Charles Thomas

My Feedback: (43)

How do you get the Spektrum Altimeter to reset to 0'. Everytime I turn it on it will be anywhere from -3' to 6' but never at 0. The is on the workbench or at the field. Took the first one back to the LHS and they gave me another one and the same problem with it. I waited until the last update came out for my DX-8 to see if it would fix it but no luck. I also checked it with my son's DX-8 and the same problem. It also gives readings in flight from -9' to 5000' It's mounted in the fuse and about as static air as you can get.

Charles

chuckk2

First you are seeing the same thing that you might see with an actual aircraft panel altimeter. They have an adjustment for barometric pressure, and have a little window to show what it is set to. You can in a pinch, also set to field altitude, if it is known.
The telemetry sensor and supporting electronics don't have this ability. It would be nice to have it in the transmitters, such that you could set field elevation as an off set. or zero for AGL instead of such things as "standard altitude". Remember that there was also an accuracy spec. for the altitude sensor. This must also be taken into account.

Charles Thomas

My Feedback: (43)

One would have thought that you could have set it to "0" when it was powered up. and that it would be a little more accurate that it is. I did not expect it to be accurate within a couple feet, but several thousand feet is a little much. I would have never got it if I would have known that[] When I got this DX8 last year, the purchase was based on the fact I did not have to send it in for updates and I could have telemetry for engine temp, voltage and altimeter. Never say the least, sure think I made a bad choice to switch radio brands

AndyKunz

Charles, in a proper installation it's very accurate. It sets itself to 0 at powerup, but 0 is within its limits of accuracy (see the manual). It has to be able to record negative altitude since that's a very common situation on the slope.

Like any barometric device, it can be rendered useless by a poor install. If an installation allows the high pressure/high noise prop (or similar high pressure) in, it will report low. Likewise if it's on the vacuum side it will report high. Also, a good engineering understanding of "accuracy" and "resolution" may help with interpretation of results. The location of a good static port on full-scale aircraft is an art.

I regularly fly my altimeters in several models, and all report well within reason and match the outputs of devices such as those from European vendors with long-time history for accuracy.

Question: Why do you think you need to send it in for updates for telemetry functions? If you are running the latest version of code (you can download it yourself) then you have all the available sensors with more coming soon.

Andy

Charles Thomas

My Feedback: (43)

I can understand prop and air pressure having an effect on the barometric pressure having an effect. But why is it when I set up a rx, telemetry module and altimeter on my workbench I get the same readings? No fan on or open window to mess with anything, in fact I do not even remember ever having it read 0 when I turn it on. Here is a photo I just took, each time I turned the radio on it had a different reading from -1.9 to -3.2.

Why do I think I need to send it in? Because I do not think it's working right.. Two different DX8's and two different Altimeters everyone tells me that it should set to "0" at power up, and I can never get it to power up at 0.

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chuckk2

So far, the bench reset for the altimeter modules I have, and bought at the end of the year from horizon, is plus or minus about 3 to 9 feet.
Given that electric motor cooling airflow through the fuselage is involved, it may be the source of the differences I'm seeing. Sorry about the confusion.
One of the sensors does, on occasion, read about 400' high, and at this point I don't know why.
Both sensors are labelled by Spectrum, made by Eagletree, and have empty space on the board for what looks like two adjustment pots.
It turns out that the 400' is about equal to the field height above sea level, just adding to the confusion.
Another seeming unrelated question. Is the DX8 software 2.04 final the same as the 2.04 beta?
Based upon your statement, the sensors should read ~ AGL.

Charles Thomas

My Feedback: (43)

That is the same problem that I am having, so looks like it would not be your motor cooling. After I made the original post I got back a reply from HH service center, wish I had not deleted it now, that stated my problem was normal and that the altimeter was not designed to be an accurate instrument.. To be honest I had just thrown it in a basket and marked it up to a learning experience now after Andy's post from yesterdays that it should power up at "0" I just feel that I cannot trust that the issue is not a problem with the radio[]

Sure wish I had my 9303 back

Franco2fly

Charles,
Cup your hands around the sensor while its on the bench and suck some of the air out..  the reading will jump up.  As Andy is telling you they are EXTREMELY sensitive.  I have 2 now, and they both like to indicate -3 feet on power up.(On a High pressure day)  rainey day and they might read +3  and as also reported, when the Air handler comes on that minimum air pressure might drive the reading to -6.  I've also seen it be -3 in the upstairs workshop, but travel 30 miles to the Flying field, and it reads "0"   ( I think the field is higher than my home)  Fly it and I believe you will find it more than accurate enough for our Model purposes.

