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Tuesday, June 21, 2016

Installing The Xpwr 3910 In A 48" EXP

Things came together so fast when I got my new Xpwr 3910 that I forgot to take installation photos.  I have transferred the motor to another plane so I could do this installation article. As always, the plane of choice for me whenever I try something new is the Extreme Flight Extra EXP. I am so familiar with this plane that is it my baseline for anything I want to experiment with.

This airframe is relatively new. It was meant to be a backup plane so it has very little time on it. This
made it ideal for this article. If you are building a new EXP or want to convert an older one to the Xpwr 3910, the process is the same.

Installation is really quite easy, but having good pictures makes telling the story much easier.

The first step was to remove the 2814 motor that I was using. The 2814  and Xpwr 3910share the same bolt hole pattern for mounting the X mount to the motor, so the X mount itself makes a perfect drill jig for mounting the Xpwr 3910. Remove the X mount from the 2814 and bolt it to the firewall. To the left is the bare firewall with the motor removed, and right is the firewall with the X mount bolted into place.

Here I have marked in red the holes we will be drilling.
Just for reference. I used a sharpie to make sure I had plenty of wood surrounding the hole I will be drilling. On the left, I am marking the holes, and on the right, I've removed the mount to check my work. You can see we have plenty of wood to work with.
You can either drill on the marks you made with the sharpie or put the mount back on and use it as a drill jig. I preferred to drill through the mount because it's more precise that way. Once you get them drilled, then make them larger for the 4mm bolts we will be using to mount the motor. 
OK. the hard part is done. Now it's just a matter of assembly. If you have built any of the 60" EXPs, you have some 4mm bolts left over. These are used to attach the X mount on the 60" planes, but it just happens to be the same thread as on the back of the Xpwr 3910. Put a washer on each of the bolts and run them forward through through the holes you drilled in the firewall.
One thing to be careful of is to use the right length bolt. 60" EXPs usually come with three different lengths of 4mm bolts. You can't use the long one because it will protrude into the motor and hit the windings, which would be real bad. The short ones are too short, so I use the middle ones. They protrude just enough into the motor that you can see them, but not enough to get close to the windings.

Since the 3910 is a shorter motor, you will need to space the motor away from the firewall. I used 1/4" spacers that I got at Home Depot in the fasteners section. Below, use a washer first, then the spacer, and then another washer. You may need to use one more or one less washer to get the spacing just right depending on how your cowling lines up.

All that is left to do now is use a long allen driver to reach through the battery compartment forward to to bolts on the back side of the firewall and screw them onto the back of the Xpwr 3910.  Work carefully and slowly to make sure you get the bolts threaded in straight and get them snug, just for now.
Then screw the cowling back on and check alignment with your spinner. Add or remove washers until you get the spacing to your liking. Once you have that the way you want it, go back and tighten the motor mounting bolts down for good. You can either use blue locktite or just check for tightness every so often. I don't really like Locktite, so I just try to stay on top of my maintenance.
You can see I used a washer on each side of the 1/4" spacer and my cowl spacing came out perfect. Yours may vary, so adjust by add/removing washers until you are happy with it. 
Here is my gap and I am actually really pleased with it. Nothing looks worse than a huge gap, unless it's the spinner rubbing on the cowling, so take your time to get it just right. I think if you start with the 1/4" spacer and a washer on each side that will get you really close. 
The Xpwr 3910 puts out 1068 watts at 73 amps.As such, we also need to change out the speed controller to an Airboss 80. Here you can see I mounted it on the bottom of the motorbox, but knowing it was heavier than the Airboss 45, I simply moved it back about 1/2 from where I normally put it, and like this my CG did not change. It's a very neat arrangement that puts the ESC right in front of the Extra's chin cooling scoop and directly in the line of incoming air. With the baffles on either side of the motor, and the ESC in direct incoming air, this keeps the whole package nice and cool.
Remember to set the timing on your Airboss 80 to "high." That's how mine is and it runs perfectly.

OK, as always, all of this stuff seems to be a never ending work in progress. we plan to do much, much more with the Xpwr 3910, and of course the Extra, so stay tuned to the blog for updates. We hope to shoot more video on the next clear day, so please follow my blog and tell all your friends.