Obligatory First Featherweight Build Log (FeatherDozer)

[Sam_Gad]

Repairs & Brushless Lifter Take 1

So, there is a lot to cover and now the 2021/22 Robodojo season is complete, it’s time to get this build log up to date. For this post we are going all the way back to May/ June 2021.

Drive Geartrain Protection

As the gears took a direct axe hit in the previous event, it was clear that like the relay wires to the weapon, addition protection was required. Damage to both the pinion gear and axle gear are shown below.

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Luckily, there is plenty of bolt holes that can be used to mount the upper drive gear covers which, of course needed to complex due to the tight packaging and weight restrictions.

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With the repairs out of the way, we can get onto the fun part: Brushless lifter.

Brushless Lifter Shenanigans

This is still (as of April 2022) an ongoing upgrade but, it is still worth going through how we got to the present setup.
To get the most benefit out of this upgrade, the setup needed to be as fast as I saw comfortable (or at least faster to full lift than the brushed setup). The existing brushed motor (Vex 775Pro) has a max RPM of 18730 which is then overvolted slightly. The brushless motor chosen therefore had to be faster with the same output shaft to mate to the existing gearbox. The motor chosen was an 1800KV outrunner motor usually used in helicopters. The original motor I wanted was out of stock at the time so this much cheaper motor was the alternative. This gave a max RPM of around 30000RPM on a fully charged 4S lipo (16.8V). This gives a lot of leeway should I need to down the final speed.
The next stage was to battle harden the magnets in the motor and attach the pinion for the planetary gearbox. The is a surprisingly easy process once you get over the fear of possibly ruining a motor just after you bought it. After this success I went back and battle hardened the drive motors.

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The switch from brushed to brushless resulted in a much smaller package and a nearly 500g weight saving.

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Early testing looked very promising with plenty of speed and power. I decided for the first iteration to use that same speed controllers as the drive as I had spares plus, they can be swapped between the systems easily.
However, it became very clear the use of limit switches would more critical than ever to stop the design for tearing itself apart. Luckily, an off-the-shelf solution was made available which would work with a speed controller to set the PWM output to centre-point (usually 1.5ms) when a limit switch was pressed.

So, with the first iteration of fully brushless FeatherDozer complete, it was time to reassemble ready for the next event that was on 26/06/21.

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