H-Bridge Problem

My HoverBot is grounded. The ducted fans that drive it require nearly 2A, but the TA78080K H-Bridges I'm using have built-in overload protection at 1A. I'd like to use H-Bridges so I can run the fans forwards and backwards. The TA8080's are lightweight and simple to use, so I really like them.

For an interim solution, I'll try using small relays. This won't give the Hoverbot turning ability, but at least it will test the concept until I can replace the H-Bridges.

Unit of the Einstein

After watching Avatar, I started thinking about the ship (the Venture Star) and how it got to Alpha Centauri. The ship is suppose to use a matter-antimatter drive that is sub-light in speed. The crew was suspended for the six year flight. Assuming a constant speed (this means the acceleration to speed was pretty fast), it had to travel at 0.7 the speed of light (0.7c).

The relativistic effects of this a speed is calculated with the equation, sq-rt[1-(v/c)^2]. Plugging in the values I get,
sq-rt[1-(.7/1)^2]
sq-rt[1-0.7^2]
sq-rt[1-0.49]
sq-rt[.51]
0.71

This means
Time passed 71% as fast for the crew
The Venture Star contracted to 71% of its length (it acually gets little more complicated)
Mass of the Venture Star and crew increased by 1.4 times (1/0.71) at speed.

I propose we give the number 0.71 the unit of the Einstein. So the ship traveled at a speed of 0.7c and the crew experienced a relativistic effect of 0.71 E.

At the speed of light, photons experience 0.0E while we traveling at nearly no speed experience 1.0 Einsteins of relativistic effect.

Perhaps Es could be integrated to account for the time the ship spent accelerating to speed. If so, the crew experienced less than 0.71 E of integrated relativisitic effects (would the unit be labled Ei?). Their maximum would still be 0.71 E.

What do you think?

Small GM Tube

I ordered the small glass GM tube from Electronics Goldmine (along with 2,000 T1 green LEDs that I will split with a sudent). A small tube like this can be powered by a transformer and 555 timer.

However, I wonder if there's a best frequency for the transformer and tube. Rather that adjust a pot on a 555, I'll use a PICAXE-08M to make the square ware. That gives the circuit a greater range of frequencies. Also, having some intelligence in the circuit will permit the tube to be shut down upon detection of a cosmic ray. Perhaps that will decrease its dead time. If that's not possible, then the PICAXE can produce a single pulse at detection and ignore the other pulses until after the tube's dead time. That will ensure a flight computer (which will monitor only the PICAXE and not the GM tube) will see a single pulse per detection (rather than the 5 or 6 it sees with the kit I've been testing).

Electronic Goldmine Geiger Counter

I added enough hot glue to the terminals of the GM tube to put an end to the corona discharge. I also ran a test of the Aware Electronics RM-60 beside the Electronics Goldmine Geiger counter. The Goldmine detector picked up six times as much radiation.

Here's what the current detector looks like.

Electronic Goldmine Geiger Counter Kit

As Mike Manes of EOSS suggested, I ran the geiger counter in a vacuum to make sure it didn't arc over. The tube has 600 volts across it, so this is an issue in low air pressure conditions. At first it looked fine. Then at 28 inches of mercury vacuum (about 94% vacuum), the LED indicator remained on. Some where the 600 volts was finding a ground and triggering the LED. I started coating the circuit in hot glue and have it running at lower pressures, but stil not in a full vacuum. I ran out of hot glue to do any more work, so I'll work again in this tomorrow.

Geiger Counter kit for Near Space

I've started my experiments with the Electronics Goldmine geiger counter kit (C6979). The kit was on special for $70 (down by $10). It operates from a nine volt battery and uses a 555 timer and transformer to boost the voltage to 600 volts. The 555 timer operates at 128 Hz. So when there's a detection of a cosmic ray, there are six (some times five) pulses during the GM tube's dead time.

Gas molecules inside a GM tube become ionized at the passage of a subatomic particle. The ionized gas lets electrons, pushed by the high voltage on the tube, pass from the wall of the GM tube to the center conductor. This makes the GM tube act like a switch at the passage of a cosmic ray. While the tube remains ionized, it's unable to detect other radiation events. How quickly the GM tube clears out this ionization is called the tube's dead time. The shorter the dead time, the more frequently the tube can detect radiation. In near space, I have detected up to 800 counts per minute. On average then, there is 75 milliseconds between detections. As long as the GM tube's dead time is less than that, it should accurately detect radiation levels in near space.

I'd like to try placing a capacitor across the GM tube to smooth out the voltage spikes. If that works, then the flight computer doesn't have to divide the number of counts by six to get the real radiation levels. Perhaps it will also let the tube clear out faster (reducing its dead time).

It's a short video about my experiments to date. Look for an article in Nuts and Volts this year.

Onwards and Upwards,

Your Near Space Guide

HoverBot Video

I've continued my experiments with designing small hovercraft. The video is short, but it shows I'm about ready to add a robot controller to a hovercraft. Balance is going to be a big issue. The lift fan is going to need lithium batteries, since they draw so much current.

Here's the YouTube link
http://www.youtube.com/watch?v=_ju40nRB_eE