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- Determined effect of battery status on cars speed.
- Determined effect of the capacitor used to filter the power on cars speed.
- Determined effect of test-bed slopes on cars speed.
- First analysis on the effect of motor and steer input on speed.
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Figure pwm.png shows the speed of the car obtained by keep the steer constant and varying the PWM. The relationship between PWM and velocity is quite linear. For some reason, when the steer input is high, the speed observed with PWM 140 is slightly lower than I would expect. On the other hand, the steer effect seems to be a little bit more complicated (see steer.png). Velocities observed for steer 92 and 120 are always very close. This may be due to the fact that curvature radius for the two steer input are very similar (the curvature radius is not linear with respect to the steer signal). Still the speed is not linear w.r.t. the curvature radius because the discrepancy between the speed for steer 36 and 64 (which I measured to have respectively a curvature radius of roughly 200cm and 100cm) tends to be reduced by decreasing the PWM.
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Work in Progress. These experiments were performed before the effect of the power filter capacitor on speed was clear and they will likely be done again for a longer time in order to get useful data.
As a side note, the low frequency oscillations should be noted. These oscillation are caused by the fact that the testbed is not completely flat, there are slight slopes.
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EFFECT OF THE BATTERY AND THE POWER FILTER CAPACITOR ON THE SPEED DYNAMICS
I made an investigation on the effect that the battery has on the car speed. Data has been acquired by running car1 car 1 on a circle with constant steer and engine input. The steer has always been set to -64. The starting position of the car has always been about (3000, 3600) in global coordinates (this if you want to make considerations connected to the test-bed slope). The voltage of the battery was measured both before turning on the car (while off) and just before run ca2 (while on). The full data gathered and the detailed description of how the experiments were performed can be found in my folder on Dropbox in "../backup/data/battery_7-30-2013".
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The behavior dynamic of the car speed is likely caused by the capacitor that filter the power source. When the car is not running the circuit is in steady state condition. When it runs the equilibrium moves and the capacitor slowly discharges. I observed the same behavior in both cars 2 and 3.
DOCUMENTATION EXPANSION
These are likely to be moved on the main wiki page at some point.
TROUBLESHOOTING
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