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Re: Hovercraft B/C
Posted: January 25th, 2017, 11:26 am
by antoine_ego
HandsFreeCookieDunk wrote:So far, I have been unable to create a device that hovers to my satisfaction after several attempts
. How do you know when you've reached that point of zero friction? I've dedicated a significant amount of time to putting holes in the skirt, but it still seems like the static friction isn't negligible. Is the solution just more holes or is there something else I'm missing? I'm starting to stress about this event because I'm blowing through batteries really fast trying to get this thing to hover right.
You'll always have friction, it's get a matter of minimizing it. You know when you have a good skirt when you can slide it across a hardwood floor and it glides for a few feet before stopping.
Re: Hovercraft B/C
Posted: January 25th, 2017, 9:26 pm
by peter_ni
Question about the testing portion; do you think the written exam will be difficult? So far the regional and invitational tests (in NJ at least) have been obscenely easy...
Also, since we couldn't sign up in the 3 minutes that MIT registration was open, was the test anything special?
Re: Hovercraft B/C
Posted: January 26th, 2017, 4:30 am
by antoine_ego
peter_ni wrote:Question about the testing portion; do you think the written exam will be difficult? So far the regional and invitational tests (in NJ at least) have been obscenely easy...
Also, since we couldn't sign up in the 3 minutes that MIT registration was open, was the test anything special?
It was more difficult that most tests I've seen. They did a lot of fluid mechanics which I think tripped people up.
Re: Hovercraft B/C
Posted: January 26th, 2017, 5:12 am
by Unome
peter_ni wrote:Also, since we couldn't sign up in the 3 minutes that MIT registration was open
What do you mean? Registration was open for ~40 minutes.
Re: Hovercraft B/C
Posted: January 26th, 2017, 11:08 am
by lumosityfan
Unome wrote:peter_ni wrote:Also, since we couldn't sign up in the 3 minutes that MIT registration was open
What do you mean? Registration was open for ~40 minutes.
I think he's talking about overall registration for schools, since it took a very short time for all the slots to be filled up.
Re: Hovercraft B/C
Posted: January 26th, 2017, 11:34 am
by Unome
lumosityfan wrote:Unome wrote:peter_ni wrote:Also, since we couldn't sign up in the 3 minutes that MIT registration was open
What do you mean? Registration was open for ~40 minutes.
I think he's talking about overall registration for schools, since it took a very short time for all the slots to be filled up.
That's what I'm talking about. It was ~2 minutes for 2 teams (though a lot more got 2 teams, I figure a lot of schools dropped) and ~40 minutes until they closed registration.
Re: Hovercraft B/C
Posted: January 26th, 2017, 4:03 pm
by H3LL0
What battery pack and brand r u using? I was using a dynamite speedpack 8.4 v nimh pack that had a voltage capacity of 11 volts on day 1 (which easily powered our fan), but on day 2, that capacity dropped to 9v, which was for some reason not pushing our craft forward.
Re: Hovercraft B/C
Posted: January 26th, 2017, 4:09 pm
by antoine_ego
H3LL0 wrote:What battery pack and brand r u using? I was using a dynamite speedpack 8.4 v nimh pack that had a voltage capacity of 11 volts on day 1 (which easily powered our fan), but on day 2, that capacity dropped to 9v, which was for some reason not pushing our craft forward.
You need to charge the battery. The voltage curve of a NiMH starts off high and then levels out. Charging it should bring it back up. If you charge it and the performance still isn't up to par, you may have too much internal resistance. Simply cycle the battery by discharging to 7V and then fully charging it back up. Be careful not to fully discharge it, as you may reverse the polarity which can permanently damage the battery.
Re: Hovercraft B/C
Posted: January 26th, 2017, 5:27 pm
by andrewwski
11 V is a lot for a 7-cell NiMH. Fully charged cells are typically 1.4-1.45 V. 11V puts it at ~1.57 V/cell. Be careful, that could be dangerous.
Re: Hovercraft B/C
Posted: January 26th, 2017, 5:39 pm
by H3LL0
I did charge after use, but it only went to 9 volts. Also, my charger stops when the battery's been fully charged, and I charged it right out of the box. After charging it went to 11v, and it didn't heat up too much during use either, so I'm pretty sure I didn't damage it. It could be that my voltmeter just sucks, but I'm pretty sure it's something else...