Chris Anderson

Basic Stamp autopilot tutorial, part 1

Over in the discussion sidebar, Wayne Garris and James Hall have been working through the details of how to build a BASIC Stamp autopilot, which we use in in GeoCrawler3 (formerly 4--sorry for the confusion!). They're doing a great job of catching bugs and otherwise sharing tips, but this has been a reminder to me that I should post a tutorial on setting up the hardware. So this will be the first of several posts on assembling the board and components for this autopilot, and customizing the software for your own needs.

First, let's just set up the board to control a single servo with the FT639 chip on the Parallax development board (later on I'll show you how to do it using the Parallax servo controller board, if you prefer that). The single FT639 chip has the advantage of being small and easy to integrate into a single-board autopilot, but it's not the greatest servo controller in the world and doesn't handle high-speed applications well (we're just using it on the rudder, so it's fine for our purposes).

In this case I've connected the FT639's serial-in pin to the Stamp's pin 8 (yellow wire), and the FT639's servo 1 output pin to the signal pin to servo connector p15 (blue wire). The black and red are ground and power, of course. Couldn't be easier.

Here's the code that just tests this servo in several position. Once you get this working, the next step will be to read the R/C receiver input signals and pass them through to this servo. Go to this next post here.

Views: 385

James Hall Comment by James Hall on December 29, 2007 at 1:43pm
Thank you Chris. As I have discovered. I had to remove my temperature IC to make room for two extra incoming channels for a total of 6 incoming channels from the Receiver. This time I have swaped out my futaba receiver for a FMA copilot receiver as its a bit smaller and will allow me to keep the flight stabilization sensors in place that where supplied with the Copilot. I now have all 6 channels, (heli) pulsing into the basic stamp 2p with a Parallax servo controller pass those signals onto each servo.

Still waiting shipment on my Parallax datalogger and hitachi 3-axis accelorometer.

Not sure at this point if I will need the FMA heat sensors for stabilization but it will be there if I need. I can disable it by unplugging the sensor for now. I will try to upload some pictures of my hardware setup thus so far.
Mike Frieze Comment by Mike Frieze on January 3, 2008 at 3:42pm
Friend at work directed me to this site. I got impressed very quickly about the topics and community participation.
Decided today to sign up after seeing these tutorials.
I have the ATOM microcontroller dev board that uses BASIC language and is very similar to the Basic Stamp. In following on to tutorial #2 I am not understanding why the receiver output goes to the the stamp? Is it a pass through until the autopilot is engaged?
Chris Anderson Comment by Chris Anderson on January 3, 2008 at 3:55pm
Mike,

Yes, that's right. To ensure that we can fully integrate the RC and autopilot systems, we pass the RC commands through the Stamp while under RC control, and then the Stamp generates its own commands under autopilot control. In some other systems that we haven't revealed yet we do it differently, using a stand-alone board that switches the servos from RC to CPU control, which has some advantages in terms of being able to handle software crashes in the CPU, but it introduces a whole other layer of complexity. Doing it the way we do in this tutorial series--ie, all in software--is the simplest (and smallest, lightest, cheapest) way, and if you write your code properly it's plenty safe.
Mike Frieze Comment by Mike Frieze on January 3, 2008 at 11:49pm
I am not that familiar with this dev board being used. In the picture and description there is a one wire signal going to the servo from the FT639. However a servo has 3 wires. Is the power and ground being supplied to the servo from the dev boards special socket?
Chris Anderson Comment by Chris Anderson on January 4, 2008 at 12:00am
Yes, the servo sockets on that board automatically provide +5v and ground.

This is the board:
http://parallax.com/Store/Microcontrollers/BASICStampDevelopmentBoards/tabid/137/CategoryID/12/List/0/SortField/0/Level/a/ProductID/126/Default.aspx
Scott James Comment by Scott James on January 30, 2008 at 9:14pm
Hi Chris,
Do you have any information / links on connecting the Parallax servo controller board? Also, is there a third party board to replace the development board. I am having nightmares of the wires falling out of the breadboard during flight. :) Thanks!
Chris Anderson Comment by Chris Anderson on January 30, 2008 at 11:36pm
Scott,

I'm afraid I don't. I don't use the Parallax servo controller board, since the FT639 chip works great for me and is much smaller/cheaper. But I assume the wires aren't much different.

As for replacing the dev board, the normal next step would be to switch to a "carrier board", which is designed for wire-wrapping or soldering.
http://parallax.com/Store/Microcontrollers/BASICStampDevelopmentBoards/tabid/137/CategoryID/12/List/0/SortField/0/catpageindex/2/Level/a/ProductID/122/Default.aspx

If that's too big or otherwise not what you want, I'm afraid the next step is custom PCBs, and you're on your own there. Not that hard, but we just haven't gotten there yet.
Simon Pan Comment by Simon Pan on January 31, 2008 at 12:39am
Scott, interfacing the Parallax Servo Controller is pretty easy, if you're using the Board of Education. You just plug the white/red/black cable into one of the servo ports.

Did you try reading the documentation on Parallax's website? It is pretty helpful. If you are using the BOE and still have questions, I can help you out.

If you aren't using the BOE, then I have no experience with that.
Simon Pan Comment by Simon Pan on January 31, 2008 at 12:41am
Sorry for double-posting, but I can't find the edit button.

Anyway here is the documentation for the PSC (Serial)

http://www.parallax.com/Portals/0/Downloads/docs/prod/motors/ServoControllerManualRevBv2_4.pdf
Scott James Comment by Scott James on January 31, 2008 at 2:42am
Thanks Simon, I think I know what is going on with it now....Maybe.... :) I just ordered all the electronics, can't wait to start!

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