Power for quadruped robot - practical aproach

Hi everyone,

it's a first time, when i decided to write on this forum, but not the first time when I visit Your forum;) and the reason why I decided to write is the problem, that i can't solve since few days, although I've ran through whole english internet.

I am building quadruped robot, every leg has 3 degrees of freedom, so it's 3 servos per leg (4.8-6V). The mechanical and software parts weren't a problem, because I have pretty big experience with mechanics and programming, but this time I have to deal also with the electronic part. And to be honest, when it comes to electronics, I'm a beginner.

Generally I have some basics, but the reality was very brutal and showed that nothing works;) I've created the circut, in which I deliver the power from 4 AA batteries (I have enelops) to the breadboard and to this breadboard all 12 servos are conected. But instead of waiting for the battery holder for 4AA (this one https://botland.com.pl/koszyki-na-bateri...pu-aa.html) I decided to check it with the battery holder for 6AA (I know, 7.2V is a "bit"too much, but I've already had one and I'm not the patient one...). So, as you probably expect, 10 of 12 servos have been damaged. But the thing that surprised me the most is, that the battery holder's cables, breadboard and the part of battery holder melted. So, since I'm not an expert in elecetronics, I have some questions:

  1. Will this circut work properly, when it will be powered from 4AA batteries? Or is there some generall mistake? (I'd like not to damage next 12 servos;) )
  2. When it's not totally incorrect, maybe the plastic breadboard and thin cables can't resist the current?
  3. If yes, what could I buy as an alternative to the battery holder and the breadboard, so they could resist the current and didn't melt?

Thank You for all Your answears;)

P.S. I control everything with Arduino Mega, but the Vin pin, as I know, can't take more than 1A, so it probably doesn't change anything, because the servos need much more;)

The problem with AA batteries is they cannot deliver a very high current.

Without knowing anything about your load on your servos and what type you have its hard to make a guess but I think it would be safe to say that AA batteries in series are not up to that current demand. I may be wrong, your robot may be tiny ( we need more detail!)

You need to find a way to deliver a stable supply to the servos. A lithium polymer battery can supply a high current but you will need to use some type of voltage regulator ( or multiple, preferably switching regulators) to supply 5-6v power to the servos.

In the RC world they use things like this for planes with many or high current servos. The input power would be from a good lithium polymer battery.

Instead of one big regulator you can alternately use many smaller ones one for each servo or whatever.

Sorry to hear about the dead servos, definitely do not give them more than 6v!

Elap:
2. When it's not totally incorrect, maybe the plastic breadboard and thin cables can't resist the current?

Every wire is a resistor when current passes through it, thinner wires have a higher resistance than thicker... If the current is too high for the wire size there will be a big voltage drop and power loss from the wire in the form of heat... things melt... bad day.

You need to budget enough current for your servos - at least 1A per servo is a good starting point,
so something like a 6V SLA battery is appropriate, AA's have no chance at all of working.

MarkT:
so something like a 6V SLA battery is appropriate, AA's have no chance at all of working.

Since you had trouble before. I would plug in a single servo and test before you plug the whole lot in if you use a 6v lead acid battery. I think the full charge voltage would be 7.2v for a 6v SLA. Most servos are ok with it but you never know.

So, if I understood correctly, I connect lithium polymer battery to this voltage regulator and on the output of the regulator I always have for example 5.5V, yes? And there is no option to power it from the AA batteries? I ask, because if I damaged servos, I thought that the problem would be too big current;) and the solution for these too thin cables is just soldiering thicker ones?

And because of this breadboard - is there any chance that such a plastic breadboard will handle current or will it melt again?

Elap:
So, if I understood correctly, I connect lithium polymer battery to this voltage regulator and on the output of the regulator I always have for example 5.5V, yes? And there is no option to power it from the AA batteries? I ask, because if I damaged servos, I thought that the problem would be too big current;) and the solution for these too thin cables is just soldiering thicker ones?

And because of this breadboard - is there any chance that such a plastic breadboard will handle current or will it melt again?

You won't damage servos by having a source that is capable of delivering a high current. The servo will draw it's required current from the source. You need to make sure the source can supply enough current for all servos.
You will damage them from too high of a voltage(as you found out). The servos have a circuit board inside populated with integrated circuits that are all rated to a certain voltage. When you exceed that voltage something will die.
As for the wires and breadboard, like the battery, they have to be sized in order to deliver that current to your servos. You can google wire guage and current and find some tables for wire sizes. You don't have to run heavy guage wire all through your quadroped but you have to look at each section of your machine and think how many servos are on each stage and size your wires accordingly.

As for the how to get the right voltage.. because it's a quadroped and a heavy battery will probably be an issue ?. I would get a nice light lithium battery and some cheap switching regulators.

And of course you will learn that cheap hobby servos are not rated for 100% duty under full load, they just
overheat and cook since they cannot dissipate much heat.

Metal body servos designed for robotics will fare much better, you may want to figure out which servos have
the highest torque to deliver and up-rate those ones.

Ok, thank you very much, I think I already know what to do. One, last question - so if I cant't deliver the current from the power source through the rails of breadboard, because it's to weak, how can I "divide" it on 12 servos?

You can get servo shields with all the connectors and a terminal block for the incoming servo power...

Ok, so there is no way to avoid buing servo shield...but thank You for all Your answears;)

Elap:
Ok, so there is no way to avoid buing servo shield...but thank You for all Your answears;)

The shield just makes the connections. There is no requirement to use it. Soldering iron works well too.