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Fitting a 4 Stroke

Trottle linkage

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Dave M02/05/2008 12:47:00
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170 forum posts
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Gents, I have put the electric gear to one side and am now assembling a Hanger 9 pulse XT 40. I want to fit a 4 stroke motor but he throttle linkage is on the left (facing forward), and the model is built with the throttle pushrod on the otherside, for a 2Stroke motor. Also the servo tray has a slot for the throttle servo  to match. I have had a few thoughts about how to solve this little problem and I think that I can fit a mini/micro servo to the base of the fire wall and have a short pushrod direct to the throttle arm. 

Would this be a good way to go? Would there be a vibration problem and should I rubber mount the servo? Or, am I going the wrong way altogether? As always, all advise, comments etc will be appreciated.

All the best,

Dave 

Eric Bray02/05/2008 14:56:00
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Simple option first - can you turn the carb round 180'?

plan 'b'   Big 180 bellcrank behind the firewall or behind the engine, depends on space, to 'change sides'  for the throttle link.

plan 'c'   micro servo behind engine, in front of firewall  it's going to get very hot, and sprayed with fuel/oil/muck.  It would be better behind the firewall, if possible. Mount it on rubber, or stick it in with a big glob of silicon (bathtub sealant) which would work as a damper, but can be peeled off if necessary.

Steve Hargreaves - Moderator02/05/2008 15:34:00
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Very confused here as all my engines both 2 & 4 stroke have their throttle arm on the right hand side (if the motor is upright & you are stood behind the model facing forwards).  The usual problem with 4 stroke throttle linkages is fouling the firewall cos it gets a bit tight in there....

Other option...I think it was Mr Ashby senior who recently reviewd the Pulse in RCM&E & I recall he stuck a 52 four stroke in it.....can David ask his dad what he did withe the throttle linkage????

Dave M02/05/2008 16:12:00
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Steve,In the mag review he bent the wire! I'n not sure I can do this evectively,  the motor I have is an OS FL 70, the carb cannot be turned around as far as I can see, and the link is definately on the left facing forward. Your right about it being a tight fit.

Eric, where can I get such a bell crank, it might be a good solution. Although I did think I could cut some vent slots in the cowling the help cool a servo.

 Dave

Steve Hargreaves - Moderator02/05/2008 16:51:00
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Yes...OS it would seem are on the left!!!!!

Is there no way you can move the servo? Fit another mounting tray on the opposite side of the fuselage in some way...this surely would be easiest.

Erics suggestion of a bellcrank would certainly work but would probably introduce a lot of slop & lost movement unless very carefully set up. (The idea is to have a length of material, pivoted in the middle....you connect the servo to one side & the link to the throttle to the other side so as the servo moves its side forward, the link to the throttle on the opposite side moves backwards...you then reverse (or not!) the servo to get the right "orientation")

A micro servo in the cowl would work but oil, vibration & heat are your enemies here......!!! Is there not room in the fuz for said micro servo.

Or you could buy an ASP70 with its linkage on the right!!!!! 

Personally I'd try & relocate the servo & get a nice straight linkage....

With regard to the space problem with 4-strokes the solution is often to take the control rod past the throttle arm & then double it back on itself (ie bend the wire 180 degrees) & connect to the throttle arm. In this way a push becomes a pull & vice versa & this usually allows sufficient movement to work the throttle fully.

 And you thought battery/prop/ESC/Motor selection was hard!!!!!!! ......Welcome to the oily, smokey "real" side of aeromodelling!!!!!!

Eric Bray02/05/2008 17:15:00
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6600 forum posts
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Re the big bellcrank, micromold used to sell them, or use one intended for a control-line model, or make one form a bit of perspex, ply or paxolin, It doesn't need to be very strong, as it isn't doing anything difficult or heavy.

Dave M02/05/2008 17:37:00
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170 forum posts
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Well, I have had another "sit and stare" at the problem, and I think that I might try relocating the servo and running the push rod along the other side, (As you have said above Steve). If I bend the wire back on its self as you suggest it should work, I didn't think of bending it that way, so thanks. I did also think about mounting the thing upside down but moving the servo will be best.

The ASP suggestion isn't allowed today, it is in the realm of hindsight, and as the OS was an impulse buy at a show (you know how it is), thats what I have to go with ,

Thanks again Chaps,

Dave

Tom Ruut04/05/2008 01:18:00
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50 forum posts

  Hi Dave,

  You described very well an important  facet of aeromodelling problem solving,the "sit and stare".

