SWING TEST USING PICO AA1 ACCELEROMETER

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hball55

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I am trying to do a swing test to ensure the PICO unit fires the ignitor and having no luck. I was never too sure of this unit, having heard that they are not reliable for deployment uses, so I have never used it. I must be swinging the unit incorrectly, as the up/down orientation is critical. I know of no other way of testing this unit, so I am asking for advice. Anybody have any advice . . . other than giving up on this unit? 😜
 

jderimig

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What exactly is your swing procedure to simulate a launch and deceleration?
 

hball55

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Simply, I orient the Pico pointing up and swing upwards and around in a circle for several revolutions and then slow down and stop. I arm the Pico and get two beeps; the igniter is one of those Chinese made ones for fireworks . . . they work fabulously when I test my magnetic apogee detectors . . . never a failure.
 

jderimig

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Simply, I orient the Pico pointing up and swing upwards and around in a circle for several revolutions and then slow down and stop. I arm the Pico and get two beeps; the igniter is one of those Chinese made ones for fireworks . . . they work fabulously when I test my magnetic apogee detectors . . . never a failure.
You need to swing the pico so that "up" is pointed towards the center of rotation (not outward). That is the direction of the acceleration.
 

hball55

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You need to swing the pico so that "up" is pointed towards the center of rotation (not outward). That is the direction of the acceleration.
That sounds like instead of swinging like a ferris wheel, I swing it like a merry go round. Is that right?
 

jderimig

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It doesn't matter. But "up" is not out, it inward towards along the string pointing to you. Now that simulates the acceleration during motor burn. Not the coast to apogee. After the swing its got to still still to simulate the coast down to zero velocity.
 

hball55

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The up on the accelerometer is pointing towards me in the center and the unit circles around me. I spin it around me for five seconds and slowly bring the speed down til it stops. Nothing happens . . . either I’m still doing something wrong or the unit is crap.

The string is attached to the top/up position of the accelerometer and I spin it around my head in the horizontal plane for five seconds and bring the speed down until the unit drops due to a lack of centrifugal force, and stops. No event happens, the battery is still in place, held in its holder and taped, the igniter still attached to the output. My only doubt is that if there is supposed to be a jumper in place for apogee deployment, not just data logging, then I’m up a creek. There never has been any jumper on the unit.

Anybody with experience with the Pico AA1 can chime in if there is a missing jumper that is supposed to be in place for apogee deployment to function. This is just a guess on my part.

I have sent off an email to Robert DeHate, who I bought this unit from, to inquire about the software required to configure this unit, and the dongle required to attach it to my computer, neither of which I ever received when purchased. It’s been years since I bought it, so I do this with fingers crossed.
 
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hartlch

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Download the data it logged and look at that?

Edit: Sorry - missed the part where you don't have the data cable...
 
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AllDigital

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@hball55 I've never used a Pico AA1, but looking at the manual it says that launch detect is triggered by 2G's for at least 200ms, after ground characterization of the accelerometer (default is for 1/2 second). It is also direction dependent, so up needs to be aligned with the arrow (important for characterizing gravity).
If I were trying to test it, assuming default settings, I would put it on the ground arrow up, power on and let sit for 10 seconds, and then throw it straight up in the air and hope that I could get 2G's for 200ms out of my throw. I doubt you will get the launch and trigger logic to fire using any type of circular tether. You also shouldn't be holding it while it is characterizing the accelerometer. If you have the cable/software you should also check the settings to verify delays, lock-outs, etc.
 

jderimig

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Thats a tricky way to test an acceleration based apogee. When you spin the acceleration integrates to a given velocity. When you stop spinning the acceleration goes to zero but the integrated velocity doesn't, it still thinks its going up. You need to apply a negative velocity or invert the altimeter with respect for gravity to allow the integration to reverse and get back to zero velocity.
 

hball55

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If I had both a cable/dongle and software, I would be able to see how it’s configured, instead of hoping that default is apogee event. The three detection modes are: launch, motor burnout, and apogee. I never received anything but the unit when I bought it several years ago, and it sat in a box because I was busy with other things. I have renewed interest in getting this thing operating . . . Perhaps too late.
 

hball55

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Found a link to the software here:

Thanks, lol, but I have been there and the link to the program leads to a possible phishing site that I’m not willing to chance.

ok, I took the chance, scanning it first. It’s a Pico reader, so now I need a dongle to attach the unit to my computer. Not sure if it lets me configure the unit, but I’ll wait to hear from Robert DeHate, afterall, I bought the unit from him.
 
