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Author Topic: What battery to drive my boat  (Read 2215 times)

Cklasse

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What battery to drive my boat
« on: August 20, 2009, 05:56:00 pm »

I am planning to use 2 modified micro servo to drive a twin screws, another unmod servo (all 3 servo same type, working voltage 4.8-6V, speed 0.12 sec/60 degrees) to drive the rudder.
These 3 servo shall be plugged into a Spektrum AR6100 receiver binded to a heli DX7 Tx.

Question; what capacity lipo battery should I use to plug into the receiver? the voltage? rating? I have a weight limitation due to the small Severn Lifeboat size at 1/72 scale, so I need a light battery.

Thanks
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andrewh

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Re: What battery to drive my boat
« Reply #1 on: August 20, 2009, 06:38:43 pm »

Er, Ckclasse its a simple question  -but the answer less so

Anyway lets try - the capacity of the cells is the time you get to sail, and the number of cells is the voltage

one lipo is 4.1 V (fully charged) and two are....... well done you at the back

I don't know exactly about spectrum receivers, but I have heard it said that they like 4.8V, not more

It may be very happy with one Cell - most other Rxs work well on a single Lipo, and you will be sailing this fellow quite close to you.  If it won't or if you don't want to try it then your only option is 2S Lipo  (8.2V full).  This is tooooooo much for the Rx and the servos- definitely
So you need a seperate BEC which can be bought or made (7805 and two capacitors) - this takes the volts and reduces them to 5V nominal for the Recceiver - which in turn feeds the servos

So that's it for the number of cells :}
The capacity - especially bearing in mind your weight problems
Forget the rudder servo and receiver as not eating much currrent.
How much will the drive motors take?  Twould help if you told us the type and model, but we can assume an absolute max of say half an amp the pair
So if you chose 500Mah Lipos they would run at this level for an hour
So if my thinking is reasonably right I feel you should be looking for a 2S1P Lipo with capacity around 250, 350,  or 400 mah capacity , or less if you need low weight
They are made and sold in capacities from 5mah  to about 4000mah

Please let us know how you go on
andrew
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andrewh

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Re: What battery to drive my boat
« Reply #2 on: August 20, 2009, 06:40:28 pm »

Oh, and another thought - if you have a heli Tx you don't need ther rudder servo - just mix the motor channels and you have differential steering :}
andrew
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barriew

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Re: What battery to drive my boat
« Reply #3 on: August 20, 2009, 07:10:30 pm »

Andrew, As far I am aware, the 6100 will take up to 9v - certainly the AR500 will. Not sure if it reduces the voltage output to the servos though.

Barrie

Just confirmed via the Micron web site - voltage range for the 6100 is 3.5 - 9 volts.
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Cklasse

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Re: What battery to drive my boat
« Reply #4 on: August 21, 2009, 03:16:28 am »

Oh, and another thought - if you have a heli Tx you don't need ther rudder servo - just mix the motor channels and you have differential steering :}
andrew

I shall try out using the 2 servo to drive and turn without the rudder servo. This will mean letting the rudder free to swivel, I supposed.
Thanks.

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nick_75au

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Re: What battery to drive my boat
« Reply #5 on: August 21, 2009, 08:09:30 am »

I used a 2s 350 mAH Kokam battery in my 1/72 schnell boat driving 3 GWS 12mm diameter motors + rudder servo. I get about 20 minutes runtime nominally, about 3 minutes at full throttle %% but the motors are drawing 6-7 amps. The servo motors would be lucky to draw 1 amp each. You can run the servos at the full voltage and the receiver /rudder at lower voltage, Its a little tricky but the sailors with their RMG winches do it. Basically its removing the red wires out of the drive motor servo plugs  and hooking them to full battery voltage and run the receiver through a bec. If your receiver can handle 9 odd volts then it wont matter.
a 6 volt BEC is the simplest answer.

If the mixed steering is used, remove the rudder/s altogether they will tangle the prop when/if you reverse and also create drag.
regard
Nick 
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Cklasse

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Re: What battery to drive my boat
« Reply #6 on: September 04, 2009, 06:33:08 am »

I will probably be using 4 AAA size rechargeable batteries to drive my boat. Question; can I charge all 4 batteries (connected in series) together with a charger? I will plug positive of charger to positive of battery and what amp should I charge?
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FullLeatherJacket

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Re: What battery to drive my boat
« Reply #7 on: September 04, 2009, 07:49:57 am »

I will probably be using 4 AAA size rechargeable batteries to drive my boat. Question; can I charge all 4 batteries (connected in series) together with a charger? I will plug positive of charger to positive of battery and what amp should I charge?


It is best practise to charge in series all sets of cells which are used together as one pack, to ensure as far as possible that they all receive the same amount of charge.

Before we can give you a definite answer to your second question we need to know the capacity (in mAH) of the batteries and the type of charger. In general terms, a safe charge rate is one tenth of the capacity of the cells e.g. 800 mAH cells should be charged at 80mA; and the time at this rate should be around 14 hours from fully discharged.

You would be best advised to buy a made-up pack of four AAA cells rather than have four separate cells e.g. fitted into a holder, as the contacts in these holders are unreliable.
 
Hope this clears things a bit for you.

FLJ
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