Hovercraft B/C

[keslerscience]

I ran my first hovercraft event at an invitational recently and a few questions came up.

1. There was one hovercraft that had about 16 9.0v batteries in a parallel circuits. The voltage never exceeded 9.0 across either of the circuits so it appeared to be in line with rule 4H. Is that right?

2. Some teams completed 1 successful run and on their second run wanted to stop their craft before the finish if they didn't think it was going to beat their first run causing a failed attempt. This doesn't seem allowed per Part 5 m. Correct?

3. Can the competitors run their device on the floor or behind the starting gate to test it during their 8 mins?

4. Per part 5 q it states that a failed attempt is triple the target time. Even if we saw that the device was crawling along the track and wouldn't make it in 51 seconds (target time 17) we were making them wait until 51 to turn it off. Any proctor discretion here? I didn't want it all of a sudden to pick up steam and cross the line before 51 seconds. The problem is that the juice on their batteries really get eaten up during this time.

5. The last, and maybe most important one, has to do with scoring. I used the spreadsheet on scioly (thanks by the way). I do see a problem with TS (time score) is calculated though. A run of 5.0 would score no time at all if the target time was 17. However, I run of 39 seconds would actually get a decent amount of points. I think it was nearly 13 points which is huge in a close competition. Clearly 5.0 is closer to the target time than 39. Is this by design?


thanks
Chris

[RJohnson]

Here is the link: http://www.digikey.com/product-detail/e ... ND/2560506

That is a really good looking blower! Specs are definitely above the requirement

Hello, Has anyone used this fan for lift?
Isn't this a bit too big?
Thanks!

That is the fan I use. It fits well within the physical bounds set by the rules. Hope that helps!

[MrGood]

What would be the CFM needed to create enough propulsion to levitate a 2kg(the max weight) hovercraft.

[windu34]

What would be the CFM needed to create enough propulsion to levitate a 2kg(the max weight) hovercraft.

You are not looking for CFM in a levitation fan, you are looking for static pressure. At least 20 CFM to be safe though (that isn't much at all)

[windu34]

I ran my first hovercraft event at an invitational recently and a few questions came up.

1. There was one hovercraft that had about 16 9.0v batteries in a parallel circuits. The voltage never exceeded 9.0 across either of the circuits so it appeared to be in line with rule 4H. Is that right?

2. Some teams completed 1 successful run and on their second run wanted to stop their craft before the finish if they didn't think it was going to beat their first run causing a failed attempt. This doesn't seem allowed per Part 5 m. Correct?

3. Can the competitors run their device on the floor or behind the starting gate to test it during their 8 mins?

4. Per part 5 q it states that a failed attempt is triple the target time. Even if we saw that the device was crawling along the track and wouldn't make it in 51 seconds (target time 17) we were making them wait until 51 to turn it off. Any proctor discretion here? I didn't want it all of a sudden to pick up steam and cross the line before 51 seconds. The problem is that the juice on their batteries really get eaten up during this time.

5. The last, and maybe most important one, has to do with scoring. I used the spreadsheet on scioly (thanks by the way). I do see a problem with TS (time score) is calculated though. A run of 5.0 would score no time at all if the target time was 17. However, I run of 39 seconds would actually get a decent amount of points. I think it was nearly 13 points which is huge in a close competition. Clearly 5.0 is closer to the target time than 39. Is this by design?


thanks
Chris

Not official etc
1.) That is legal - kinda a waste of money
2.) Correct
3.) I don't see why not if the supervisor permits it
4.) What you did was correct. Teams may bring spare batteries (I think don't quote me on this) if needed
5.) I'm not fit to answer this

[chalker]

I ran my first hovercraft event at an invitational recently and a few questions came up.

1. There was one hovercraft that had about 16 9.0v batteries in a parallel circuits. The voltage never exceeded 9.0 across either of the circuits so it appeared to be in line with rule 4H. Is that right?

2. Some teams completed 1 successful run and on their second run wanted to stop their craft before the finish if they didn't think it was going to beat their first run causing a failed attempt. This doesn't seem allowed per Part 5 m. Correct?

3. Can the competitors run their device on the floor or behind the starting gate to test it during their 8 mins?

4. Per part 5 q it states that a failed attempt is triple the target time. Even if we saw that the device was crawling along the track and wouldn't make it in 51 seconds (target time 17) we were making them wait until 51 to turn it off. Any proctor discretion here? I didn't want it all of a sudden to pick up steam and cross the line before 51 seconds. The problem is that the juice on their batteries really get eaten up during this time.

