HELP!: Making a circuit so that a 7.2v batt produces 6v
 

Hey im making an rc car and need to power the servos. I got 4 4600mah 7.2v batts but no 6v batts n dont really want to fork out 60 odd bucks for a 6v battery so im going to make a little circuit board to bring the voltage from 7.2v down to 6v.

Now my question is, what do i need to achieve this. Its been a while since year 11 physics so i forgot the majority of how to work this stuff out.

I worked it out that i need a .24 ohm resistor but im not sure if this is right.
I used ohms law and made the potential difference as 1.2v (7.2-6v) but i dont no if this is right. Then 5A is constant so
R= V/I
Therefore R= 1.2/5
= 0.24 ohms.

Can someone help me out here. Thanks.

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

A dropping resistor works only when the current is constant, and servos draw a few mils at rest and much more when moving and working.
What you need is an IC voltage regulator - MC7806 - which will supply 6V regardless of load. It is a simple three pin device: In, Out, Ground. Luck mate, Eloy

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

You shouldn't have to do anything. The ESC that controls the motor should provide an output of around 5V to the receiver and servos. If the ESc doesn't have a built in BEC, then an external BEC device will do the job of providing regulation from your main battery pack
Pete[8D]

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

Its petrol powered, no esc, no electric motor.

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

Regarding the Voltage regulator i see it only puts out 1A. Is that enough to power two 15kg servos and one 5kg servo? If not, which voltage regulator will i need?

Will one of these do? http://www.jaycar.com.au/productView...r&form=KEYWORD
http://www.jaycar.com.au/productView...r&form=KEYWORD

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

better yet - something like the 10A BEC here:

http://www.castlecreations.com/products/ccbec.html

or any of a multitude of similar products. Being a switching regulator, it won't get nearly as hot as a linear regulator under load.

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

Iuse these:

http://hobbyking.com/hobbyking/store...idProduct=3735

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

Or put a 50 cent 10 amp diode in the line. .7 volt drop right there, might be enough to do the job.

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

How many amps will i need to power two MG995 15kg servos and a 5kg Tamiya servo TP-S3003?

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

Hey guys thanks for the help, ive decided its easier, better and cheaper to buy a 5-10 amp 6v SLA battery. I need some weight on the front so it will do the job and give more than enough power to the servos and wont run out for ages.

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

If you don't have much invested in those batteries just yank a cell and resolder.

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

That sounds like a winner to me.-BW

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

Agreed..
And to the OP - where the heck are you paying $60 for a simple 6v rx battery??? Is it gold plated or something?

RE: HELP!: Making a circuit so that a 7.2v batt produces 6v
 

I never used a dedicated 6 or 5V battery pack to power the receiver and the servos. When not powering my boats with a 6V battery, I usually use my homemade BEC: a 7805 5V regulator, rated at 1A (more then needed). It's not recommended to use the 7806, 6V regulator because you need at least 2V more at the input.

Better use the LM2940 which requires a lower voltage difference at the input. I usually solder it to the ESC positive and negative terminals (homemade electronic ESC's).

Regards
Robert