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Re: Hovercraft B/C

Posted: February 26th, 2018, 9:09 pm
by Adi1008
So are you basically saying that even 8.4 v NiMH3000 mAh batteries may not even be enough to run a successful hovercraft? (BTW, sorry for all these questions, I can't "experiment" with different materials because once I buy something online using the school's money, I can't sell it back/reimburse it.)
I've seen devices using batteries like that which are pretty successful. A little voltage drop is okay as long as you're able to get some successful runs in.
Yeah don't get me wrong, they work perfectly fine, but even at 3000 mAh, you can tell the batteries have limitations. I wouldn't go any lower.
I definitely agree with you there (at least from my experience). 3000 mAh is good enough to have a working, semi-reliable device (which is often good enough to do very well at many competitions), but it'd help to have a bit beefier battery, especially if you're aiming to have a consistent time score.

Re: Hovercraft B/C

Posted: February 27th, 2018, 8:37 am
by sciduck
Can anyone help with these two physics questions?

1. With what constant velocity can a 4.00 hp motor raise a mass of 125 kg?

The answer key says 2.76 s.

This is what I did, but it's giving me the wrong answer:
v = 4.00 hp * 746 W/hp / 9.8 m/s^2 / 125 kg = 2.44 m/s

2. A train car of mass 1500 kg. moving with a velocity of 1.2 m/s collides with a 3000. kg car that is stationary. Assuming no loss of energy to friction, calculate the subsequent velocity of the stationary train car assuming the collision is perfectly elastic.

I calculated the 1500 kg car to have a velocity of -.4 m/s and the 3000 kg car to have a velocity of 0.8 m/s, so my answer was 0.8 m/s. The key said -0.4 m/s. Is it just me, or does it not make sense for the stationary car to go backwards after the collision?

Sorry if these questions seem dumb, I just want to be sure.

Re: Hovercraft B/C

Posted: February 27th, 2018, 12:15 pm
by mattruff
Is there a maximum lenght for the hovercraft track?

Re: Hovercraft B/C

Posted: February 27th, 2018, 1:59 pm
by MattChina
Is there a maximum lenght for the hovercraft track?
I don't know if there is a maximum length but the manual says that the track has to be at least 215cm long

Re: Hovercraft B/C

Posted: February 27th, 2018, 2:12 pm
by MattChina
Can anyone help with these two physics questions?

1. With what constant velocity can a 4.00 hp motor raise a mass of 125 kg?

The answer key says 2.76 s.

This is what I did, but it's giving me the wrong answer:
v = 4.00 hp * 746 W/hp / 9.8 m/s^2 / 125 kg = 2.44 m/s

2. A train car of mass 1500 kg. moving with a velocity of 1.2 m/s collides with a 3000. kg car that is stationary. Assuming no loss of energy to friction, calculate the subsequent velocity of the stationary train car assuming the collision is perfectly elastic.

I calculated the 1500 kg car to have a velocity of -.4 m/s and the 3000 kg car to have a velocity of 0.8 m/s, so my answer was 0.8 m/s. The key said -0.4 m/s. Is it just me, or does it not make sense for the stationary car to go backwards after the collision?

Sorry if these questions seem dumb, I just want to be sure.
For the first one, I also got the same answer and did it the same way as you did so Idk, maybe the answer key is wrong

For the second one, the velocity of the stationary train should have a positive velocity it doesnt make sense that the answer is negative. I also got 0.8 m/s. Idk maybe the answer key is extremely wrong.

Re: Hovercraft B/C

Posted: February 27th, 2018, 2:28 pm
by geniusjohn5
Is there a maximum lenght for the hovercraft track?
I don't know if there is a maximum length but the manual says that the track has to be at least 215cm long
MattChina is correct. Minimum length of track is 215.0 cm long. BUT I believe the TESTING PORTION OF THE TRACK(the part of the track where the Hovercraft is tested on) can either range from 165-260 cm. I'm not 100% sure though since I lost my rules sheet lol.

Re: Hovercraft B/C

Posted: February 27th, 2018, 2:29 pm
by MattChina
Is there a maximum lenght for the hovercraft track?
I don't know if there is a maximum length but the manual says that the track has to be at least 215cm long
MattChina is correct. Minimum length of track is 215.0 cm long. BUT I believe the TESTING PORTION OF THE TRACK(the part of the track where the Hovercraft is tested on) can either range from 165-260 cm. I'm not 100% sure though since I lost my rules sheet lol.
For division B it is set at 165 cm

Re: Hovercraft B/C

Posted: February 27th, 2018, 8:44 pm
by 404ic
Hi y'all,

Am I allowed to use alligator clips to wire my hovercraft? I remember some team getting chewed out last year for doing that...

Re: Hovercraft B/C

Posted: February 27th, 2018, 9:04 pm
by reed303
Hi y'all,

Am I allowed to use alligator clips to wire my hovercraft? I remember some team getting chewed out last year for doing that...
S-O Battery policy says:
• insulate the battery terminals and attached wires when not connected;
• do not use bare wire at any time in the construction of your device;
• make sure that all wiring connections are properly insulated

https://www.soinc.org/sites/default/fil ... _18_17.pdf

We've soldered & shrink-tubed some connections, and used wire nuts for others.. You could also use crimp connectors for wire-to-wire splices. The connections to lugs on motors and switches were soldered.

Re: Hovercraft B/C

Posted: February 27th, 2018, 9:20 pm
by 404ic
Hi y'all,

Am I allowed to use alligator clips to wire my hovercraft? I remember some team getting chewed out last year for doing that...
S-O Battery policy says:
• insulate the battery terminals and attached wires when not connected;
• do not use bare wire at any time in the construction of your device;
• make sure that all wiring connections are properly insulated

https://www.soinc.org/sites/default/fil ... _18_17.pdf

We've soldered & shrink-tubed some connections, and used wire nuts for others.. You could also use crimp connectors for wire-to-wire splices. The connections to lugs on motors and switches were soldered.
Is it okay if I use electrical tape to insulate the wire connections?