21 octobre 2010

Converter I2C to PPM

This is a protocol converter for I2C to PPM. It allows the use of standard ESC controler on Mikrokopter or similar.

One of the major drawback of I2C currently, is in case of severe failure on one controller, you may impact all other controllers connected to the I2C bus and lost all motors.
Choosing PPM is more reliable, as each controller is connected separately, it may not interfere with others and reduce a lot the risk of loosing all motors. It allow also to use well proven standard controller with a wide range of choices.

- I2C input from Mikrokopter or similar Flight Control supporting same I2C protocol
- output PPM signal suitable to standards ESC motor controllers
- support 4 or 6 controller (8 controller version coming soon)
- optimized for Turnigy plush or TowerPro Mag8 (re-flashed for Fast PPM)
- smoother motor handling
- PPM frequencies available: 400 Hz (recommended), 200 Hz, 50 Hz (for standard servos)

Any ESC may not work good enough for smooth control on a multikopter. If unsure, tests to check both PPM frequency and motor reactivity.
Also, there is *no* feedback from the ESC to return current or temperature from the controllers, so information such as current consumption from the controllers will not be available anymore.

The version 4/6 from Flyboard is available here:

09 octobre 2010

Update on DSSS and video TX

This is an update to my previous measurements and comments on DSSS/FHSSS technology:
Some spektrum measurements

Recently I had problems with transmission video. It looks that some videos TX in 900 Mhz or 1.2-1.3Ghz band may generate harmonics on the 2.4Ghz band. See this thread:

So it may be very dangerous if you switch ON your RC equipment *before* the video TX: as in DSSS only 2 channels are used, you may well be unlucky and your RC may choose some channels that will be used also by the harmonics of your video TX.

To reduce this problem, you may try to switch ON your RC *after* switching ON the video TX, because then the RC will choose a free channel among those remaining free by the video TX.
But this solution is not very safe, there is another one here:
low pass video filter or here.

Overall, surely the best solution is to add this filter, but you can note that DSSS technology is not very safe in that situation.
Unless DSSS system could dynamically reallocate a new channel if the current one is detected as being saturated, FHSSS or better AFHSS has more chances to work fine in this environment, as shown here:
Review: Hitec Spectra AFHSS 2.4GHz receiver and Optima 7 module (part 2)