i have a sprawling type quadruped spider robot. I have 4 Sg90 and 8 mg996r servos used for the legs. I am using a Arduino Mega and I wanted to know if I would be able to power this with the batteries that I have... Currently I have 8 cells of 1.2 V 2600mah Recyko Nimh batteries. I plan to put 4 cells in one battery holder and 4 in another and solder them together which would provide about 9.6 V. The Mg996r datasheet needs around 300-800 mA of current and S90 around 100- 300 mA of current. Should be around 2-9 A of current that my circuit needs. Would my battery be enough to provide this kind of power? If not is there a workaround? Lipo or any other type of battery is not an option.
That seems to me to be something you can easily test!
Right I know , but my project is running on a budget so its highly risk to try and burn off the wries, and I dont understand how i could solve on paper whther this thing is a viable option or not. Can you guide me on how i can go about solving this on paper ?
So fix that problem with heavier wires! Then you can test.
sure , but my problem is still not solved. This total current requirement is around 8 ish Amperes, would my 2600mah batteries be able to provide this? Im not very sure how i would be able to calculate this on paper? I dont want plug it in and overdrain my batteries
There are high current AA NiMh available, good for 6-8 Amps maybe, try an RC model shop.
Most normal AA NiMh batteries would not be suitable for such a high current discharge.
How will you drain the batteries in a 5 second test?
Rechargeable batteries have a "C" rating, which gives the maximum safe discharge rate.
A 10C 2600 mAh (2.6Ah) battery can theoretically supply 10*2.6A = 26A, if your wires don't vaporize.
A 1C 2.6Ah battery can provide 2.6A.
Mg996r datasheet needs around 300-800 mA of current
That is under light load. A genuine MG996R briefly draws the stall current of 2.6A, every time it starts moving. Beware of knockoffs.
I agree with the suggestions above to buy a high discharge rated, racing car NiMH battery pack from an RC supplier.
So if i understand you correctly the entire robot will at the beginning draw around 2.6*8, which is around 20 A of current? Then i would extremely thick wires to allow this to happen as well as a battery with a high discharge rate. the highest capacity nimh battery i have seen in RS components is 10Ah with 1.2 V . Then again if we do end up using this , i would be able to run my circuit for just 30 mins no?
What was the C rating?
You have to make a reasonable estimate of the maximum current draw and use wires of the right size. The published wire tables are handy for this.
the beginning draw around 2.6*8
If all 8 servos start at once, that current is drawn for about 10 milliseconds, then drops to the load current, which still could be over 1A per servo.
Currently i have 18 awg wires, which allow around 10 A of current but i do have 14 awg wires at disposal as well.
The one i found was RS PRO NiMH Rechargeable D Battery, 10Ah | RS (rs-online.com)
the standard discharge according to its datasheet(linked on the website) was Discharge at 2.0CmA to 1.0 V/cell
, which honestly I do not know what it means.
A pack of those cells would probably be a good choice for your robot. The data sheet states:
That means you can draw 10A maximum on average, 30A absolute maximum for short pulses (like the startup surge), until the battery voltage drops to 1.0V per cell. At that voltage, turn off the robot or the cells will be damaged.
At 10A continuous draw, the robot will run for about an hour on fully charged batteries. That run time will decrease as the batteries age.
Right but this battery provides only 1.2 V so i would have to connect more batteries in series to increase the voltage? Which im running out of budget for , say I was to redesign the entire robot to use 12 sg90 servos, would my old batteries be capable providing the current to do so? Stall current/ start current of the sg90s is around 0.8 Amperes, so 12*0.8 is 9.6 A as start current , I couldnt really find any C rating for my recyko batteries but I could link the website for you if you can find out something i am missing. I would really appreciate it!
GP ReCyko battery 2600mAh AA (4 battery pack) | GP Batteries International
Most people use a pack of 4 (about 4.8V) or 5 (about 6.0V) NiMH batteries for servos.
The 2600 mAh batteries linked would be totally unsuitable for your robot.
I have 8 such cells, in series, which would be 9.6 V in total. Is this still not enough?
Those cells cannot supply the required current.
Get serious about your project.
I am serious about my project. I have certain restrictions posed by my university that do not allow me to buy other batteries? Why would keep posting if i wasnt serious?
Then this would be a good time to work on improving your understanding of very elementary electrical circuit concepts: voltage, current, power and energy relationships.
Especially for a university project.
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