Help mounting a motor

[Liam Ryan]

I'm missing something very obvious here so apologies in advance. I did search this forum for "mount" but didn't find anything basic enough for me to understand

I have the motor pictured below and I'm at the point of needing to drill the mounting and cable holes in the firewall before I glue it in. I assume there's more to it than drilling 4 holes and using m3 bolts to stick the thing to the plywood?

It feels like it should be easier to fit and remove the engine later on. I'm guessing the 4 screws at the back have something to do with it? Have I got it back to front and the cruciform goes inside the firewall?

I also have no idea what the three tiny threaded holes are for at the front of the motor around the shaft and the little hole on the shaft (well I guess the one on the shaft is for a locking grub screw but I didn't get one with the motor )

[Former Member]

[This posting has been removed]

[Liam Ryan]

Thanks for the reply Tom,

I received this collet with the motor. From reading your post it should be mounted inside the firewall with the shaft coming through or can I just mount outside and screw on this collet ? I've also attached a picture of the plane showing the mounting point of the firewall.

If it's a case where I should buy an adapter or mounting kit that's not a problem

[Geoff S]

The cruciform mount is used to fit the motor onto a firewall just like a glow engine. I usually fit T nuts/threaded inserts inside the firewall so mounting from outside is easier.

The part you illustrate is a prop driver designed to fit directly on the motor shaft. A better method, and one becoming more popular, is to use those 3 threaded holes on the rotating part of the motor body to mount a more substantial prop driver. A lot of motor manufacturers include those together with the cruciform mount when you buy it.

The usual problem with fitting the motor inside the fuselage behind the firewall (common in gliders) is that the 3 motor wires end up at the front and have to pass closely to the rotating outer case. I'm always afraid the motor will commit suicide by cutting its own life support system It's never actually happened to me but there's often very little space. HobbyKing's Glider Drive series overcome this by enclosing the outrunner motor in an outer case and putting plugs at the back for the esc connection.

Geoff

[Liam Ryan]

Thanks Geoff,

Following the advice of yourself and Tom I went ahead and drilled out the holes for the bolts and the wires. I also coated the wire cavity with a thin layer of pva after sanding it to hopefully prevent some wear on the wires from the plywood

[Shaunie]

Hi Liam,

It is normal convention to fit these motor mounts on an X formation rather than a + formation, simply to make adjusting downthrust or sidethrust with washers easier. It also means the motor wires will come through the bulkhead at the top or the bottom rather than a corner. Not that there is anything wrong with your layout, it's just that its not so easy to adjust.

Fit T-nuts from inside the bulkhead facing out **LINK**

Shaunie.

[Geoff S]

Now we tell him . But, as Shaunie says, it's not a big deal.

Geoff

[Liam Ryan]

Thanks guys, I had already epoxied the firewall in but if I need to re-do the fuselage I'll do X it for the next firewall ( My wing isn't sitting very well, updated the build blog asking for advice)

Edited By Liam Ryan on 18/10/2016 15:47:47

Edited By Liam Ryan on 18/10/2016 15:48:01

[Mike T]

Is that a 'DYS' motor, Liam? What size is the shaft?

[Liam Ryan]

Sorry Mike don't know what DYS is? The model is Turnigy D3548/4, shaft is 5mm

http://www.hobbyking.com/hobbyking/store/__18233__Turnigy_D3548_4_1100KV_Brushless_Outrunner_Motor.html

Edited By Liam Ryan on 18/10/2016 22:23:24

[Max Z]

Liam, check that the stub axle on the rear does not protrude beyond the mounting face, otherwise make a recess (or a hole) in the firewall.

Max.

[Mike T]

Posted by Liam Ryan on 18/10/2016 22:23:03:

Sorry Mike don't know what DYS is? The model is Turnigy D3548/4, shaft is 5mm

**LINK**

Edited By Liam Ryan on 18/10/2016 22:23:24

They come out under various names... I was guessing it was a 5mm shaft, in which case that collet will be fine. Most motors that size have a 4mm shaft, which is OK, but this particular brand does 5mm, which is better!