How to use the AUX motor on TREX or TREX JR

I would like to use the AUX in the TREX or TREX JR as a weapons control on my robot, but the AUX is showing .35 volts with a meter. why?

my robot is being controlled by R/C - not Automatous at this time.
I am using both the TREX and TREX JR.
the BEC is off
RX is powered by it’s own supply.
and the TREX’s run off a 7.4v 4amp ion battery.

I would like to be able to get 1.5volt - 2.0 volt from the AUX. how could this be possible?


The aux output alternates between high impedance and ground, so what you’re seeing is normal. Section 3.a of the TReX/TReX Jr user’s guides explain how to connect a motor to the aux output. Note that incorrect connections could damage the board, so please read the user’s guide carefully.

- Ben

ok thank you Ben


I read about the Trex and Trex Jr. I think i would like to go with the Option 2 wiring scheme for the Aux.
however I am not using a motor, I am using a mini glow plug which is rated at 1.5-2volt max. I do not
know the mili amps of the glow plug.

I am using a 7.4 volt bat at 4amps. ( this is used in parallel to power all devices )

a few questions
Do I still need to use a diode even though I am not using a motor?
what resistor would I need to use inline from AUX to the small device I am powering (1.5 - 2volt) ?

Can you link me to some information about your glow plug?

- Ben


All i have is the OS site and tower hobbies site but they do not have the mili amp rating.
the voltage is 1.5volts. … XCB27&P=ML

I don’t have any experience with glowplugs, so I can’t really give you too much advice on using them safely. For example, I am not sure if it is reasonable to power one from a PWM, especially a low-frequency one like the 38 Hz auxiliary output. You might be better off using a single NiMH cell as your auxiliary power source and toggling the auxiliary output between 0% and 100% duty cycle (rather than using a higher voltage battery, such as a 7.2 V pack, and limiting your auxiliary output to a maximum duty cycle of 20%).

Since a glowplug is not an inductive load, you will not need the diode.

- Ben


Yes it worked find, I just had to make sure the Neg of the Aux Bat is connected to the Neg of the Aux Motor.

Worked Great !

Thank you


Great, thanks for letting us know how it turned out!

- Ben