KKKKFL

AndyKunz

Charles, let me make it very clear. THEY DO NOT NECESSARILY SHOW 0 ON POWER-UP, as Franco confirms. As they start up they take a bunch of samples and average them to arrive at what it will call 0, but that doesn't mean the sampling isn't changing since then. Sound in your workshop can affect the reading! This is totally and entirely within the sensor, and has nothing to do with the transmitter. Our telemetry system displays what it is given as data - if the sensor tells it 250', then it displays 250'. If you were using your 9503 and STi to show the telemetry, you'd see the same thing.

The altimeter reports AGL, assuming it was near ground level when starting up. This is why it can report negative altitudes - it has to be able to do that for slopers since they often fly below the launch point.

We only released 2.04 final; 2.04 beta was only for our beta testers. Unless you're in the beta test program, you never saw it. The radio is also smart enough not to install a new file of the same version over top of the same version.

Andy

Charles Thomas

My Feedback: (43)

OK,

So whatever the reading is after you turn it on is the true "0" for the flight and sound can affect the reading?? That answers a lot of questions, I always have the TV on in the shop and that explains why my flight readings are so bad. I can assume that it was designed for the slop guys and not to be inside of a fuse with a DA-100 bolted on the front

AndyKunz

Not "for slopers" but "applicable to slopers" as well as most other model types. We try not to design anybody out of a product.

The vibration from a DA-100 will affect ANY MEMS sensor - airspeed, altimeter, gyro, G-meter. If you mount it in foam (like an old-style rx and rx pack) then it should be much better. Airspeed will be less affected, since it works on a differential process, and G-meter (g-meter for the OCD) will average out the vibrations better.

A poor installation will nullify an otherwise outstanding product. Not that your installation is bad, but it is something that all my remember.

Andy

Charles Thomas

My Feedback: (43)

Thanks,

I had mine mounted with velcro. Do you need to have a hole in the fuse to allow the pressure to equalize? I do not have any open holes in the fuse outside of where the hatch meets the fuse.

Franco2fly

I doubt any extra hole in the Fuse is necessary, unless you have an extremely tight, (I mean watertight) contact between the wing and Fuse.  Remember the Altimeter is sensing  a Lack of pressure as the plane moves up.  I have the receiver in a block of Foam rubber like what you find in a seat cushion.  On one edge I took a razor and put an inch long slit.  the Altimeter fits nicely into the slit, and works well.

KKKKFL

AndyKunz

You should be fine there, Charles, so far as openings go. The important thing is to NOT have an opening where it will be pummeled directly by pulses off the prop or by airspeed.

Velcro isn't going to be your friend, though. With the noise and vibration, I really think you want to consider wrapping it in soft foam (not the rubber mat that comes with battery packs sometimes). The soft, spongy type is what you want.

Andy

Charles Thomas

My Feedback: (43)

Thanks,

Will give it a try.

jrazzarelli

Andy,
But wouldn't it be great if my very nice DX18 could reset the power-on altitude to zero using the 'clear' key, and then do the math during the flight by adjusting the reading received accordingly?

Joe

AndyKunz

Joe,

In case you haven't noticed, 0 changes during the flight. Some time try starting on the ground and just sit there. Watch what happens as clouds pass over and as the wind changes direction. The altimeter is so sensitive you can see those barometric changes.

Numerous times I have started, had 0, then -6ft, then taken off, flown to 1500 feet, landed at 12 feet. Or scramble the numbers a little.

Andy

jrazzarelli

Andy

So far the altimeter is a little disappointing.

First it is almost never zero or even a few tenths off at startup. Usually like -3.6 ft, which is a bit large of a variance for just starting up and sitting in a room without air movement. The tolerance should be able to be attenuated (?) if you were able to set the practical range of the sensor. If I have no intention of ever going above 1000 ft AGL, then its ability to sense pressure change to 50,000 ft or whatever is not relevant for me.

