We are stuck on type of battery to use. Our craft is at 500 gms. The blower fan we got hovers little with 9 V alkaline battery (blower capacity is ~ 900pa). Debating whether to buy Li-Po cells or Nimh battery pack. In either case does anyone have experience wiring it together with a switch or is there a battery holder I should buy? Are these batteries safe for 6th graders to handle?
Here are what I feel are the pros and cons.
A LiPo battery is significantly lighter than a NiMH. The tradeoff is that you can have a maximum of 7.4V according to the rules, as per the voltage per LiPo cell. The biggest problem however, is that if you handle them incorrectly, they have a tendency to catch on fire. Since you are using them with 6th graders, this may not be a good idea.
A NiMH (what I'm using) is extremely heavy. The one I'm using weighs about the mass of your craft. You can probably find a less heavy one though. The good thing is that they are significantly more durable than LiPos, and you don't run the risk of them catching on fire. I suppose they could, but not sure how that would happen. You also can get a greater maximum voltage, going up to 8.4V. Since you are running big fans, that extra 0.8V might be useful.
As for chargers, if you are planning on buying a big pack, I would recommend a smart charger, which cuts off the current when you reach the desired capacity. You can adjust the amperage depending on whether you need it to charge quickly (which might damage the battery), or slowly and safely. A nice perk is that you can leave the battery to charge overnight and it'll be ready the next morning. The charger I have is this
, which works lovely.