Hi,
On Jun 18, 2011, at 10:45 AM, David Conger wrote:
> Hi World,
>
> May I ask a favor?
>
> I have wired my Lisa/M and hoped maybe I could get a review before I attempt to power it this way.
>
> If wiring will work I'll gladly offer it to the Wiki as an example. I've tried to follow advice given in the past for wiring.
From how I see it it should work, not having the ground of the BEC connected may be bit sketchy, but adding it will create a ground loop. I am not sure which setup is the safest here. The resistors on the vertical board should protect the stm32 from any reverse current from the servo though. :)
In my opinion, and I do not have actual experience with Lisa/M yet :P (hopefully soon), but checking out the schematics I would say that connect the ground BEC is better than let it unconnected.
If you connect the BEC ground, all the current demanded by the servo will return along this line to the BEC. If you don't connect it, all the peaks, "high currents" (compared with the rest of the electronics), etc, will return using the servos ground line (the same way chosen by the PWM to return), and these "noisy currents" will step across all the PCB, maybe disturbing analog or other critical signals. From the board, it will go to the main battery ground, and finally it will return along this path to the BEC.
So, yes xD, I will strongly recommend you to connect the Ground BEC to the Ground Servo line. If you can do it at servo's side will be better than PCB side.
The possible ground loop created by connecting this, could be mitigated just twisting the power and ground lines.
What do you think Esden?
>
> Question. Is the resistor required on each PPM out pin? I want to remove the extra pins by removing the daughter board and put only 1 row of pins on the end for only PPM. Will i have to also somehow get the resistor there as well?
The resistor is not a life and death requirement. I added them to protect the gates of the STM32, as I realized already in Lisa/L that sometimes shabby servos like to do strange things to their PPM input lines and manage to fry the STM32. After addition of the resistors on Lisa/L V1.1 this issue was gone that is why I carried it over to Lisa/M.
Yeah, I had the same issue in the past, the problem is that shabby servos (and low-quality electronics in general) tend to generate current peaks (like tiny shorcuts generated for many reasons). This current peaks are mitigated adding a small series resistors, with the capacity of the line, you are making a low pass filter.
As you probably can see there is not very much space on Lisa/M ... but I add the move of the resistors from the vertical board to the mainboard as todo for the next revision of the board, when that happens. :)
Cheers Esden
Looking forward the next revision :P. I recently discover your project, and my passion are the UAVs as well. Hopefully I can help to the next iteration of the board xD.