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Jul 09, 2014, 02:20 PM
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rover success





The 1st road test with motor sensors worked perfectly. It definitely needed breaks & slightly faster startup. The stalls were gone. 7.4V got it to the 7.5mph range, without getting hot. Based on the rolling distance, it probably was near the no load current of 0.3A. It was virtually silent. Radio range was only 10ft.

It easily rolled over rough terrain. The rolling distance without breaks was surprisingly long. Even with no power, it rolled into curbs hard enough to flip over, but didn't flip over on rough road. The sensors seemed to withstand it. The castor wheel assemblies crumpled, reducing the impact.

Startup was a hard coded stepper acceleration, transitioning to commutating mode, to keep the wheels from slipping. That failed miserably. It slipped when rotating to the 1st step. The sensors couldn't make it transition into commutating mode seamlessly. Tried ramping PWM without a stepper state & it still lost steering. Carefully setting it to wait for the right stepper phase would probably solve the transition problem, but not the 1st step.

The only practical way to get straight driving was to go straight into full power. It didn't slip as much as feared. It used less current. Stepper acceleration is a dead topic. It consumes a lot of current for purely visual appeal.

After implementing heading hold steering & all the manual controls, it worked perfectly. All the issues with bang bang steering were gone. Manual steering was effective. Steering by unbalancing the motor PWM was indistinguishable from the fully articulated suspension. The difference was it could only do straight lines through software.

As soon as it hit a puddle, it was dead. The surface mounted boards need a conformal coating. Radio range was another issue, being nowhere close to what it was on the g-buggy. Finally, the gyro is extremely temperature sensitive. It reused the 9 axis IMU from the balancer, but being back to 4 wheels means it could use the more temperature resistant gyro.

It's probably the fastest a 60mm Pololu wheel has ever gone. It's certainly the fastest a brushless direct drive rover ever went. The current performance has averted the need for a hobby grade car.
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