AeroTech DMS UDDT - easiest way to remove 1 additional second?

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JSW

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Need to use the AeroTech DMS UDDT to remove 5 seconds of delay instead of the standard 2s, 4s, 6s, or 8s. Can you check me please?

My thought:

Calibrate the UDDT so that the drill is 1/32" (1 second) longer than it should be. To do this: An old key card is 1/32" thick. Punch a hole in it. The "calibration adapter" sits on the key card while the drill itself sits in the hole punch,... making it hang 1/32" beyond the base of the "calibration adapter". See pics below.​
Then use the 4 second side of the drill, and with the +1 second calibration offset = 5 seconds removed​

Is this correct? Is there an easier way?
 

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Sounds like a good plan. Yes, the delay grains burn 1/32" per second at atmospheric pressure, after motor burn out.

Although, practically, the delays are +/- some seconds anyway, so I'm not sure adjusting by -1 second is any real difference.
 
If you have access to a 3D printer, you can either download or make your own 1 second washer for the delay tool. That way you don't need to uncalibrate the drill bit.

However... The percentage of error for delay time is so high, I personally wouldn't bother doing that, Depending on age of motor, what propellant the load has in it, the weather, your altitude, ignition characteristics, you'd be very lucky to land on the exact delay you want anyway. I would just go with the closest default delay.
 
I used a piece of styrene sheet 1/32" thick to make a washer for 1s. Yeah, it may not really matter, but it sure isn't hurting anything.

I would suggest avoiding the calibration hack; as it is likely someone at a launch may need to borrow your delay tool sometime and that would just add confusion and you may not want to be known as someone who won't loan out your delay tool :)
 
I just made an additional spacer from aluminum stock. That way, I can set the delay in 1-second intervals. As had been noted, actual milage may vary but I figure it is best to put the center of the scatter as close to the mark as possible.
 
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Need to use the AeroTech DMS UDDT to remove 5 seconds of delay instead of the standard 2s, 4s, 6s, or 8s. Can you check me please?

My thought:

Calibrate the UDDT so that the drill is 1/32" (1 second) longer than it should be. To do this: An old key card is 1/32" thick. Punch a hole in it. The "calibration adapter" sits on the key card while the drill itself sits in the hole punch,... making it hang 1/32" beyond the base of the "calibration adapter". See pics below.​
Then use the 4 second side of the drill, and with the +1 second calibration offset = 5 seconds removed​

Is this correct? Is there an easier way?
Just use the thing you made as a +1 spacer in place of or alongside the included washer. No need to mess with the drill bit then.
 
Just use the thing you made as a +1 spacer in place of or alongside the included washer. No need to mess with the drill bit then.
Exactly!

I was wracking my brain trying to think what I could use for a 3mm or 1mm spacer washer,.... instead came up with the calibration hack using the key card.

For whatever reason - it didn't occur to me to use the key card as the spacer. Doh! That's the right way to do it - calibrate the UDDT as normal and use the 1s spacer.

Thanks!
 

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Exactly!

I was wracking my brain trying to think what I could use for a 3mm or 1mm spacer washer,.... instead came up with the calibration hack using the key card.

For whatever reason - it didn't occur to me to use the key card as the spacer. Doh! That's the right way to do it - calibrate the UDDT as normal and use the 1s spacer.

Thanks!
I trimmed my spacer to match the standard 2-second spacer and keep both on the drill in storage. Easy peasy.
 
Need to use the AeroTech DMS UDDT to remove 5 seconds of delay instead of the standard 2s, 4s, 6s, or 8s. Can you check me please?

My thought:

Calibrate the UDDT so that the drill is 1/32" (1 second) longer than it should be. To do this: An old key card is 1/32" thick. Punch a hole in it. The "calibration adapter" sits on the key card while the drill itself sits in the hole punch,... making it hang 1/32" beyond the base of the "calibration adapter". See pics below.​
Then use the 4 second side of the drill, and with the +1 second calibration offset = 5 seconds removed​

Is this correct? Is there an easier way?

I used a card key also. The Country Inn & Suites card was the perfect thickness for 1 Second.

You shouldn't need to alter the drill. Just use the card as a 1-second spacer.

Been using this for a long time.

DelaySpacer-1-Second-A.jpg

DelaySpacer-1-Second-B.jpg
 
Since NFPA allows delay to vary 2 sec or 20%, there is no reason for 1 sec drilling accuracy. If your recovery can't handle 2-3 sec away from apogee, you have a serious problem. It will fail in an arcing flight where the rocket never reaches a low velocity at apogee. Don't rely on simulation programs. You will want a shorter delay on windy days, especially if aiming into the wind.
 
I have brass sheeting of various sizes. It's easy to cut a circular 1/32" brass shim and keep it with the 1/16" washer the tool come with.
 
Since NFPA allows delay to vary 2 sec or 20%, there is no reason for 1 sec drilling accuracy. If your recovery can't handle 2-3 sec away from apogee, you have a serious problem. It will fail in an arcing flight where the rocket never reaches a low velocity at apogee. Don't rely on simulation programs. You will want a shorter delay on windy days, especially if aiming into the wind.

Using your approach, especially with an arcing flight condition, aren't you increasing the likelihood that the
chute will deploy overly early - with the rocket potentially at a higher velocity?

I am not familiar with the allowable 20% variance in the delay. Can you point out the particular section?
Or maybe someone on the forum can provide that?

I need to add that your 2-second variance could be +2 or -2, which you can’t know in advance.
 
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Since NFPA allows delay to vary 2 sec or 20%, there is no reason for 1 sec drilling accuracy. If your recovery can't handle 2-3 sec away from apogee, you have a serious problem. It will fail in an arcing flight where the rocket never reaches a low velocity at apogee. Don't rely on simulation programs. You will want a shorter delay on windy days, especially if aiming into the wind.
Drilling the 1 second improves the result, regardless of the variance. If the target is 7 seconds, +-2 gets you to a worst case of 3 seconds off if you drill to even, 2 seconds off if you drill to the exact value.
 
Using your approach, especially with an arcing flight condition, aren't you increasing the likelihood that the
chute will deploy overly early - with the rocket potentially at a higher velocity?

I am not familiar with the allowable 20% variance in the delay. Can you point out the particular section?
Or maybe someone on the forum can provide that?

I need to add that your 2-second variance could be +2 or -2, which you can’t know in advance.
Its in NFPA 1125 iirc which pertains to the manufacture of model rocket motors. Typically most hobbyists are aware of 1122 and 1127 from which the Safety Codes draw from.

Thrustcurve.org has made the pertinent parts available under the NFPA Standard.
https://www.thrustcurve.org/info/certification.html
 
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One more thing that is 1/32 thick, if you go to the cabinet area at lowes or home depo, the formica samples measure 1/32. I use them for spacers for hinges in box making, and glue scrapers.
They are free samples to take home, and I justify taking a few every time I go, by saying it will make the formica salesman happy to have something to do.

They have rounded edges and look cool.
 
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