Good value for money 10-15kW brushless

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NexusG

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Hello,

I'm looking for a reliable, light and affordable brushless motor for my future powered paraglider
The max power must be around 15kW, although 10kW should be ok
The KV must be around 50 in order to spin a 130cm propeller at 3000 rpm (the battery will be a 16S : 65V max)
After some research, I found 2 suitable motor :

- The MAD M40C30 KV50 IPE from Mad Components
https://mad-motor.com/product/mad-m40-kv50/
https://madcomponents.en.alibaba.com/product/60861053657-807649398/MAD_M40C30_50KV_79KGS_Electric_Heavy_Duty_DC_Motor_for_Paraglider.html

The rated power is 17700 watt and the weight is only 2700g, that's is impressive, not to say suspicious
They have also the "PRO" version which is even more powerful and light (19000W and 2300g !)
https://mad-motor.com/product/mad-torq-m40-c30-pro-kv43/
https://www.alibaba.com/product-detail/MAD-M40C30-PRO-50KV-Lift-70KGS_60826792307.html?spm=a2700.icbuShop.41413.65.5f753c7abpDHD7

The other one is the U15L 43KV from T-Motor :
http://store-en.tmotor.com/goods.php?id=896
https://fr.aliexpress.com/item/33057488010.html?spm=a2g0o.store_home.productList_46672189.pic_0
The power rating is 16kW and the weight 3600g

Unfortunately, I haven't been able to find any feedback for these motors so I don't know if there are good value. However, T-Motor is a reputable drone powertrain manufacturer

The RV-100E from Revolt (cheaper but what about quality ?) could be also a good one, from what I have read on this topic : https://endless-sphere.com/forums/viewtopic.php?f=30&t=94975

I'll be more than happy if someone can give me a feedback on these motors or give me a recommandation for an other suitable motor
 
-17 and 19kW are absolute peak power, not rated. It’s likely only possible for something like 60 or 120 seconds..

-To get 3000rpm with load you’d need more rpm without load. Furthermore: since torque drops with rpm you’d need even higher noload rpm to have some torque left at 3000rpm. M40C30 pro test report is done at 98V to solve this and recommended voltage is 22-24s.

-Power P=M*n/9.55 means that you need 47Nm torque@3000rpm for 15kW output.

-kV 50 means you’ll need at least 246A output to get this torque.

-According to the specs for M40C30 PRO 50KV it’s just about possible to reach the power you want in peaks. It will not be possible continuous and they don’t say for how long.

- It won’t be possible to achieve power goal with your planned 65V battery voltage and kV 50

What to do:
I’ve read that the RC crowd estimates about 3kW/kg motor as a rule of thumb for achievable propeller motor power, Following that you’d need at least a motor weight of 5kg to really get your 15kW.
Getting a light but powerful setup would also be easier with a faster motor but would affect propeller choice.

-Build a geared setup? It’s easy enough.

Skip the revolt motors. They don’t care about quality or customer service. I know since i’ve tried to get warranty for two faulty motors. They are not to be trusted with your money.
 
agree with lars above, particularly on revolt. I've heard the E range are better quality, but their QC and service is poor enoguh to not bother. My motor (100pro) was ok but others have had issues and poor support.

kv wise you'll want something in the 75-100kv range, to maintain that rpm through the voltage sag and SOC of your battery.... (3000/58/.8/.8) for rpm, SOC, sag, and torque drop off respectively. 0.8 is probably too high for things like voltage sag but its a ballpark figure.
 
larsb said:
Skip the revolt motors. They don’t care about quality or customer service. I know since i’ve tried to get warranty for two faulty motors. They are not to be trusted with your money.
Click to expand...

sn0wchyld said:
agree with lars above, particularly on revolt. I've heard the E range are better quality, but their QC and service is poor enoguh to not bother. My motor (100pro) was ok but others have had issues and poor support.
Click to expand...

