I am designing my own remote-controlled rover project and would like to check a few things regarding power to make sure nothing blows up or gets damaged when I wire it up.
For driving, I have four FIT0579 6V geared DC motors and the CE08038 Makerverse motor driver. Based on the 430 mA stall current (and 61 mA load current) for the motors and 1.6A continuous and 2A peak current maximums, I feel like I could get away with connecting two of these motors to each channel of the motor driver, right? Would it be safer to just use a second motor driver?
In addition, I have two CE09378 6V servos for steering. Given all the motors run off 6V, I have a 4 x AA battery holder that I was going to use, but measuring the voltage of the output with four alkaline batteries, it came out to be 6.3 V. Surely the extra 0.3V wonât damage anything right?
And lastly, since my pico 2 microcontroller can only take a 5.5V max input voltage, I was thinking I could attach a wire to the same battery pack after 3 of the batteries, instead of all four, and get a 4.5-ish volt output to power it. Is there a better way to power the pico? I am trying to save as much weight on the rover as possible.
The Makerverse Motor Driver board actually has a regulated 5V output built into the board. You could always try running your Pico and Servos using this output instead?
The pico will absolutely not handle an input voltage of 6.3V, but the servos will probably be fine. Best practice would, of course, be to use an input in the recommended range of 4.8-6V, so if itâs practical for you to use the 5V output on the motor driver board, I would go with that.
Hey @Samuel , thanks so much! Given the pico will only draw a small amount of current, it shouldnât overwhelm the 5V output of the motor driver. Thatâs a good pickup!
With regards to the main 6V motors used for driving the rover, would the 6.3V be too much for them?
And looking at the motor driver again it should be fine to run all four motors using the one driver, just using 2 per channel, correct?
MY advice here would be NO, donât do that. A reason could be that you might want to run these motors at different speeds. For the price of another controller not worth it.
I donât think 4 AA cells would last very long
Definitely NO. Never do this sort of thing as some cells will discharge faster than others and unbalance everything. Using any cells in series the weakest will dictate the final result so if only 1 cell is discharged the resultant voltage available will be close to zero even if all the other cells are fully charged.
Cheers Bob
Great points, thank you. I have a second motor driver I was just hoping I could simplify the circuitry if possible.
In terms of using AA batteries, I wasnât sure how else to get a sustained 6V output for something mobile. The main motors draw 60 mA each under load so itâs not a lot but I understand as the batteries discharge they lose voltage so the lifespan would be cut shorter. Are there any better ways to get the 6V supply?
Not a lot each but they add up. Donât forger you HAVE to allow for stall current. Plus the servos.
I would have a look at 6V Lithium batteries. 12V is common but I think 6V are available.
Jaycar have one, SKU SB2200 4.5 Ahr
If you go down this path get the correct charger for it. Donât just use any old 6V charger or you could find problems.
Cheers Bob
Looking into it that looks like a good option. Given the total weight is important due to the torque of the gear motors, maybe 5 NiMH batteries could be the go. A bit more costly upfront plus the charger, but thatâll get me a more stable 6V compared to alkaline. What do you think?
Edit: I also have lithium AAs from a previous project but they measured at 1.8V each unfortunately.
Probably but it is the capacity Vs weight ratio which would be important on a Robot. In which case Lithium would be the Go To.
The battery on the Jaycar site uses LiFePO4 nominal 3.2V cells which I believe are more stable and longer lasting that the LiPo 3.7V ones and get you a bit closer to your 6V mark. Note that freshly charged cells will be a bit more V and will fairly quickly settle to the nominal value and stay there for far longer than Alkaline would.
Getting back to capacity. Sure 60mA per motor does not sound like much but you have to consider WORST CASE which all motors (and the servos) stall at once which can happen if a Robot happens to run into a wall. Irrespective worst case consideration would be the ânormalâ thing to do.
Incedently this âstallâ current will be the start up inrush when the motors start to turn. The same thing, you are applying voltage while the motor is stationary.
Cheers Bob
