One of the other alternatives to the Arduino is Launchpad from Texas Instruments. The TI controllers have specifications similar to STM32 controllers, and both are based on ARM's Cortex-M architecture. The clock speed of the controllers ranges from 48 MHz-330 MHz. The flash memory capacity is also high: up to 1 MB. The GPIO pins and cost are almost similar to STM32 boards. Some of the commonly used Launchpad boards are TM4C123G Launchpad and EK-TM4C1294XL, which is based on an ARM Cortex-M4F-based MCU. The 123G works at 80MHZ and 1294XL at 120 MHz.

The good thing about these boards is that we can program them using a modified Arduino IDE called Energia (http://energia.nu/).

This is how the EK-TM4C1294XL looks:

We have seen some popular controllers; now let's look at some of the high-level embedded processing units that can be used in robots.