Comment by shagie

Was it the battery pack? Looking at https://www.adafruit.com/product/5579 and https://www.adafruit.com/product/1201 it should be fairly possible to get to a more reasonable size. As an alternative to the leg, having the vibration as something in the collar might be an alternative.

One of the "hmm... things to make" is a lidar detector for things behind a car that then is mapped to an array of the vibration motors that are in the back of a driver's seat - so that you could feel a car passing you.