Low KV 1000W BLDC

stevetto · Jul 10, 2019

Hello,

I have been working on a custom DPV and looking for a motor.
I have been googling and reading forums for a while but I have not found the motor I really need.
Revolt seemed to be the best choice until I found a detailed review on this forum.

My requirements are:

input voltage: 36 V (can be changed if necessary)
power: ~1000W
rpm: max. 1500 1/min

I would like to avoid using a gearbox or timing belt to reduce rpm.

Revolt RV-100-pro has a 40 kV version, 24-96V input range and 3kW continous power.
http://www.revolt.org.il/rv-100-model/rv-100-pro

Can you offer me an alternative choice?

kdog · Jul 11, 2019

What's a dpv? Have you looked at the myriad hub motors out there to see if adaption of these would suit. (without knowing your application, I'm guessing ) The stoke Monkey is already pre-prepared for you.
I'd stay away from revolt... Promised so much but they have a poor history here on ES.

stevetto · Jul 11, 2019

kdog said:
What's a dpv? Have you looked at the myriad hub motors out there to see if adaption of these would suit. (without knowing your application, I'm guessing ) The stoke Monkey is already pre-prepared for you.
I'd stay away from revolt... Promised so much but they have a poor history here on ES.

DPV means Diver Propulsion Vehicle.
Hub motors have to big diameter and they are too heavy.

LiTrEx · Jul 11, 2019

You could use cheap hoverboard motors, I use one for similar propulsion.

Remove the tire and unnecessary material and waterproof it with epoxy, only issue could maybe too low KV (~18kv stock).

I rewired mine to Y (increases the KV) and with 10s lipo and a standard 7" outboard prop it draws about 500w.

With a bit bigger prop and a bit more voltage 1000w is in sight.

LiTrEx · Jul 11, 2019

Closer look.

neptronix · Jul 11, 2019

Read some experiences with the revolt motors before you buy. It seems that the power ratings are not honest.

larsb · Jul 11, 2019

Interesting application!
You can underdrive any motor at lower rpm. Changing kV to get low rpm use and running on low rpm by low throttle is not so different, the full potential of the motor is not used in both cases.

One way to get low rpm efficiently is by using a high pole count motor (often hub motor) or a geared motor (hub motor

)

How will you seal it? The magnets will corrode like crazy if they get in salt water.

QS motor 1000w mid drive motor maybe? What's your weight and power targets?

stevetto · Jul 11, 2019

LiTrEx said:
You could use cheap hoverboard motors, I use one for similar propulsion.

Remove the tire and unnecessary material and waterproof it with epoxy, only issue could maybe too low KV (~18kv stock).

I rewired mine to Y (increases the KV) and with 10s lipo and a standard 7" outboard prop it draws about 500w.

With a bit bigger prop and a bit more voltage 1000w is in sight.

Thanks for the suggestion!
Kv is too low. I need around 30-40KV to get 1000-1500 rpm at 36 volts. I do not really want to go above 36V and propellers
work efficiently in this rpm range.
The prop size is more or less given, I would use a commercially available one.

stevetto · Jul 11, 2019

neptronix said:
Read some experiences with the revolt motors before you buy. It seems that the power ratings are not honest.

Yes, I know.
That is why I'm looking for other motors.
The RV-100-pro is rated to 3000W, 1000W is enough for me.

neptronix · Jul 11, 2019

Have you read up about the gng big block / small block motors?
They seem to be right around what you're looking for.

stevetto · Jul 11, 2019

larsb said:
Interesting application!
You can underdrive any motor at lower rpm. Changing kV to get low rpm use and running on low rpm by low throttle is not so different, the full potential of the motor is not used in both cases.

One way to get low rpm efficiently is by using a high pole count motor (often hub motor) or a geared motor (hub motor )

How will you seal it? The magnets will corrode like crazy if they get in salt water.

QS motor 1000w mid drive motor maybe? What's your weight and power targets?

Sealing is not a problem. The whole body of the DPV is watertight. The motor's shaft goes out at the tip of the tail cone and there a high pressure simering is used.

The DPV itself ~20 kg.
The required thrust ~300-400 N
Top speed ~ 4-5 km/h
Battery 10s10p, ~ 1000Wh
Motor ~1000W, 1000-1500rpm

QS mid drive motors are too heavy, 8-9 kg and 2000-3000W rated.
I need only 1000W and would save several kilogramms.

larsb · Jul 11, 2019

I guess 99% of the drag comes from the rider so weight doesn't need to be critical? You can just add volume on the dpv?

