(08/10/02) I saw a thread on RMR about a new Estes' rocket with the capability to determine altitude. I decided to purchase one from the local Walmart. It is a Ready to Fly rocket (for all practical purposes) included with a starter set. Launch pad, controller and two motors (B6-4 and C6-5). The rocket is called the MaxTrax™. Walmart sold it for $18.99. You have to purchase a "button" battery for the nose cone and the (4) four AA batteries for the launch controller separately.

THE LAUNCH EQUIPMENT:

Not much to say here as it is Estes' standard stuff. The pad assembles easily by sliding the three legs into the base slots. The rod comes in two pieces and has to be "bounced" together. The rod, stand-off and deflector plate then go into the 1/8" slot. It has an adjustable tilt with a wing nut to loosen or tighten as needed.

The launch controller is a black plastic box with a place to insert a safety key which lights a bulb indicating continuity. The safety key has a feature which is nice. It must be pushed in to be active. If you let your finger off, it springs back breaking continuity. Nice safety add. By pressing the safety key and then the launch button the rocket is ignited. The 15' wire runs from the launch controller to the launch pad and attached to the ignitors with two "toothless" alligator clips.

THE ROCKET:

The rocket is Ready-to-Fly after you tie the pre-assembled parachute to the elastic shock cord. You also need to put the battery into the nose cone MaxTrax™ Electronic Capsule. You will need a small Phillips-head screw drive to do that.

The rocket has fairly nice looks. It has a black plastic fin can with 4 fins and a motor retention ring. The ring is a twist-lock type that holds the motor in place during flight. The 1.35" (BT56) body tube is covered with a holographic looking silver paper with MaxTrax™ displayed on the side. The nose cone has a black section and a removable red foam covering. Not bad over all.

Overall, for CONSTRUCTION I would rate this kit 5 points . After all, it would be hard to be anything else.

FLIGHT/RECOVERY:

To prepare the MaxTrax™ for flight, you need to put wadding in and then place the parachute into the body tube. Next you put the streamer and nose cone in place. Next place your motor into the mount and twist on the retainer ring. Slide the rocket onto the launch rod, then your turn on (or turn off then on to reset from a prior flight) the electronics capsule.

My first flight was on a B6-4 and was straight and stable. But no reading on the electronics capsule. My second flight was a repeat and still no reading. Both of these flights were on a perfectly calm day and in taller grass. So I felt that maybe the electronics capsule needs to hit a bit harder than the tall grass allowed it.

I tested my theory by setting up the next flight in our newly mowed lawn. With another great lift-off on another B6-4, the nose cone ejected and fell to the ground. With great anticipation I picked it up and low and behold it said 339.1 feet. Success at last.

The next flight was again on a B6-4. It definitely flew higher and the delay seemed longer (which makes me wonder about the variability between motors). It ejected and fell to the ground. This time the reading was 411.9 feet. This was interesting because my RockSim predicted 436 feet.

The last flight in this series on a B6-4 gave me another no reading. Hmmmm. 2 for 5 flights, 40%. That needs to improve.

You may wonder how the MaxTrax™ electronics capsule works. There is a small switch that is held in place by the body tube. The capsule is reset while in this position. Upon ejection the switch activates a timer in the capsule. When the capsule hits a solid surface it stops the timer and calculates the altitude based on the time of the fall.

Below is an interesting report from Jeff Vincent that he said I could use. Check out his experience.

For FLIGHT/RECOVERY, I would rate this kit 2 ½ points . since I have only gained 40% on the readings. The rocket itself flies and recovers nicely.

Overall, the MaxTrax" Starter Set was a great buy for $19. It is unique and adds some additional fun to flying model rockets. The electronics capsule can be used in other Estes kits too. The instructions mention the Tidal Wave, Ionizer, and Code Red. I'm ready to try it with some C and D motors! I give the Starter Set an OVERALL rating of 3 ½ points .

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:

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:

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.

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™

Brief:
A new member showed up at our launch one weekend with a MaxTrax (EST1434), a new starter set from Estes that included an altimeter payload. He had flown it once before and it had claimed an altitude of over 700 feet on a C6-5. When he flew it at our launch, he used the other included motor, a B6-4, and it registered over 350 feet. The shock cord separated, but after some repairs carried out by some of our other members, the bird flew again that day.

At the time, few on-line vendors even listed the MaxTrax, and those that did had it marked as "overdue" or "not released". The flyer in question found his at a local Meijer, and as I had to go get cat food that evening ("uh ... yea, cat food, that's the ticket"), I stopped by the new rocket display at my local store, and there one was. The price was a stunning $21.99 (list is $39.99 and the cheapest I saw it on-line was ~$28), so I snapped it up.

Modifications:
Recovery systems, as noted below.

