GeoCrawler 4 (Predator airframe and AttoPilot autopilot)

Description: This UAV is not functionally very different from GeoCrawler 4, with its off-the-shelf Picopilot GPS-guided autopilot, but it's so much cooler! If you're going to build a UAV, why not make it look like a UAV? And there's no UAV better looking than the Predator B. The challenge with using scale airframes like this is they're usually not as inherently stable as the high-wing trainers we use for the other UAVs, and they typically don't have as much room inside for electronics. This one is better than most. It's an inexpensive and nicely made ARF from Nitro Models, and with a 63" wingspan, it's got the flight performance of a powered glider.

Features: Up to 20 pre-set GPS waypoints. Integrated inertial stabilization. Tried and true system, which offers reliability in exchange for limited flexibility. Camera has a programmable time-lapse function, which is best for autogenerating aerial shots to later assemble over a Google maps grid.

  • Airframe: Nitro Models Predator ($80, modded with an AXI 2208/34 brushless motor, $70)
  • [UPDATE] I crashed that version, in part because the V-tail just isn't enough control by itself and in part because the AXI wasn't enough power. I've now moved back to another Predator model ($67) which has ailerons, and given it a more powerful Hacker A30-28s motor. My post on how to build and enhance it is here. If you do decide to stick with the original Predator without ailerons, you'll probably want to cut off a few inches of the tail, put in a proper motor bulkhead and give it a more beefy outrunner like the Hacker. You might want to extend the area of the V-tail control surfaces, too. It really is hard to control as it is.
  • Autopilot: AttoPilot, the most powerful under-$1,000 autopilot.
  • Imaging: Pentax Optio A30, which is the smallest high-res camera I've found that allows for IR shutter trigger, plus a Prism R/C-controlled IR trigger. (both are around $200). This is also good candidate for the DIY stabilized camera mount described here, which doesn't require the Prism trigger, although note that you'll need to build the version with the Futaba "Pilot Assist" sensor, since this UAV doesn't use IR stabilization.
Build notes (these refer only to the Nitro Models Predator without ailerons; ie, the one I crashed. Build notes on the current Predator, with ailerons, are here.):

1) The Nitro Predator doesn't come with landing gear. I bought an aluminum main gear (something like this would probably do), and used the front gear from Nitro's aileron-enabled Predator model. Something like this would work, and you could make it steerable, too.

2) Because the rear-mounted motor doesn't get any airflow to cool it, I converted the little hatch door underneath it into an airscoop. I also drilled out some holes in the motor mount disk to allow the air to flow through. Here's a pic (click for larger version). NB: this won't be an issue if you cut off some of the tail and put in a proper motor bulkhead and an outrunner motor as described above.

3) You can see details of how I created two equipment layers in the nose, one for UAV gear, one for R/C gear, in this post.

Views: 3483

Comment by Frank Cates on July 16, 2007 at 7:22pm
http://www.rcdude.com/servlet/the-441/Wireless-2.4ghz-Camera-System/Detail

Would this work as a downlink? It is only $80 so if it would work it would bring down the total price of the system.
Comment by Frank Cates on July 16, 2007 at 7:23pm
And the previous comment is actually on the wrong post, I will see if I can get it to the right one.
Comment by Ken May on August 15, 2007 at 10:37am
That motor lists this as it's performance envelope.

"Tiny high torque motors for 7 to 18 oz. airplanes and electric helicopters up to 18 oz."

The airframe has a base weight of 24.7 oz without all the addons. Does this motor have enough power to get this thing going?

Also, I'd love to see a test video of this thing flying. Nice job Chris.

3D Robotics
Comment by Chris Anderson on August 15, 2007 at 4:43pm
We use the 2208/34, The specs on that page are if you want vertical performance for foam acrobatic planes. What we want is slow and sedate flying and good battery life, and this one seems fine for that. (You really don't want to overpower a Predator, which are a bit squirrly at the best of times)

You can see it flying at the end of this video:

3D Robotics
Comment by Chris Anderson on September 9, 2007 at 9:52pm
After more experience, I think Ken May's concern about the power of that motor was well taken. The combination of marginal power and the undersized V-tail eventually did that Predator in. I've now upgraded the replacement Predator to a Hacker A30-28 motor, which is about half again as powerful.
Comment by Ayaz Khan on October 24, 2007 at 5:24pm
how much for this plane
Comment by Harvey Hildreth on January 13, 2008 at 8:23am
Thanks for this post. I'm using your model as a bluprint. It will be my first UAV.
PS: Nitro have the Predator back in stock. I just recieved mine.
Comment by Jason Carter on May 5, 2008 at 10:18am
Chris,

Did you ever get a RTF weight of this airframe?
Comment by UAidiot on May 27, 2008 at 2:19pm
We just ordered a Predator B but I just realized the one I ordered doesn't have ailerons. Would it be difficult to add them or possibly buy a new wing with them installed? We plan on the Co-pilot and nav gear doing most of the flying.

3D Robotics
Comment by Chris Anderson on May 27, 2008 at 3:43pm
Yes, adding ailerons would be pretty difficult. I'd try it with the ruddervators alone (don't make the mistake I did and underpower it) and see if you have a better experience than I did.

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