Building a UAV for photo mapping - Packing it all in


The first image shows the recommended distribution of components for the electric version of the Cularis. (Click for higher resolution). In this configuration, the plane balances at the CGO with 3 weights (supplied in the kit) fixed under the tail plane. The component weight budget is


  • Motor/Prop Assemply 225gm
  • Multiplex ESC 34gm
  • Fight Battery 149gm
  • 7Ch Rx 30gm
  • Rx Battery 112gm
  • Cularis cable set 50gm
  • 6 servos 70gm

This gives a total of 670gm. The manufactures claim an all up weight of 1680gm with a wing loading of 30.5g/dm2.



In this image, I have added the Pentax A30 camera and a PicoPilot with PicoGPS. The camera is about 8mm wider than the center opening in the fuselage, so I will have cut back the sides for it to fit. I will also machine out a stepped hole in the base for the extended lens to sit in and see through. If I try to locate the camera further back, then I will have to machine out the two servo openings as well.

The addional weight is


  • Pentax A30 with battery and SD Card 150gm
  • Pico Pilot and GPS 63gm



However, I think the real problem is not the weight but the COG. A simplified calculation of the moments of the camera, the autopilot and the new position of the Tx about the COG, suggest that I will have to add about 70gm to the tail in order to bring the plane back into balance. So the total additional weight will be in the order of 283gm. This will increase the all up weight to 1963gm with a 16% increase in wing loading to 35.6g/dm2.


Although it may be standard practice, I am not really happy about have separate Fight and RX batteries. There are two things to charge and check before each flight and it just seems more elegant to have a single power source with a switch mode SportsBEC. With some searching, I found a DuraMax UltraPro 3s 3600mA Li-po with a flat form factor. The dimensions are 145mm x 50mm x 16.2mm. With a small amount of machining, this will fit in the space previously occupied by the Rx battery. The weight at 280gm plus a Sports BEC is only 35gm more than the previous battery configuration. The real gain is in the balance, as the new heavier battery is behind the COG.

By moving the Rx and autopilot back as shown, the balance weight reduces to 25gm, so in all this solution is a little lighter than the previous one and I get more battery power




Conclusions and Questions


  1. With some careful cutting, I can fit the camera and PicoPilot into the Cularis airframe.
  2. What will happen to the performance of the plane with a 16% increase in wing loading?
  3. Is it a good idea to use a single battery with a SportsBEC? How about noise on the 5V power for the autopilot and GPS?

Building a UAV for phot mapping - Previous Posts

  1. The Goal
  2. Camera Selection
  3. Packing it all in

Views: 2437


3D Robotics
Comment by Chris Anderson on December 22, 2007 at 11:17am
Paul,

Great post, and I love how you thought through the options. Two thoughts:

1) Why not use an ESC with a built-in BEC? You said it's standard practice to have a separate RX battery, but I think that may be mostly for sailplanes, where they can be in the air long after that battery has hit the cut-off threshold for the ESC. For our non-sailplanes, we land as soon as the power starts to fade, so we never have a risk of losing RX power. If you did away with the BEC you'd save a bit more weight and wire clutter.

2) I think when you're editing or republishing your older posts, you're clicking on "Publish now" as opposed to keeping their original date. That's a bit confusing since it messes up the chronological order of everyone's posts. The way you're referred to your previous posts in the post above is just right, although you might want to phrase it "Building a UAV for Photo Mapping: previous posts in this series"
Comment by Wai Weng Kong on December 22, 2007 at 7:02pm
I think another point of using separate Rx battery is to reduce interference. In some cases, the noise generated by the motor may go into the Rx through the BEC of the ESC.
Comment by Paul Gregory on December 23, 2007 at 8:23am
This is my concern. I have already ordered the SportsBEC so I will try it out with the Rx efore deciding which route to take.
Comment by Paul Gregory on December 23, 2007 at 8:36am
Chris

A Multiplex ESC with BEC come with the motor kit for the Cularis, but the instructions tell you to disable the BEC and use a battery instead as it does not give sufficient power for the 6 servos. I have now found several high current switch mode BEC - I just ordered the SportsBEC as I found it first.

The date thing when editing the blogs is most confusing. It would seem that an edit should have the option of leaving the original post date. I have changed the dates on my edited blogs so that at least they are in the right order.

By the way, is there a search facility on this site. I wanted to reference a post I saw a little time ago, but I could not find it.
Comment by Jeffrey Johnson on December 23, 2007 at 8:49am
Paul, I recently posted some images of the latest Cularis we are building. Check here http://www.flickr.com/photos/ortelius/sets/72157603523467101/ ... There has been some serious problems with the wings (check RC Groups for info), so see our solution with dowels holding them in.

We are intending to fly this one with a Nokia N95 and a Canon SD1000.

Jeff
Comment by Jeffrey Johnson on December 23, 2007 at 8:51am
Also notice that we moved the servos to the back.

This implementation still flys a bit nose heavy, so we are working on adding some weight to the back. In the end this bird should also fly our downlink gear as well.
Comment by Paul Gregory on December 23, 2007 at 10:56am
Jeff

Many thanks for posting the photo's. It's quite useful to know that the wings could fall off BEFORE loading the plane with camera, autopilot and other expensive stuff. I will check out RC groups as you suggest.

I also like the idea of moving the elevator and rudder servos to the rear. It not only moves weight to the back, but frees up the cabin area for more cutting if necessary.

Have you any photos with the camera mounted yet?

Paul
Comment by Jeffrey Johnson on December 23, 2007 at 11:00am
Paul, We have not mounted a camera on this particular bird yet, but will be doing so over the next week or two, and will post more photos for you to check out.

Also, regarding your newer UAV post, it is not totally necessary for you to fly an autopilot to cover the 2km2 you are trying to do. With a simple video downlink and video goggles, you can dramatically increase the range you would get from flying normal RC, and the Co-Pilot can do alot to help you level the plane out so it is making nice photos at Nadir.

Anyway, stay in touch, and we are very happy to help you process and publish your images as soon as you have them.

Jeff

3D Robotics
Comment by Chris Anderson on December 23, 2007 at 11:20am
Paul,

The search bar should be at the right of the black strip at the top right of page, opposite of where your name is. Not there on your screen?

Chris
Comment by Paul Gregory on December 23, 2007 at 12:45pm
Chris

Sorry, I did not see the search bar as it got a bit lost up in the top right hand corner.

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