Radial Cooling of RC Outrunner

[spata]

I now have some datalogged results of the effects of my outrunner cooling setup and I thought they may be of interest.
The results are from my road legal Honda MT50

The important specs are:
Motor: Turnigy C80100 - 130kv
Controller: Lyen 18FET
Batteries: Lipo 15S 4P (nominal 55.5v - 20ah)
2 stage reduction
Primary: 14T front – 45T rear
Secondary: 14T front – 60T rear
Speed: approx 32-35mph
Weight 75.5kg

The cooling solution I used needed to perform 2 functions: first was obviously keep the motor cool, but equally important was to cover all the rotating parts of the outrunner. I needed the final design to be road legal - pass any safety inspections, and ensure that nothing could get caught by the rotating can.

I also needed to keep the design as slim as possible, this effectively ruled out the 'regular' solution of putting a fan on the motor shaft. I looked for a fan that could work at a high static pressure (needed to get air through the stator) I considered leafblowers and ducted fans, but the sizes and noise were not particularly appealing. Eventually I came across this:


It is an Attwood Turbo 3000 and is used to vent air out of the bilge of boats. It is 3" in diameter - they make a 4" one as well
The idea was to surround the C80-100 outrunner in a piece of 110mm diameter plastic waste pipe and connect this to the bilge pump.

These images should give you the basic idea:




Here are the datalogged results:


Up to about the 360 second mark the fan cooling was off, the temperature measurement is embedded in the stator and you can see it got up to around 85 degrees C before I chickened out and turned the fan on. I averaged the power in the first green rectangle, it came out at 1.38kW. as you can see the load then dropped but the temperature was still on the way up. I think the eventual temperature, without fan cooling, would likely end up somewhere between the 2 trend lines; ie between 87 - 100 degrees C. Some time after the fan came on the load increases, the second green rectangle (when the cooling was on) shows an average of 1.83kW, temperature however now stays fairly constant peaking at 68 degrees C.

Summary is that the air cooling drops the stator temperature by at least 17 degrees C and my guess is more like 20 degrees C.

It is of course worth remembering that if your motor is uncovered then it will have better cooling in the first place - this was not an option for me as I needed it protected. Unfortunately I do not have any datalogged results for an uncovered motor.

If there is any interest in further details of the construction - air baffles etc, then let me know and I can append the thread.

- Spata

 

[einkleburt]

Looks good

If there is any interest in further details of the construction

I'm interested

Are you filtering the air in anyway or are the baffles you mentioned there to help prevent things getting drawn in?
Also how much power does the fan draw (I didn't spot power consumption on the spec sheet)

 

[amberwolf]

I'd guess you are pulling the air thru the motor, rather than pushing it thru? (that usually seems to work better)

If there is any way for you to pull the air onl thru one end, rather than around the whole shell of hte motor, I suspect it would cool the stator even more (which would in itself keep the rotor cooler).

There is some info on this type of thing in the Definitive Testing thread about cooling hubmotors (which are also generally outrunners, albeit of a slightly different design).

 

[ferret]

I also needed to keep the design as slim as possible, this effectively ruled out the 'regular' solution of putting a fan on the motor shaft. I looked for a fan that could work at a high static pressure (needed to get air through the stator) I considered leafblowers and ducted fans, but the sizes and noise were not particularly appealing. Eventually I came across this:

Since you use an outrunner, you can mount a fan on the motor's case and keep the slim design.

Avner.

 

[spata]

I guess I should put more constructional detail in here about how the design works.

Are you filtering the air in anyway or are the baffles you mentioned there to help prevent things getting drawn in?
Also how much power does the fan draw (I didn't spot power consumption on the spec sheet)

The fan spec is 2.6A at 12V -120 CFM in free air and 90 CMF in a 'typical loaded system'. Realistically with the static pressure required to get through the stator windings of the inrunner it is much less than that. I am pushing air through the motor, as Amberwolf points out it would probably be better to pull the air, but that would risk ingesting muck straight into the rotor. The filter is nothing fancy - in fact it is a modified tea strainer, see below:


The main thing to convey is how the air flow/baffling works within the design. Here is the whole motor assembly complete with side plates viewed from the primary side.

This is a close up of the primary side engine plate, The 110mm plastic motor tube fits snugly over the 3 crescent shaped retainers.

This is detail of the secondary side engine plate.
View attachment 4
The air baffle ring is accurately machined so the outside is a snug fit inside the 110mm plastic motor tube. The inside has about 0.1- 0.2mm clearance for the motor endcap. The holes in the engine plate are to vent the exhaust air from the motor (the big one is for the motor wires).

Here you can see the air baffle and how it fits with minimum clearance around the motor endcap.

It is important to keep this clearance as small as possible as any leak here reduces the airflow through the motor. You can also see that the air baffle ring is spaced away from the engine plate, this is done to maximise the available area for the exhaust air.

And now a view of the motor in place.

Now the cooling assembly has been fitted and pushed over the outside of the Air baffle ring.

Hopefully you can see how the design works, the bilge pump pressurises the air in the 110mm plastic motor tube, the air baffle ring stops the air shooting straight out of the exhaust holes, so the air has to go through the holes we can see in the exposed end of the motor, it then flows between the stator and the rotating motor can and finally exhaust to atmosphere via the holes at the other end of the motor and the exhaust holes in the secondary engine plate. The primary side engine plate fits over the exposed motor shaft and clamps/seals the whole assembly. (There are bearings/support blocks etc missing from some of the pictures if anyone is trying to work out how the motor and layshaft are supported).

Finally the whole lot is powered by this

It is a Hobby king 20A brushed speed controller. Stupidly cheap and it easily runs the fan motor, better yet it has a 5v regulated output that I use to run an Arduino and it is controlled via a servo style PWM output from the Arduino which controls the fan speed. In my case I have the ESC connected to the bikes 12v.

- Spata

 

[aCeMadMod]

hi how did this setup go. did it last

I may copy some of it thank you

 

[spata]

Still going strong. It definitely keeps the motor temperature under control, at least in my setup. I used to keep an eye on the motor temperature all the time on my arduino based handlebar readout but I hardly even look at it now.

The bilge air blower is designed to run for long periods of time so it is not stressed in this application. The advantages I see over an axial blower cooling solution are: It does not add anything to the length of the motor. It keeps going even when the main motor is stopped. This is really useful in stop start traffic, which tends to heat the motor up fast, the heat comes off remarkable quickly when waiting at traffic lights etc.

- Spata