5. The last, and maybe most important one, has to do with scoring. I used the spreadsheet on scioly (thanks by the way). I do see a problem with TS (time score) is calculated though. A run of 5.0 would score no time at all if the target time was 17. However, I run of 39 seconds would actually get a decent amount of points. I think it was nearly 13 points which is huge in a close competition. Clearly 5.0 is closer to the target time than 39. Is this by design?


thanks
Chris

As usual, this isn't the place for official statements or clarifications. In response to your items (unofficially of course):

1. Yes, having lots of 9V batteries in parallel is fine
2. Correct, teams can't stop a run in progress. However we don't really have an explicit penalty in the rules for if they do. It'd be up to the individual event supervisor, but if I was running such an event I'd prevent the team from trying to do another run as the penalty.
3. Testing it not on the track during the adjustment period is something I'd personally allow, assuming there is sufficient space available. Again, it'll be up to the individual supervisor.
4. There is ALWAYS event supervisor discretion in situations like this, as long as it's applied uniformly to all teams.
5. Yes, the scoring formula by design penalizes devices that err on the side of being faster (this was a safety decision on our part). Instead of thinking about it in terms of absolute time, I prefer to think about it in terms of % speed. A run of 5s is 3.4x the ideal speed, while a run of 39s is 0.4x the ideal speed (e.g. a 2.5x ratio, compared to the 3.4x ratio of the 5s run). Note it would have been very complicated to craft a scoring formula that worked based upon absolute time error.

[HCCoach]

That is a really good looking blower! Specs are definitely above the requirement

Hello, Has anyone used this fan for lift?
Isn't this a bit too big?
Thanks!

That is the fan I use. It fits well within the physical bounds set by the rules. Hope that helps!

Thanks much! We are using foamboard for our base material. Would we be able to mount the fan on it or would it need a more sturdier plywood base?
Also do you have thoughts on what strategy to use for adding weight to make the craft heavier?

[RJohnson]

Hello, Has anyone used this fan for lift?
Isn't this a bit too big?
Thanks!

That is the fan I use. It fits well within the physical bounds set by the rules. Hope that helps!

Thanks much! We are using foamboard for our base material. Would we be able to mount the fan on it or would it need a more sturdier plywood base?
Also do you have thoughts on what strategy to use for adding weight to make the craft heavier?

I prototyped in 1.5 inch foam myself. I used the pink, Owens Corning insulative foam, it supported everything well. In terms of weight, strength, and rigidity; my one problem was it held everything very high, creating an unsturdy craft and barely being under the height requirement. As for weight, the biggest thing for me is to balance the craft, so I figure out where non-fixed things such as the batteries will go then I used various types of weight to balance the craft and to try to lower the center of gravity. Examples of things I used are Pinewood Derby flat weights and scientific weights (like those in a physics room). I would also recommend having a place for a small, numerous weight to calibrate the device to any scale if going for 2000g. I use BBs in a little container; I'm sure there are other ways of achieving the same idea.

[Complexity]

Just some scores from my recent Ohio invite:
Division C:
1. 67.75
2. 61.14
3. 59.4
4. 52.08
5. 50
6. 44.31

Division B:
1. 58.99
2. 57.35
3. 50
4. 44.86
5. 41.17
6. 32.35
*The first three places all belonged to the same school

There were a couple nat teams in each division, and I think that <15% of the 40 schools successfully hovered their craft. Competitive invitational in December, but the teams prob have not had enough time with hovercrafts yet
We got tiered because our shielding lifted in the back corner on the thrust fan, and fell down to 22nd.

[Complexity]

Just some scores from my recent Ohio invite. I dont feel inclined to share school names, but here we go:
Division C:
1. 67.75
2. 61.14
3. 59.4
4. 52.08
5. 50
6. 44.31

Division B:
1. 58.99
2. 57.35
3. 50
4. 44.86
5. 41.17
6. 32.35
*The first three places all belonged to the same school

There were a couple nat teams in each division, and I think that <15% of the 40 schools successfully hovered their craft. Competitive invitational in December, but the teams prob have not had enough time with hovercrafts yet
We got tiered because our shielding lifted in the back corner on the thrust fan, and fell down to 22nd.