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Estes - MaxTrax

Published:2002-09-10
Manufacturer:Estes

Contributed by Jeff Vincent

 

For those not familiar with the MaxTrax, it is a new starter kit from Estes with an onboard "Electronic Altimeter". This uses a capsule which drops at a fixed descent rate. The capsule physically senses ejection (apogee), times the interval until it detects landing, then outputs calculated altitude in feet and meters. Promising...

I had a chance to fly the MaxTrax yesterday (Sat.), which was a disappointing experience. Tonight, I did some analysis of the data, which was equaling disappointing. For those not interested in reading further, the short form is that this is a toy that doesn't work (at least my sample didn't), and, even if it did work, it wouldn't be very accurate.

First, a couple of bits of foreshadowing. The Estes instructions read: "NOT INTENDED FOR PRECISE MEASUREMENT". Take them at their word.

Also, the MaxTrax includes a snippet of paper to inform you: "IMPORTANT NOTICE! "Occasionally, the MaxTrax Electronic Capsule will not display the altitude after a launch. If this happens, there was an internal electronic error during the launch or descent. The capsule is NOT DEFECTIVE! Switch the capsule "OFF" and prepare another launch following the directions. "If after the second launch, the capsule still does not display the altitude, there is still an internal electronic error that can be fixed by the factory. RETURN just the CAPSULE to Estes for resetting or new replacement. DO NOT RETURN to place of purchase."

As I mentioned in a previous post, I had some trouble getting readings from my unit in ground testing -- at times under four seconds and around eight seconds. For that reason, I also hand-timed the descent of the MaxTrax capsule (ejection to landing) in my test flights, so I could extrapolate the value it would have returned if it chose to not give an altitude reading.

I made nine flights with a scratchbuilt model (18" BT-56 tube). The weather conditions were hot but calm at Mt. ASTRE. wRASP gave approximate altitudes of 220' (for Bs) and 560' (for Cs) for a Cd of 0.6. Here's data from the flights:

Motor Descent Time Altitude Reading
B6-4 6.75 sec ---
B6-4 7.28 sec ---
C6-5 17.53 sec 371.2'
C6-5 18.31 sec not turned on
C6-5 15.94 sec 98.0'
C6-5 16.62 sec 0.0'
C11-5 17.78 sec 146.9'
C11-5 18.69 sec 20.6'
C11-5 17.84 sec 0.0'

Several things were noticed from the start. The B flights were not giving any data, but I wondered if that might be related to the "no data around eight seconds" glitch previously noted. That's why I went to the C motors early (I had intended three B6 flights and three C6 flights [and maybe C11 flights] for NARTREK Gold data). Perhaps I should have dropped it into the nearest mailbox at that point.

Another thing noted was that the capsule had a tendency to tumble on descent. It has a factory-installed drogue streamer that you are explicitly told not to alter. However, it seems like it isn't long enough / draggy enough to stabilize the capsule in a vertical descent. My hunch is that the shock sensor that detects landing requires a decceleration along the vertical axis -- if it lands at an angle, it may fail to trigger the capsule, resulting in no data.

Things got more interesting when I moved up to C power. The unit gave readings (usually), but they were wacky. The highest value given may have been "close" to (within 33% of) the achieved altitude, but the other three readings were *way* off (>= 75% error). The capsule was still tumbling on descent, so I can only hypothesize the the low altitude readings were the result of it experiencing sufficient decceleration from the tumbling to prematurely trigger the landing sensor.

On a bright note, my hardware worked fine. The model made nine stable and successful flights with no damage aside from normal wear and tear (singed but still quite usable shock cord and mylar streamer).

