Won't I fry my MC with tomany amps?

Help & Support Apps & Software
1

Hi again,

After getting my first servopulses out of my mc, I connected 3 servos together. None of them responded anymore, when disabling 2 of them, the last would respond correctly.

Now my own theory would be that the amp’s I’m suplying to my mc are not enough to serve 3 servos io pulses.
I’m using a 6v - 8w power supply, measured with my grand new multimeter it supply’s me with 8.2 volt. This should lowered to 5.5 on the development board I buyed(I hope)

So the u*i=r hocus-pokus would tell that I would have on and about 1amp going in my mc.

After measuring its amp it displays me 1.64 amps telling me either my calculation or powersuply totaly screwed up.
I wouldn’t mind even if both screwed up alldue I would really would like to know howmanny amps I COULD and SHOULD supply to my mc, as the datasheets are just telling me 5.5V

I’m using the development-board comming down to:

(The manual provided was indeed very Quick.)

So could my theory be right?
And if so howmany amps are needed to pulse all my 18 servo’s together with the sensor turret I haven’t ordered yet, without frying my mc?
A quick calculation would say on and about 15amps, common sense tells me to stop writing right now!

 Thanks 4 reading
2

I’m just going to try and clear some things up here.

First: You don’t “supply” current in a sense. You supply the voltage required, and then your device will draw the current it needs. How did you measure the current? Was it with the circuit connected? or across the power supply?

Second: The power for your servos should not come from your microcontroller power supply, as you will fry the voltage regulator. You should plug your servo power directly into your power supply. The pulses supplied by your microcontroller do not have a significant current draw, so you can plug heaps of them in.

Also, you will need a better power supply when you decide to plug in more servos. Most people just use a battery pack, as they can supply heaps of current, but then they do have to be charged regularly.

Please tell us how you are connecting your servos, this would help.

3

Hi, tnx for your reply,

I measured the current on my power suply.

I toulght beeing as smart as I am, why don’t I use the 5v supplied by my dev board. (so not from the MC but from the board itself)
But reading your story makes me understand thats not going to work.
In theory it might be possible to get it the way I have it in my head, its just not worth the nonse.

I have a 7.2v batterypack, that according to a frend should be connected directly to my 6v servo’s. I did some searching on the internet finding stories about smoking servos at that voltage so I’m kinda cautious with connecting them,… Any sugestions?

4

If your power supply has a current meter, that is fine. Make sure when measuring your current, you have a load on it, otherwise you will blow up your power supply and possibly your mulimeter.
(current goes through multimeter, then through load, back to power supply)

Bear in mind that the voltage regulator on your board is probably rated at a max of 1A, so you wouldn’t really want to draw too much from it.

As for the 7.2v battery, it seems a lot of people use them for the servos on their Lynxmotion stuff with no problems. However it’s recomended not to use them on mini/micro servos, only on standard analogue ones.

Did you get them all working yet?

5

My first question would be… did you program the servo conroller yourself, or did you buy it from a known good source? If you programmed it yourself, how do you know that there aren’t programming issues involved?

6

Tnx for the replies,

I measured the amps correctly (I think as both my power supply and my multi meter are still working. About the 7.2v battery… Tnx I’m feeling much saver to try to connect it now.

I did program the MC myself, but becuase of my former programming skills and the fact that when connecting them one at a time,… I can say pretty sure that that is not the issue (looping a single centering pulse can’t be that hard)

I did not manage to get it working yet as strange things happen.
When I have 3 of them connected to the board(and battery) only the first 2 move. When I tough the + pin row, the last starts to move.
Kinda weird I think.

I made a interface board to connect my servo’s to my MC and battery, I think I made an error there.
I solded like 18*3 pins on the board and solded 1 wire over every + pin and 1 wire over every - pin.

I think what happens is that when connecting the battery,… power/current doesn’t flow true every pin, but is sucked out by the first 2 servo’s.

Could this be true,… How do you connected the battery to the current-pins of your servo.

battery __||||||
__||||||

__ = a solded wire.
| = the pins where the servo gets it power supply.

is this such a paralel/serial connection mistake?

7

If you can get one servo to perform exactly as desired (left and right) on each of the different servo pins with no load on the servo, then then the programming is probably good. There should no problem supplying all the servos power from a single ± bus as long as the wiring is large enough and you have a sufficiently large power supply. Below is how I powered two lightly loaded servos from a wall wart power supply.

geocities.com/zoomkat/ezservo.htm