We have an old robot that started to have some trouble, it was a kiwi drive train that had 3 Omni wheels. We used a meccanum mixer and a cheap and dirty receiver and transmitter combo. Everything worked well until last year where a kid at our event hit it a bit too hard and it didn’t work. We decided to redo the robot and when we turn it on, the robot just spins.
I would have guessed you would be better off using an Omni Mixer, since it’s designed to provide the 3-wheel mixing for a Kiwi drive. I cannot think how you’d use a Mecanum Mixer to power a Kiwi omni drive…
If you are using an RC transmitter, I’d verify the switch position. Oftentimes the switch can be set up for throttle hold which sets the channel to a preset amount.