Electric motocross bike air cooling motor questions!

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Hi,

I am looking for advice or info about cooling the motor on my sons 50cc KTM motocross bike which I have converted to electric.

The bike has run great for about a year. Yesterday in the 95 degree Mississippi heat we let a larger faster kid ride the bike and he made about 5 fast laps before the motor gave out. the motor still turned over, but it runs very rough and only at partial throttle. It looked like resin or something was seeping out of the motor too.

I opened the motor up and it smells like electrical death. There are also some chips out of the magnets.

What I would like to do is plumb an air inlet and outlet in the Oset 48v brushed motor ( new motor, not the one we burned up) and force air through the motor and through the bikes original aluminum radiators.

Can anyone tell me if a radiator originally used to water cool a gas engine will pull heat out of air circulated through a motor?

Will the circulated air even cool the motor?

Thanks!

this is a video of the bike in the shop.
https://www.youtube.com/watch?v=ASsHoo_udd8

This is a video of me riding it for a very short time. It is usually ridden by a 6yo.
https://www.youtube.com/watch?v=nFHJIrzT3Iw
 
You don't want to use air thru the radiators; the flow restriction means that unless you have REALLY high pressure you won't get enough airflow to make any difference. You'd need to use a liquid for that.

Instead, just open up as much of the motor as you can at one end (preferably the brushed end), and at the other end use a high-velocity / high airflow squirrelcage type fan with it's open round end (suction end) on the other end of the motor, also opened up as much as possible, and just let the squirrelcage fan's exit blow the hot air away in a clear direction, no ducting or anything else to decrease velocity. Down is probably better, so you're not heating the rider. ;)

It wont' be quiet, it may sound like a turbojet. ;) If that's a problem, then add a temperature control so it only runs when the motor gets hot enough inside to need it. (like some computer case/power supply fans have).

If the environment it's used in is really dirty, you may have to clean the motor out after each ride, but you can't really use any kind of filters on the input because it will slow down the airflow, which will mean it doesn't cool the motor as much. The dirt may wear the brushes faster, so may need replacement more often.


Brushed motors heat up more than brushless for the same power, because the brush arcing creates heat, and are harder to cool (can't just flow oil or water thru them for instance, like you could with brushless), so if you get the chance to change to a brushless motor and controller, it would make cooling easier (and take just a little bit less cooling to start with). It does add complications to control, and there are more things to go wrong with the controller, but it is less maintenance and easier to cool if you have to.

But if you do switch over, get a bigger motor to start with, so it isn't so overloaded that it makes enough heat to destroy itself. :)
 
I'm no expert, but I don't think it will. You would do just as well to just blow the hot air away. The radiator is only there because you're trying to keep using the same coolant, so with an effectively unlimited supply of outside air, there's no reason to cool and recirculate the same air again.
 
Post pics of the Oset motor you want to use (hopefully opened up, showing the inside) and we can provide you with links to discussion threads with pics that will be appropriate for cooling that style of motor.
 
Voltron said:
I'm no expert, but I don't think it will. You would do just as well to just blow the hot air away. The radiator is only there because you're trying to keep using the same coolant, so with an effectively unlimited supply of outside air, there's no reason to cool and recirculate the same air again.

Absolutely :)
 
I originally thought using the radiator would cool the air in a closed system, keeping dirt and such out of the motor. But it looks like the radiator might not take much heat out of the circulated air, and would require a powerful blower to circulate the air in the first place.
 
I have seen brushed motors air-cooled by a fan, but as it was mentioned above by voltron, put the air inlet behind something to keep it out of the dirt and splashes, and use an air-filter. I would suggest two fans, one pulling air out with no filter, and one pushing air in, with a filter.

Look for a 48V server computer fan with ball bearings. The centrifugal style will pump more air than the typical "air fan" axial-flow (shaped like a boat propeller), and you might be able to get $5 used ones locally from a junk electronics dismantler/recycler...Here is a random pic from the web. https://www.ebay.com/itm/Ball-Beari...all+bearings&_from=R40&rt=nc&LH_TitleDesc=0|0

Here is a screencap of your motor pic

MotorOset1.png
 
spinningmagnets said:
I have seen brushed motors air-cooled by a fan, but as it was mentioned above by voltron, put the air inlet behind something to keep it out of the dirt and splashes, and use an air-filter. I would suggest two fans, one pulling air out with no filter, and one pushing air in, with a filter.

If you use a filter of any kind, it's going to DRAMATICALLY decrease airflow from an unfiltered version. A screen might not, if rocks are expected and the holes big enough to admit them, but anything that keeps dust out will. Even a screen *will* decrease airflow and make more noise.

To correct that, you'd then need to use a much more powerful (and noisy, and larger) fan. That fan will either have to have a separate battery (more weight and space on the bike) or have it's higher power draw begin to sap range from the main battery.

A push-pull might make some difference, vs a single larger fan, but it is going to be louder, with a vibration from the resonance difference between the two fans' RPMs.



The centrifugal style will pump more air than the typical "air fan" axial-flow
Definitely--that's the "squirrelcage" type.

Here is a screencap of your motor pic
MotorOset1.png
Based on that pic, I'd say to open up all the space you can between and/or under the brushes--anythign that doesn't compromise the mounting points for the brushes and the central motor bearing.

Then the same on the other end; you can open it up more there because there's no brushes. Have to leave enough material to withstand the sideloading of the drive system on the motor shaft, so you could leave it thicker in the line parallel with the chain loading forces.

Bigger holes are better (less turbulence, so more airflow and less noise), so rather than drilling a bunch of little holes, just open up the space completely as much as possible.

If you can machine the motor can itself, too, then the end where the brushes are will probably have a bigger gap between the end and the magnets than the other end. On *only* that end, if you can add more holes in the gap, preferably only where the magnets are (rather than in line with the gaps between magnets), that's more airflow in.
 
Got it, thanks!

Any suggestions about dealing with the dirt and dust? Can I just flush the motor with something after each ride?
 
here is a thread about a dual agni electric enduro, it mentions keeping desert sand out of the motor, etc, might be of some interest .. :
https://endless-sphere.com/forums/viewtopic.php?t=44016
 
You may be able to find a little OEM plastic ICE air filter housing that will work in conjunction with a centrifugal blower. Those filters are made for the job and cheap to replace (or washable). Copy what the ICE bikes do IMO as their requirements for unrestricted, clean air are greater than a motor.

The filter will restrict flow, but any cooling air is going to be a worthwhile compared to the stock motor :)
 
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