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cerving

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It's difficult to properly test a rocketry accelerometer, and even harder if you have a baro sensor in it too and want to test both. When I was designing the Proton, I played around with a number of testing scenarios, and decided that the easiest way to test it was just to launch it a bunch, as a ride-along at first of course.
 

hball55

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It's difficult to properly test a rocketry accelerometer, and even harder if you have a baro sensor in it too and want to test both. When I was designing the Proton, I played around with a number of testing scenarios, and decided that the easiest way to test it was just to launch it a bunch, as a ride-along at first of course.
No baro on this unit, just accelorometer. I suppose I could set it up to ride along . . . though probably easier for me to use motor ejection and have an igniter only attached to the accelerometer; I can switch out one of my magnetic apogee detectors that’s installed in a nosecone and the igniter will be in the payload bay where it won’t interfere with anything.
 

Tetrahedron

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Simply, I orient the Pico pointing up and swing upwards and around in a circle for several revolutions and then slow down and stop. I arm the Pico and get two beeps; the igniter is one of those Chinese made ones for fireworks . . . they work fabulously when I test my magnetic apogee detectors . . . never a failure.
Yes, that should work. That is how I test my homebuilt Arduino based altimiter (now using Seeduino XIAO SAMD21 Cortex M0 processor)
that uses accelerometer (MPU-6050) and baro (BMP-280).
Like you said, you start in a position with the altimiter pointing up and then swing it around in a circle a couple of times and then stop and slow down.
When you swing the unit around in a circle, you generate centrifugal force which the altimiter senses as Gs (kinda like when astronauts train in the centrifuge)
and with enough "swing force" you should generate at least 2 Gs. When I look at the data from my swing tests it shows anywhere from 2-4 Gs.
Then you slow it down and hold it UPSIDE DOWN ("simulating archover"?) so that the altimiter will integrate the accelleration to zero velocity,
it could take several seconds. The unit should then fire apogee charge and main should follow right after since the baro is already at ground level.

-John
 

Voyager1

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I haven’t used the swing test with accelerometers, so I can’t comment on its reliability in this instance. However, intuitively, I don’t think this is the best way to do it. I agree with Cris‘ recommendation for launching it on actual flights.

What I did last year when testing a IMU-based prototype altimeter was to launch it in a bottle rocket with air impulse only. It was sufficient to achieve a suitable launch detect acceleration and altitude. It was also able to detect barometric apogee to deploy a servo-actuated chute. Very simple and no pyro to worry about during a fire season. It was all I required for proof of concept before using normal motors in a standard rocket for verification.
 

AllDigital

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Simulating launch conditions with an accelerometer is hard. I've been known to put my electronics inside a cut-out Nerf football (with a kite tail) and use a water balloon launcher. Two G's no problem. Landing in the pool, a problem.

Screen Shot 2021-02-22 at 10.33.04 PM.png
 

kjs

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I've tested AltAcc's before with the swing test, and it is easy but you need to do both parts of the 'flight'.... you attach to one end and swing a few revolutions... that is the 'thrust'... and then you attach to the other end and swing a few revolutions (the deceleration) and then the ematch fires... you can play with fast swings for the thrust and slow for the 'coast' ... if your unit has a "direction" that it needs to be mounted (i don't know about the pico), you need to really think about it (I do too) as to what the unit 'feels' relative to what the rocket would give it (where are the Gs going).... if a unit is 'bi directional' (can be mounted either way), then it doesn't matter.
 

Ez2cDave

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Thanks, lol, but I have been there and the link to the program leads to a possible phishing site that I’m not willing to chance.

ok, I took the chance, scanning it first. It’s a Pico reader, so now I need a dongle to attach the unit to my computer. Not sure if it lets me configure the unit, but I’ll wait to hear from Robert DeHate, afterall, I bought the unit from him.
Here are the files . . . Virus free !

Dave F.
 

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