Formalize hardware features of car

[irapha]

This includes...

• measuring wheel_base
• re-measuring wheel_circumference (the rosparam we have was taken from buzzmobile-old)
• re-measuring max_steering_angle
• considering changes to the way we compute travel_distance

---

About the last point, right now, travel_distance is a value that is a "good enough" approximation of the distance travelled per tick. In buzzmobile-old, this was computed by the odometry interface, which assumed that the car was moving at a constant speed, and published:

distance_travelled = (ticks_elapsed_since_last_keep_alive * wheel_circumference) / ticks_per_revolution

We don't have odometry interface anymore, and we don't need it, because we're not simulating the car in the world model to make decisions about what to do when in a future state. So, to us, travel_distance can be an approximation because all it does it codify the granularity of the tentacle points. But I wanted to make sure this was mentioned somewhere ack'd

https://github.com/gtagency/buzzmobile/pull/32/files#diff-803bc1ddda718a341d80de27f0125f74R14

[joshuamorton]

However, we do potentially have a complication because we (will soon) have brakes and those can make our real world speed not a direct function of our motor controller. It would be nice to have something (PID, Optical flow, a magnet attached to a tire, kalman filtering, etc.) to give us a real world feedback on speed so we don't have to guess.

Alternatively, as a stopgap, we can try and do something to lower our speed estimate when the brakes are being applied, but that is a hell of a lot of estimation.

[irapha]

I'd say we come up with an odometry solution to make our tentacle predictions more accurate after mvp. Can you make issue about that maybe? On Tue, Oct 18, 2016 at 19:15 Josh Morton notifications@github.com wrote:

However, we do potentially have a complication because we (will soon) have brakes and those can make our real world speed not a direct function of our motor controller. It would be nice to have something (PID, Optical flow, a magnet attached to a tire, kalman filtering, etc.) to give us a real world feedback on speed so we don't have to guess.

Alternatively, as a stopgap, we can try and do something to lower our speed estimate when the brakes are being applied, but that is a hell of a lot of estimation.

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[dacohen]

Front Axle to Rear Axle Distance: 2.032 m Left Wheel to Right Wheel Distance: 1.3716 m

[irapha]

max_steering_angle eyeballed to about 15 deg

[irapha]

road_width ~8feet (needs conversion to meters)

[irapha]

min_fix_distance can probably be bigger than 0.01 meters (that might be in gps' margin of error)

This is outdated. Related issue: #78

[irapha]

travel_distance will be calculated with odomcallback #41 num_points_in_tentacle will be updated to use that ^ correctly, or can be done to say "total travel needs to be 6 meters, so do as many points as needed, except have a max number of points"

[irapha]

breaking_distance will be based on odometry too #54

[irapha]

buzzmobile_width ~= 66 in (convert to meters)