Range finder / altimeter ideas for a small model craft

I'm working on a hobby RPV (remote piloted vehicle) and we are trying
to come up with an instrument loadout. Initial platform will be a 1/5
scale model plane; working altitude 20-200 feet above ground, ground
speed 10-40 mph. We'll be using an IMU from the autopilot project, but
would like some sort of height-above-ground indication in addition to
absolute altitude data we can gather via GPS/barometric sensors. I've
looked into it, and found 3 basic approaches:

1) Ultrasonic sensors, esp. polaroid sensors. Disadvantage to these
seem to be low range, and low tolerance to flow noise. Cheap, light,
fairly low-power.
2) Radar. This seems like a fairly good application for an UWB radar,
but information is scarce. Anyone have more specifics (price,
availability in small quantities, power, design requirements, etc)
than is available from www.time-domain.com?
3) Lidar. Laser diodes are cheap, but I haven't seen many circuits for
cheap lidar designs. I recall one design using a digital camera CCD
for timing, but can't find it again. LIDAR does have the advantage of
eventually allowing sweeping and amateur cartography, but I'm not sure
if it's possible in our payload / price range. Commercial units seem
fairly big (optics?).

Anyone have suggestions, corrections, pointers to information I've
missed?

Thanks,
R C

 

Hi

One word. Air pressure. O.K. 2 words.

Checkout http://www.steveonweb.com/index.php

Checkout the his "Unmanned Aerial Vehicle"

Jay

 

Eh? I'm looking for a height-above-ground sensor to couple with
absolute altitude provided by GPS and barometric sensors. I would
_like_ to be able use LIDAR to generate topo maps, but it's likely out
of budget.

R C

 

Try www.shfmicro.com. They have cheap, and quite tiny DRO's. The 24GHz
version is around 1" cubed, the 10GHz version is larger and flatter. The
former uses a waveguide, the latter a patch antenna. Both come with a
varactor diode for modulation. There output is the doppler frequency
cuased by motion, however by modulating them you can also derive range
quite simply. Both operate from 5V, although one has a high modulation
voltage. Output is simply a lowish frequency sine wave into a typically
2K load resistor. The patch antenna doesn't have huge range, but it may
be simpler than building a squat horn. You could probably get away
without the horn antenna, haven't tried that. Oh, yeah they work best
when temperature stabilised. I used a very simple set up with an Analog
Devices TMP01 and a 10R 20W TO220 resistor. M/A COM also sell these and
pre built horns. There is a free horn design program via the web site.

Al

 

Sorry, I misread and misunderstood. Double Bad Me. A real bad case of tunnel
vision.

Jay

 

No problem. I probably could've written a more descriptive subject, too.

R C

 

Seemed OK to me?.
The Hang gliding people use silicon, barometric pressure reading
transducers to give altitude and rate of change.
regards
jhon

 

Hi John,

RC is already using GPS and barometric sensors for altitude. I missed that.
He's looking for something additional.

Jay

 

Even worse, I managed to miss it *twice*.
regards
john

 

shfmicro has scaled back operations considerable, it seems.

M/A-COM looks like they have a lot of useful building blocks. I was
hoping to find a complete design somewhere; I haven't built anything
anywhere near microwave frequencies.

Thanks for the pointers, I'll have to see if I can find some reference
works.

R C