hello everyone. i made a robot with 12 sg90 servo's connected to an arduino nano i tried using 2 9V batteries in parallel
but it was far from enough power to power my robot

thank you in advance.

 

Measure the current it takes on full load, then you can work out what capacity pack you need.

 

The sg90 needs to power 4.8V~6V.
The current of 9V cookie batteries are too small, so they are not good for the motor.
You may find two 3.7V lithium battery and in series with them, and through a LM317 or LM2576 module or LM2596 module to step down to 5V.

 

The sg90 needs to power 4.8V~6V.
The current of 9V cookie batteries are too small, so they are not good for the motor.
You may find two 3.7V lithium battery and in series with them, and through a LM317 or LM2576 module or LM2596 module to step down to 5V.

I think SMPS makes a lot more sense than linear, efficiency wise. SMPS could allow much greater battery life, and much less heat. So get a lithium battery pack and a DC-DC buck converter off of ebay or something like that. Just make sure it can handle the current. Also, get a proper BMS/charging circuit.

 

I think SMPS makes a lot more sense than linear, efficiency wise. SMPS could allow much greater battery life, and much less heat. So get a lithium battery pack and a DC-DC buck converter off of ebay or something like that. Just make sure it can handle the current. Also, get a proper BMS/charging circuit.

I know that, it just provides another option if the TS considering the space, I'm also think that maybe could use three batteries then it can be spend more time on air.

 

In addition to what has already been said, look into LiFe batteries. They are also lithium based, but do not exhibit some of the bad characteristics that LiPo batteries do. They have slightly less voltage. Two cells in series are 6.6 volts nominal. Perfect for operating servos directly. No regulator or buck converter needed. The drawback to lithium batteries is that they MUST be charged with a specialized charger.

 

Two cells in series are 6.6 volts nominal. Perfect for operating servos directly.

Did you see the spec of Vmax(voltage)?

 

In addition to what has already been said, look into LiFe batteries. They are also lithium based, but do not exhibit some of the bad characteristics that LiPo batteries do. They have slightly less voltage. Two cells in series are 6.6 volts nominal. Perfect for operating servos directly. No regulator or buck converter needed. The drawback to lithium batteries is that they MUST be charged with a specialized charger.

You can't treat a battery with a certain nominal voltage as a power supply that will supply that voltage until it suddenly dies. Power = V^2/R for a resistive load. So, for standard liion batteries, with a range of 4.2-3V, that is 17.64/R vs 9/R. So it will get half the power towards the end. This is why a regulator is needed.

I know that, it just provides another option if the TS considering the space, I'm also think that maybe could use three batteries then it can be spend more time on air.

Let's say he does uses a 2s liion pack, closest to the standard 5-7.4V of servos. He goes with a 6V regulator. Let's say all the servos need on average 1-2 amps. When the batteries are at 8.4V, that's (8.4V-6V)*2A. 5 watts is a lot to dissapate for a small robot. A heat sink will probably be necessary, taking up a lot of space and adding a lot of weight. So, even if battery life doesn't matter, a linear regulator is still not the better option.

 

a linear regulator is still not the better option.

Yes, it is not the better choice, but it is still a choice and it is working on the free air not in the box, so using a small heatsink will still hot, but it won't damage.

1. 4 diodes : In series with three 1N5400~5408/3A(0.7V) and one Schottky diode 3A(0.3V~0.4V), voltage drop ≅ 2.5V.

2. LM2596 module : Output voltage set to 5V, voltage drop 2.77V, Imax = 3A, if the chip didn't add any heatsink then it can't be reach up to 3A.

3. LD1085 with two 1N5400~5408/3A(0.7V) : 5V, 3A low drop(1.3V) positive voltage regulator, adjustable and fixed, the original I only think about the traditional linear, and I found out LD1085, but the Vdrop is too small(1.3V), and it can't be just connected its output to the motors, so I added two diodes.

4 legs toy robot - The robot in the video is different from the one in the post #1, the video just to shows that how the motors work when the robot is moving, the motor may not all working at the same time, so I assuming that there are only 3/4 motors are working when the robot is moving, there are 12 motors in the post #1, and each motor will draw Imax=120mA, so I = 120mA*9 = 1080 mA.

FEETECH (Fitec) FS90 9G Mini Servo with Accessories -- there is the info of draw current inside.

 

this is very easy .. there's only One battery type now ...Lithium ....all the others don't come close ...

Every size imaginable from very small ...

5 mm thick x 22mm x 48mm but can still deliver a few Amps @ 3.7V ... to as large as you like

 

this is very easy .. there's only One battery type now ...Lithium ....all the others don't come close ...

Every size imaginable from very small ...

5 mm thick x 22mm x 48mm but can still deliver a few Amps @ 3.7V ... to as large as you like

There is still the choice between lipo and liion, or other lithium technologies. And you need to be able to choose the size, cell number, capacity, C rating, etc. Some higher quality lithium batteries will have more available watts and more watt-hours than others.

Also, one thing to look out for. When choosing a BMS, make sure it cuts off at a reasonable voltage! Some boards cut the batteries off at dangerously low voltages. For liion or lipo, 3V is the absolute max, and 3.3 or 3.4 is ideal if lifetime is more important than using the remaining 20%. And it should go without saying, but be very careful to avoid shorts. Make sure the BMS has over current protection. If the overcurrent protection looks sketchy, then add a fuse.

 

thank you all SO much for helping me with my project i finally got it to work

thanks

 

thank you all SO much for helping me with my project i finally got it to work

thanks

Please post your final solution, it might help some other members when they have the similar issue.