by mraiser, published
Snap together 3D printable truck-like robot. Unlike the cool-but-ultimately-non-functional Tank designs ( http://www.thingiverse.com/thing:6554 and http://www.thingiverse.com/thing:8080 ), this bot actually works. Sadly the motors could not generate enough torque to actually move the tank robot due to the amount of friction introduced by the worm gear and tank treads. Encouraged by the success of my 27 to 1 Reduction Gearset http://www.thingiverse.com/thing:9414 I designed this bot from the ground up to be low friction, snap-together and almost entirely 3D printable. The only non-printable components are the motors, the motor mounting screws, the batteries, the wire and the nuts that serve as contacts in the battery holders. I hope to upload some PCB mounts soon so you can easily add the electronics necessary to make this bot autonomous, but if you are impatient I recommend looking into NBitWonder's awesome DC Motor Driver http://www.thingiverse.com/thing:7618 which was designed for the tank-bot.
I used this script to design the gears: http://www.thingiverse.com/thing:3575 (You will need to download the scad to use the attached truck.scad file). I also used this script to generate the battery holders: http://www.thingiverse.com/thing:5079
VIDEO: http://www.youtube.com/watch?v=F-qvDO9QZV4 As you can see from the video, the left rear axel isn't spinning freely and needs some sanding/filing.
UPDATE: I fixed the drag on the left rear axel by replacing "axelholder.stl" with "wheelholder.stl" in conjunction with "axelend2.stl". http://www.youtube.com/watch?v=o3SWtk4X-1Q
NOTE: This design is based on the tolerances of my cupcake 3D printer. As several folks who printed out the 27 to 1 gearset pointed out, the Thing-O-Matic has much better tolerances, so some of the snap-together parts may need some glue (or openscad tweaking) if your printer is better than mine!
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In addition to the printed parts, you will need 8 AA batteries, 16 3mm hex nuts, some wire, 4 flat head machine screws (to mount the motors-- 3mm x 6mm) and two 600 RPM DC motors. I used a pair of these: http://www.batteryspace.com/dcmotorhightorquemini12vdcgearmotor600rpmforhobbyproject.aspx
4 x axel.stl 4 x axelend.stl 2 x axelholder.stl 2 x batteryholder3.stl 2 x batteryholder4.stl 4 x connector1.stl 1 x connector2-mirror.stl 1 x connector2.stl 2 x connector3.stl 2 x connector4.stl 1 x connector5.stl 3 x connector6.stl 2 x connector7.stl 1 x connector8.stl 4 x connector9.stl 1 x connector10.stl 2 x connector11.stl 2 x gear1.stl 2 x gear2.stl 2 x motoraxelsupport.stl 1 x motorholder-mirror.stl 1 x motorholder.stl 4 x wheel.stl 4 x wheelholder.stl
UPDATE: Replace 2 of the axelend.stl with axelend2.stl and use 2 more wheelholder.stl in place of axelholder.stl. This will significantly reduce friction on the rear (non-geared) wheels.
Assemble the parts as shown in assembly.stl. Connect the batteries in series to achieve the 12 volts required by the motors. Thread wire through the battery holder holes and use pliers to snap the hex nuts into place. The hex nuts will hold the wires in place, but if you add 3mm bolts and additional nuts to the exterior of the battery holder (as suggested by obijuan in his battery holder design) that will simplify the wiring. Wire up the motors in parallel and let it rip.