Hey guys,
I'm part of a group project where we are designing a UGV to follow a set path and drop a payload. We currently have a problem with regards to picking the right motor shield to connect to the 2 motors. The motor we picked is one with 79A stall current and 12A max efficiency current. However, since our budget for the project is pretty low, we are not finding the right motor shield. Any ideas? Also, we have to be able to connect the sensors and solenoid to the arduino. My assumption is that we can connect that to the shield too. Is this correct? Thanks for any help!
You will not likely find a "shield" that can handle a 12A "running" current and a 79A "stall" current motor. Finding something for two of them - good luck.
You can, however, find a motor driver board that you can connect for such specs. It won't be inexpensive. Don't try to cheap out on this, either - unless you like fire and wasting money.
Normally, I point people toward Pololu - but this time, they don't seem to have anything that would fit your requirements. The difficulty is finding something to match that stall current; 79A is not anything to sneeze at. Since such a stall current occurs (however briefly) at startup, you need something that can handle it for a short while. Ultimately, you want to size your h-bridge to be a tad larger than the stall current ratings (10-15%) - which in your case would bring you close to 100A.
At that point, looking at something like these controllers (likely the RDFR33 - which should handle two motors with a 95A surge, and 35A continuous):
https://www.vantec.com/acatalog/spdcat.html
Unfortunately, such a controller isn't anywhere close to "inexpensive".
Building such a controller is likely out of the question; when you are dealing with currents above about 10A or so, things get really tricky with h-bridge designs - anything homebrew will likely be a matter of burning up a bunch of expensive parts before you get something stable (and even when you think you have something stable, you may find it going up in a puff of smoke and fire when you least expect it).
I can't even recommend a relay circuit to you, because while such relays (well, at those current levels, they're going to be called "contactors") do exist, purchasing such will likely run you as much as the vantec controller, and you won't have PWM speed control, either (unless you add a bunch of high-current n-channel mosfets or IGBTs to the low-side - and at those currents, that might just be asking for trouble ultimately).
You might want to re-think your design to try to use a more reasonable motor - that, or increase your budget.