8Ah 4S runs at $99. The cheapest option I found was 5Ah 4S Lipo for 23.59. This is from Gens Ace, which is one of the few brands for Lipos that I trust. There might be cheaper options in hobbyking but I don’t know how many times we’ve received doa packs from there.
So if we go with the Gens Ace 5Ah 4S packs, we would need 15 for a 12S 20Ah pack or 12 for a 15Ah pack. That is $354 for 20Ah or $283 for 15Ah.
The only real reason why I personally stay away from LiPos is that I absolutely hate how bulky they are lol. That is my main gripe with them. Nothing else!
I understand their use for applications where more than 10-15C current draw is required, but anywhere else, I think Liions come out on top the downside being that you have to build your own pack or buy prebuilt for a stupid price tag. I dont think I have seen a decent pack with decent cells with less than a 50% markup.
