Jack Banner Posted June 14, 2014 Share Posted June 14, 2014 Hi, i am continuing to re-fit an old plane that I inherited but have hit a snag. The plane uses bell cranks for the Aileron activation with a central brass tube, which has a hole drilled in it, joining the two threaded rods from the bell cranks as below: Does anyone recognize this type of fitting and know how I can join it to the servo arm for actuation? Of course the servo will be mounted on it's side using a commercial mount but I am not sure at all how to connect it all up. As always, any help appreciated! Quote Link to comment Share on other sites More sharing options...
Stephen Jones Posted June 14, 2014 Share Posted June 14, 2014 Hi, i have made a similar connection on one of my models i just need to take another picture to show how it works . Not sure this one is clear but you can see i have a snake the operates both ailerons and is connected by the wire to the servo arm . I used wire to allow for the none linear movement of the servo arm . I guess on yours you would insert a threaded rod on to which you would put a commercial horn . Steve . Edited By Stephen Jones on 14/06/2014 21:19:19 Quote Link to comment Share on other sites More sharing options...
Martian Posted June 14, 2014 Share Posted June 14, 2014 looking at that I'd hazard a guess that a linear servo was used, if it was a standard servo horn I thin kit would bind as it traveled through it's arc of movement Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted June 14, 2014 Share Posted June 14, 2014 How big is the hole? If it will take a 2mm bolt then I'd use a short pushrod from the servo with a ball link connecting it to the pushrod joiner, otherwise a short pushrod with a bend on the end to go through the joiner, retain it with a soldered washer. Pete Miller's your man for pushrod and bellcrank setups, personally I prefer to strip them out and fit dual servos in their place, I've done it a few times now. The servo extendions can usually be fed through by removing the plastic shroud at one end and taping the exposed connectors to the pushrod end before pulling it out. Once the lead is through pop the shroud back on, Bob's your Uncle. Servo goes on the bellcrank mounting plate, job's a good'un. Quote Link to comment Share on other sites More sharing options...
Jack Banner Posted June 14, 2014 Author Share Posted June 14, 2014 Thanks for the replies all. I will cobble something together from a threaded rod and see if it binds or not. If it does then I will most likely follow Bob's method and look at fitting dual servo's. cheers Quote Link to comment Share on other sites More sharing options...
Dave Bran Posted June 14, 2014 Share Posted June 14, 2014 Possibly, as I was given on a plane in the 70's, the hole in the rod had a pin/rod sticking out, this would run in a servo horn which was slotted to fit the pin. The slotted servo arm rotates, pushing the pin away either direction. Aileron level would be half slot. Quote Link to comment Share on other sites More sharing options...
Jack Banner Posted June 15, 2014 Author Share Posted June 15, 2014 A slot is a great idea! That will completely remove the vertical movement. I will give that a go. Quote Link to comment Share on other sites More sharing options...
Dave Bran Posted June 15, 2014 Share Posted June 15, 2014 Have also seen it done using thin piano wire as the bent up slot part, this fixed as a extension to a std arm. Gauge chosen correctly, this will prevent surface blowback but allow some spring for avoiding damage during handling knocks. Early RC and before radio was common in the 50's big scale engine powered slot racing cars were also done like this on the steering. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted June 15, 2014 Share Posted June 15, 2014 These should show you how to do it. You can either have a quciklink or just bend the wire and have a swing keeper fitted to stop it coming out of the output arm. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted August 16, 2014 Share Posted August 16, 2014 The single servo with bell-cranks for the aileron was used a lot back when a servo cost a fortune . Not worth the agro now as a servos are comparatively much cheaper and one fitted in each wing gives much better control .The linkages in the bell-crank eventually wear causing sloppy ailerons .Even minute amounts of play case sluggish sloppy control . Quote Link to comment Share on other sites More sharing options...
ZK BAP Posted August 17, 2014 Share Posted August 17, 2014 I agree. Just fit 1 per control surface. Less slop more positive drive. I lost a plane due to bell cranks in the past. Quote Link to comment Share on other sites More sharing options...
Ernie Posted August 17, 2014 Share Posted August 17, 2014 Hi Jack. Have you considered mounting a separate servo for each aileron. Modern servos are very small and light. You have much more control when you set things up, and a bit of insurance if one fails. ernie Quote Link to comment Share on other sites More sharing options...
Jack Banner Posted August 17, 2014 Author Share Posted August 17, 2014 Hey Ernie, indeed I have considered that and have now actually gone that way. I initially set it up with a single servo and the bell cranks but couldn't eliminate the slop inherent in the system, as installed. I now have a standard servo in each wing, it was a simple job to fit some servo boxes in place of the cranks. In fact the most difficult bit was matching the exact shade of yellow solartex I just need to fit a remote glow and the plane will be ready for a test fly. Quote Link to comment Share on other sites More sharing options...
IanN Posted August 17, 2014 Share Posted August 17, 2014 Dual servos have obvious attraction and are favoured by the majority, but that isn't to say bellcrank operation is a poor relation. If properly installed and maintained it's 100% perfectly adequate - albeit you'd need to set up any diff mechanically, although that's not such a chore Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted August 17, 2014 Share Posted August 17, 2014 Not everything that's old was good as I remember...........rip it out and fit twin servos! Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted August 17, 2014 Share Posted August 17, 2014 Posted by IanN on 17/08/2014 12:41:31: Dual servos have obvious attraction and are favoured by the majority, but that isn't to say bellcrank operation is a poor relation. If properly installed and maintained it's 100% perfectly adequate - albeit you'd need to set up any diff mechanically, although that's not such a chore True, but two servos are much easier to install and require zero maintenance. Quote Link to comment Share on other sites More sharing options...
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