Are we all stupid, or just me?

[Marchie]

So I recently put a heatsink on my Super Stock TZ, one of those simple alluminium-fins-plus-a-fan affairs. the sort of thing that comes up by the dozen if you search 'RC motor heatsink'.

I noticed however, that the fan would spin up fine but slow or completely stop when I put it on the motor. Now I'm no engineer, but at this point it occurs to me that the fan has a tiny electric motor that I have just placed within the magnetic field of the motor itself with it's much larger, more powerful magnets and hence it's function has been compromised.

So now I'm wondering: when has a small fan attached to the outside of an electric motor ever worked?? Why does anyone make or sell them?? Or have I just tried with a motor with unusually strong magnets?

[alvinlwh]

That is strange, I never had that happening to me before although I had not tried it on one of the Z's. Now I got to stick a fan on that just to try it out. 

[Superluminal]

The superstock motors do have pretty strong magnets, you can feel that when you try and rotate the shaft by hand

[compass]

rotate the heatsink until the fan is out of the magnetic field. This has happend to me to with a simpel torque tuned motor. just rotated the heat sink and the fan turns fine.

[OoALEJOoO]

@Marchie what you describe is indeed the magnetic field of the Super Stock TZ affecting the magnetic field of the fan's own motor. This is the first main reason to keep a fan away from directly contacting the heatsink fins and maximize the fan's free rotation.

The second reason to keep some distance is to allow the airflow to fully develop into axial flow before it reaches the heatsink. The zone directly in front of the fan has the airflow in a considerably tangential (spiral) profile which shears against the fins. This area also has a flow dead zone right in front of the fan hub. Once you separate the fan a bit, the airflow develops more axially (i.e. orthogonally away from the fan face), thus maximizing flow and heat dissipation. I am stumped to see how many fans are mounted directly into heatsinks by RC manufacturers.

A combination of zip-ties plus all those leftover CVA shock spacers can be used as an easy way to attach fans to the heatsink with custom spacing.

[Marchie]

2 hours ago, OoALEJOoO said:

A combination of zip-ties plus all those leftover CVA shock spacers can be used as an easy way to attach fans to the heatsink with custom spacing.

Right now it’s duct tape

 

[Pylon80]

@Marchie I had one of these 4$ fans on a BZ (which is a TZ with a different color...) and it was working perfectly fine. Before we all diverge on magnetic field theories I propose you perhaps flip the fan upside down and see if it makes a difference? Then if not I would try a new fan. These cheap fans are very much hit and miss in my experience.

[skom25]

How do you mount fan? Horizontally? On the side?

I found that cheap fans work bit weird, if they are not horizontally. I have not found this issue with good quality fans.

[Pylon80]

23 minutes ago, skom25 said:

I have not found this issue with good quality fans.

I now use Protek aluminum fans and never looked back. With a bad fan you can cook an expensive motor if it fails at the beginning of your 5 min run.

[skom25]

I have <cannot use name, check below> fans. I am not sure if it is local brand with fancy name or something international.

This from photo below is a beast. A lot of air flow and really good quality. 

I have it in TT-02 with Torque Tuned motor. When temperature outside was around 20 C degrees, motor was totally cool after around 15 minutes of constant running.

[Marchie]

3 hours ago, Pylon80 said:

@Marchie I had one of these 4$ fans on a BZ (which is a TZ with a different color...) and it was working perfectly fine. Before we all diverge on magnetic field theories I propose you perhaps flip the fan upside down and see if it makes a difference? Then if not I would try a new fan. These cheap fans are very much hit and miss in my experience.

My experience has been in-line with others above - it makes a difference where around the barrel the fan is positioned. I’ve ultimately decided to put the fan at the end of the motor blowing along the length of the fins.

[Honza]

This is something I noticed when I did fan mount in my MF-01 - whether the fan runs or not depends not only on its position relative to the motor, but also on its rotation. Plus, cheap noname fan might not run anyway, while slightly more expensive Sunon in the same position works well...

[MadAnt]

Use spacers or a stronger fan.