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The Ohmen

My first electric powered aerobatic model

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Peter Miller20/06/2019 08:26:45
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10062 forum posts
1189 photos
10 articles

MIne is just where Trevor put his. You can hardly notice it. It has the advantage that it is cose the the rear of the battery. The air flows in under the motor, over the speed controller where it is most needed and then past the battery and straight out. IT WORKS

Nigel R20/06/2019 08:32:53
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2968 forum posts
471 photos

"there is plenty of strength provided by the epoxy joint so no need to add any stock"

Out of all of the joints in an airframe, the motor bulkhead to fuselage side is the one I would least want to reduce the strength of.

Dean Sarelius20/06/2019 10:21:55
21 forum posts
17 photos

Thanks Peter and Trevor,

As I will be placing just one pilot into the rear seat I will make the hole in the front seat same as per Trevors pic.

I will also place the re-enforcing for the motor bulkhead.

Cheers,

Dean

Chris North 322/07/2019 05:47:40
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279 forum posts
459 photos

Hi Dean - how is the progress of your Ohmen build going?

Dean Sarelius22/07/2019 09:39:59
21 forum posts
17 photos

img_20190722_172110.jpgimg_20190722_171936.jpgimg_20190722_171914.jpgimg_20190722_171633.jpgHi Chris,

I have completed the cowl but slowing down now as I try to work out a good colour scheme.

Also since I will be covering the fuselage with metallic I was thinking of covering the cowl also but I think it will be easier just to paint and would welcome any feedback on this..?

Here are some pics of the cowl and the plane as it is more or less ready for covering.

cheers

Dean

Martin McIntosh22/07/2019 17:19:10
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2901 forum posts
1062 photos

As you can see from my pics I covered the fus. with metallic and painted the cowl over tissue and dope, by far the easiest way to do it. By the way, that looks like a very neat job.

Edited By Martin McIntosh on 22/07/2019 17:20:35

Chris North 331/07/2019 10:16:08
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279 forum posts
459 photos

Hi Dean - yes it is looking very neat job. You are a lot further along than I am with my build although seeing how others are doing really helps to keep the motivation up. I have not thought about the cowl yet - to be honest I'm not really looking forward to it as i have not made a made up cowl before and the cowl ring is being cut by hand so will not be particularly even either - hopefully it will all come together in the end!

I think the cowl screw cut outs make the covering a little intricate so perhaps painting i the best way to go.

Looking forward to seeing how you get on.

Chris

Chris North 331/07/2019 10:20:18
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279 forum posts
459 photos

Dean - a little off topic but how do you find your laser cutter - is it something you would recommend and if so what type / model do you have?

Chris

Dean Sarelius31/07/2019 11:57:09
21 forum posts
17 photos

Hi Chris,

The laser cutter I have is the Chinese made K40 which I purchased from ebay for around AU$550.

As I prefer to keep things more simple the model I chose is with the analog dial not the digital version.

You will need to invest in making some additions like adding an air compressor, hose and jet as well I would recommend to add LED lighting and replace the cutting table with a sheet of perforated steel with magnets to clamp your pieces, all up extra AU$150. I can send you some pics of the mods which I made if you are interested just let me know.

With these mods I find it to be a very good laser cutter and engraver. I never use it at maximum power normally I cut at about 30-50% maximum. At 50% for example soft balsa up to 3mm is a single pass while 3mm plywood requires a second pass.

I get the plan scanned at my local Office supply shop then I use Solidworks to trace allowing about 0.1mm for the cut. After tracing I copy and paste, laying out the traces into Inkscape with custom dimensions set for the width and length of the balsa wood I will be using for cutting. Inkscape allows you to change the colours of the traces which the K40 laser cutter automatically interprets Red for cutting and Blue for engraving.

I could share the Ohmen files here if anyone is interested in doing it themselves just let me know.

All in all if you plan on building a few models then you will find it a good investment.

I have set up the laser cutter in my garage so should I need to re-cut any parts its super quick and great for all those plywood bulkheads.

