Hovercraft B/C

[sciolyFTW_aku]

Hi,

My battery's voltage drops by ~0.1-0.15V every time I run, so I am only able to do 2 runs before I have to recharge. I'm not sure if a 1V difference would considerably change my speed; could someone provide some advice for this?

My consistency is about +-0.05 seconds

Really??? That's crazy

Agreed. Good job!

Thanks,
sciolyFTW_aku

[Ashernoel]

We know the resistance of the rheostat from prior measurement, so, ignoring nonlinearity in the rheostat, by measuring the voltage across it, we know the current flowing through it by V = IR.

What's your consistency between runs? We are able to get about plus or minus 0.5 seconds consistently, no matter what distance.

were within 5 seconds. maybe10 when longer. but our hover gets 13 points for mass so it makes up for it.
most of the time our potentiometer goes ham and decides to either go supppppper fast or not move at all. :0'
hopefully at state we pull through and the Cow doesn't go haywire so we can be in contention for a medal

[cheese]

Hi,

My battery's voltage drops by ~0.1-0.15V every time I run, so I am only able to do 2 runs before I have to recharge. I'm not sure if a 1V difference would considerably change my speed; could someone provide some advice for this?

What kind of batteries do you use? Nimh batteries have an early current drop but then stay steady as this graph shows:

[petermai6655]

Is there any formula for calculating the rotation speed given the voltage? We are experiencing in constant values in our testing because of the voltage variance of our battery.

[antoine_ego]

My consistency is about +-0.05 seconds

Really??? That's crazy

That is just... Amazing! Congrats! If you're using a potentiometer based system, how do you account for different track surfaces? Also, if you are trying to vary the velocity of the hovercraft, how do you take into account the acceleration before the velocity levels out? That's the thing that is causing my inconsistency.

[quote = "sciolyFTW_aku"]
I'm not sure a 1V difference could considerably change my speed
[/quote]

I've found that a 1V difference on my hovercraft can cause a great amount of havoc. As cheese said, buying a NiMH battery is a good idea, because of the voltage plateau. A good strategy is to discharge the battery to just above the plateau, that way you have consistent voltage throughout your runs. For longer testing time, buy two batteries and switch when one becomes depleted. (General tip, don't fully discharge your batteries, because you potentially reverse the polarity and ruin the battery.)

[sciolyFTW_aku]

Hi,

I'm using a NiMH battery. I think the problem might be that I'm overcharging my batteries, and it falls to its voltage plateau but I take it out and recharge it due to losing my expected voltage.

Thanks,
sciolyFTW_aku

[antoine_ego]

Hi,

I'm using a NiMH battery. I think the problem might be that I'm overcharging my batteries, and it falls to its voltage plateau but I take it out and recharge it due to losing my expected voltage.

Thanks,
sciolyFTW_aku

Are you very reliant on having that higher voltage? At least for me, the voltage plateau is slightly higher than the voltage rating of the battery. Is it plateauing at a lower voltage than the rated voltage.

[cheese]

Is there any formula for calculating the rotation speed given the voltage? We are experiencing in constant values in our testing because of the voltage variance of our battery.

I'm not sure exactly what you're saying, but for calculating rotation speed for the voltage, you can do some tests. First hook up a voltmeter to the ends of the battery, and record that, then run the motor with a slow mo cam and put a stopwatch next to it to calculate rpm. Then do multiple tests, and see if there is a curve. Hopefully this helps

[Ashernoel]

Is there any formula for calculating the rotation speed given the voltage? We are experiencing in constant values in our testing because of the voltage variance of our battery.

I'm not sure exactly what you're saying, but for calculating rotation speed for the voltage, you can do some tests. First hook up a voltmeter to the ends of the battery, and record that, then run the motor with a slow mo cam and put a stopwatch next to it to calculate rpm. Then do multiple tests, and see if there is a curve. Hopefully this helps

You could also wing it and hope for the best!

[ericlepanda]

Is there any formula for calculating the rotation speed given the voltage? We are experiencing in constant values in our testing because of the voltage variance of our battery.

I'm not sure exactly what you're saying, but for calculating rotation speed for the voltage, you can do some tests. First hook up a voltmeter to the ends of the battery, and record that, then run the motor with a slow mo cam and put a stopwatch next to it to calculate rpm. Then do multiple tests, and see if there is a curve. Hopefully this helps

You could also wing it and hope for the best!

Best strategy in this whole thread.