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Old Jan 05, 2015, 03:31 AM
H.Lauer is offline
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Camden Maine
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Can't wait!!! Harry
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Old Jun 14, 2015, 02:59 PM
johngnh is offline
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Hobby-horsing at high speed

I have the brushless motor with a 14.4V, 5000mAh, NiMH battery and the MACK speed control for that motor. Everything is great up to about 3/4 throttle. If I advance the throttle further (boat is moving pretty fast at this point), the boat starts to "hobby-horse" unstably. Conditions are as flat as you could hope on a small river. The boat is going in a straight line. If I allow the unstable hops to continue more than a couple of seconds, there is high probability that the instability will grow and the boat will make one final hop and then dive -- literally, sticking the bow under water.

How do I stop this? Is there some handling trick or skill I need to learn? Should I add weight, or will that make the problem worse? Or do I just need to keep the speed down? Is the brushless motor overkill?
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Old Jun 14, 2015, 03:29 PM
Andre Anderson is offline
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John,

One thing to say about the voltage cut off, it is really there for LIPO batteries, these kind of batteries can not take being over discharged, they can be severely damaged by over discharging. LIPO batteries tend to maintain a flatter discharge line so by the time that you can see that the battery is slowing down you have already gone to far. NIMH on the other hand do not have this tendency, they will slow down as the voltage comes off the battery so you will know that they are reaching the end of the charge.

As to the hobby-horsing I would not add more weight I would try rearranging the existing weight first, maybe moving one of the batteries forward or something along that line. Or set the throttle servo to about 75% of available. One of the problems with scale model boats is that we can over power them so easily and that may be what you have done. I have USCG 47' motor life boat that I put new brushless motors in and then figured out that I probably could have put in motors that were half the size of the ones that I put in, I now have my throttle set with dual rates, my high rates are set at 60% forward and 45% backwards, the low rates are set at 40% forward and 20% backwards. I use the low rates to move away from the shore and then once I am out aways switch to the high rates and go as fast as I want to go. At full 100% the boat goes STUPID FAST and just does not look right.

I hope this helps some,
Andre
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Old Jun 14, 2015, 07:04 PM
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Jongnh- I would refer you to post #215 of this thread to see the picture of my battery placement in the Miss Severn. If the model is skipping too much at speed I would try moving the batteries a little forward if she is popping bow high. If she is skipping level I would let her be, just remember that you have to back off on the throttle in the turns.
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Old Jun 17, 2015, 02:44 PM
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One other note about running the Miss Severn or any of the other Legend Model Boats running brushless motor systems. All our power packages for the boat kits are setup to run NI-MH battery packs and when we show running pictures of the models it is with NI-MH batteries.

The speed control and program card that come in the brushless power package can be used to setup the speed control for use with LI-PO batteries with cut off voltage settings. It must be noted that with the reduction of weight and the increase of discharge amperage with LI-Po batteries, the model will be running much faster than with the NI-MH batteries, and the model will have to be rebalanced for the reduced weight.
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