I built an Otto robot based on an Arduino Nano board and powered it with a 9 V block battery and everything worked as intended.
I'm currently recreating the project with a group of kids, but we only had Arduino UNO boards available. I did not think anything of it... but now when I have uploaded the sketch and switched it on to run (only) from battery power, the UNO just makes ticking noises and flashes its lights. The battery is connected to VIN and GND, and cables run from 5 V and GND to the servos.
I understand that the ticking indicates the power is too low, but the exact same setup works with a NANO... so do they consume power so differently?
Another problem: if I just connect the battery to the servos and power the board via USB, the servos will not work either.
So where's my error?