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Time Adjustment Step

Posted: March 3rd, 2010, 9:08 am
by htmlfreak
I have a quick question for the state competition: the time is between 60 and 90 seconds, so one needs to have a time adjusting step.

Would it be okay to use the electric motor (which we use as an archimedes screw) to waste time (have it exceed 40 seconds)?

Re: Time Adjustment Step

Posted: March 3rd, 2010, 9:50 am
by bugsrcool
Yes, many teams used it that way.

Re: Time Adjustment Step

Posted: March 18th, 2010, 7:12 pm
by brouhaha
how accurate is every one getting their times?

Re: Time Adjustment Step

Posted: March 23rd, 2010, 10:51 pm
by cypressfalls Robert
brouhaha wrote:how accurate is every one getting their times?
My question kind of goes with this one;
To what time is evveryone timing for, in other words how much is it off from the original time? EX: 60 secounds for regionals, you time the device for 59.5 .5 human reaction time ,etc

Re: Time Adjustment Step

Posted: March 26th, 2010, 4:55 pm
by Primate
cypressfalls Robert wrote:
brouhaha wrote:how accurate is every one getting their times?
My question kind of goes with this one;
To what time is evveryone timing for, in other words how much is it off from the original time? EX: 60 secounds for regionals, you time the device for 59.5 .5 human reaction time ,etc
Human reaction time is usually measured at about .24s, so it's not quite as significant as that. Plus, you'll want to go slightly over the ideal time to get maximum points (a run time of 59.9s is the same as a run time of 62.9s). Therefore, it's probably best to time your mission out to 60.5s precisely, and adjust accordingly for states. That way, you encompass your reaction time in calibrating, the timer's reaction time, and any discrepancies between runs.

I was able to consistently get within one or two seconds of the ideal time at practice. The best teams'll make that happen in competition, too :P.

Re: Time Adjustment Step

Posted: April 25th, 2010, 7:58 am
by Balsa Man
Primate wrote:
cypressfalls Robert wrote:
brouhaha wrote:how accurate is every one getting their times?
I was able to consistently get within one or two seconds of the ideal time at practice. The best teams'll make that happen in competition, too :P.
Just back from State (yesterday). Judges set 72 seconds for the ideal time. There were 5 teams that hit within 2 seconds (with full points on everything else). I was a little surprised that that many got that close. Second was a 3-way tie that went down to the flagpole length tie-breaker....!

We were optimistic going in; on Friday night calibration runs, our team 1 hit two in a row inside the magic 1-second perfect score window (working at 75 seconds)., but we knew from testing there was an inherent roll of the dice aspect. Our timing step is a motor winding a string, pulling a little block up a ramp (aluminum angle iron) till it trips a microswitch. Microswitch mounted on a slider, so you can move it up and down the angle iron to set timing. The distance between 60 sec and 90 sec is about 15 cm. All the other steps take about 4 sec.

3 significant variables with this approach. The inherent variability of a dc motor w/ brushes, variability in batteries over time (1.5v C-cell), and variability in the winding distance as the string winds around the shaft. They controlled the first by using a relatively new motor that had been run in for about 15 min (to seat the brushes). They did a lot of battery testing; setting the mechanism up for about 1:30, and keeping track of times, and total load times on the battery; found a window between 6 or 7 min of use and about 20 min, where things got more stable- 3-4 sec variation in the fist few minutes, settling down to close to 1 sec. Last, they used a very fine string (0.005" Spider Wire), with little washers on the shaft, so the string winds back and forth 3 times to 90 sec. The small diameter means very little change in effective winding diameter.

During setup they made 3 runs; last one was a couple tenths over 72.
And, lo and behold, when they ran, it did it again; perfect score/gold. They attribute the success to something they added to the box last week; a gremlin party house - a beer bottle, with a label, "Gremlin Party House - Free beer while the machine runs, come on in; girl gremlins drink free!" What can I say,it worked.... Our Team 2 was one of those within 2 sec, but were 2 sec over, so ended up 5th

Re: Time Adjustment Step

Posted: April 26th, 2010, 9:39 pm
by Uncle Fester
BalsaMan's approach and methods work far better than just blaming the event sup. I wouldn't tell anyone to do it any differently. Might want to tighten the time up a bit if he knows I'll be the Stopwatch Elf, though. . . .

72 seconds? Doesn't anyone remember the time-honored tradition of using A VERY LARGE PRIME NUMBER?

Serious congrats, Balsa.

Re: Time Adjustment Step

Posted: April 27th, 2010, 3:06 pm
by Balsa Man
Uncle Fester wrote:Serious congrats, Balsa.
Thank you very much, sir. Just coached them in the direction of the basic engineering process; they executed it nicely. But, maybe it was the beer bottle....