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: 253

Comment by Ben Levitt on March 18, 2010 at 6:23am
Hi Phil,

I run my UDB with a DX7 and an AR6100, and mine works great once the GPS figures out where it is.

It sounds like your board hasn't achieved a GPS lock yet. Do you have a GPS plugged in? Can the GPS see the sky, or are you in your basement? :)

Until you get GPS lock, you can't switch out of manual mode. You'll know you've gotten a GPS lock when the rudder and ailerons wag 4 times. (They wag twice when the board has calibrated the gyros about 10 seconds after powerup, and then 4 times upon GPS lock.)

Comment by Ben Levitt on March 18, 2010 at 6:43am
I should also point out that:

a) MatrixPilot 2.0.3 has fixed the problem you mentioned from the troubleshooting page. We should probably update that page... :)

b) In my experience, Spektrum receivers have been working fine with the UDB since the get-go. Or at least since I began work on MatrixPilot 2.0.

Comment by Rana on March 18, 2010 at 8:20am
Ben, can we enter absolute lat long in MatrixPilot 2.03 ?
I have seen in repository r300, we can do in that.
Comment by Phil Giacalone on March 18, 2010 at 8:29am
Hi Ben,

Thanks very much. That explains it! Now I DO feel silly. My GPS unit has not arrived yet, so the UDB is running without one. I'm waiting for a GS407, which has been out of stock at sparkfun.

BTW, thanks for the wonderful job on the software. This project team amazes me.

Thanks again

Comment by Ben Levitt on March 18, 2010 at 2:41pm
Hi Rana, no 2.0.3 was just a small bugfix release. We're still working on getting the new big features stable and ready for a real release.

Comment by Morli_ on March 18, 2010 at 3:15pm
Hi Phil,
I have been using AR6200 & AR7000 with spectrum module system , they work fine , i have used gear ch for manual to stab mode & Aux 3 mixed with gear for WP mode selection, the issue of-course as you found is no GPS connected to your UDB , once connected , you need to enable it in option file too.
Comment by Phil Giacalone on March 18, 2010 at 4:05pm
Hi Morli,

Thanks for the info and confirmation. Do you mind if I contact you directly once I get my GPS unit? It sounds like you could help me if I have questions about configuration steps for mode selection.

Thanks again!
Comment by Ben Levitt on March 18, 2010 at 4:18pm
Hi Phil, I suggest joining and posting questions to the UAV Dev Board email list here:

Many people on that list could help you out.


P.S. Using my DX7, I prefer to use my 3 position flap switch for mode, which works great, and I also have failsafe set up for RTL if the receiver loses the transmitter signal.
Comment by Phil Giacalone on March 18, 2010 at 4:29pm
Thanks, Ben.

I'll get on that email list. Ok, I'll setup my Spektrum to use the 3 position flap mix switch.
Comment by Morli_ on March 18, 2010 at 4:29pm
Hi Phil , yes you can but Like Ben suggested , join the uavdevboard google group where lot more people can help you , we all are there too.and there is lot of wiki /knowledge base for reference in there


You need to be a member of DIY Drones to add comments!

Join DIY Drones

© 2020   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service