GPS guidance
 

Start a new thread and we'll see if we can whip out a new simple guidance doobermerhinkie.

Matt


OK, Matt. :D Lets figure out the new doobermerhinkie. (Thats a nice word by the way) I seen big things referred to as Hogermongombie but it just doesn't have the same impact.

What can we do with this when it's done? Can we sell them? I guess we should start a list of specs.

Dan

RE: GPS guidance
 

I think initially, the thing to do is to simply replicate the operation of the PDC-10. Most consumers will want just that.

1. Reads track error and heading information from NMEA 0183 GPS info sentences RMB and RMC.

2. Connects to servo for steering with a reversible output.

3. Has adjustable gain for max throw adjustment.

4. Output servo command is proportional to track error.

5. Uses a buffer transistor rather than a MAX 242 chip. http://www.rc-cam.com/forum/index.php?showtopic=1014

6. DB9 is optional.

7. Enabled through a spare channel. Should enable with long (close to 1.5ms) pulse so guys can combine enable operation with Y cable to co-pilot or other altitude lock units. Maybe 1.2 to 1.3 ms?

Hows that to start?

Dan

RE: GPS guidance
 

Hmm, let me shoot some pictures of the board I made up last year when we talked about this the first time.

Matt

RE: GPS guidance
 

The new run of PDC-10’s didn’t come about but it appears as there is a suitable sub becoming available. I don’t know anything about this device except to say it is supposed to work the same way as the PDC-10 does.

Good luck. If anybody uses one can you report back on the results?

Dan

http://scalerobotics.com/store/catal...7a024074a5f5b0

RE: GPS guidance
 

Too big!!!! Must be smaller!!!

Matt

RE: GPS guidance
 

That looks GREAT !!! I hope it works as well as the PDC-10... Its not to big, its just big enough for the chip and connectors... Most of the weight and size can be taken off by removing the Serail computer connector and just soldering servo wires with a plug to the GPS unit.... Weight would be almost nothing with that Serial connector cut off :D

JettPilot

RE: GPS guidance
 

Thats funny, my wife always tells me that 3 and 3/8 inches is too small? :) I guess it's all about perception.

The RCAP board is 3 and 3/8" long, and 1 and 5/8" wide. It could be made smaller, but I wanted to keep it non surface mount so less people would be afraid to assemble it. It weighs just 0.8 ounces (23 grams) if you do not install the DB9, and leave out the future use headers.

Walter

[link=http://www.uavs.net]www.uavs.net[/link]
[link=http://www.scalerobotics.com/store/catalog]www.scalerobotics.com/store/catalog[/link]

http://www.uavs.net/rcap2.jpg

RE: GPS guidance
 

Here is another one..
Runs on waypoints like the PDC-10, and also has altitude hold, and a 3rd servo or stepper output to function upon waypoint arrival.
PCM type failsafe and optional failsafe upon large course deviation (+/- 500' alt or 1 mile off course)
Open source code plus it's cheap!

Edit Added: Weight 22gr, 1" square, with Atmel 28 pin

RE: GPS guidance
 

Go Radiohound go........developing the board that is and I think you know we all want altitude lock :)

RE: GPS guidance
 

lvspark,

Can you provide a link for that Atmel-based AP?

Thanks,
Chris

RE: GPS guidance
 

Chris, I can not provide a link at this time.
Wish I could but my hands are tied for now.[:o]

RE: GPS guidance
 

No problem, I understand. I will check periodically for updates...

Chris

RE: GPS guidance
 

I am stumbling on to this without all the info but:

Looking at the board I would suggest a 18F252 pic to increase your code space while retaining pin for pin compatibility. Also if you want to loose the db9 then add a FTDI serial to USB converter chip ($9) and use a usb mini B jack. The ftdi chip also lets you loose the max inverter chip, gives you usb compatibility and doesn't require you to change your code. Unless your using the db9 to attach to the gps unit. In that case forget everything I said. :D

RE: GPS guidance
 

Here's a next generation RCAP. Still being developed, but should be out sometime this summer. It is 1 inch by 2 inches with altimeter hold. It weighs half an ounce. More details when it nears completion. Pictures in order are Top, Bottom, and compared to the size of the RCAP2.

