Speed Control PWM Voltage/Frequency

[Mitch]

Setting up my quad and discovered an interesting issue. Two of the four speed controls (Turnigy Plush 18a) will not initialize from the gluonpilot pwm output. I've swapped the outputs around, recalibrated multiple ways, reprogrammed the escs.... Each seems normal when connected directly to the receiver but two of the four behave as though they are getting no pwm signal on the gluonboard.

The two escs that are working will initialize on any of the four gluonboard pwm outputs. The other two will not initialize on any output, and exhibit no beeps when I try to calibrate them directly from the gluonboard.

Wondering now if there is a tolerance issue - pwm pulse voltage insufficient or frequency too high. I'll keep looking at it and try to narrow down the problem.

[Mitch]

Status update - the two escs that will not initialize. Neither will initialize at a standard 20ms pwm period from the gluonpilot board either. Looks like the 3.3 volt logic level from the pic is not triggering the esc pwm input.

[Mitch]

That was definitely the problem. The pic 3.3 volt logic output was insufficient to trigger the esc pwm input for two of the four escs. I cludged together an amplifier with a TC427 Mosfet driver to bring the pwm voltage up to the 5 volt rail and the inoperative escs will now arm and operate properly at both 20 and 2.5 ms pwm periods. I think I am going to make up a tiny plugin 4 or 6 channel amplifier board as a permanent solution.

[Tom]

Very strange! The PWM standard for servos should allow everything to work with a PWM below 3V... My 18A plush ESC's all handle the 3V3 perfectly.
Can you see some difference in hardware version or anything?

[Mitch]

I purchased 5 at the same time and they were backordered so it seems they came from the same lot. All appear the same and are marked the same ver 3.1. The 3.3 v output has worked with every other speed control and servo I've tried so far so I don't know if this is anomolous. I'll experiment with some pullups ... maybe that will be a simpler solution. At any rate the amp won't be a huge issue - just a tiny bit of added weight and hardware.

[Mitch]

Here's my permanent solution - hopefully this is due to a batch of escs and nobody else will have to do this. If you do here are the details.

I used the toner transfer method and etched tiny amplifier circuit boards to solder in line for the two escs that would not work. Surface mount TC427 Mosfet drivers are a "single part" solution that I had in my spare parts box so I used those.

Eight parts layed out, toner transferred to board, and sealed


Etched board


Trimmed and soldered in line


A few dabs of hot melt glue and some heat shrink tube to finish

[Tom]

That is one very clean solution! Let's hope this was indeed a single bad batch.

[Tom]

Something similar:
I've been thinking to create an addendum board with 6 opto-isolators for the servo signals. Most opto-isolators can also have 3v3 input and 5V output when needed.

[Mitch]

That's a good idea - may eliminate some noise. I was considering using a 4N26 above but that would require an extra resistor or two.

[Tom]

That's pinuts if you use an 0806