I am trying to control 12vdc motors (that appears to be the max voltage any Arduino Board can handle). I would like to control multiple motors, but 4 appears to be the maximum through the MKR MOTOR CARRIER. The overview of the product page says two high-performance and two standard performance: does not define the difference. Also, under the “Tech Specs” tab, it says for Overview:
The MKR Motor Carrier (also known as MKR motor carrier board) is an MKR add-on board designed to control servo, DC, and stepper motors.
and then lower in the Tech Specs section:
When plugging the MKR1000 and the Motor Carrier, some of the pins will stop being available for you to use in your code, as they will be needed to control some of the features of the Carrier.

so from this it would appear that the MKR MOTOR CARRIER is not a functioning board by itself, but can only be added to the MKR1000 ? And the purpose of MKR1000 is to control the MKR MOTOR CARRIER, as if you can’t send computer code to the MKR MOTOR CARRIER directly. Somehow you write a C++ program, plug the MKR1000 into your computer or use WIFI, and then the MKR1000 controls the MKR MOTOR CARRIER to control the motors? Doesn’t seem logical so I am asking for a reality check. Also, there must be an easier way to actually get the schematics or logic to these boards than asking on the forum and hoping/waiting for a response, or second-guessing the information posted under tech specs, or trying to find the right links when links on the pages don’t link to anything, such as the link for pdf at the very bottom of the MKR MOTOR CARRIER “tech specs” page:
Documentation The Arduino MKR Motor Carrier is open-source hardware! You can contribute to the design using the following files:
-Schematics (MKRMotorCarrierV3.0-sch.pdf)

I’ve not used this carrier myself, but I can help you read its documentation. First of all, yes to your reality check question. The logic of it is that sometimes you can attach multiple carriers (or shields) to the same microcontroller, so you can include just the peripherals you need. Plus you can reuse the controller for other projects when you’re done with the current one. Secondly, the “standard” and “high” performance descriptions on the overview tab look to be quantified on the tech specs tab: check out the max current ratings for each of the 2 motor driver chips on the carrier. Thirdly, you can find a working link to the schematic on the documentation tab. Finally, if you want to drive higher voltage motors, you should take a look at the carriers from Pololu. They won’t be as convenient to use as Arduino shields, which just plug in, but they are inexpensive and high quality.