Author Topic: Making a bar-clamp motor mount (Read 3505 times)

RknRusty · « **on:** August 07, 2017, 04:49:37 PM »

I've been wanting to make a bar-clamp mount, and since my FP.40 has a busted tab corner, now's as good as any for my P-40 ARF.

I'll be using 4-40 brass inserts in the maple beams to hold the bar down. As far as I can tell, I should mount a 1/16" aluminum bearer on the face of the beams. My question is if it would be best to cut away enough of the ply doubler to mount the bearer right on the maple beam. That would keep the engine from setting that much farther outboard. Especially considering it'll also be on top of 2 degree nylon wedges(which I hope will stay put).

Or just slap the whole thing right on top of the doubler??? That sounds kind of cheesy to me.

Thanks for any advice,
Rusty

Gerald Arana · « **Reply #1 on:** August 07, 2017, 04:56:05 PM »

Rusty,

Are you planning on mounting the engine on the Al. and then fastening it to the plane?

If so, I'd go with at least 3/16" Al. and cut out the Plywood for the pads to set directly on the maple beams.

Just my two cents worth......

Jerry

RknRusty · « **Reply #2 on:** August 07, 2017, 05:56:51 PM »

Jerry, my idea is to install the threaded inserts into the beams, glue/screw a strip of 1/16" aluminum to the face of the fuselage with holes that align with the inserts. Then place the engine and offset wedges on top of that and pull it all down tightly with a heavy aluminum bar with 4-40 bolts through the bar, bearer and into the inserts.

Here's a picture that might help:

Oops, the picture is bigger than I intended.

Robert Zambelli · « **Reply #3 on:** August 07, 2017, 06:46:23 PM »

That'll work perfectly - I've done it many times.
But, make the bar clamps from 6061-T6.
I probably have some if you need it.
Bob Z.

Chris Fretz · « **Reply #4 on:** August 07, 2017, 06:46:59 PM »

Quote from: RknRusty on August 07, 2017, 05:56:51 PM

Jerry, my idea is to install the threaded inserts into the beams, glue/screw a strip of 1/16" aluminum to the face of the fuselage with holes that align with the inserts. Then place the engine and offset wedges on top of that and pull it all down tightly with a heavy aluminum bar with 4-40 bolts through the bar, bearer and into the inserts.

Here's a picture that might help:

Oops, the picture is bigger than I intended.

Rusty did you make this cool picture? I'll find the replys interesting on this one.

RknRusty · « **Reply #5 on:** August 07, 2017, 07:39:26 PM »

Thanks, Bob.
Chris, yeah, that's just a Microsoft Publisher page, not even rendered and saved. Then I took a snipping tool picture of it to post.

I think I'll cut away the ply where the thinner bottom aluminum strip will fit. That way it'll be embedded a 16th and flush.
Rusty

RknRusty · « **Reply #6 on:** August 08, 2017, 09:03:14 PM »

I spent some time in the shop today making his bar mount. I worried back and forth about cutting out the doubler so it could sit right on the beam, and be flush with the fuse sides. I was concerned that it might weaken the nose and allow vibration. But Jerry advised me to do it, and Bob didn't say not to, so I dug in, and here's what I got:

(I am also experimenting at hosting my own pictures, so please let me know if it shows up okay on your end.)

I have not yet installed the 4-40 threaded inserts, and I'll use JB Weld tomorrow for that.
I shouldn't have made the lower bearer plate so wide, I didn't realize it was wider than the beam and so the cutout for that one is ugly. I'll pack any gaps in that area with tightly twisted strands of CF-tow fibers and CA. The beam is not molested.

In addition to the 4-40 inserts, the bearer plates will be JB'd and fastened with small wood screws to prevent bowing. Now this clamp will fit any of many engines if I decide to swap out the LA.46 for another engine. I'll also place 2 degree nylon offset wedges under the engine tabs.

Thank you guys for your responses,
Rusty

Chris Fretz · « **Reply #7 on:** August 09, 2017, 03:52:26 AM »

Quote from: RknRusty on August 08, 2017, 09:03:14 PM

I spent some time in the shop today making his bar mount. I worried back and forth about cutting out the doubler so it could sit right on the beam, and be flush with the fuse sides. I was concerned that it might weaken the nose and allow vibration. But Jerry advised me to do it, and Bob didn't say not to, so I dug in, and here's what I got:

(I am also experimenting at hosting my own pictures, so please let me know if it shows up okay on your end.)

I have not yet installed the 4-40 threaded inserts, and I'll use JB Weld tomorrow for that.
I shouldn't have made the lower bearer plate so wide, I didn't realize it was wider than the beam and so the cutout for that one is ugly. I'll pack any gaps in that area with tightly twisted strands of CF-tow fibers and CA. The beam is not molested.

In addition to the 4-40 inserts, the bearer plates will be JB'd and fastened with small wood screws to prevent bowing. Now this clamp will fit any of many engines if I decide to swap out the LA.46 for another engine. I'll also place 2 degree nylon offset wedges under the engine tabs.

Thank you guys for your responses,
Rusty

What do you mean by hosting your own pictures? I see the picture. How come you aren't using epoxy for the inserts? I guess JB Weld holds to wood just as good. Where did you get the aluminum pads? Home depot?

Chris

Gerald Arana · « **Reply #8 on:** August 09, 2017, 09:13:42 AM »

Quote from: RknRusty on August 08, 2017, 09:03:14 PM

I spent some time in the shop today making his bar mount. I worried back and forth about cutting out the doubler so it could sit right on the beam, and be flush with the fuse sides. I was concerned that it might weaken the nose and allow vibration. But Jerry advised me to do it, and Bob didn't say not to, so I dug in, and here's what I got:

(I am also experimenting at hosting my own pictures, so please let me know if it shows up okay on your end.)

