Cheap manipulator using car door lock actuator

manipulators-tools

#1

Hello! I’m attempting to rig a (hopefully) simple manipulator using a car door lock actuator (small geared dc motor). They’re super cheap and plentiful, so I won’t be too heart broken if it doesn’t last long underwater. I know my 2.8 has a 9V PWM channel available, but can it be used di-directionally? If not, I could use that PWM channel to power a potted brushed ESC, and then one of the servo channels to control it. I’d be wasting an output, but the plus would be that I could program it to cut power to the manipulator if its current draw exceeded 2A. I believe that pin A0 measures non-ESC current, correct?

Alternately, is there a way that I could wire the brushed ESC inside the e-tube so that its output could be routed through the existing aux wires easily? Thank you in advance for your ideas!


#2

Hi There:

You are right, the PWM channels are uni-directional.

For your application, I’d do exactly as you suggested- use a brushed ESC, and attach it to a couple of the auxiliary outputs that are currently set for a servo output. You’ll need to disconnect the D9 servo channel from aux ouputs TP23-TP25 by removing jumpers R70-R72 – see sheet 2 of the schematic. You can drive the ESC by connecting it to the 3-pin connector for servo channel D9. Then comes the fun of powering it- if you run it off of V_BAT, the current monitoring at this point is capped at 2 amps, as you say. Probably better to try to pick off ESC_POWER at some point, since that’s designed for high currents. See Sheet 3 of the schematic for more details.

-W


#3

Thanks for the advice, I ended up taking the spring loaded approach and just used the existing pwm setup. I modified the external lights plugin for axis control, then limited the output to 50%. The manipulator never draws more than 1 amp, and still has a very strong grip.

Still working on buoyancy and trim, but the manipulator is working, and was really easy and cheap to build.