Construction:
The altimeter is housed in a black styrene capsule that fits into the body tube. On the other end is a foam rubber nose cone tip that fits over the molded "thumb" of the altimeter bay. Despite claims to the contrary, two 1.5 V calculator button cells for the device are included. A nice touch. Mine were Vinnic model L1154, though the more common silver oxide models 357 and A76 would last longer. Only one is required so the other is a spare. A very nice touch. To install the battery, the capsule's rubber tip and two tiny, deeply recessed Phillips head screws must be removed and the halves folded open. The battery fits in a molded holder in the "thumb" with a flip-away upper clip, and the altimeter is in the body.

The electronics are a custom PC board with a single chip covered in carrier material. The board also mounts the on-off switch, LCD display and shock sensor. Off-board is the ejection-detect switch that is held open by the body tube, and closes when the motor charge separates the capsule from the rocket. With only three moving parts and minimal wiring, the device promised to be relatively durable. I was a bit worried that ejection gasses might enter the bay though the two switch openings, but I've yet to see any evidence of that.

As I had designs on this little gizmo for some other birds, I wanted the thing back, so I modified the MaxTrax carrier rocket extensively before its first flight. I added a length of 300# Kevlar and upgraded the elastic to 1/4 inch from the included 1/8th inch wide junk. I also replaced the included pre-built 12-inch plastic chute with the same size Rogue nylon unit, and added an HSPP-4Y Medium HeatShield from Pratt Hobbies. The altimeter capsule is supposed to recover by streamer, but as our launch site is surrounded by tall grass, I added a large snap-swivel to the elastic and hooked it to that. Total dry weight after the modifications was three ounces even, and with an estimated drag coefficient of 0.573, I predicted the altitudes found in the estimated performance table below.

Estimated Performance

As Estes only requires you to assemble the pad, insert the included battery and attach the parachute to the shock cord, the assembly of the bird in stock configuration is pretty easy. As it is likely to fail after just a few flights, though, I'd only rate this bird a 2 on the Essence scale for assembly, needs improvement.

Finishing:
The bird is a standard Estes BT-56-based RTF, with quick-change motor mount and the new two-lug one-piece launch guide. The shock cord is attached though a hole in the body tube to this, making for one of Estes' worst mounts ever, and that's saying something. The body wrap is a nice silver holographic sticker, so the bird will be easy to see in the air, and overall, the rocket is a rather good-looking example of the RTF genre. The launch system is Estes' standard Electron Beam, in all black.

Construction Rating: 2 out of 5

Flight:
I flew the bird nine times in my configuration, on five B6-4s and four C6-5s. I didn't get an altitude reading once. I called Estes and they said that the reason the thing wasn't working was because I had it tied to the parachute. I reconfigured my MaxTrax back to the way Estes intended it to be, swapping out the 12 inch parachute for a 9 inch version. I flew her on the recommended motors again, with the following results.

Fearing that the unit I had was defective, I broke out my back-up MaxTrax and flew it for the last three flights. The ejection sense switch on this unit was intermittent, and it took a little adjusting to get it to work consistently. The two readings I got from it were just as bad as the ones from the first unit, and this capsule was lost in only moderately tall grass on the third flight. Two of us saw right where it came down, but we gave up after thirty minutes of searching. The bird itself survived its repeated flights without damage.

This is how I think MaxTrax works. The ejection sense switch starts an internal timer, which is stopped by the shock switch when the unit hits the ground. The assumed descent rate is then multiplied by the elapsed time to determine the altitude. If the shock switch is activated prior to touchdown (the capsule does tumble pretty badly, the streamers did not keep either of my units pointed straight down), the altitude will be low. If the shock switch isn't activated at touchdown (as it will not be when tied to a parachute), no altitude will be displayed. If the capsule does not fall at the assumed descent rate, the altitude will be erroneous. While the idea behind the MaxTrax is ingenious, it just doesn't work in practice, at least not the way Estes has implemented it.

Recovery:
The bird is over stable and does have a tendency to weathercock. At 2.5 ounces in stock trim, the B6-4 is late, but the C6-5 is nearly perfect. These are the only two Estes motors you can fly in the stock bird, though, limiting the altimeter to two general altitudes, somewhat boring. If it worked, that is; the values I got from my two units just aren't believable. I'd rate the flight characteristics of the MaxTrax a one on the Essence scale, needs a lot of improvement.

Flight Rating: 1 out of 5

Summary:
When I initially saw MaxTrax, I imagined all the kids that would be using it for their school science projects. Once I got some experience with the thing, I realized that there were going to be a whole lot tearful young scientists and frustrated Dads this year. Twenty-one flights on an RTF has got to be some kind of record, but I'm afraid that my MaxTrax's durability was due to my preemptive mods. Given the overall quality of the bird, poor altimeter design, limited flight scope and ensuing high possibility of disappointment, I'd rate the MaxTrax a 1½ overall on the Essence scale, needs drastic improvement.

Overall Rating: 1 ½ out of 5