Sunday, 10 May 2015

A better motor arming system for the Taranis

In this post I'll review some common features for motor safety as provided on modern transmitters, and describe a simple and secure system for OpenTx.

Throttle check

The first line of defense against accidental spinups is the ubiquitous 'throttle check':

It's better than nothing. However, it means that the throttle is armed before it's needed. Furthermore, the dialog pops up even if the motor is safely disconnected; this in turn can encourage a bad habit of skipping the check.

Throttle lock

Some transmitters offer a 'throttle lock' function, whereby the throttle control can be disabled via a switch. This is a better solution, and is the basis of the alternative approach that I will describe for the Taranis. However, it too suffers from some drawbacks if implemented using a regular switch.

Is there a better solution?

Arming/disarming system for OpenTx

The solution presented here is an arming/kill system which doesn't rely on physical switches being left in a particular position. Instead, it depends on the pilot carrying out a simple sequence in order to arm the motor. The sequence I use is:
  1. Motor to 'off'
  2. Full up elevator + full right aileron, and hold
  3. Pull momentary switch. Hold until confirmation (2 seconds), then release
  4. Release stick
The motor is now armed.

To kill the motor and reset the system:
  • Pull momentary switch

In the field

The arming system has been tested with my MPX Cularis, and it works very nicely. I arm the system just before launch and disarm immediately upon landing. Knowing that the motor can't fire up on the way to the flight line is very reassuring. 


I am currently working on a setup for full-house electric sailplanes, which incorporates this system. [edit 19 July 2105: the finalised E-Soar setup is available from here]

Taranis and Multiplex Cularis testbed for E-soaring setup


Tilman Baumann said...

Using a momentary button for power is a great idea.
I think I will adapt that.

RC Soar said...

Hi Tilman, FYI the code is modified from this virtual latch. The state of L3 would be ANDed with the motor switch.

Miami Mike said...

I'm just getting into OpenTX and currently setting up my new Taranis Plus for a Shadow 2-E. (a 6-servo electric-powered sailplane.) I've looked over your arming system and it sounds great, but I'm worried that if I accidentally pull up the SH switch while flying then I'll have to pull up-elevator to re-arm the motor, and that might be a really bad thing to do if I'm at a low altitude.

I'm thinking of doing something with the right slider (RS) instead. The sequence would begin with the motor control at idle (off) and RS fully down. To arm the motor, move RS fully up, then down to center. With the motor armed, moving RS up would have no effect, but moving it down would disarm it.

I don't know if this is even possible but I'll see if I can figure it out. Meanwhile, I'll keep checking back here. Thanks,

RC Soar said...

A simple solution which I'm already using is to set a minimum pull period on SH, say 2 seconds, so a quick pull won't kill the motor. It'll be integrated in the next versions of E-Soar and ESP. Meantime, the mods are described here

ken meeks said...

I can't get the motor to arm using the steps listed above...full right ail and full up the pull switch for two seconds...HELP flying a radian pro..

RC Soar said...

If you're stuck, suggest look at one of the E-Soar templates to see how it's done. Also make sure that your sticks are properly calibrated.