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Some help needed with my build

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terry callaghan03/04/2020 17:55:35
237 forum posts
10 photos

Hi chaps.i am trying to sort out a Martin Evans design Columbia. The regulator control runs along the outside of the wrapping and is made up of two rods and three fork connectors. My problem is with having too much slopp in the movement. The rods are on two levels and as a link arm in the middle. Due to lack of space in the position the rods are in the fork connectors are quite small, with only a 2mm hole for a fixing pin. I have tried just fitting a nut and bolt, but the play is too much. What would be a better way to lock the fork connectors, . Thanks.

David George 104/04/2020 08:14:02
1715 forum posts
500 photos

Hi Terry can you put some pictures on as it helps to see what the problem is.


Nick Clarke 304/04/2020 10:58:08
1322 forum posts
53 photos

The fork connectors in the magazine article are not really drawn or described - but the holes on the intermediate rocker and at the throttle handle end are 1/8" so your 2mm bolt would be better if 3mm at least. The hole in the throttle arm at the smokebox end is drawn as 3/32" so 2 mm may be OK here.

However what I suspect was intended, although neither indicated on the drawings or described in the text, would be for the holes in the various arms to be reamed to size and case hardened and a close fitting pin turned to suit each one.

terry callaghan04/04/2020 11:31:46
237 forum posts
10 photos

Thanks chaps, here is a picture of the centre linkage. I think that using bolts is a bad idea as there is far to much play if you add up all the kinks. The movement of the regulator main body is less then a 1/4 turn at best. I think nick your case hardened fork with close fitting pins maybe the answer. Do you think using silver steel for the pins would be ok. 648a21e5-221c-403d-8a5a-f389b4cc015c.jpeg

Nick Clarke 304/04/2020 11:42:54
1322 forum posts
53 photos

I would as that is the small ground finish material I have in stock - but others with wider experience (and a wider range of stock!) may make other suggestions.

Martin Connelly04/04/2020 11:45:31
2013 forum posts
214 photos

I think what you need is like a DIN 609 fit bolt made to suit your requirement. Free machining steel may be best to get a good finish to the correct size.

Martin C

Perko704/04/2020 11:54:42
407 forum posts
31 photos

I know this might be frowned on, but the linkages sold for use in R/C aircraft would seem have the right size range available and appear to be relatively slop-free, reliable, and readily adjustable. Only question is whether they have the strength and durability for this application?

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