Just a thought, fishing line melts to a rather gooey mess on a hot wire, but cotton thread burns cleanly, and quickly.
You might think about the 32 gauge Nichrome wire from Apogeerockets as a heated bridge wire between two copper conductors. Pretend you are making an igniter, have a bridge wire about a centimeter long, and take a few turns of cotton thread around the bridge wire. That should burn it in two, but testing is in order. Hope 50 milliseconds is going to be enough.
From: Bdale Garbee <bdale(a)gag.com>
To: Aysu Sarı <sariaysua(a)gmail.com>; altusmetrum <altusmetrum(a)lists.gag.com>
Sent: Sun, Jan 20, 2019 2:29 pm
Subject: Re: [altusmetrum] TeleMetrum Deployment
Aysu Sarı <sariaysua(a)gmail.com> writes:
> The current that is sent by the Telemetrum needs to melt the fish
> line instead of firewire. Can Telemetrum do that or can i make it do
The design of the pyro circuits on Altus Metrum flight computers
including TeleMetrum provides is a FET switch to ground on one terminal
and pyro voltage on the other. So in a normal configuration, you attach
an e-match, and when the channel fires the FET switch closes the circuit
and causes the match to fire.
Whether TeleMetrum can help you melt your line depends on two things:
The first is how much power you need... we can switch a ridiculously
large amount of current, but TeleMetrum provides the unregulated voltage
from the LiPo which is in the range of 3.7-4.2 volts. It's possible to
use some other voltage source, ignoring the v_pyro terminal and just
using the FET switch to ground to close the circuit on some other
battery. We should be safe with any battery up through nominal 12V, on
the order of 15V absolute max.
The second is how long the power needs to be applied. All of our flight
computers including TeleMetrum default to a 50 milli-second on time,
which is way more than enough to fire a typical e-match. Bench tests I
did some years ago showed that 13-15 micro-seconds was enough to fire
the commercial e-matches most of us use. However, this may be too short
to melt a bridge wire wrapped around fishing line. Unfortunately, for
TeleMetrum, the only way to change this is to customize the firmware.
That's entirely possible since everything is open source, but may or may
not be within your capabilities. Our TeleMega and EasyMega boards with
6 pyro channels allow the "extra" pyro channels to have a user defined
pyro on-time, so one possibility would be to switch to one of those
boards. It's also entirely possible that you could build up a small
circuit with it's own battery, FET switch, and a timer / pulse generator
configured to trigger on our FET closure switching a pin to ground, such
that your switch "latched on" for as long as necessary to melt your
I hope this helps. We've seen teams work around rules against loose
black powder in the past, but this is the first time I've heard of a
contest that doesn't allow pyro charges at all. Please let us know what
you end up deciding to try, and how it works out!
altusmetrum mailing list
I am new to the HPR and I have a few questions regarding the use of
As a team, we are planning to attend an HPR competition and one of the
we're facing is the competition bans using black powder or any other kind
of explosives, basically, we're planning to use a fish line to deploy the
chutes. The current that is sent by the Telemetrum needs to melt the fish
line instead of firewire. Can Telemetrum do that or can i make it do that?
Thank you in advance.
Altus Metrum announces EasyMega v2.0 and AltOS 1.9
Announcing EasyMega v2.0
We're pleased to announce the next version of our EasyMega flight
computer. Version 2.0 is feature compatible with version 1.0,
incorporating a new 200g high-g accelerometer along with the updated
9-axis IMU first used in TeleMega v3.0.
EasyMega is an advanced flight computer with 9-axis IMU and 6 pyro
channels. We designed EasyMega to be the ideal flight computer for
sustainers and other complex projects for environments not requiring
telemetry. Read more about EasyMega here:
Announcing AltOS 1.9.
Along with support for EasyMega v2.0, AltOS 1.9 uses a new embedded C
library for ARM devices. We've taken this opportunity to clean up the
code which should make future development easier.
AltosUI, TeleGPS and MicroPeak changes
* Restrict firmware image selection to images designed only for the
target device. This should make it harder to flash the wrong
firmware on a device.
* Fix TeleGPS v2.0 battery voltage display in AltosUI and TeleGPS.