so my 4wd build is coming along slowly due to so delays getting parts, however i know someone in the uk that is getting some new flipsky 140kv BH 6384 and now i am tempted to go 16s with the lower kv (and bigger) motors but is that stupid?
just to put this in perspective im coming from a 6s single motor 240kv board lol
i havent built the battery yet so i could very easly reconfigure and do 16s but the problem is the charger and bms, i know llt have a 16s bms but i havent found any in the eu/uk yet and would really like to get the build don’t before the new year if possible. with the charger im not too worried i have a big 2000w “bench” power supply and i could just make a current limiting circuit to charge it for now until i can get a proper charger in.
so what do you guys think stick with the plan for 12s or just send the extra money now (its like 50ÂŁ more XD) and go for 16s
ps (i already have the uboxes so am ready to handle 16s)
I would ask others who have been using HV on the Ubox before doing anything. My memory fails me, but if you scroll around on the vendor thread I think you’ll see some results. Off the top of my head, I think people have been having good experiences with 14s, but I don’t recall too much about 16s builds.
TL;DR: Switching to a lower KV motor because you now have a high voltage ESC is not smart.
The point of going higher in voltage is to increase total power without increasing the current going through things. For example, you don’t have to upgrade to a beefy charging port to charge your battery fast, and you don’t need as thick battery wires or nickel connections in your battery. You can also drive motors faster, which increases their power, assuming you can gear it down to actually have more torque.
Usually, motor power is the limit heavy riders face here. Lower KV motors tend to heat up more easily, so are usually rated for less power than their higher KV counterparts. (Note: applies to the field of esk8, and only to an extent. For more info search the forum about copper and iron losses in motors) Why do people go with low KV motors then? Well, because they’re riding a mountainboard and their ESC is at their limits; they need more torque than speed!
Anyway, ideally, you always want to maximize your gear ratio, and run your motor as fast as possible, obviously within limits. And don’t spec your board way faster than you’ll ever ride, because then your ESC needs to work harder than it should.
So, in your case – you’re building a 4WD board, so most likely neither your motors nor ESCs will be overwhelmed. So do you need high voltage to squeeze more power out of them? Nope! So the only benefits you would get with going higher voltage is charging up and building your battery. And you definitely don’t need 140kv motors, because you probably won’t be maxing out your 170/190/idk what you have motors anyway.
ok sure, but while it don’t need more toque what’s the downside the cost difference is almost nothing vs the 170kv and since i have the vesc and can get the battery us there any real down side, if i use the same gearing i will have pretty much the same speed but with wayy more torque. the cost difference isnt going to be my concern its just the feasibility and if its a good idea. I get the downsides of lower kv being a thinner wire and longer so there are more losses but the 16s should make up for that
how would it make up for that? Less efficient motor will be less efficient. Unless you think 100A per motor won’t be enough (Ubox rated max), you have nothing to gain by going lower kv. (Well, less stress on the ESC I guess, but it’s hard for me to say which option is better)
But yeah, 16S will require a slightly more expensive BMS and charger, but otherwise no harm done, go for it if you want!
Has anyone tested the typical 190KV maytechs at 16S yet? UBOX will definitely do it, fully charged 16S is only 67 volts and its rated for 75, but are we burning up motors typically rated at 14S while doing this?
I’m planning on going 14S on my larger builds this year at some point but i’m not eager to start replacing motors on warranty claims every month or two.
Don’t know; personally I’m sticking with ~170kv on 16s because then the RPM is about the same as 12s on a 220kv motor, and Maytech do offer motors with that KV, so the bearings should be within spec.
Edit: for you 14s and 190kv also works out to be around the same
reminds me of that time when skateboard bearings were using ABEC ratings designed for motors and take no account of the forces present in skate wheels… oh wait…
I am assuming less amps for same power (speed if geared correctly? ) and thus less losses in the wires, nickel ect I could be wrong but that was my thought process
Is 170kv on 16s not way too high? Most gearing is around 1-3 / 1-5 kinda range and that puts you at 40ish top speed at the highest gearing on an mtb. Unless I am missing something?
You can go lower. My current board is at 1:6.2, and I’m actually thinking I set it too low with 190kv and 12s. At 170kv on 16S with drivetrain losses of pneumatics, you’re only looking at a top loaded speed of around 26mph on that gearing.
I read up a bit to refresh my memory since yesterday, and although what I said still holds, I might have been too harsh on your desire to switch to a lower KV motor. So:
An important fact to remember is that differently winded motors (different KV) will still have the same “torque per heat loss”. So even though your lower KV motor will require less amps for the same torque, it will still get just as hot. That’s why gearing is so important – the higher the gear reduction, the less torque your motor needs to produce
So, by switching to a lower KV motor with the same gearing, nothing changes in regards to motor performance. But what does change is the current your ESC needs to drive the motor at – a lower KV motor will be easier for your ESC to drive (less phase amps). So potentially you get a cooler ESC. But what won’t change, is the battery current your ESC draws in either scenario, because low amps X high volts or high amps X low volts will still be the same power requirement. So no, motor choice won’t impact the amount of current your battery’s nickel strips see
Yup, that is quite fast. So if you are going 16s, then the lower KV motor makes sense to keep your ESC cooler. But! Remember, that at 12s the 170kv motor would have been just fine, so at 16s the 170kv motor is also just as fine on your ESC. So you don’t have to switch to the lower kv motor, it’s just if you really want maximum efficiency (Personally I would do it if it’s just a few bucks more)
For completeness skate, in case anyone was wondering how
and
can be true at the same time – If both motors are producing the same amount of heat (same torque load at the motor) at a constant voltage, the higher KV motor is still spinning faster, so it’s creating more mechanical power. If you can gear it down to match the speed of the lower KV motor, then you’ll have more torque at the wheel!
The future appears to be high kv motors, high voltage and huge reduction dual stage drives. For now the smart move is to run high kv motors with high voltage and use a watt limit to restrict yourself from going too fast. This gives you the benefits of extra power at your finger tips (P = I X V), reduces stresses on components due to the lower duty cycles being ran (for the equivalent power output at 12S) as long as the motor and ESC can run at the increased E/RPM. I personally think 170kv and 16S will make a really nice combo for eMTB and I am building a mountainboard with these exact specs myself and aim to test this at 100 phase A on a pair of alien motors
edit - ill be running this on a 5:1 reduction for now, to clarify
Less efficient motor will be less efficient. Unless you think 100A per motor won’t be enough (Ubox rated max), you have nothing to gain by going lower kv. (Well, less stress on the ESC I guess, but it’s hard for me to say which option is better)
