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Dec 13, 2014, 10:33 PM
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Upgrading the TBLE-02S to 12V

Some video of the 7.4V drive:

8 mile lunchbox drive (3 min 49 sec)

Tamiya Lunchbox run highlights (3 min 58 sec)

Almost got hit by a golf ball. It hit the ground inside the cage, then bounced into a pole. It was an astoundingly bad drive to even reach the cage, but an inevitability if you run through there enough.

Then came the 1st running selfie anyone ever took from a side looking rover. Just pulling that off with the 1 handed controller inspired a lot of ideas, with big technical challenges.

It was time to upgrade the TBLE-02S to 12V, to increase the range. The answer is no, you can't plug 12V into it without modifying it.

The servo header gets 6.1V from a home grown regulator made of a 2SB772 PNP transistor + a bag of discrete components. The 10V 220uF cap takes battery input directly after a 0.7V diode drop. The microcontroller is a Fujitsu 95F636 capable of 2.4 - 5.5V. The regulator supplying 2.7V to the microcontroller says G2JC4 & is fed directly from the 220uF cap. The rest is discretes. The conformal coat is the same polyurethane used on hardwood floors.

Not knowing what would fry the 2.7V regulator, it needed an alternative supply. With the diode removed to isolate the 2.7V regulator, the rest could be powered from 12.6V. At this point, the servo regulator put out 6.7V which could feed the 2.7V regulator but not a servo. The 2nd rework was to power the servo from a proper 6V regulator.

With that, it worked perfectly on 12.6V. It relied on software to keep the PWM from applying a full 12.6V to the motor.

It seems driving in a fertilizer covered field caused corrosion which ate away a trace.

With the battery position known to be on the underside, repositioned the board on the inside to try to keep it from getting wet.

Steering glitches which had dogged all RC cars for the entire year ended up being from analog glitches in the remote control. It used a voltage divider to generate a single steering signal from 4 buttons. Converted it to digital buttons & the glitches finally went away.

Range when directly using 12V with PWM scaling was 5.5 miles. Then the battery hit 8V & there wasn't enough to power the gyro. There was no correlation between PWM scaling & speed, only battery voltage & speed. The linear regulator gave the best results, but the shortest range. It may be a matter of manually changing PWM values on different parts of the course.

Gyro drift was unacceptable. Need to sample the gyro reference voltage instead of using CPU Vdd which is unstable. Merely turning on the headlights sends the gyro reading off. Who knows what bluetooth is doing to it. Need a configuration option for throttle_v0.

Lost the computer at mile 9 from water intrusion & had to carry it the final half mile. Conformal coating would seriously gum up some expensive parts.

After going 18 miles, there's no problem with the stock plastic bushings, the brushless motor, or the plastic servo. Didn't use any lubrication on the bushings & only a tiny amount of lubrication on the differential gears. The servo may still go, someday. An ancient Tower Hobbies el cheapo servo fit Tamiya's servo saver perfectly. More expensive Hi-tec servos didn't.
Last edited by Jack Crossfire; Dec 13, 2014 at 11:48 PM.
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