That's such a shame... Their motor looked good on paper and they are considerably cheaper
In terms of cheap motors, I was looking at Alien Power System brushless. The 12090 would be perfect : https://alienpowersystem.com/shop/brushless-motors/120mm/12090-outrunner-brushless-motor-80kv-18000w/
But... I have seen several feedback pointing out the bad quality or/and customer service :?

For my application, I need at least 50kg thrust from the 51" propeller which means 2500rpm. The propeller must never spins over 3000rpm which is in fact the absolute max
I want to use 16S max battery for security and cost reasons. 20S+ good quality BMS and ESC are scarce and expensive
I also prefer to use a direct drive powertrain for simplicity sake

You're right, the speed under load will be lower but how much ? A 80KV motor will be probably better for my application, if I'm even able to find one
 
I’ve seen some tests where 12090 was a low performer. Really high rotor losses if i remember correctly.

Geared setup is not so complex and i think it’s probably worth it due to the propeller efficiency is higher for a large, slow propeller (high motor torque needed)

Something like an 8000 rpm setup and a 1:2 reduction would tick most boxes for you.
 
larsb said:
I’ve seen some tests where 12090 was a low performer. Really high rotor losses if i remember correctly.
Click to expand...

I suspected something like this. It's too bad again, because they offer a large choice of motors with different KV and power

larsb said:
Geared setup is not so complex and i think it’s probably worth it due propeller efficiency is higher for a large, slow propeller (high torque needed)

Something like a 8000 rpm setup and a 1:2 reduction would tick most boxes for you.
Click to expand...

I have already ordered the largest possible carbon fiber propeller (130cm) that suits in my frame, for efficiency sake
Mad Components has just told me that they produce a 80KV version of the M40C30, it will be available in January

I hope that it will be OK for my application, Mad Components is a very recent company : not so much review about them but at least their motors look good.

The (falsely) open-source OpenPPG project uses four custom wind 180KV Mad Components M10 motors with apparent success. Of course the efficiency is not great due to the small 22" props
https://openppg.com/

If I'll order this motor, I will make a benchtest and put here as much information as possible
However, I'm still listening for other good motors suggestions
 
If money is no problem here are top-end motors https://hacker-industrial-solutions.com/
for the q150 its arround 2000€ without tx :shock:
 
RE your 3000rpm limit - a good modern controller will allow you to set such a limit electronically... so you can safely use a motor that may well spin well over your desired max. main reason to not go too far over though is that a higher kv is inversely proportional to the torque per amp... ie doubling the kv will halve the torque per amp, necessitating a beefier controller (battery amps will be much the same however, all else being equal).

The usual rule of thumb for rpm of a loaded motor is ~80% of unloaded... but thats a very rough guide. prop loads are non linear with rpm... so 80% probably isn't a bad first guess but YMMV. I'm sure someone on the net has the answer though. Still, a good reason to have a no load speed at least 20% higher than your desired top speed, and also worth accounting for both battery SOC and sag as already mentioned.
 
bionicon said:
If money is no problem here are top-end motors https://hacker-industrial-solutions.com/
for the q150 its arround 2000€ without tx :shock:
Click to expand...

That's way too much. I know that some electric paramotor manufacters use European brushless motors such as Paracell, Geiger, etc... they are probably good but not cheap at all. 1000€ is my limit

sn0wchyld said:
RE your 3000rpm limit - a good modern controller will allow you to set such a limit electronically... so you can safely use a motor that may well spin well over your desired max.
Click to expand...

Yeah that's a good idea ! I will use a VESC 75/300 controller which includes RPM limit, battery amps limit, etc. It's very complete in terms of functionality and open-source. 300A will be more than enough for my application. However it's costly (600€)

sn0wchyld said:
The usual rule of thumb for rpm of a loaded motor is ~80% of unloaded... but thats a very rough guide. prop loads are non linear with rpm... so 80% probably isn't a bad first guess but YMMV. I'm sure someone on the net has the answer though. Still, a good reason to have a no load speed at least 20% higher than your desired top speed, and also worth accounting for both battery SOC and sag as already mentioned.
Click to expand...