I think you should choose inrunner motor since cooling will be difficult on outrunners. So hub motors might be out anyway - even though there are small ones.

EDIT: i understood the scale now from the pics. Why don't you want gearing?

stevetto · Jul 11, 2019

larsb said:
I guess 99% of the drag comes from the rider so weight doesn't need to be critical? You can just add volume on the dpv? I think you should go inrunner since cooling will be difficult on outrunners. So hub motors might be out anyway.

You are right, weight is not critical. It can be compensated by the volume of the DPV's body.

I'm looking for something like theese motors:

SlowCo · Jul 11, 2019

Like Lars already asked: why not a geared motor? My DPV (cheap Chinese Seadoo knock off) uses a geared motor. Look at Cyclone motors: http://www.cyclone-tw.com/motor.html The 650-1680W geared version might work for you?

stevetto · Jul 11, 2019

SlowCo said:
Like Lars already asked: why not a geared motor? My DPV (cheap Chinese Seadoo knock off) uses a geared motor. Look at Cyclone motors: http://www.cyclone-tw.com/motor.html The 650-1680W geared version might work for you?

I would like to avoid gearing if it is possible, because it is noisy, needs more maintenance, can add extra unwanted weight and it
also can be one more source of issues. In technical diving we do not like complicated equipments. Everything has to be very
simple and reliable.

Overclocker · Jul 11, 2019

see my sig for the BHT motor. 36kv but i'm not sure if they're still selling them.

Grantmac · Jul 11, 2019

Qs1000w has the advantage of being a bit smaller diameter. I think they are around 60kv and can easily sustain 1kw at that voltage.

nieles · Jul 12, 2019

i would go with a 6384 brushless outrunner motor and a neugart PLE gearbox 5:1

motor something like this:
https://alienpowersystem.com/shop/brushless-motors/63mm/aps-6384s-sensored-outrunner-brushless-motor-200kv-4000w/

neugart PLE gearbox: pretty cheap on ebay.

36v with 200kv and 5:1 gives you 1440rpm no-load

larsb · Jul 12, 2019

Better in this case to just buy one of the cyclone motors. plastic planetaries don't sound a lot, and i guess the PLE has (louder) metal planets and also needs adaptations to make it fit.

I would like to avoid gearing if it is possible, because it is noisy, needs more maintenance

Do you assume or know this from experience?

I don't think reliability with the cyclone motors will be an issue, prop driving is an easy application, no shock loads and the needed run time of a DPV will never compare to that of a bike. I've run cheap chinese geared (overvolted and overpowered) motors for years, 500-1000 hours use without gear issues (they didn't break, i just don't use them anymore)

By then it's time to replace the battery anyway since it probably will be used at max range.

I agree that the alien power and PLE combination has more shine to it than the cyclones though

stevetto · Jul 12, 2019

nieles said:
i would go with a 6384 brushless outrunner motor and a neugart PLE gearbox 5:1

motor something like this:
https://alienpowersystem.com/shop/brushless-motors/63mm/aps-6384s-sensored-outrunner-brushless-motor-200kv-4000w/

neugart PLE gearbox: pretty cheap on ebay.

36v with 200kv and 5:1 gives you 1440rpm no-load

I also found something interesting here:
http://www.bonex-systeme.de/static/motor_e.php

They are talking about servo motors but I do not think it is necessary. A simple stepper or bldc is enough and much cheaper.

Do you think if it is a geared motor?

larsb · Jul 12, 2019

It's a planetary gearset at the front of the motor on the pic.

stevetto · Jul 12, 2019

Nearly perfect, just too heavy:

https://www.aliexpress.com/item/90-efficiency-high-torque-24v-48v-bldc-motor-1000w/32818875603.html

nieles · Jul 12, 2019

you might be able to get away with a lower power servo motor. and then use it a 1000W.
that is, if you can directly cool the motor with water

stevetto · Jul 12, 2019

nieles said:
you might be able to get away with a lower power servo motor. and then use it a 1000W.
that is, if you can directly cool the motor with water

I was thinking about to use water cooling as it is used in rc boats.

But I still think it is too risky.
There is 1 bar air pressure inside the DPV, the target depth is 200m, so there are ~20 bars water pressure outside.

nieles · Jul 12, 2019

Why run a water cooling jacket if you can just use the environment water. Seal the front and back properly and make sure the moving water is guided over the cooling ribs of the motor. With an inrunner motor you will get pretty impressive cooling I think. As the water is in almost direct contact with the heat source (motor windings)

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