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Battery Question

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By finster

October 15, 2009

Hi all,

I am very new to building robots and don't have much knowledge of electronics, apart from the basics many years ago at school.

However, I got an arduino at the weekend and have started doing experiments with it. I've just managed to take apart a cheap RC toy car and get the arduino to make it go backwards and forwards via a L293D motor driver and a very basic program. There are two motors in the car - the other one is a DC one attached to rack and pinion steering - I've not connected this to the other side of the L239D though yet.

I measured the voltage across the motor in the car before I took it apart and it was 4-5 volts (can't remember exactly what).

At the moment, I've got 4xAA rechargeable batteries connected to the L293D to power the motor. I'm using a separate battery to power the arduino.

I now want to use something a little better for the motor power. From what little I understand, the motor driver causes a voltage drop of 1.5v. Are there any recommendations for batteries? I've seen plenty of 7.2v RC battery packs with tamiya connectors but would this be too much? Alternatively I've seen a few 6 volt packs too.

Any recommendations to what's the best to spend my money on? I'd prefer to buy a battery/charger that can be used in my future robot projects.

Thanks in advance - sorry for the long post!

 

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By robologist
@ Fri, 2009-10-16 07:21
robologist's picture
It would probably be helpful to know how big the RC car is, but it's likely to be ok to use a 7.2 volt RC pack. It is a bit bigger than 4 AA packs, as it is 6 C sized batteries put together. What was originally powering the car?  My RC conversion robot used the orignal pack, which is a Tyco FLexpack, a 7.2 volt pack made of AA NiMh cells. On other robots, there has usually been 4 AA packs, one with a pair of 7.2 racing packs in parallel, and one with a couple of LiPo packs series for 14.4 volts.  A charger I've felt was the best value was a Hobbico Quick Field Charger, that can handle NiCd, NiMh, and LiPo batteries, and charge 2 packs at once. It requries a 12 volt supply though. Something like this 12 volt power supply could be used.
By finster
@ Sat, 2009-10-17 00:39

Hi,

Thanks for the reply - very useful information.

The car originally used 4 x AA batteries - its 1:15 - this one: http://direct.tesco.com/q/R.207-3490.aspx . Thinking about it, when I measured the voltage across the motor (as the remote control joystick was on), it was around 4.5 volts, but I was using NiMH batteries, so the original supply voltage was 4x1.2 = 4.8 volts. So I think a supply voltage of 7.2v going through the L293D should be OK.

Thanks for the links, but I'm actually in the UK. I've also decided after reading your post that I can probably get away with using 6xAA NiMH batteries for the 7.2 volts to start with. I'll maybe buy a decent battery & charger later.

Thanks for the help.