There is also a lot of video and user tips on the net.

Dean

Chris North 301/08/2019 01:19:22
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279 forum posts
459 photos

Thanks for the feedback - I will have look and see if I can see it.

And then I need to learn solidworks or turbocad and inkscape! This hobby never ends!

Trevor Crook01/08/2019 07:25:36
833 forum posts
63 photos

Chris, if the cowl screw cut-outs bother you, there's a simple solution - don't have them. The cowl on my Ohmen is located using a couple of small dowel pegs, and retained by the film covering. Electric motors don't need maintenance, but if you need access you can run a scalpel around the join to remove and re-apply covering to replace. I used this method on my electrified Ballerina a few years ago, and it hasn't been off since.

p1010431.jpg

Chris North 302/08/2019 01:08:30
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279 forum posts
459 photos

Hi Trevor - that is a neat trick. I will have a think about that one.

Today I attached the bottom keeper rails to the hatch cover. Simply taped the hatch in position...

20190801_210025.jpg ..turned the fuselage upside down, placed the rails hard against the fuselage sides and tacked with a drop of cyano....20190801_210037.jpg...then removed the hatch and ran a bead of superphatic glue along the inside edges of the rails.

20190801_210325.jpg

Job done and a nice tight fit.

(Still haven't figured out how to rotate my photos in W10 as they are fine on the laptop but not once uploaded to the website)

While this was drying I decided I had better finish the wings so that I can install the wing keeper plate. First thing is to shape the replacement aileron and so this was started with the razor plane- no pictures as it is the same as before and the building board is a complete mess!.

Hopefully I can find some more time over the weekend.

Dean Sarelius02/08/2019 09:20:11
21 forum posts
17 photos

Hi Everyone,

Thank you for all your positive comments on the plane.

I was unable to purchase a hatch clip aka retainer and have been racking my head as to other options.

I see one of the other builds used magnets but I would prefer a mechanical method so was just wondering what if any are the alternatives..?

Peter Miller02/08/2019 10:54:43
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10062 forum posts
1189 photos
10 articles

4-Max and SLEC do them.,AlsoEBay has them by the dozen

kc02/08/2019 13:42:22
5954 forum posts
168 photos

This is what i devised for the Ballerina and should work for any open cockpit design. Can be disguised as a control column etc.   The brass bit is a servo ferrule with a washer and was tinned with solder before assembly.  When assembled  it is jammed in with a bit of wood and the soldering iron touched on, remove the wood when really cool.

hatchcatch.jpghatchcatch.jpg

Edited By kc on 02/08/2019 13:47:15

Dean Sarelius02/08/2019 14:00:15
21 forum posts
17 photos

Thanks KC

Thats perfect..

I will make up one of these which will fit nicely into the cockpit.

Many thanks again,

Cheers,

Dean

kc02/08/2019 17:06:18
5954 forum posts
168 photos

Dean, glad you like the idea. You will notice I also fitted another brass ferrule to stop the wire going too far forward - so my fingers can grab the bent part to operate easily. Of course the hatch had a dowel at the front to prevent hatch lifting off. The hardwood guide block stops the wire from dropping right out of the bulkhead when pulled too far back.

Start saving all the old ballpoint pen springs......they are just right.

Martin McIntosh02/08/2019 19:53:38
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2901 forum posts
1062 photos

I have made these in the past but much simpler to buy a SLEC one. None too easy to position correctly which ever way you go.

Dean Sarelius07/08/2019 08:59:17
21 forum posts
17 photos

Hi KC,

I assembled the hatch latch you kindly provided and it worked a treat.

Here is a picture of the latch below.

Its very easy to simply pull the wire and the hatch is free to lift out.

Also I like the fact that there is nothing protruding above the hatch.

Thanks Again

img_20190807_172036.jpg

Dean Sarelius07/08/2019 09:00:34
21 forum posts
17 photos

Hi everyone,

Just want to know if I should be making some cut outs on the wing for the servo leads..?

img_20190807_172050.jpg

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