Reverse engineering the Tacx Bushido
The Bushido is a top of the range turbo trainer from Tacx. It consists of a brake unit based around an alternator which is linked to a head unit mounted on the handlebars using the ANT protocol. The head unit can be used alone, or linked to a PC using the ANT wireless protocol. From the PC the user can design training programs and log data such as the rider power output, heart rate, cadence etc.
Unfortunately the PC software is expensive, runs only on Windows and crashes frequently. This led Will and I to reverse engineer the protocol allowing full control over the turbo trainer without using the Tacx software. More details will follow shortly, but for now we have documented the protocol here.
Update 24/10/12: We have almost completely documented the brake to the computer protocol (see link to the wiki above) using a “man in the middle” approach developed by Will. It appears that the brake sends back much more data to the head unit than is actually made available to the user. A graph showing the data sent back from the brake is shown below. Whilst we’ve identified which values correspond to those displayed on the head unit, we’re still trying to figure out what some of the other quantities are. We’ve uploaded an example log of brake only communication here, and the data from the graph below here, if you are interested in helping.
A: Related to power somehow?
B: Power (confirmed)
C: Very similar to A, left/right version of?
D:Roller speed (rps) of brake? Note: Assuming roller radius of 30mm, at a speed of 30kmph the roller rotates at 45rps, which is in good agreement with this assumption.
G: Actual wheel speed (confirmed) – note wheel speed displayed on head unit is computed from power. Actual wheel speed is used to calculate distance.
H: Cadence (confirmed)
I: Pedalling balance (confirmed) – affects bar at bottom of head unit
L: Some sort of counter: Doesn’t affect distance on head unit. Resets when pedalling is stopped.
M: Brake temperature?