So with a 50KV motor, 16S battery :
- Estimated RPM with fully charged battery : 4.2*16*0.8*50=2688 RPM (60kg thrust, that's good !)
- At nominal voltage : 3.7*16*0.8*50= 2368 RPM (47kg thrust, still ok :) )
- Depleted battery : 3.2*16*0.8*50= 2048 RPM (35kg thrust, weak but still flying straight or even slow climb)
In fact it does not seem so bad !
I don't know if the sag is included is this 0.8 factor. I can't calculate it because I don't know the internal resistance of my future battery. It will be a 16S16P Samsung 30Q Li-Ion cells DIY battery.

The other solution is a higher KV motor and RPM electronical limit but there must be some drawbacks :
sn0wchyld said:
main reason to not go too far over though is that a higher kv is inversely proportional to the torque per amp... ie doubling the kv will halve the torque per amp, necessitating a beefier controller (battery amps will be much the same however, all else being equal).
Click to expand...
I do not understand why a beefier controller is needed if I limit the RPM of the higher KV motor
If I'll take the 80KV motor, the RPM will be between 3200 and 4300. That's way too much of course, but if I set the RPM limit at 2688RPM (same as the 50KV motor max RPM), both motors will have similar performance ?
 
both motors will have similar performance?
Click to expand...

Simplified and disregarding saturation and heating of motor:
Torque constant kT=9.55/kV

Torque= kT*I

So 80kV motor needs proportional to 80/50 (60%) more current for the same torque as a kV 50 motor with a given current.

That’s why you might need a larger controller with a higher kV motor.
 
larsb said:
both motors will have similar performance?
Click to expand...

Simplified and disregarding saturation and heating of motor:
Torque constant kT=9.55/kV

Torque= kT*I

So 80kV motor needs proportional to 80/50 (60%) more current for the same torque as a kV 50 motor with a given current.

That’s why you might need a larger controller with a higher kV motor.
Click to expand...

Oh that's not good... The motor will draw more amps with the same propeller at the same speed so... it's less efficient ? If it's the case it will be not good for the motor either, heating more for the same output power

But why the battery amps will be the same ?

Is it because the voltage on motor phases will be limited by the ESC ?
 
Energy in equals energy out plus losses as always.. It’s marginally less efficient as there are some added switching losses and copper losses.

Reason is this:
You need lower applied volts to reach same rpm with a higher kV motor so there are volts to spare.

If available battery volts are higher than you need then the controller can transform the high volts to higher phase current (which is what matters for torque). It’s not magic but almost. :D
 
larsb said:
Energy in equals energy out plus losses as always.. It’s marginally less efficient as there are some added switching losses and copper losses.

Reason is this:
You need lower applied volts to reach same rpm with a higher kV motor so there are volts to spare.

If available battery volts are higher than you need then the controller can transform the high volts to higher phase current. It’s not magic but almost. :D
Click to expand...

I understand better now, thanks :)
What I'm going to do now is to estimate the max amperage draw with the 80KV motor at desired max RPM
The VESC 75/300 is rated at 300A continuous but the M40C30 is rated at only 200A !
 
larsb said:
Current rating depends on winding choice. A higher kV winding can take proportionally higher current.

200A with kV 50 is 320A for kV 80
Click to expand...

You're absolutely right, I completely forgot it !
Anyway, I will put a temperator sensor on the motor because it's the sole way to know if the motor is actually overpowered, right ? The max rated amp is not very relevant because it depends on the cooling of the motor, etc...
 
NexusG said:
bionicon said:
If money is no problem here are top-end motors https://hacker-industrial-solutions.com/
for the q150 its arround 2000€ without tx :shock:
Click to expand...