I put the sensor into a small block of open cell foam and it started counting down and kept going down to -487 ft. or something. Reset everything and it did it again. Apparently something occured when I stuck it in the foam. So I took the Spektrum sticker/housing/decoration off. I think the sticker was stuck to the top of the sensor or the micro-molex leads had poked through the sticker and there was some conductivity - heck I don't know.. But It seems for a few pennies more you should/could have put a small piece of foam inside to cover the sensor, which would help it be more accurate without the end user having to put it in a block of foam.

And finally, there is no way to get the DX18 to show the altitude and the voltage at the same time, which is disappointing. Even adding a 'current reading' to the telemetry min-max screen would be welcome.

Best,

Joe

Franco2fly

Just re-read through this thread and wanted to enter an update. 

Since the latest Airware update there seems to have been some software modifications that impacted several sensors, notably Altitude.  This combined with my own modifications seem to have "Smoothed" out readings.  I now mount the Altitude sensor in all aircraft within a small pill bottle that has an airtight snap cap.  Holes for cables are cut into the cap, and subsequently glued with Silicon sealant.  I use the very fine yellow tubing that is used for GoldenRod motor twisted wire motor control as the pressure vent.  It can be routed into a wing, or out the bottom of a fuselage.  In any case, my readings now are much more reliable.

KKKKFL

AndyKunz

No, Franco, the only changes are those which we put in the PDF.

Andy

Franco2fly

Ya'know, I'm so accustomed to looking at data that the STi application puts out, that might be where I see the altitude less "Jumpy".  Since I started putting the sensor inside the pill container about the same time as all the recent upgrades, I'm not certain where the real improvements came from.  I do recall difficulties getting consistant readings prior to these upgrades.  Now, I fire up a model in the garage and the read-out will usually be between 0.0 and  minus .3 feet and it doesn't really change much.  Last month, I would see anything from -12 feet to plus 20 feet and the reading would either move up or down but not stay in the same place.  Might be that its Fall.

heheheh

KKKKFL

hogflyer

Franco,

Do you have a picture of your bottle set-up? I want to use an altitude sensor for a power glider with my DX8, but need it to be accurate as I'll be flying with-in 1 mi. of an active Air Force base where we have a 1000' ceiling by agreement with the AFB.

Hogflyer

Franco2fly

I can take a picture, but there's not much to it.  The bottle is plastic, like the one that aspirn comes in.  I've used two one a little larger than the other, but I'm sure you've seen them in your medicine cabinet.  One has a snap cap, the other is the "Kid" proof twist lid. They're about as big as a US quarter around, and maybe an inch long.  I drilled a hole for the tubing and a seperate one for the x-bus cable/connector.  Then I sealed the hole with a bunch of Silicon sealant.  I've poked the vent tubing out into the airstream, in one application and the other one has it into the wing.  Both work equally well, and seem to remove the pressure differences caused by the prop wash on the front of my EAA bi plane (this one gave me fits until I did the canister).

I'm just guessing here, but I believe that encapsulating the sensor in a small container makes it less sensitive to surrounding pressures.  A skinny vent tube seems to smooth the atmospheric pressures out, however there could be software changes that might account for the better readings I'm getting today over the ones that I was getting a month ago.  One last note, I put a small piece of foam, like the stuff you would use to protect a receiver, inside the capsule just to keep the sensor from banging around.

KKKKFL

Franco2fly

Here are some pictures
Some containers


here the goldenrod extends into the airstream


Here I push the tubing into the wing just prior to attaching the wing



Size of the container doesn't seem to matter nor where it pokes out.

I like the smaller container.


KKKKFL

Aerocal

Very good idea to isolate the static pressure source.One thing to remember though is that it can be tough to find a reliable static pressure source outside the fuse as well.If you just stub the line outside the fuse and the opening is facing into the airstream its going to introduce pressure into the static line.If the opening is facing back it could create a vacuum.Its also hard to find a spot against an outside surface that doesnt have a slight pressure difference from static.Generally in full scale applications the static source is routed to a central location on each side of the fuse and then has a tee in the center to equalize any pressure/vacuum effect from the plane being in a slip or skid.The orfice is also as small as possible and is introduced into the airstream at a 90 degree angle. There is a trick or actually more of an art to finding the exact location of a true static pressure source outside the fuse.In some applications it is not reliably possible so static pressure is taken from a outside probe usually integrated into the pitot system.If your running an airspeed sensor you may be able to tee the static line from your can into the static line from the pitot tube and get a more reliable source.