While the raw data was discouraging, I had some hope that the capsule descent times that I had recorded would salvage the effort. I could use those times and the values observed in ground testing to come up with an altitude figure that the capsule would have reported if it had fallen that length of time. Tonight, I did that calculation, and the other shoe dropped. Here's the data:

Motor Descent Time Calculated Altitude Reading
B6-4 6.75 sec 236'
B6-4 7.28 sec 260'
C6-5 17.53 sec 781'
C6-5 18.31 sec 818'
C6-5 15.94 sec 707'
C6-5 16.62 sec 739'
C11-5 17.78 sec 793'
C11-5 18.69 sec 835'
C11-5 17.84 sec 796'
Motor Average Altitude Backtracked Cd
B6-4 248' 0.171
C6-5 761' 0.153
C11-5 808' 0.105

Those altitudes are too high (from 13% for the B flights to 36% - 44% for the C flights). Even worse, the backtracked Cds are way too low (from 72% for the B to 75% - 83% for the Cs). My estimates may not be perfect, but the Estes data is just plain wrong.

I plan to contact Estes about repair/replacement and any further info they can give on the unit, but I don't expect it to change my opinion of its usability. If you are looking for an altimeter you have two choices: spend the money on a real barometric unit or go the cheap route with a hand-timed drop-streamer (you'll have to calibrate such a streamer yourself in drop testing from a known height and calculate altitude from descent times, but your efforts will yield a cheap, reliable, replaceable method of altitude determination).

