Hip Pocket Builders' Forum

Indoor Free Flight Forum => Indoor Building Tips and Problem Solving => Topic started by: TWWARCH on April 25, 2018, 07:18:55 PM

Title: Motor Pegs
Post by: TWWARCH on April 25, 2018, 07:18:55 PM
Hi. I'm working on my first scale kit and have questions - LOTS of questions. I have Don Ross' book and I tried the search thingy, neither one answered this directly so now I'm asking.

The plan I'm working from calls for a hardwood motor peg glued into the fuselage of the plane. This would mean I can't use a winding stooge (unless my boy counts) and that the motor would have to live in the plane. I've seen hollow aluminum pegs on photos of some models.

1. Is there a hardware store widget that will work as the motor peg or should I go ahead and order the aluminum tubing from a supplier like EBM?

2. Is the peg just friction fit into a sheet balsa panels in the sides of the model? If so, have they ever been known to "walk" out of place in flight?

That's it for now. I'm sure there will be more. Thanks everybody.

Title: Re: Motor Pegs
Post by: tom arnold on April 25, 2018, 07:46:32 PM
Hello TW, welcome to the challenge of scale rubber. If it was easy everybody would do it!
To answer your questions:
1. Order the aluminum tubing (a good amount)----1/8th diameter works well. While you are at it order about 4 feet of fuel tubing.
2. Yes, they can be friction fit and yes, they can walk out with disastrous results, usually while winding. Slice off little donuts from the fuel tubing you bought and slip them on the ends of the peg and you'll never lose it.

Whacha building?

Title: Re: Motor Pegs
Post by: skyraider on April 25, 2018, 08:18:34 PM
Hi TW,
  I'm with Tom on this one. Also, if you glued in the motor peg, how are you going to replace the rubber
without excessive damage to the fuselage?  Your peg depending on what you use, should follow along
the guide lines of what Tom laid out.


Title: Re: Motor Pegs
Post by: TWWARCH on April 25, 2018, 08:44:29 PM
Fantastic! Thanks guys. I brought home a piece of 1/4" waterline from the hardware store today but it was clearly too heavy to go in the plane. The clerk bent over backwards to help me and wouldn't charge for the WL so I didn't have the heart to tell him that it just wouldn't work.

The plane's a Miles Mohawk from Easy Built Models. I picked it because I had a couple of simple stick models behind me and wanted to try something with a fuselage and a low wing. EBM categorized it as easy/easy as regards building/flying so I thought I'd start there. The fuselage is done (and straight!) except for the motor peg. I'm about to start the control surfaces as soon as I round up some cardboard stock to make laminating forms for the tips. I'm not going for scale accuracy really, not even using the proper color tissue, just hoping to get good clean craftsmanship and a nice-looking model that will be durable enough to keep and fly more than a couple of times.


Title: Re: Motor Pegs
Post by: flydean1 on April 26, 2018, 12:11:32 AM
In addition to the stooge, use a winding tube.  That will ensure you can fly more than a couple of times.

Title: Re: Motor Pegs
Post by: gossie on April 26, 2018, 01:14:10 AM
Stooge and winding tube/blast tube FYI.

Title: Re: Motor Pegs
Post by: calgoddard on April 26, 2018, 01:41:02 AM
You should reinforce the balsa wood panels (uprights) that have holes drilled through them for the 1/8-inch diameter hollow Aluminum motor peg. Balsa wood is relatively soft and over time the holes will enlarge and the motor peg will start to loosen.

Buy a sheet of 1/64-inch birch plywood. There are many sources.

Drill two 1/8-inch diameter holes near the edge of the sheet.

Cut two small rectangles from the sheet so that each has a hole in the center. You can easily cut the 1/64-inch plywood with sharp scissors.

Glue one of the rectangles to the inside of each of the balsa wood panels (uprights) that have the holes drilled through them for the 1/8-inch diameter motor peg.  Use white glue or carpenter's glue and use the motor peg to align the holes in the plywood with the holes in the balsa wood panels. Pull out the motor peg right away so that it is not glued in place.

I am attaching a picture from my build of a Dime Scale Hellcat.  It is fairly small (16-inch wing span I think). So the motor peg will be a 3/32-inch diameter Aluminum tube.  If you look closely, you can see one of the small reinforcing plywood rectangles.

Such reinforcement is standard practice in building stick and tissue rubber powered models, at least in my experience.

There are many experts that contribute on this web site.  They will give you excellent advice.  