I have not yet installed the 4-40 threaded inserts, and I'll use JB Weld tomorrow for that.
I shouldn't have made the lower bearer plate so wide, I didn't realize it was wider than the beam and so the cutout for that one is ugly. I'll pack any gaps in that area with tightly twisted strands of CF-tow fibers and CA. The beam is not molested.

In addition to the 4-40 inserts, the bearer plates will be JB'd and fastened with small wood screws to prevent bowing. Now this clamp will fit any of many engines if I decide to swap out the LA.46 for another engine. I'll also place 2 degree nylon offset wedges under the engine tabs.

Thank you guys for your responses,
Rusty

Rusty, That looks perfect! The only thing I'd do differently is to use epoxy (I guess JB Weld is epoxy) and file (dremel) a couple vertical slots in the threads of the inserts to insure that they won't come out.

Good job!

Jerry

RknRusty · « **Reply #9 on:** August 09, 2017, 02:11:25 PM »

Quote from: #Liner on August 09, 2017, 03:52:26 AM

What do you mean by hosting your own pictures? I see the picture. How come you aren't using epoxy for the inserts? I guess JB Weld holds to wood just as good. Where did you get the aluminum pads? Home depot?

Chris

I usually use JB Weld 24 hour(Not JB Quick) for things involving metal. I have used 30 minute epoxy with no obvious difference in reults.

Chris, I just have a folder in my Dropbox account where I put pictures for forum hosting, and then hot-link straight from there. You have to make one minor change to the filename suffix for hotlinking. That's also the same place I link your newsletter from.

I had part of an old mount that I used, but a source for small quantities is at the following website:
http://www.onlinemetals.com/merchant.cfm?id=68&step=2&top_cat=60

john e. holliday · « **Reply #10 on:** August 09, 2017, 03:24:47 PM »

Thanks for the link.

RknRusty · « **Reply #11 on:** August 15, 2017, 08:39:28 PM »

Here's the finished mount with the motor installed and bolted. It also has 2* thrust wedges. With the brass inserts allowing 12 turns of the 40tpi screws to be biting the brass, I was able to crank the bolts down tighter than could've been done with T-nuts(blind nuts). I also used Loctite on them. I had to chase the threads with a tap, as they must've gotten a smidge of glue in them. Even though I took precautions against that sort of sloppiness.

If you look at the aluminum spinner backplate, there is a screw protruding from the back side that I used as a go-no-go gauge to make sure it has no up or down thrust.

So, what are y'all's opinions on this thing? I'm interested if you approve, disapprove, or are indifferent.
Thanks for watching,
Rusty

john e. holliday · « **Reply #12 on:** August 16, 2017, 11:56:47 AM »

How do you keep the engine in place in case one of the bolts breaks or gets loose? I know on my engine test stands there is a pin that fits through the engine mount holes that keep engine in place in case vibration loosens things up.

RknRusty · « **Reply #13 on:** August 16, 2017, 01:40:13 PM »

Quote from: john e. holliday on August 16, 2017, 11:56:47 AM

How do you keep the engine in place in case one of the bolts breaks or gets loose?

Hmmm, uhh, I don't?

Quote from: john e. holliday on August 16, 2017, 11:56:47 AM

I know on my engine test stands there is a pin that fits through the engine mount holes that keep engine in place in case vibration loosens things up.

I need to add some sort of restraint. One of my buddies on another forum said as much. Thanks for the reminder.
Rusty

Jim Carter · « **Reply #14 on:** August 16, 2017, 02:19:09 PM »

Rusty, just use a couple of drops of thread locker on the bolts and that problem becomes moot! I've used those bar clamps on the old metal motor mounts that were available for r/c and with thread locker I don't think I've ever had a screw back out unless I was intentionally trying to remove it!

RknRusty · « **Reply #15 on:** August 16, 2017, 08:16:53 PM »

Jim, I did. I used red Loctite. I hope that wasn't overkill, maybe the blue would've been smarter, but I figure I can get them back out with soldering iron heat if I ever need to. It was Doc's thought of a bolt breaking that got my attention, I hadn't thought about that. But I've never had it happen before either.

Got my LG on today, control rod and tank tomorrow. Better tape over the chinakote seams too. Shooting for Sunday to fly it. Then I can start working on a Real build, my Windy Cardinal kit. I've had the plans hanging up for a month.
Rusty

Chris Fretz · « **Reply #16 on:** August 17, 2017, 03:38:39 AM »

Quote from: RknRusty on August 16, 2017, 08:16:53 PM

Then I can start working on a Real build, my Windy Cardinal kit. I've had the plans hanging up for a month.
Rusty

What is the difference between a Windy Cardinal and a Brodak one?

Engine mount looks good Rusty.

Chris

RknRusty · « **Reply #17 on:** August 17, 2017, 12:21:53 PM »

That's what it's called on the Brodak box label, "The Windy Urtnowski Cardinal"... or something like that. It's a Brodak kit.

Chris Fretz · « **Reply #18 on:** August 17, 2017, 05:42:03 PM »

Quote from: RknRusty on August 17, 2017, 12:21:53 PM

That's what it's called on the Brodak box label, "The Windy Urtnowski Cardinal"... or something like that. It's a Brodak kit.

Ohhhhh

duhh I should of looked at my box a little closer.

john e. holliday · « **Reply #19 on:** August 18, 2017, 09:51:33 AM »

Don't feel bad I have the same problem of not reading to closely.

Chris Belcher · « **Reply #20 on:** August 19, 2017, 07:41:29 AM »

Brodak carries these...they come in a cardinal arf kit too if I remember correctly.