Homemade Alti-trak!

[Weldo]

Hey guys n gals! I just wanted to share this nifty little tool!

So a few months ago my dad was leafing through an Estes catalog when he noticed the Altitrak, altitude measuring device. I guess inspiration struck and now that he's retired he has some time for projects so he came up with this...





He really surprised me with it! I think it's a brilliant idea. It will give you a rough estimate on the angle from the horizon so with a known distance over ground from the launch rod you can do a simple trigonomic calculation to get an estimate on altitude:

D x Tan(A) = altitude

Where D is the distance from the launch rod and A is the angle observed from the instrument.

I went out to do some launching last weekend and tested it out. It worked very well. I measured my steps at home and two walking paces (one left, one right) for me is about 5 feet, so at the range I paced out about 100 feet and took readings from there. My sister usually comes to the range with me, so she pressed the launch button while I collected the data.

On one small "A" motor model I got about 174 feet and another "B" motor model yielded 284 feet! Data! Even if they are rough estimates it's still really cool to have quantifiable numbers.

So after the concept was proven successful I decided to make a more permanent version of the device.

Here's what I came up with:





I went with a plastic Speed Square to save weight. The wire arm is an 1/8" stainless steel welding rod and the weight on the end is a scrap piece of brass round bar left over from another project with two holes drilled to accept the wire. The screw in end of the brass weight acts as a set screw on the wire, holding the weight in place. The brass piece was drilled and tapped to 8-32 thread. A small notch had to be filed into the pivot point to allow the wire to swing freely.

To fasten the square to the wood handle I carefully pre-drilled down through the edge of the wood and the edge of the square and fastened it with two #6 x 1-1/2" wood screws. These holes were made on a drill press but you could do them with a hand drill if you are very careful.

So there you have it! I just thought I'd share with the hopes that someone might get inspired to try building one for themselves. It's really cool to have real data from a launch! You can make one of these on just a few hours with minimal tools or supplies. The plastic square is only abut $5 from Home Depot and the wire can be made from a coat hanger. The weight can be anything with some mass. The handle can be anything as well, a small PVC pipe, old broom handle, find a nice stick in the back yard, whatever. Get creative!

If anyone decides to try this out, please share your creation!

Thanks for reading!

 

[BBowmaster]

We made some using cardboard, marked with protractors, and dangling sticks we’d freeze in place with a finger to get our measurements. That was... sixth grade? 1975?

 

[ThreeJsDad]

Nicely Done. I will always Applaud Creativity.

 

[kuririn]

Very nice! Who needs all this fancy electronic stuff?
(OK I do)

 

[Weldo]

Haha Thanks! With this one, once you have tracked apogee you can cock your hand to the side and the hanger rests against the square. If you're careful you can freeze it that way.

I've been eyeing up one of the cheapo Estes altimeters but I'm not 100% confident in getting my rockets back every time because of the size of the field where I've been launching.

I really like the Jolly Logic 3 where it makes graphs and stuff on your phone/tablet. That's really cool!

 

[RocketT.Coyote]

Once made one from a protractor, a soda straw, a fishing weight, and a piece of twine.

 

[Voyager1]

But where do the batteries go?

Seriously, that’s a pretty neat low tech solution for a field estimate. Hopefully there’s not too much apogee drift so it can give you a reasonable ballpark altitude. Good stuff!

It would be interesting to compare the low tech estimate with an onboard altimeter.

 

[Scott_650]

But where do the batteries go?

Seriously, that’s a pretty neat low tech solution for a field estimate. Hopefully there’s not too much apogee drift so it can give you a reasonable ballpark altitude. Good stuff!

It would be interesting to compare the low tech estimate with an onboard altimeter.

