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<html> <h2>How To Work With The Third Motor</h2> <br> <b>The problem:</b> The electronic speed controller in the kit is rated for 8 amps maximum current. If the maximum current is exceeded, the speed controller will burn out (and will be permanently ruined). When using two motors with the speed controller, this is not a problem - two motors will draw less than 6 amps when they are spinning freely. But when three motors are hooked up in parallel with the speed controller, almost exactly 8 amps are drawn from a freshly charged battery. The system will work, but it will be on the verge of failing. <br><br> <b>Three solutions: </b><br><br> <b>A technical solution</b><br> One approach is to simply wire a 7.5 amp fuse and fuse holder between the battery and the speed controller. This is often beyond the ability of my customers, but I'm sure someone at the university could do it. <br><br> <b>A behavioral solution </b> <br>Alternatively, the students could be told that if they decide to hook up all three motors to the speed controller, they should not use full power when using a freshly charged battery. This solution is problematic, because the students will inevitably be over-cautious or under-cautious. <br><br> <b>An educational solution</b><br> I think the best solution might be to tell the students that if they decide to use a third motor, the third motor must not be hooked up to the RC unit, and instead, it must be controlled manually, powered by the AA battery holder, or by one of the extra RC batteries. The students will see a competitive advantage in using the third motor for more power, but they will have to weigh that advantage against the disadvantage of having one motor that can not be remotely controlled, as well as the disadvantage of more onboard weight from the extra battery. <br><br> There are a number of configurations in which the students can have complete RC control of the vehicle's movement despite having one motor that will always be on, but they may not be immediately obvious. For example, if the lift and the steering are controlled by RC, the craft's movement can be completely controlled even if a thrust motor (or pair of thrust motors) are constantly running. Depending on how the competition is setup, this might even be the best strategy. For other competitions, having the lift motor(s) run continuously might not be a problem. The students will have make the analysis for themselves. <br><br> It is also worth emphasizing that there are many good RC hovercraft setups which require only one or two motors total. This is might also be a good opportunity for the students to realize that sometimes, particularly with flying vehicles, "less is more". <br><hr><br> <h2> Extra Batteries and A Wall Charger</h2> The RC GH-2 kit comes with an 8.4 volt battery. The students will probably need to use at least one battery for testing their construction while another battery is being charged so that it will be ready for the competition. I've enclosed two additional batteries - another 8.4 volt battery, and a 7.2 volt battery, which is suitable for powering just one motor (See the "safe voltage chart" at the bottom of the smart charger instructions.) <br><br> I've also enclosed one "ch-76 wall charger". Occasionally, a battery will be discharged so much that its voltage is too low for the "smart charger" to detect it and start charging. If this happens, you can use the ch-76 wall charger to revive it. The ch-76 charger is "dumb" - it'll try to charge anything. Use it for a few minutes to rev-up the battery and then switch over to the smart charger. It is likely that you won't need to do this for February's competition, but it is a good "plan b" if you have any trouble with the chargers.<br><br>