larsb
1 MW
at those power levels there's no need for active water cooling. just connect the inrunner stator to the casing with good heat path and use an efficient motor.
Low KV 1000W BLDC
- Thread starter stevetto
- Start date
larsb
1 MW
How will you build the enclosure? This seems like the most difficult part together with sealing cables and shaft.
larsb said:
That is the easy part. There are aluminium and composite tubes available for the body. A custom made aluminium casting is necessary for the nose and tail. High pressure cable glands, o-rings and simerings are also available.
For me the motor and controller is the biggest challenge.
larsb
1 MW
Gears will make it possible to have a smaller motor for the same torque so in the end you won't need to add "an extra kilo" by planetary gears
How much torque is actually needed for the prop?
1000W 1500rpm is about 6Nm if the numbers you have are correct
A c80100 in 50kV will need about 32A to do this, should be possible continuously.
https://alienpowersystem.com/shop/brushless-motors/80mm/c80100-outrunner-brushless-motor-50kv-6000w/
It's a small enough motor, i'd guess?
How much torque is actually needed for the prop?
1000W 1500rpm is about 6Nm if the numbers you have are correct
A c80100 in 50kV will need about 32A to do this, should be possible continuously.
https://alienpowersystem.com/shop/brushless-motors/80mm/c80100-outrunner-brushless-motor-50kv-6000w/
It's a small enough motor, i'd guess?
larsb said:
I have no idea how much torque is necessary.
The 1000W power is my assumption based on the battery capacity and runtime.
For example this one:
nominal capacity/run time full trigger 1340Wh/1.66h = 807 W
And from another manufacturer:
The 1000-1500 rpm was also an assumption, now I think it should be around 1000 1/min.
And the torque calculation based on these details:
larsb
1 MW
Found this link, nice writeup on a DPV build:
http://pettersen-prod.com/project/dpv/index.html
Maybe it contains something useful.
http://pettersen-prod.com/project/dpv/index.html
Maybe it contains something useful.
larsb
1 MW
Doesn't conclude how succesful it was though 
Sources mention 800-1500 rpm for different DPV motors. The c80100 is large enough to cope with different drive rpm and current and the rpm and load torque should be possible to match with different props - i guess motor choice is not so sensitive.
If you want the smallest possible motor (like an 8318 which could work) it will be more critical with torque and current capacity vs heat. Probably wise to set lower goals /easier target for a first build.
Sources mention 800-1500 rpm for different DPV motors. The c80100 is large enough to cope with different drive rpm and current and the rpm and load torque should be possible to match with different props - i guess motor choice is not so sensitive.
If you want the smallest possible motor (like an 8318 which could work) it will be more critical with torque and current capacity vs heat. Probably wise to set lower goals /easier target for a first build.
I have started to thinking about this motor:
https://alienpowersystem.com/shop/b...sensored-outrunner-brushless-motor-30kv-2800w
https://alienpowersystem.com/shop/b...sensored-outrunner-brushless-motor-30kv-2800w
larsb
1 MW
Torque 7.5Nm (normally given torque is max output at full Amps) is probably too low as you might use 6Nm/ 80% of max for longer periods.
It's a bit of a chance, it will probably overheat used at full throttle.
It's a bit of a chance, it will probably overheat used at full throttle.
larsb said:
I have made some more research and found that most probably I do not need higher rpm than 1000, and the required torque is around 10Nm.
So the other option would be to use this motor:
https://alienpowersystem.com/shop/brushless-motors/80mm/c80100-outrunner-brushless-motor-50kv-6000w/
A 6s lipo would result 22,2*50=1110rpm, which would be good for me. But I do not know the motor's torque vs. speed curve at lower voltages.
larsb
1 MW
BEMF will lower your achievable rpm to about 85% of unloaded / 900rpm as a maximum.
It's better to run 10s and have some headroom left if you want/need to try different props or higher RPM.
The c80100 motor is good, i’ve run one on an ebike for a long time.
Your DPV shell will need to be thermally conductive for any motor and battery to work without overheating. What is your plan for this? An alu tube for the main body would be perfect, don’t know if you can find large enough diameters at a reasonable cost.
