Altimeter deployed drogue during coasting - Low Power

[Tolppisouth]

I'm looking at putting together an altimeter circuit to deploy a drogue at a specific altitude during the coast phase to control the apogee altitude. Why? TARC of course.

I've been looking at the Freescale MHX 5100a altimeter sensor but am stopping to wonder if I'm reinventing the wheel (probably) and the fine folks here could point me in the right direction.

Ideally, an off the shelf solution would be ideal. A project write-up would be a close second.

For those who are going to point out that the kids are supposed to do the work. They will, after I build one for myself. They will build and test it for next year's contest.

By no means is this a new idea by the way.

Thanks!

John

[WillMarchant]

From the TARC rules comes:

Each student member must make a significant contribution to the designing, building, and/or launching of the team's entry. No part of any of these may be done by any adult, by a company (except by the sale of standard off-the-shelf components available to the general public, but not kits or designs for the event), or by any person not a student on that team.

So you must be a team member to propose deploying a drogue and to do the design.

[troj]

Not only that, but how are you going to reliably deploy the system without making use of an ejection charge? The kids cannot handle ejection charges themselves, and thus would be unable to use the rocket in finals.

There are better, easier ways to reaching the goal.

-Kevin

[Pantherjon]

What Kevin and Will said..If the rocket is going too high, add some drag to it, an extra fin..don't bevel the fins..etc..

[Tolppisouth]

I know it has been done before. Some of the Madison teams had used them somehow in the past. If suggested to students that it has been used in the past they can choose to or not.

The use of a drogue combats the variability of motors (as much as 20%). The strategy is to use a ever so slightly over powered motor and depend on the drogue for a reproducible apogee.

The use of motors in a tight weight range narrows things also.

As for adding more drag, it still doesn't address the issue of motor variability.

As for the design and building. There is nothing preventing kids from using a design on the internet and my son has breadboarded 555 based circuits for years and has done some soldering. He can build it.

Again, has anyone designed one of these or not. Is there an off the shelf solution?

John

[jsdemar]

The use of a drogue combats the variability of motors (as much as 20%). The strategy is to use a ever so slightly over powered motor and depend on the drogue for a reproducible apogee.

Actually, the total impulse for tested motors has low variability. The NAR S&T data includes the variance of the tested lot. Peak thrust is somewhat less consistent, but the total impulse has the strongest affect on altitude.

-John DeMar

[hardinlw]

I think that last year they were using Pyrodex which is not regulated like black powder is. The rules have been modified to explicitly rule out any pyrotechnic charges other than the one in the engine. It is possible to use a Quest igniter to burn through a thread to release something and that is within the rules. The Raven altimeter has the option of activating one of its three channels on the way up. I asked Trip if he had intended to leave that window open and he said if a team could make it work reliably, more power to them.

[Tolppisouth]

Thanks Larry.

That's information I can pass on to the kids.

We've started a rocket club this year and there is a bunch of kids who will tear into information like this. This bunch will not let me dictate how to do something, I can merely inform. I suspect a couple of the young ladies have the makings to be solid engineers.

Thanks again.

John