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Old May 14, 2001, 03:17 PM
heli on the brain
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Apple Valley/Victorville, Ca
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Car Batteries and Speed Control in TwinJet?

...since i have about three 2000 6 cell car battery packs lying around from my offroading days, i was wondering if they could be used in a TJ along with perhaps a Novak DusterII speed control. Has anyone used car speed controls or batteries in their TJ? Would be cool if i could just slap them into one and not have to worry about purchasing batteries and a speed control specifically for the TwinJet.

...any thoughts?

DeZ
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Old May 14, 2001, 05:27 PM
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San Diego, CA, USA
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I've thought about doing the same, i don't thin there should be any damage to the speed control as a rc car motor spins pretty darn fast. the only thing you might have to worry about is whether or not, the speed control can handle two motors. but give it a try, it 'll prolly work.
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Old May 14, 2001, 05:42 PM
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A possible problem with your battery packs is that they are only six cells or 7.2 volts and everyone I know is flying on a minimum of 8.4 volts to 9.6 volts. The batteries might not be powerful enough for the Twin Jet. You may not be at all happy even if it does fly with the slower speed only six cells will produce. Let us know. Mike
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Old May 14, 2001, 05:59 PM
heli on the brain
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Apple Valley/Victorville, Ca
Joined Apr 2001
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...i was planning on making 7 or 8 cells packs from the ones i have lying around. After reading a few posts im finding the 2000 r/c batteries to be pretty popular amongst TJ owners. My main concern now is if my Novak DusterII speed control (sans the case) will work properly. My guess is yes since it can handle modified car motors up to 7 turns which are much more powerfull than a 400. However, i am not quite sure about its amp rating.

DeZ
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Old May 14, 2001, 06:10 PM
BEC
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Auburn, Washington USA
Joined Jan 2001
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No, no, no!!

The question is NOT whether the over-inflated car speed control ratings are real or whether they'll handle two S400's in parallel (probably will) BUT that most any car ESC has NO motor cutoff or other means to prevent the battery from being discharged to the point that control is lost.

In a car, it just turns to one side as the steering servo goes hard over and runs into whatever obstacle is nearby. In an airplane, depending on where you (and any other people) are and where it is when this happens you can definitely hurt someone when you lose control of the airplane.

DON'T DO IT! Get a Pegasus 35 or a Sun 3000 even a GP C-30 instead (which will save you an ounce or more as well).
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Old May 14, 2001, 06:19 PM
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Oxford(ish), England
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Is anyone concerned by the fact that Car ESC circuits often don't have the BEC low-voltage shut-off that plane ESCs do? That is to say a plane ESC will shut the motors down when the pack starts getting drained to allow for a safe glide in and landing, but most car escs will keep running the motors until the radio gear dies from lack of volts.
That having been said, if you listen for the dying motors and land IMMEDIATELY when they start to go, you might be okay. Personally I would not trust such a crude method, especially if flying near other people/property. ESC's are not that expensive, it would be a worthwhile investment unless you simply don't have the money and are prepared to risk a the consequences of sudden control loss. An alternative would be to use a Car ESC for speed control and a Seperate battery for the reciever, just like in a glow/diesel or glider model. This adds a little weight, but not a lot and will be a LOT safer than the car ESC & BEC method! This is the way I would go, for sure, but bare in mind that car escs are often heavier than plane ones that plus the weight of the battery may be a problem to models smaller than maybe 1000mm, depending on configuration.

As far as the packs go, i've had perfectly acceptable results experimentally running my TwinStar on budget 7.2v buggy packs. Performance is a little limited, but it's perfectly safe if you give it a little time to build airspeed before climbing out from a launch. 8.4v or 9.6v packs will work better and provide more safely due to their larger power reserves, though.
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Old May 14, 2001, 06:25 PM
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Oxford(ish), England
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Ah, seems like while I was typing that someone else brought up the same point.

Well done sir!

Incidentally. I have a TJ and a Twinstar. I would not recommend the TwinJet as a first model, if you've not flown RC before. I'm not sure about using 6-cell packs in it. It's not always the easiest of planes to launch, and you really need the extra power of the seventh cell. But then again six cells are lighter, so you never know you luck. I use 7-cell sanyo packs (1700Mah) in my TwinJet, and they work fine. If it was my choice i'd have to say split the packs and make two 9.6v, 8-Cell packs from them, you will need the extra power.

[This message has been edited by gdb1973 (edited 05-14-2001).]
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Old May 14, 2001, 07:39 PM
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Moved to Modeling Science...
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Old May 14, 2001, 08:45 PM
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Va
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Although the DusterII dosnt have the normal BEC cutoff it dose have radio priority circutry. The motor will die off enough that you wont be able to stay aloft but will still have directional control(at least it works for one servo). I would still agree that its not the best choice to use.
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Old May 15, 2001, 01:56 AM
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Novara ,ITALY
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If you're not going to buy new stuff you can still think of using separate batteries for the RX - BEC ain't compulsory!

As for the car ESC I think it would be safer to stick with 6 cells and be sure to cool it down quite well. I don't know if your ESC is the "switching" type, but for sure a controller designed to handle 7.2V and high currents in very short bursts is different from one designed for 30 A continuous up to 12 cells.

As for using 6cells packs, you can compensate the performance loss by fitting a couple of 5.5x4.5" or 6x4".
If you are a daredevil buy a couple of the Speed400 RACE 4.8V, with the Gunther props they should scream at about 17000rpm, drawing something more than 30A together... No more than 6 cells here!
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