Dave M04/05/2008 09:14:00
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Doug Ireland07/05/2008 08:38:00
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2088 forum posts
42 photos

Hi Dave,

I've had the same problem in the past fitting OS strokers but a quick look at my daughters' bike provided a workable solution. I now use "bowden" cables on all my throttle linkages and they wotk perfectly! To get around the potential "noise" issue when using metal-to-metal linkages; simply epoxy a plastic clevice to the end of the cable that connects to the throttle.

Works for me!

00108/05/2008 07:59:00
2212 forum posts
1 photos

If using a Bowden cable (bike gear or brake cable) it is possible to use a modified ball joint and save about 10mm of clearance between the firewall and throttle arm. It does require small drills and a small woodscrew and a bit of trial and error.(And patience).

Take a ball & socket, as used on helicopter control rods, normally black, not the white ones with an offset socket. Fit the ball, with its nut to the throttle arm. Use a drill bit the size of the Bowden cable and open up the hole in the plastic part where the threaded control rod normally fits and carefully make it deeper without breaking it into the 'socket'. Make sure that the cable is a good fit. With a fine drill bit make a hole at right angles across the first hole as close to the socket as you dare so that it will take a small woodscrew, one of the smaller servo screws will do. Cut some of the shank of the plastic off, push the cable into the socket and insert the screw so that it splits and grips the cable, tighten & cut the pointed end of the screw off. Pull on the fitting to test.

I have used this method several times and providing you measure everything first, may allow the engine to sit quite close to the firewall.

Dave M24/05/2008 09:33:00
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170 forum posts
3 photos

Thanks everyone who replied to this question, lots of good advice as always. I have finally got on and fitted the motor and connected the throttle linkage. I used a flexible control rod (snake) and a bellcrank set up, fitting ball link end fittings on the short connecting rod between the bellcrank and the throttle arm.I used these as they allow a slight angle where the two ends are not perfectly aligned. There is no access play and I have now run the engine on the ground and it all works well. I will try to add a picture of the set up, not done it before so we'll see if it works!

http://i280.photobucket.com/albums/kk174/davemills123/P5230097.jpg
http://i280.photobucket.com/albums/kk174/davemills123/P5230097.jpg


http://i280.photobucket.com/albums/kk174/davemills123/P5230099.jpg

http://i280.photobucket.com/albums/kk174/davemills123/P5230099.jpg

http://i280.photobucket.com/albums/kk174/davemills123/P5230100.jpg

http://i280.photobucket.com/albums/kk174/davemills123/P5230100.jpg


Once again chaps, thanks for replies,

Dave

Dave M24/05/2008 09:36:00
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170 forum posts
3 photos

By the way, I have used a short length of fuel tube over the little antenna on the spekky rx's to protect them, (picture 3 above), does this seem a good idea ?

Dave

Tim Mackey24/05/2008 09:59:00
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20920 forum posts
304 photos
15 articles
yes.
Dave M24/05/2008 10:00:00
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170 forum posts
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Good!
Eric Bray24/05/2008 21:45:00
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6600 forum posts
2 photos
One comment - It might be a good idea to fasten down that blue outer for the throttle cable. Having a long curve that is unsupported could lead to a variable setting of the throttle, as the cable can flex rather than slide! Otherwise it looks as though you have found a solution to the linkage problem.
Tom Sharp25/05/2008 01:09:00
387 forum posts

Be warned, the undercart on the Pulse is only high enough for an 11 inch prop. 

You may find that a 13 inch prop, as required for an OS 70 four stroke, will catch on the ground in anything but perfect conditions.

Dont ask me how I know.

Dave M25/05/2008 09:04:00
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170 forum posts
3 photos

Eric, you are right, I will brace the outer as it does move and result in a very slight change in throttle opening. I have 12" prop fitted and it seems to have good clearence, unless the model is really nose down, I,m lucky to fly off good grass or a concrete surface, what do you think Tom?

Dave

Marko27/05/2008 18:49:00
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469 forum posts
101 photos
hi Dave would this help i have a wot4 with an 52 2stroke i have just bought a bigger 4stroke so whet i thought i would do is to put it on my wot4 easy to run in but... 2 stroke throtle is on the right hand side but the other engine isn't so what i did was to fit a micro servo onto the engine mount not using the original servo it seems fine so far ...try it ,it might just work for you as well!!!  I dont know how the engine set up is but it might work?................mark
Tim Mackey27/05/2008 19:09:00
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20920 forum posts
304 photos
15 articles
The only thing that bothers me alittle about that plan is a micro servo attached to an IC engine mount - vibration and muchk will not be kind to a micro servo which are really designed for electric flight.

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