Nitro throttle set up

[jwatts007]

Measure from centre of screws from the throttle horn and too the centre of the screw in the servo this will give you the correct lenth for the linkage..........

[Steve]

OS50 has 3 marks on the carb body - high, middle and stop.

Set your push rod length as per jwatts post above - measure centre of throttle arm retaining screw to centre of servo output spline and make the push rod the same dimension between the centres of the holes on the ball links at each end.

Make sure the servo is going the right way.

Set your throttle curve to a 50% flat line across the range.

Set throttle endpoints to 100% each way and zero sub trim.

Switch on the radio and heli.

Find a servo horn position that puts the output arm at almost 90 degrees to the push rod - just a hair towards the high end away from 90 degrees is perfect, but not towards the low end.

Install the balls and fit the push rod - the throttle position on the carb body should be just above the middle mark line - 1mm or so. I can't remember of the OS50 has 3 carb marks around the centre - if it does then you want it lined up with the highest of the 3 middle marks at 50% stick. Make this adjustment now by loosening the M3 cap bolt in the centre of the throttle arm and turning the throttle barrel until it's lined up before retightening.

It's important to do all the above at exactly 50% stick position (hence the flat line suggestion), as getting all the above right will pay dividends later on.

Now with the throttle stick in the middle, adjust the throttle curve to zero-50-100.

Carefully check the full control throw of the servo travel - watch out for binding at full and bottom stick. At full throttle, the throttle arm should line up with the high mark on the carb body, and at bottom stick, it should be 1-2mm above the bottom mark. If the throttle servo over stretches and binds at one or both ends, move the ball in a hole on the servo arm, or out a hole on the carb arm and try again. Vica versa if it doesn't go far enough. You want it to be as close as possible to full natural throw with your endpoints at 100% each way - this helps with governor function. You should aim to keep the high and low endpoint values very similar to each other and between 95 and 110%

You can now use a little sub trim top to offset the whole travel range if you need to, and tweak the endpoints to get full stick bang on the high mark, and low stick about 1.5mm above the bottom mark - this is a good starting point for tickover throttle, which will have to be tweaked when the engine is running.

Set your throttle curves in flight modes, and give it a try. Take care with the first start in case the throttle is a tad high - no big deal, but just be prepared to hold onto the head firmly. I always have the travel adjust screen open on the Tx ready to immediately tweak the low endpoint when I make that first start. After many years of doing it, I can basically get it bob-on on the bench, just from being familiar with the engines and where the tickover position is on the carb.

Don't think I've forgotten anything.

[Adsmalan]

Steve,
Just to clarify a point. You mention sub-trim, subtrim to me refers to the servo subtrim to align servo arms and normal trim the trim lever on the transmitter. I assume youre referring to the transmitter trim?

[Steve]

Steve,
Just to clarify a point. You mention sub-trim, subtrim to me refers to the servo subtrim to align servo arms and normal trim the trim lever on the transmitter. I assume youre referring to the transmitter trim?

I meant sub trim, but now you mention it, I do the whole setup with the 'normal' stick-side trim in the middle as well. I never use the throttle stick-side trim on helis at all - I do the setup as per above, and use the dedicated throttle cut on my DSX9 as described earlier in the thread.

If you have a Tx that doesn't have this function, then do all the setup as above with sub trim at zero and stick-side trim in the middle, then when you've finished, you should find that dropping the trim to the bottom is enough to kill the engine. The DX7 has a nifty function you can activate where just touching the trim pushes it straight back up to its default position (i.e. in the middle), ready to fly again.

[Steve]

Just to add - using the trim to adjust the tickover isn't a good idea as it can mess up your governor control. When you setup a governor, you calibrate it to tell it where the tickover and full throttle servo positions are. If you then start fiddling with the tickover position of the servo without recalibrating the governor, then it can all go a little bit pear shaped. Best to get the tickover correct using the endpoints at middle trim position, then run in your engine, then calibrate the governor.

[Adsmalan]

Thanks again thats much clearer. I did have a concern with the gov after throttle set up as I know they need to be as close to 100% as possible with a linear throttle curve. Using a set up with the normal trim to the bottom on the DSX9 lowers the throttle curve to -15% so the curve is no longer linear. The mid trim trim position you mention will obviously negate this issue. One of the benefits of experience is it is much easier to set up if you know how far the throttle barrel needs to be open to produce a reliable idle.

[Steve]

The throttle cut on the DSX9 doesn't adjust the whole curve. It only works when the throttle stick is very low.

And yes, basically the lowest carb mark is engine off, so tickover will be a little bit above that, and you can adjust the throttle cut value so that it hits the mark.

[bolders]

You may also find this link useful. ITs a finless bob vid where he is setting up an OS 50 on a trex 600

Trex600 Nitro Pro Build Vids - HeliFreak

download step-13 throttle servo install and setup