carpetbagger

I would be suspicious of a wood mount that would "indent" easily. Course one could glue-stick a scrap of cheesy 1/32" balsa to the firewall, that would take a push impression fairly well.

thepiper92

Balsa would indent fairly easily, even thick balsa. the firewalls on my builds are balsa, no problem making a mark with something hard with very little pressure, actually anywhere on a build would, but the area is still plenty strong. I am not talking about destroying the wood, just a small area where the mount can make a slight mark, even angle it a tad to make edges touch, just to give a good estimate of positioning.

time bandit

It's a plywood mount and I'm not sure it would make any decent mark. Balsa would easily work for that technique.

thepiper92

Best bet would be ink or paint on back of x mount. Line it up carefully and stamp the wood with it. That, or you'll be going to measuring the hole distance from top, bottom and sides, making note that there could be right thrust built into the area, so the mount may be not in line with the cowl hole, or the cowl itself could be a little off to allow the motor to be centered but angling and coming out of the cowl not quite evenly.

Stevephoon

...

Stevephoon

Draw two lines corner to corner on the mount. Center the X mount hole on the center of the X you drew. Keep the legs evenly spaced to the lines and mount. You should be able to get close enough with that method.

Steve

solentlife

This is my way :

WITH A FIREWALL THAT IS NOT AT ANGLE = perpendicular to fuselage centre lines


a) Fit cowl to model.
b) Marker pen through prop hole - mark centre on firewall.
c) Remove cowl.
d) Lay X mount without motor with centre at mark. Mark best orientation of X.
e) Fit X to motor.
f) Stand model vertically.
g) Hold or fix a straight edge along fuselage top centre line extending past motor. BBQ skewer does nicely.
h) Place motor with X on centre spot.
i) Looking at front of model from ahead ... now move motor slightly RIGHT and UP tilting as you do to keep shaft end in line with BBQ skewer and centred. Tilt should be as required for down and right thrust.
j) Sharp point - mark through at least two of the X mount holes.
k) Note gap of two arms to the firewall - this is the spacer / washer amount to have the thrust amount.
l) Drill and screw the two made .. so motor is reasonably fixed ... make other two marks ... drill and screw up all 4 screws with packing as required.
m) Fit cowl and check.

For Firewalls with offset angle to set thrust lines :

a) Fit cowl to model.
b) Marker pen through prop hole - mark centre on firewall.
c) Remove cowl.
d) Lay X mount without motor with centre at mark. Mark best orientation of X.
e) Slide motor along forewall so shaft aligns with centre, with X mount flat to firewall.
f) Mark, drill and screw


Then reason for marking ORIENTATION of X .. is so that you have a reference for having best way the X sits .. no arm touching cowl or near edge etc.

Some people I know actually tape paper on the firewall to allow a pencil to mark.
Simple .. it works. I know others will have their ways to do it.
Once you've done it a few times ... you basically do it by eye.

Really good kits give a template for mounts .. but those are rare nowadays.


Nigel

time bandit

Thanks for all of the suggestions from everyone. I may try the tapped screw idea out first. If that looks sketchy to me I will use the nut and bolts that I picked up the other day. I really like the idea of a nut and bolt, but as Steve pointed out, the motor mount on the EVA is pretty tight as far as fitting a nut on the backside of the motor mount.

thepiper92

Screws will work fine. Make sure you have a pilot hole before the screw goes in. Due to lack of space, a just my blade or an extremely small flat head to ream out a pilot hole before using the screw

time bandit

I ended up using the 4/40 nut and bolts. I did add some 1/8th plywood braces to the inside of the motor mount on top and bottom behind the holes I drilled for the motor to connect to. That allowed the nuts that hold the motor to have clearance past the side of the motor mount for easier installation. I used the 1/8th thick plywood stick motor mount base to extend the motor forward to clear the front of the cowling.