I need to purchase the correct bluetooth module for interfacing some simple functionality between an arduino and a motor. The tricky bit is getting the bluetooth radio to play nice with android and apple ios. There are things like MIT App Inventor, but I'd love to hear from someone with experience how to reliably control arduino from tablets/phones. Preferrably in a way that lets me define the control on the arduino. I can build android apps (slowly), not ios apps, but I would then have to either ask users to install untrusted apks or get it out through the google app store, which would take too long. Any help on this would be great.
You may want to have a look at the Adafruit BLE modules: https://learn.adafruit.com/introducing-the-adafruit-bluefruit-le-uart-friend/bleuart?view=all
They have provided great examples of how to connect from Android and iOS devices, as well as providing apps or code to integrate into your own apps and you get to implement the motor controller code yourself on the Arduino so should have full control over that side.
They even have an example where they are controlling a motor using an Arduino and Bluetooth, it may not be exactly what you need but hopefully gets you closer to an answer: https://learn.adafruit.com/bluetooth-motorized-camera-slider/overview?view=all