It's better to run 10s and have some headroom left if you want/need to try different props or higher RPM.
The c80100 motor is good, i’ve run one on an ebike for a long time.
Your DPV shell will need to be thermally conductive for any motor and battery to work without overheating. What is your plan for this? An alu tube for the main body would be perfect, don’t know if you can find large enough diameters at a reasonable cost.
larsb said:
10s lipo will result 10*3,7*50=1850rpm which is too high. So I need to reduce it with a planetary gearbox or a 2 step timing belt reduction. Planetary gearboxes not availble with 1:2 reduction so a KV80 or KV130 motor might be necessary.
Resulting 10*3,7*80=2960rpm and 10*3,7*130=4810rpm speed. 1:3 and 1:4 planetary gearboxes are available, so I can reach my target rpm (2960/3=986 rpm and 4810/4=1200 rpm) at nominal battery voltage.
I would like to have the motor, gearbox and the propeller placed inline to maintain balance as much as possible.
Like this:
I also need a torque limiter for safety reasons.
The gear ratio/planetary gearbox and the torque limiter need a lot of space together. It makes the drive too long.
That is why I always go back to the first idea and would like to avoid any gearboxes.
Commercial DPVs use a clutch plate outside of the DPV's body. But I do not want to manufacture a custom clutch, it would be much easier to use a professional one. And it would also compensate the the axial/radial differences of shafts.
The DPV's body will be an aluminium tube and if it is necessary I can use a fan inside the DPV to cool the motor and the driver.
The tail cone will be a custom aluminium casting, it also helps to eliminate heat.
larsb
1 MW
You don't need torque limiter or any reduction if you don't want to. drive the motor with a (low) throttle, you can choose rpm freely. If you want you can include a dead mans grip instead of the torque reducer for added safety. 6Nm isn't a lot.
If you want a small motor then it's better to reduce rpm by a gear to get low rpm, high torque but since you don't want gearing, don't do it. It will work well anyway. :thumb:
Balancing of the DPV should not be so difficult since the main weight will be batteries and a big part of the volume will be airspace. A battery carrier with adjustment possibility would be great for the fine adjustments of center of gravity.
If you want a small motor then it's better to reduce rpm by a gear to get low rpm, high torque but since you don't want gearing, don't do it. It will work well anyway. :thumb:
Balancing of the DPV should not be so difficult since the main weight will be batteries and a big part of the volume will be airspace. A battery carrier with adjustment possibility would be great for the fine adjustments of center of gravity.
I made an Excel sheet to calculate BLDC performance curves to help compare operation conditions at different inputs.
It has not been tested yet!
View attachment BLDC curve calculation.xls
It has not been tested yet!
View attachment BLDC curve calculation.xls
larsb
1 MW
Input values don't make sense. Is it just for a trial or is it a calculation? What do you want to do?
- The controller can turn high voltage low current input to low voltage high current output - are you aware of this?
- eddy losses go up by the square of the rpm
if you input 55mohm phase resistance and noload current at 1.5A then you'd see that the difference is not large between the driving. You also miss the effect of nonlinear losses like the eddy losses which lowers the high rpm efficiency.
- The torque is not related to the voltage, only to current and efficiency..
- The controller can turn high voltage low current input to low voltage high current output - are you aware of this?
- eddy losses go up by the square of the rpm
if you input 55mohm phase resistance and noload current at 1.5A then you'd see that the difference is not large between the driving. You also miss the effect of nonlinear losses like the eddy losses which lowers the high rpm efficiency.
- The torque is not related to the voltage, only to current and efficiency..
larsb said:
Input values are just kind of some random numbers..
My purpose was to see how current, torque, efficiency changes if I use the same motor at different input voltages or compare different motors.
I know that this tool is not perfect, but at least quantitively shows the tendency.
I also would like to compare alienpower motors if I can get somehow real motor parameters.
larsb
1 MW
I think you should try the motor simulator at ebikes.ca to simulate some load cases. It's quite good :thumb:
