Saturday, 26 August 2017

A simple way to measure stick tension

My trusty Taranis X9D has finally suffered its first major issue in four years - a broken spring on the elevator gimbal. And yes, it failed in flight! Fortunately I was able to land the model safely.

The elevator was not pleased!

The cause was a fatigue fracture. Naturally I'm not particularly pleased, but a Google search would indicate that it's a rare failure and not restricted to FrSky either.

Back home, I replaced the broken spring with the unused one from the throttle axis. However, I was concerned that this spring might be weaker, as it had spent all of its life under tension (in order to disengage the self centring mechanism). The question then became: how to measure the stick tension.

The method I came up with is simple: take a rubber band; hook one end round a steel rule and the other round the top of the stick; then read off the extension required to reach the end stop:

Measuring stick tension
It looks crude, but it's good enough to match up the tension on the three self-centring axes. A nice bonus is that even the slightest friction in the gimbal is immediately apparent as the rubber band is pulled. I really like the stock X9D gimbals, so it was surprising to see the amount of friction in the mechanism. The next step is to try this trick with the Horus gimbals to see if they really are better...

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