How does this work?

[Daniel G]

Hi everyone, I was looking at this site (http://rcpilot.sourceforge.net/modules/rcap/index.php) which discribes building your own RC autopilot. It mentions that it needs to be connected to a GPS so it can follow the waypoints.
I was wondering how this works, where it plugs into the GPS, and if a Geko 201 (http://www.garmin.com/products/geko201/) GPS would work with it?
Thanks for any help and information. :cool:

[direwolf]

Most hald-held GPS units use the NMEA 0183 (National Marine Electronics Association) digital protocal to communicate with a PC via RS-232 serial interface. From what I've read, the Geko 201 does support NMEA 0183. You'll either have to purchase or build an interface cable to connect to the autopilot. http://pfranc.com/projects/g45contr/g45_idx.htm

If you want to read up on GPS serial communication protocals, this is a good place to start...
http://www.boondog.com/%5Ctutorials%5Cgps%5Cgps.html

-- Brian

[JettPilot]

Yes a gecko 201 will work :D I have one and it is the best GPS to use with this autopilot :)

You buy a cable for your 201, and hook the data cables to the autopilot, program a route into the 201 and you have yourself a UAV :eek:

[Daniel G]

Great!!!! :cool:
Thanks for the info.
Any idea of where I can get the parts for the autopilot?
The links on the website appear to be old and broken.

[kd7ost]

These styles of GPS guidance packages are typically employed with a roll control device, such as a co-pilot from FMA, and an altitude lock device all on your airplane. It steers your plane with rudder input so you have to have an effective rudder. (You don't want to turn on a dime though) This makes a nice setup for aerial photography since it keeps the plane stable. I use a similar device, a PDC-10 from U-nav. U-nav stopped selling the PDC-10 as they advanced their product line to higher levels. I am going to have U-nav's
small amount of remaining PDC-10's available for sale in a few weeks. Let me know if there is any interest in purchasing from any of you guys out there. There will be a limited amount, all new.

Dan

[Daniel G]

So I would still need something that would control and hold my altitude?
If so, what device does that?
Thanks again. :cool:

[kd7ost]

Check this one out. It's the only one I'm aware of that fits in a class of cost we can swing in our projects.

http://www.u-nav.com/picoalt2.htm

I use a unit like this instead of the co-pilot pitch control. The pitch control in a devise like the co-pilot won't keep you at altitude. It will just keep your attitude level in pitch. You can sink or balloon and change altitude.

There are a few devices, (AP4 or something like that) which will work with the same NMEA string from a GPS and keep your altitude where you set it. I'm personally leary of GPS altitude control since it wasn't originally a very dialed in characteristic of GPS units. (altitude I mean) However, with WAAS enabling, there seems to have been significant improvements. I still can't attest to how much porpoising you may get with a GPS unit. 20 to 50 feet of altitude error as each string comes in can have you bouncing up and down around that altitude. Hand held GPS units like the geko 201 only sends altitude information at a rate of once every 2 seconds. GPS altitude comes from the $GPGGA string. Your platform has to deal with that delay. Decreasing resolution will slow down the bouncing by allowing you to porpoise bigger.

The barometric sensor units are hard to beat if your looking for altitude control in and accuracy in a photo platform. But, it's your call. I think several guys on here would jump in with more detailed information on GPS as altitude control. If you just want to avoid hitting the ground or rising out of site, the GPS will do very well with less parts. It is harder to find though. Developers and end users know BP is a more accurate way to go if you need accuracy.

Dan

[Daniel G]

It's the only one I'm aware of that fits in a class of cost we can swing in our projects.
I can't find the cost. Could you tell me what I could expect to pay for one of those units, it definately looks like a good option. :)

[kd7ost]

I should have posted the Home page. From here it's easier to navigate. I'll also post the link to their price list.

Dan

http://www.u-nav.com/
http://www.u-nav.com/Price.htm

[Daniel G]

800$ for the whole setup, plus a co-pilot.
Not too high of a price, I wonder what would happen if I made two of those autopilots one for the elevator and one for the rudder. Do you think that it could be hooked up to work? :)

[Daniel G]

Oh wait, I think messed that up.
The altitude control alone is what I would need, the rest I could build or buy separately. In that case it's only 250$ plus GPS, the copilot, and the parts to build the autopilot. :)
Is that right? :)
Thanks again. :cool:

[kd7ost]

That sounds correct. Cost will naturally vary depending on the parts you chose. Always account for nickel and dime items that you don't concider up front. For example, the geko is a good WAAS enabled unit that operates off of two AAA batteries. You don't want to fly in battery save mode because refresh rate slows way down. AAA batteries die pretty quickly. So you need to keep a good supply on hand of AAA cells. Or, I keep a single 1200 mah LiIon battery, through a 3.3 vdc low drop out regulator powering my geko through the serial port. That resolves power issues but you need a few parts extra to do it.

Dan