I am in the process of designing a small bot based on four of the Pololu 30:1 micro gear motors. I will be running the motors (and electronics) off of a 2000 mAH 3.7v LiPo battery. I would like to boost the voltage to 5V for the motors. Using a 5V boost converter, I can only seem to find ones that handle around 500mA (such as the LTC3426). Should I use two boost converters? One boost converter to run two of the motors? Does it really even make sense to boost the voltage to 5v? Will I get enough speed out of 3.7v?
3.7V is kind of low for the motors. You could consider our boost regulator, which can handle more than 500 mA. You also didn’t say which motor you’re using; it might be easier, and you might get better performance, using the HP motor at 3.7V than the non-HP one at 5V. The right choice might also depend on the rest of your plan for the electronics, including the motor driver circuitry.
We do the boost approach for the motor supply on the 3pi robot, and it’s quite nice to have relatively consistent performance as the battery discharges.
Thanks for your help. I plan on designing the PCB myself (this will be my first big SMD project). I plan on using two TB6112FNG drivers (one for the left motors, one for the right motors). So, would it be a smart idea to have a seperate 5V boost circuit tied to each TB6112FNG driver?
I bought two of the non-HP motors for testing. Maybe I will pick up the HP version to compare the two. Are you using the HP motors with the 3PI bot?
BTW, awesome motors, and great 32mm x 7mm wheels. Nothing compares to the quality of those wheels!
I managed to miss the four-motor aspect, in which case you are getting into a lot of current, even without the HP motors. (The 3pi does not use the HP motors). At that point, you might need multiple units (e.g. one per motor driver) like the one I mentioned earlier, or go to a boost regulator with an external MOSFET. You have to be careful, though; I have a design based on such a part (from National) that has been sitting around unfinished and not working; another switching regulator we did for someone had an intermittent problem initially that got solved by small changes in the PCB layout. Your situation might be a bit simpler if you can work on a relatively small input voltage range and a fixed output, but still, this stuff can get tricky when you’re talking about many amps.
Jan, thanks so much for the help…learning a lot here.
What if I ditched the 5v boost regulators, and put two 3.7v LiPo packs in series? Then maybe use something like your Qik 2s12v10? Do I even need something that big? I will just run the two right motors in series, and the two left motors in series, and treat them as if they were one motor through the controller. Or use the two LiPos to power two TB6112FNG drivers. I know the LiPos can handle about 5-6A before the overcurrent protection kicks in, so I should be good there. What do you think?
The 2s12v10 is quite a bit of overkill, though we don’t have anything much more appropriate. You might consider the TReX Jr, which is a bit cheaper and overkill in a different sense (though having the RC control option might be nice). If you don’t need the constant-voltage operation, skipping any extra regulators will definitely make things simpler. If you’re okay doing the PWM generation yourself, one of our higher-power dual motor drivers might be worth considering.
Putting your motors in parallel is probably better than a series arrangement, which will cause a motor under more mechanical load to get less power.