That's way too much. I know that some electric paramotor manufacters use European brushless motors such as Paracell, Geiger, etc... they are probably good but not cheap at all. 1000€ is my limit

sn0wchyld said:
RE your 3000rpm limit - a good modern controller will allow you to set such a limit electronically... so you can safely use a motor that may well spin well over your desired max.
Click to expand...

Yeah that's a good idea ! I will use a VESC 75/300 controller which includes RPM limit, battery amps limit, etc. It's very complete in terms of functionality and open-source. 300A will be more than enough for my application. However it's costly (600€)

sn0wchyld said:
The usual rule of thumb for rpm of a loaded motor is ~80% of unloaded... but thats a very rough guide. prop loads are non linear with rpm... so 80% probably isn't a bad first guess but YMMV. I'm sure someone on the net has the answer though. Still, a good reason to have a no load speed at least 20% higher than your desired top speed, and also worth accounting for both battery SOC and sag as already mentioned.
Click to expand...


So with a 50KV motor, 16S battery :
- Estimated RPM with fully charged battery : 4.2*16*0.8*50=2688 RPM (60kg thrust, that's good !)
- At nominal voltage : 3.7*16*0.8*50= 2368 RPM (47kg thrust, still ok :) )
- Depleted battery : 3.2*16*0.8*50= 2048 RPM (35kg thrust, weak but still flying straight or even slow climb)
In fact it does not seem so bad !
I don't know if the sag is included is this 0.8 factor. I can't calculate it because I don't know the internal resistance of my future battery. It will be a 16S16P Samsung 30Q Li-Ion cells DIY battery.

The other solution is a higher KV motor and RPM electronical limit but there must be some drawbacks :
sn0wchyld said:
main reason to not go too far over though is that a higher kv is inversely proportional to the torque per amp... ie doubling the kv will halve the torque per amp, necessitating a beefier controller (battery amps will be much the same however, all else being equal).
Click to expand...
I do not understand why a beefier controller is needed if I limit the RPM of the higher KV motor
If I'll take the 80KV motor, the RPM will be between 3200 and 4300. That's way too much of course, but if I set the RPM limit at 2688RPM (same as the 50KV motor max RPM), both motors will have similar performance ?
Click to expand...

you need an extra 0.9 or 0.8 multiplier in there, because the battery will sag under load. probalby not by that much but idk how critical thrust is in your application. 300/16/18A per cell... hard for a 30Q. I'd consider a higher power cell with a little less capacity (sonty vtc6, 25R, though im not a 18650 expert).

beefier controller needed becaus a higher kv motor will need to be fed more phase amps to produce the same torque (as i mentioned). so your controller needs to be able to feed that kind of phase amps, into a motor thats relatively (though probably not significantly) harder to drive (higer kv = lower inductance and resistance = harder to control phase currents). The motor performance (if the controller can push the higher current) will be the same, but with less effect due to voltage sag and SOC drop, so you'll get more torque at the top-end of your rpm.

edit
just to update/add on to more recent posts
the power draw from the battery for a higher kv motor (at the same torque output, ie higher phase amps) will be roughly the same... possibly a little higher but not anywhere near as significant as the change in phase amps.

to produce (just for arguments sake, these numbers are wrong, just here for illustration) 100nm of torque at 100rpm...

50kv motor needs 50 phA, and will draw 25A from the battery to do so, the controller will step down the battery voltage by ~50% to the motor such that it draws that 50A.
80kv motor needs 80phA. Controller will still draw 25A from the battery, but this time will step the voltage down to ~35% of the battery voltage, because the motor has a lower resistance and inductance, it doesn't need the same voltage to produce the higher current.
if you let both motors go up to max rpm you can see that the low kv motor will hit the limit of the 'battery voltage' sooner, as its already at 50%, so it can only spin ~200rpm no load, ~160 loaded. the higher kv motor, though harder to drive, can spin out to more like 285rpm, or 220rpm loaded.

Just to labor the point, this is all just numbers for illustration, not actual values that you'll get, sorry just a bit to tired atm to do much more hahah.
 
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