Teensy 3.2 using External Servo Power Control Design Reference

Development Boards Teensy
1

Hi all -

Using a Teensy 3.2 as a control platform, and servose that are separately powered, is there a design reference or example for how to enable / disable that external servo power. Servo power is 6V. 3 Mitec D89MW servos. Stall current (likely max current draw) is 2200 mA per servo.

Any reference muchly appreciated :slight_smile:

2

You’d just need to send 3x PWM signals from the Teensy to the servos via their respective signal wires; poke aroud online for ‘teensy pwm servo example’ or similar and that should get ya goin

3

I wasn’t clear in my inquiry. Let me re-phrase:

I have no problem with controlling the servos. I am building a high-power rocket that employs ailerons for flight control - to chase apogee and maintain a straight flight in the face of all sorts of things, like wind-shear or launch-rod “whip”, or …

I am trying to address “fail-safe” code in my design. There is a fair amount of code involved with detecting when a failure occurs. For example, if, I am compensating for airframe roll, and over some delta-T, the roll does not correct as predicted, then I will set a fail flag. “Roll” is the least likely to be significant problem. Pitch and Yaw on the other hand can be more problematic, and may result in a very errant flight and certain hazards.

So …if I trip a failure condition, I want to release the control surfaces (the ailerons). If I release servo control, the ailerons will move to a neutral position just due to the aerodynamics involved, just as if when you release you sterring wheel in a car, steering will revert to “straight-ahead”, modulo road pitch, alignment, …, etc.

Servos are often powered with an independant source, for somewhat obvious reasons. So my question is “Are there any design references that address how to disable power to a set of servos as might be needed in a design that has a separate power source of the servos, using Arduino / Teensy as the control platform?”

I imagine that someone has already coded servo-power control for any of a number of robotics projects that employ servos with a separate power source.

Hope this helps :slight_smile:

4

If you’re using analog servos, then servo.detach() (which stops sending the PWM control signal) should work. Analog servos “go limp” when they stop receiving the control signal, but for digital servos, you have to cut the power.

Depending on how big your servos are, a regular N-channel MOSFET might work, connected in the usual way as though you are driving a DC motor, across the power lines to the servo. Pull the control pin high at the beginning of your Arduino sketch, and then when a fault is detected, immediately pull that pin low, which will cut power to the servos.

1 Like
5

I am using DC servos (Mitec D89’s and recently discovered Detach is no-op in the Teensy pwmservo library (not sure why mind you …).

Hence I was looking a schematic of sorts to use a Mosfet circuit to do exactly what you are suggesting, and / or a sketch that reflects use of the Sparkfun Mosfet Power Controller (PRT-11214).

Thx for the response!