by Jeff Vincent - Rocket Cynic™

    Flight Log

    DateRocket NameMotor(s)AltitudeNotes
    2002-08-02Donald Besaw's Estes MaxTraxB4-489 feet Another perfect flight. Altimeter indicated 88.5 feet which must have been the altitude at ...
    2002-08-02Donald Besaw's Estes MaxTraxB6-4- Wind test. Included altimeter indicated 248 feet which looked about right. No damage.
    2002-08-04EMRR's Estes MaxTraxB6-4- Good 1st flight. Nose cone fell, not necessary pointy end down. Read out was blank. Remainder of ...
    2002-08-08EMRR's Estes MaxTraxB6-4412 feet This time it was noticably higher and the delay seemed longer, hence it had fully arc'd over. ...
    2002-08-11EMRR's Estes MaxTraxB6-4311 feet Another good flight. 311.4 on the reading.
    2002-08-24EMRR's Estes MaxTraxC6-5701 feet Great flight. Recovered the Nose Cone which read 701.5 feet. Lost the body.
    2002-08-25Donald Besaw's Estes MaxTraxB6-465 feet Nice flight. Altimeter measured 64.5 feet which was probably ejection altitude.
    2002-09-13Donald Besaw's Estes MaxTraxB4-2296 feet Great flight. Altimeter measured 296.2 feet which looked reasonable. I think short delays give ...
    2002-09-23Donald Besaw's Estes MaxTraxB6-2351 feet Another perfect flight. Altimeter measured 350.6 feet which looked about right. The shock cord ...
    2002-11-28Donald Besaw's Estes MaxTraxB6-4- Wind test, nice flight. Altimeter did not give a reading though.
    2003-01-26Donald Besaw's Estes MaxTraxB6-4- Wind test, good flight, I did not get a readout though.
    2003-01-26Donald Besaw's Estes MaxTraxC6-5- Great flight, very high, I forgot to turn on the altimeter prior to launch, DUMB!!! Short walk for ...
    2003-02-05Donald Besaw's Estes MaxTraxB6-4344 feet Wind test, nice flight. Altimeter indicated 344.0 feet.
    2003-02-21Donald Besaw's Estes MaxTraxB6-4200 feet Wind test, good flight. Altimeter indicated 200.4 feet.
    2003-02-23Donald Besaw's Estes MaxTraxC6-5759 feet Great flight, very high. Altimeter indicated 758.9 feet. Looong walk for recovery. No damage.
    2003-04-15Donald Besaw's Estes MaxTraxB6-4- Nice launch but the shock cord seperated resulting in my first lawn dart. Sustained just a few ...
    2003-04-27Donald Besaw's Estes MaxTraxB4-4- First flight after the previous lawn dart. Nice flight. I didn't get a readout due to the ...
    2003-05-04Donald Besaw's Estes MaxTraxB6-4235 feet Wind test, nice flight. Altimeter indicated 234.5 feet. Booster recovered at the pad. No damage.
    2003-05-13Donald Besaw's Estes MaxTraxA8-3- Although this motor was not recommended for this rocket, I couldn't resist trying it. Didn't get a ...
    2003-05-13Donald Besaw's Estes MaxTraxB6-4- Wind test, good flight. No readout due to altimeter landing in tall grass. No damage.
    2003-06-01Donald Besaw's Estes MaxTraxB6-4216 feet Wind test, nice flight. Altimeter indicated 216.1 feet.
    2003-07-21Donald Besaw's Estes MaxTraxC6-5- Nice high flight. Altitude not known because I couldn't find the altimeter. The search continues ...
    2003-07-30Donald Besaw's Estes MaxTraxB6-4- I never found the first altimeter and got a second one and lost it in tall grass. This rocket is ...
    2004-01-11Mike Kimbler's Estes MaxTraxC6-5- Nominal
    2004-01-31Mike Kimbler's Estes MaxTraxC6-5- Altimeter yet to work
    2004-03-16Serge Zoruba's Estes MaxTraxC6-5- Not a true altimeter. An internal timer starts at ejection and stops when it hits the ground to ...
    2004-03-26Serge Zoruba's Estes MaxTraxC6-5- Ready-to-Fly models have weak link in shock cord to tube connection. Reinforce before flying. Nose ...
    2004-10-12Dave Thompson's Estes MaxTraxB6-5- First test flight. Rocket went straight up, dead perfect line, coasted then ejected. Eject gas ...
    2005-05-24Jerry Nishihira's Estes MaxTraxC6-5741 feet another perfect flight & recovery. Both booster and nose cone landed within 50' from launchpad.
    2005-05-24Jerry Nishihira's Estes MaxTraxB6-4203 feet Perfect flight, recovered 50' from launchpad.
    2006-04-08Dennis Vigil's Estes MaxTraxC6-5- Nice launch and ejection. Nose cone altimeter did not detect impact on grassy field. Recovery of ...
    2006-06-04Daniel Higdon's Estes MaxTraxC6-5918 feet Second flight for my new rocket, and it went almost out of sight! The altimeter/timer read 91.8, ...
    2006-06-04Daniel Higdon's Estes MaxTraxB6-4754 feet Got this from my son for my birthday, and this was its maiden flight. Flight was straight, ...
    2006-06-11Jillian+Benjamin Fried's Estes MaxTraxB6-4- After 3 perfect flights with a B6-2 we tried a B6-4 and the extra 2 secs drifted it into a tree. ...
    2007-04-28Jeff Lane's Estes MaxTraxC6-5- Good flight but no reading.
    2007-05-12Jeff Lane's Estes MaxTraxC6-5- No reading
    2010-08-21Thayne Runyon's Estes MaxTraxB6-4- Altimeter battery was not installed. Perfect flight.

    Comments:

    R.H. (November 19, 2002)

    I just bought this rocket starter set about 3 weeks ago. I just bought it for the new launch pad and the rocket looked cool. My first launch was on a B6-4 my reading was 253 ft. and the next launch was at a school football field, my dad was also flying his new rocket and I flew it on a C6-5 it went straight and was one of the best launches I have ever had. I had to chase the rocket for along time and had to go to another field to get my rocket and the capsule landed about 100 feet from the launch pad. When I got the capsule it read 752 ft. I plan to launch it again next month on some C6-5?s and I'm also testing another Estes rocket 'Stormcaster' that I built it with a 29mm motor mount.

    D.O. (July 13, 2004)

    On 7-13-2004 my kids flew this model 3 times, every time it reported a believable altitude. On a B motor it reported 256ft and 268ft and on a C motor it reported 349ft. Will put my altimeter from my Aerotech Mustang in it and see what happens, although I'm not sure how the model will lift a circuit board with a 9 volt and a baro-tube strapped to it, it seems a bit heavy for even a C engine

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