Introduction and UDB mode switching question


I've been silently following the progress of the UAV Dev Board team for a while now, and want to congratulate Bill Premerlani and his great team for their amazing accomplishments.

This is my first posting, so please let me introduce myself. I'm relatively new to RC flying, and have very little experience with micro programming, but do have some background in aerospace and software engineering. Anyway, after crashing a few planes, it's exciting to see that such a capable and inexpensive auto pilot has been developed. I've just started digging into all the UDB technical details, so I'm green behind the ears, but hope to contribute in some small way to the team eventually.

I hope you won't mind if I also ask a technical question. I'm having a problem and could use some advice.

At this point I've got the UAV Dev Board setup, programmed with MatrixPilot 2_0_3, and connected to Spektrum servos in an aileron/elevator configuration. BTW, getting to this point is due to the terrific UDB instructions and tips, as well as Pete Hollands' excellent videos, so thank you!

However, I am having an issue getting the UDB to switch modes from my transmitter/receiver. The UDB remains in manual mode (Green light on, Red light off). My apologies if my question is silly, or has already been answered.

The Troubleshooting page ( has the following note.

"Sometimes the board starts ignoring manual controls, or switches back to RTL mode unexpectedly. This is a problem with some receivers that output servo signals at slightly low voltages. This causes the UAV Dev Board to not be able to see them. One solution is to change to a receiver that sends out stronger signals. Another option is to lower the voltage at which the UAV Dev Board runs from 5.0V to 4.5V. This makes the low receiver voltages look stronger relative to the UAV Dev Board's voltage."

I'm wondering if this might explain my problem. If the signal voltage is too low, what voltage is recommended?

Here's my setup:
Red UAV Dev Board
MatrixPilot 2_0_3
Spektrum DX 7 transmitter
Spektrum AR7000 receiver

UDB Spektrum AR7000
---------- ---------------
radio ch 1 --- AILE
radio ch 2 --- ELEV
radio ch 3 --- THRO
radio ch 4 --- AUX 1 (for mode control)
gps --- No gps connected (yet)

UDB Servos & Power
---------- ----------------
servo ch 1 --- Aileron Servos
servo ch 2 --- Elevator Servo
servo ch 3 --- ESC/BEC measured at 5 volts

I've verified that AR7000 AUX 1 output voltage is effected by the 3 way 'Flap Mix' switch on the transmitter. The AUX 1 signal voltage is 0.25, 0.20, or 0.15 volts, depending on switch position. Are these voltages too low? Regardless of switch position, the UDB board does not change modes.

Here's what's observed during testing.

1) Turn on Spektrum Transmitter
1) Connect power to the ESC/BEC:
AR7000 lights turn on
UDB Green light turns on
UDB Red light turns on
2) UDB Red light blinks 6 times
3) UDB Red light turns off
4) UDB Green light remains on
5) Change the position of the 3-position 'Flap Mix' switch on Spektrum transmitter
- this has no effect on UDB modes
6) UDB Green light remains on and Red light remains off
7) UDB provides auto pilot servo control and also allows manual control from the transmitter

One other observation. If the transmitter is turned off, the mode remains the same (Green light remains on, Red light remains off).

The options.h file is currently set to the default values. Do these need to be changed?


It's not clear to me what values the AR7000 (AUX 1) is producing, or how best to measure them.

Thanks in advance for any advice, and sorry for the long-winded first posting.


Views: 252

Comment by Morli_ on March 18, 2010 at 4:36pm
Also pls post questions in forum if relevant topic is already there( look for it in there first) else start a new post in forum. Blog is for sharing new information of common interests to the community.
Comment by Matthew M on March 18, 2010 at 7:36pm
I think you can turn the GPS off as an option in the code; also as NS Rana suggested though I haven't done it my self you could hard code your lat/long if your just testing?
Comment by Riccardo Kuebler on March 19, 2010 at 1:58am

the option to turn GPS off is only for debug. Don't fly with it.

There is a work in progress to have stabilization without GPS, but it is work in progress.

Best regards,

Comment by Matthew M on March 19, 2010 at 6:38am
Thanks Riccardo, I was only suggesting turning it off for debug/test. He doesn't have the GPS yet.


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