Ways to measure brushless motor velocity?

Question

I am using an RC car chassis for some robotics work, I am interested in sensing motor velocity.

With brushed motors the only option appears to be using an external encoder(though I wonder if spikes associated with brush contact could be used).

I'm wondering if there is a way to sense brushless motor velocity without using a physical sensor? What would be the correct way to do this?

No RC ESC that I know of give motor velocity information(unfortunate) so I would either need an ESC which included it or tap into the wires.

Answer 1

Magnetize a nut, or fitting, on the shaft somewhere then use a Hall effect sensor.

A method used on turbos to get the rpm and some do 180000rpm so your motor should be in range.