Couple of years ago I did a rocketry activity with the 8th grade algebra kids at my wife’s school (she taught the regular math class) using the printable altitude trackers Quest used to have on their website. We had multiple teams tracking the rocket - my Custom Rockets Equinox 6 footer - and my altimeter in the rocket. The kids did pretty well on the second launch, if I remember correctly they were within a 3-4 feet of the altimeter reading. Admittedly that was with a fairly large target flying relatively low and slow - 450 feet on an Estes D motor, I think. So yes, these can be accurate but you need three things: practice, multiple tracking teams, and sharp (read young!) eyes!

 

[Voyager1]

You could actually have it reading the altitude directly off a pre-calculated printed scale stuck on the square’s diagonal. A couple of scales for different values of D from the launch pad. No calculators needed!

 

[Weldo]

You could actually have it reading the altitude directly off a pre-calculated printed scale stuck on the square’s diagonal. A couple of scales for different values of D from the launch pad. No calculators needed!

Oh! Nice idea!

 

[GlenP]

Nice project.

The Estes Altitrak has the altitudes printed for a base length of 150 (m, but would work for ft too, right?),

so at a 45-deg angle your altitude is the same as your base length... or pretty close...
it has a finger release that locks the weighted indicator when you release it.

A little target sight or a viewing tube might be helpful on the top of the tracker, one at either end so you know you have the line of sight lined up right for a good measurement, this is a little off, for example, the bug on the handle side is not quite lined up with the cross-hairs sight at the end.

 

[ThreeJsDad]

Nice project.

The Estes Altitrak has the altitudes printed for a base length of 150 (m, but would work for ft too, right?),
View attachment 409422
so at a 45-deg angle your altitude is the same as your base length... or pretty close...
it has a finger release that locks the weighted indicator when you release it.

A little target sight or a viewing tube might be helpful on the top of the tracker, one at either end so you know you have the line of sight lined up right for a good measurement, this is a little off, for example, the bug on the handle side is not quite lined up with the cross-hairs sight at the end.
View attachment 409423

That is a good idea, one could make a chart for different distances and already have the altitude based on the angle. There may not be room on the unit but a small chart could be kept handy.

 

[Buckeye]

If you are serious about using these devices, then you need 3 of them. Illustration by Stine. Equation by me.

 

[Weldo]

Whoa! Next level math! pardon my ignorance but what's COT? Is that the same as Atan or Tan-1?

Also, in this case, the distance from launch rod need not be a known value?

 

[Buckeye]

Whoa! Next level math! pardon my ignorance but what's COT? Is that the same as Atan or Tan-1?

Also, in this case, the distance from launch rod need not be a known value?

COT = cotangent = 1/tangent

It helps make the equation more compact and with less division bars.

The one-station tracker and simple tangent calculation is correct only when the flight is perfectly vertical, ie, never. That's why the old-school competitions use 2 stations that measure both elevation and azimuth. This 3-station measurement with elevation-only is also correct and requires less complex equipment.

The angle measurement stuff is useful for teaching kids, but not as practical as a modern-day altimeter or GPS payload. Don't bother with the Estes How High altimeter. It is a piece of junk. Get a $20-$40 barometric unit from a reputable source. They work very simply and very well.

 

[Weldo]

Ah, I see. That's something I've never thought of. If the rocket's flight path is not perfectly vertical you no longer have a proper right triangle for the trig to work.

I think it's probably close enough for what I'm doing right now. I'd like to try an altimeter sometime in the future but for now it's satisfying enough to have at least some data.

 

[Voyager1]

Ah, I see. That's something I've never thought of. If the rocket's flight path is not perfectly vertical you no longer have a proper right triangle for the trig to work.

I think it's probably close enough for what I'm doing right now. I'd like to try an altimeter sometime in the future but for now it's satisfying enough to have at least some data.

That's correct. Very few flights will have an apogee that is directly over the launch pad, particularly as you go higher and into wind. There is often wind cocking or a slight angle of the launch rod/rail that will send the rocket off a vertical path. The apogee drift will introduce an error into your altitude estimate, unless you use triangulation.