Walter

RE: GPS guidance
 

Is GPS altitude information sufficiently accurate to use for altitude hold?

RE: GPS guidance
 

There is a BP sensor in the picture on the board. I can't speak for Radiohound but I surmise he isn't using GPS information for altitude hold. That would be a crude method alright.

Dan

RE: GPS guidance
 

If the GPS had baro altitude it might be. GPS with WAAS or standalone is not accurate enough. If I set my GPS on the ground I can watch the altitude change every time it updates. Some of these changes are within a 20 foot range. When you thing about it.. If your plane was flying at 60mph and the GPS was updating every 60 seconds.. If it was asked to drop 20 feet to correct its altitude only to update a minute later.. You'd have one heck of a ride.

RE: GPS guidance
 

And we're also dealing with refresh rates in a handheld GPS. Also a processor that has to parse out heading information in some strings and altitude in others. The refresh rate may be as slow as two seconds. In a 60 mph plane by the time it gets that information and acts on it, you might be overshooting your target altitude above and below. Porpoising. Unless you drop the gain way down but then you continue to risk going quite high above and below your altitude or not having enough gain to stay where you set it to hold at.

In My Pico Alt 3 E I can set the gain pretty low but if I have even a degree of up thrust, the plane will climb anyway at full throttle. I have to turn up the gain to get the elevator to react enough to stay at target altitude. But then it can begin to porpoise. Head winds also become a factor in all this. That's with a unit using BP and doing nothing but constantly checking altitude. If the unit only checked altitude once every 2 seconds or so, I would be all over the place altitude wise. Even if the GPS is BP corrected.

Dan

RE: GPS guidance
 

The SR-71 had a couple thousand foot whoopie-do in cruise when relying on baro altitude.. :)

RE: GPS guidance
 

Cool,

I bet that was a fun ride. The error really opens up when flying at mach 2+ eh?

Dan

RE: GPS guidance
 

It's probably not the error so much as going from one airmass to another so rapidly! :)

RE: GPS guidance
 

Radiohound, Amazing job on shrinking the rcap while increasing capabilities at the same time! Great Work!

RE: GPS guidance
 

I have been working a little one and it is progressing very well....

Here is some "log-book" videos taken during this last week of testing...

Video of a hand launch with AP enabled (radio off). The aircraft took off, and completed a 2 waypoint route on auto pilot control.
http://www.rsnw.com/handlaunch.wmv

Video of a return to home scenario. Only one waypoint programmed.
Just after the video cuts, the hovering plane starts flying backwards (big headwind) and fouls gps nav info and I choose to take control..
I am using a garmin 301 with the elec compass turned off... In the set-up of the garmin elec compass, you can set at what speed the gps compass takes over. If would have used the elec compass (set for up to 7mph), when the plane came to a hover, the elec compass would have kept the directional data correct. ( I think :D) Need to test that...
http://www.rsnw.com/return.wmv

Video of easystar completeing the 7 waypoint route and circling the last waypoint attempting to maintain 200' altitude.. It circled the last waypoint for about 3 minutes and drifted down to within 50' AGL. I need to turn up the throttle gain..
http://www.rsnw.com/towpt.wmv

EDIT: In my eariler post I said it was PCM failsafe, it is not. The AP activtes upon loss of control channel.

RE: GPS guidance
 

Went out for another run tonight. Worked like a champ!
The route was 4 waypoints, total distance was 1.67 miles and it completed it in about 1 minute 45 seconds. Average speed somewhere around 57mph! I used a 3 cell on a "27 series" eflight inrunner with 5x4.5 apc.. That easy star really moves out.. It is to fast for smooth runs but it worked so I'm happy.. It is much better on a 2 cell..

pic of track http://www.rsnw.com/track.jpg

RE: GPS guidance
 

Pretty cool video lvspark, will this work in a helo?