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Kestrela

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Dear All,

Thanks for reading this but i need a little help.

Im doing a "drop test" from 200ft and when the drop frame hits exactly 50ft i have to sequence some servos before it lands. I have a couple of small RC sequencers but do you have any idea what type of SIMPLE altimeter i can use that i can preset to start the sequencer at 50ft? It needs to be very accurate.

Thanks in advance.
 
Kestrela said:
Dear All,

Thanks for reading this but i need a little help.

Im doing a "drop test" from 200ft and when the drop frame hits exactly 50ft i have to sequence some servos before it lands. I have a couple of small RC sequencers but do you have any idea what type of SIMPLE altimeter i can use that i can preset to start the sequencer at 50ft? It needs to be very accurate.

Thanks in advance.
Click to expand...

All of the rocketry altimeters “arm themselves”, meaning they zero their initial setting when the rocket they’re riding within launches. All altitudes measured and used to trigger events are relative to that zero elevation.
What you’re discussing is something that actually measures its current altitude based on detection of the actual ground and triggering at a precise distance above it. None of the rocketry altimeters that I know of will do that. With some reprogramming you might be able to get one of the Altus Metrum (open source) devices to set zero when released at 200 feet and trigger at -150 feet from that.
The most accurate way to do this would be with a proximity or position sensor constantly measuring distance to ground and triggering at 50 feet.
 
The Eggtimer Classic and Eggtimer Quantum both support PWM servos natively. The deployment altitudes only go down to 100', but we can probably take care of the 50' requirement for you... especially with the Quantum because there's tons of available memory for enhancements. Drop me an email, [email protected]
 
Steve Shannon said:
All of the rocketry altimeters “arm themselves”, meaning they zero their initial setting when the rocket they’re riding within launches. All altitudes measured and used to trigger events are relative to that zero elevation.
What you’re discussing is something that actually measures its current altitude based on detection of the actual ground and triggering at a precise distance above it. None of the rocketry altimeters that I know of will do that. With some reprogramming you might be able to get one of the Altus Metrum (open source) devices to set zero when released at 200 feet and trigger at -150 feet from that.
The most accurate way to do this would be with a proximity or position sensor constantly measuring distance to ground and triggering at 50 feet.
Click to expand...

Thanks Steve,

I had looked at a drone controller with a laser range finder fitted to it but the programming and setup would take quite some time. I was hoping some rocketry electronics already existed that may be better suited.

Regards
 
Kestrela said:
Thanks Steve,

I had looked at a drone controller with a laser range finder fitted to it but the programming and setup would take quite some time. I was hoping some rocketry electronics already existed that may be better suited.

Regards
Click to expand...

If I were you I would immediately PM Cris Erving (cerving above) to see what he can do to help you. He’s very clever and has a very nice line of Rocketry electronics.
 
Steve Shannon said:
Good luck! Please let us know how you solve this. Are you dropping this from something that is flying or a static platform attached to a tower, or what?
Click to expand...

Its being dropped from a tower to test and dial it in, then it will be dropped from a helicopter.

Regards
 
I'd be careful, a lot of this depends on decent rate, waiting till 50' indication to deploy or activate something is pretty low in my experience, if you watch a lot of the deployments with chute release there seems to be a pretty good range of actual release even when set at 500'.
 
burkefj said:
I'd be careful, a lot of this depends on decent rate, waiting till 50' indication to deploy or activate something is pretty low in my experience, if you watch a lot of the deployments with chute release there seems to be a pretty good range of actual release even when set at 500'.
Click to expand...

We actually deploy a chute higher than 50ft but we need to accurately measure its height so that at 50ft something else happens on the frame
 
Kestrela said:
We actually deploy a chute higher than 50ft but we need to accurately measure its height so that at 50ft something else happens on the frame
Click to expand...

Ok what is your decent rate, if in the 20fps range maybe it isn't as critical since you have some margin/delay.
 
burkefj said:
Ok what is your decent rate, if in the 20fps range maybe it isn't as critical since you have some margin/delay.
Click to expand...

We are using a iris ultra 60" chute so that handles 19lbs @ 20fps. We are slightly below that weight.
 
If you need the 50 ft. trigger to be very accurate and since you will be under chute and have a know orientation as you drop, I would very seriously consider the altitude range finders used in drones. I've never checked, but are the units available as separate units instead of integrated into the drone already? If so, it shouldn't be too difficult to integrate into your unit.
 
Personally I wouldn't trust anything not to swing. If it were me I'd just stick with a simple barometer- modern units are incredibly accurate for a few bucks.
 
You will want to increase the descent sampling rate on the Quantum if you're going to be firing anything that close to ground, the default is 2 samples/sec but it can to go 10 samples/set. At 10 samples/sec and a 50 ft/sec descent rate (not atypical for a drogue chute) that would deploy your "other" device between 45-50ft. Bear in mind that there will be some time for your other device to deploy, so 50 feet may not give you the result that you're looking for. I'd be thinking about triggering at 100', that would give your secondary device time to fully deploy by the time you hit 50'.
 
If you have Arduino-based electronics already on board, there are some Arduino barometers that might be useful. If I'm understanding your system properly, you would have to arm the Quantum at ground level, lift it up into the tower, then drop it. The Arduino system might let you arm at drop level instead. That approach would take a lot more effort building a board and software, though.
 

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