The following parts were designed using Autodesk Fusion 360 CAD design software. Fusion 360 is free for students, startups, hobbyists, and enthusiasts. The files are available from Autodesk's A360 cloud service and may be downloaded in a wide range of formats. Each of the images below connect to the corresponding design. Users are encouraged to use these files, modify them, create their own designs, and share them with other LoCoRo builders.
The LoCoRo project is a community effort. Builders are encouraged to share their designs with other builders.
3D printers are great tools but they are not 100% accurate nor are they 100% consistent from printer to printer. Each printer will have small variances. These variances have little effect on esthetic parts but even 0.1mm can prevent parts from mechanically interconnecting. The tolerances are especially important when mating a multiple printed parts and when mating printed parts with commercially manufactured parts. Examples included matching the mounting hole of the Raspberry Pi, fitting a servo horn into a wheel, or attaching an RC servo to a chassis.
The LoCoRo project provides the source CAD design files so users may make changes - whether to add features or adjust for the variances of their particular printer.
The interlocking block test model may be used to help calibrate the 3D printer slicing software. The model consists of two parts which - when printed accurately - interlock snuggly. Each half is 20mm x 30mm x 10mm. The three rails are 5mm wide while the two rails are 7.5mm wide.
If the printed parts do not fit together, there are two options. First, attempt to adjust settings in the slicer software. As a final solution, make adjustments to the model. If the latter solution is used, similar adjustments will be required for the other models.
Tip: Once the interlocking block fit, write the slicer adjustments directly onto the blocks and save them for future reference.
There are several electronics parts used to control a LoCoRo. For the basic robot using a USB battery, the parts include the Raspberry Pi and the I2C PWM servo control board. When using a 7.4V or 9.6V battery pack, the electronics also include the DC converter. It's helpful to organize the parts on a mounting board.
The basic electronics mounting plate is very simple and contains mounting posts that align with the holes on the Raspberry Pi and the servo controller. There are also mounting holes to allow the plate to be attached to one of the chassis models.
The Raspberry Pi enclosure with a housing for a camera is an example of the possibilities available with 3D CAD and 3D printers.
This model houses the Raspberry Pi along the bottom and the I2C PWM servo control board is mounted vertically at the back. The DC converter mounts under the top of the enclosure with its LED voltage display exposed. There are mounting posts on the underside of the top for a gyroscope/accelerometer board. The recess in the top left corner supports a standard DC battery pack connector. A Raspberry Pi camera may be mounted to toe top with the optional housing and there is a slot in the enclosure top for the ribbon cable. Two small holes near the rear of the top are for brass injection molding inserts which provide a pass-thru of the switched battery power for use with electronic speed controllers or other accessories. Not visible in the image is a hole for a power button.
Wiring this enclosure takes patience and care as not much extra room is provided.
Note: this enclosure does not currently mate to the multi-purpose chassis.
Updated LoCoRo chassis design which may be used for the two servo Basic LoCoRo as well as a two server tank drive or four servo mecanum drive configuration. The basic Locoro installs servos in the two rear locations. The tank configuration uses the same two rear locations. The mecanum drive uses all four servo locations.
The basic LoCoRo uses two drive wheels and a free casting front wheel. This tricycle configuration uses differential drive for motion and direction.
Normal sized RC servos have consistent mounting holes and dimensions which make them well suited to this 3D printed mounting plate.
This chassis design has holes which match the basic electronics mounting plate.
There is sufficient space between the chassis plate and the electronics plate for most USB battery packs.
The 120mm wheel is a good match for a continuous rotation RC servo. The servo will have a typical speed of between 50 and 60 revolutions per minute. Using a little arithmetic, the 120mm wheel results in a top speed of a LoCoRo of approximately 0.35 meters per second or approximately 1 foot per second. While not fast, this is a good speed for indoor use.
The model has a recess at the center for a typical RC servo horn. The design may be adjusted to match the actual mounting options available with the servos in use.
The wheel performs well on a soft surface such as rugs or carpet. A large wide rubber band fits around the circumference for better traction on hard surfaces.
An example of the wheel was posted to the blog here.
A mecanum wheel has the useful property of being relatively efficient at normal forward/reverse motion and turning while also being capable of lateral motion.
Here is a short animation of the operational aspects of the wheel.
The construction of this mecanum wheel model requires two different hubs. There are twelve rollers on each wheel. The rollers are installed at ±45 degrees to the wheel's axle. Two wheels have the rollers at +45 degrees and two wheels have the rollers at -45 degrees. The rollers are held in place with pins. The four wheels require printing two left hubs, two right hubs, 48 rollers, and the creation of 48 pins.
The pins are created using 3D printer filament and the technique was described on the blog here. The mecanum wheel model assumed 2.85mm filament for the pins and must be adjusted when using 1.75mm filament for the pins.
The rollers perform well on a soft surface such as rugs or carpet. The rollers may be printed from a flexible material or covered with heat-shrink to improve traction of hard surfaces.
An example of the wheel was posted to the blog here.
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