Title: Re: Motor Pegs
Post by: Rich Adams on April 26, 2018, 08:30:29 AM
Hey TW,

Here is a picture of a pretty standard setup on a motor peg. Aluminum tube with sliced fuel line to retain as Tom described. Some folks flare or glue a ring of one size up aluminum tubing to secure one end.

I was using the thin ply reinforcement technique for the motorpeg balsa and then forgot to do it one day so I just put a drop of CA in the hole to harden it. I had to redrill afterwards since the CA raises the grain a bit. I now use this technique on all of my models and I have never had a hole wear out. Some of my models are seven years old and have flown a lot.

Second, there is a trend of using a tube within a tube for rubber. The motor gets looped around a piece of tubing with the inside diameter the same (or larger) as the outside diameter of the motor peg. Secure the rubber to the middle of the tube with a rubber band. When you install the motor, the peg end is allowed to rotate around the motor peg. This setup allows the rubber to move around at the back when it unwinds and helps to avoid bunching up.

Lastly, you'll also be needing a stuffing stick which is basically a dowel with a forked end to assist you in installing the rubber from the prop end of the airplane. Since I use the tube in a tube system, the forked end fits the motor tubes and then some.

Title: Re: Motor Pegs
Post by: calgoddard on April 26, 2018, 10:02:15 AM
Rich - Thanks for your suggestion about hardening the motor peg holes in the balsa uprights with CA.  Your suggested technique saves time, and more importantly, weight, compared to gluing on plywood rectangles.

TW- Here is a picture of an example of the so-called "wobbly motor peg" that was recommended by Rich.  It helps if the ID of the outer Aluminum tube is larger than the OD of the inner Aluminum tube so that the outer tube can wobble and assist the rubber motor in unwinding evenly.  As Tom Arnold explained in an article somewhere, the science of why this works is mystifying.

Flare the ends of the outer Aluminum tube to help retain the rubber motor on the wobbly motor peg. This can be done by inserting the tip of a Phillips screw driver in each end of the tube and simultaneously pushing and twisting.

If the length of your unwound rubber motor is 2X the hook-to-peg distance, or more, your model will definitely benefit from using a wobbly motor peg. It helps prevent rubber motor bunching during unwinding which can lead to CG shifting and stalling.

Easy Built Models makes nice kits. Keep us posted on your progress in building your Miles Mohawk.

Title: Re: Motor Pegs
Post by: TWWARCH on April 26, 2018, 06:38:06 PM
This is great! You guys have answered all my questions and anticipated a bunch of others. Thanks. Looks pretty straightforward.

Now what about the wire for pinning the plane into the stooge? I was planning to cobble together a stooge with a scrap of wood, a pair of 1/4 ply scraps, a c-clamp, and a section of coat hanger. Thing is - the coat hanger won't fit thru the 3/32" alum tube which I already have because I wanted to try it for prop hangers on stick models. Back to the hardware store to see what i can find i suppose.

Title: Re: Motor Pegs
Post by: calgoddard on April 26, 2018, 07:21:43 PM
TW -

1/16-inch (.062) music wire will easily fit through 1/8-inch Aluminum tubing.

Make a pin for use with your stooge this way. Bend over about 1/2-inch at one end of a six-inch segment of .062-inch music wire in order to keep the pin from sliding all the way through the stooge. It would be a disaster if you are winding and the pin disengages completely from the stooge and your model. I sometimes loop an office rubber band over the opposite ends of the pin and over the stooge to ensure that the pin won't slide out.

Tie a segment of brightly colored ribbon to the bent over end of the pin. It will help you find the pin when it falls into dirt or grass.

Volare Products sells music wire. It is steel.  I am not sure why they call it music wire - I guess because the smaller diameter sizes like .009-inch are used as guitar strings.

You will hear SWG sizes discussed.  I like to use diameter measurements that are in fractions of an inch, specified in decimals.

Buy .032, .047, .055 and .062.  These are standard sizes used in our hobby.  

I just checked. Volare has all these sizes except for .062.  You can probably buy the latter from Walmart.

Title: Re: Motor Pegs
Post by: TWWARCH on April 29, 2018, 06:37:08 PM
Done. Although, as it turns out, drilling precise holes in balsa sheet is not a skill we're born with. After splitting a couple of carefully fitted sheet panels and several pieces of scrap I came back to the forum and did a search. Found the clue I needed here:


After that it went together smoothly. The fuselage is done. And straight! I'm starting to laminate my wingtips tonight.

Thanks guys.