Robotic Cam Steered Vehicle

Fifty plus years ago I received a toy car for Christmas that had one electric motor powered by two D cell batteries. While the electric motor drove the rear wheels to propel the car forward, the car also included a unique steering system using a gear driven rotating "cam" which steered the car in a geometric path. The car came with a variety of cams, and by changing the cam, the car would travel a different path.

The car has long since disappeared and I could not locate another, so in today's world of micro controller and servo / stepper motor driven vehicles, I thought I would recreate my decades old electric motor driven / cam steered toy car in 3D printed form entitled "Robotic Cam Steered Vehicle" for the kids, grandkids, and of course, me!

As usual, I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to ask as I do make plenty of mistakes.

Designed using Autodesk Fusion 360, sliced using Cura 4.4.0, and printed in PLA on an Ultimaker 3 Extended and an Ultimaker S5.

One final note, I receive no compensation in any form whatsoever for the design, equipment, parts and/or materials used in this model.

I used the following supplies in assembling this model:

• Wire
• Solder
• Thick cyanoacrylate glue.
• Double sided tape.

I acquired the following parts for this model:

• One 3.7vdc 100ma Lithium Battery (https://www.adafruit.com/product/1570).
• One JST PH 2-Pin Cable (https://www.adafruit.com/product/3814).
• One N20 6VDC 150RPM gear motor.
• One micro switch (Uxcell a12013100ux0116 High Knob 3P 2 Position 1P2T SPDT Vertical Slide Switch, 0.5 Amp, 50V DC, 50 Piece, 3 mm).
• One extension spring (6.35 OD, 22.2 length, .5mm section, local hardware store).
• Four O-Rings (30mm ID, 3.5mm section, local hardware store).

You will also need a suitable battery charger.

I 3D printed the following parts for this model:

• One "Axle, Cam.stl", .15mm layer height, 20% infill, no supports.
• One "Axle, Gear, Worm.stl", .15mm layer height, 20% infill, no supports.
• One "Bellcrank, Left.stl", .15mm layer height, 20% infill, no supports.
• One "Bellcrank, Right.stl", .15mm layer height, 20% infill, no supports.
• One "Body, SUV.stl", .15mm layer height, 20% infill, PLA supports (this is a long print).
• One "Bolt, 3mm Shoulder, Long.stl", .15mm layer height, 50% infill, no supports.
• Seven "Bolt, 3mm Shoulder.stl", .15mm layer height, 50% infill, no supports.
• Four "Bolt, Wheels.stl", .15mm layer height, 50% infill, no supports.
• Two "Bolt.stl", .15mm layer height, 50% infill, no supports.
• One "Bumper, Front.stl", .15mm layer height, 20% infill, no supports.
• One "Bumper, Rear.stl", .15mm layer height, 20% infill, no supports.
• One "Cam, Figure Eights.stl", .15mm layer height, 20% infill, no supports.
• One "Cam, Ovals.stl", .15mm layer height, 20% infill, no supports.
• One "Cam, S Curves.stl", .15mm layer height, 20% infill, no supports.
• One "Cam, Squares.stl", .15mm layer height, 20% infill, no supports.
• One "Cam, Triangles.stl", .15mm layer height, 20% infill, no supports.
• One "Chassis.stl", .15mm layer height, 20% infill, no supports.
• One "Gear, Cam.stl", .15mm layer height, 20% infill, no supports.
• One "Gear, Motor.stl", .15mm layer height, 20% infill, no supports.
• One "Gear, Worm, Drive.stl", .15mm layer height, 20% infill, no supports.
• One "Gear, Worm.stl", .06mm layer height, 20% infill, PVA supports.
• One "Mount, Spring.stl", .15mm layer height, 20% infill, no supports.
• Two "Rollbar, Support.stl", .15mm layer height, 20% infill, no supports.
• One "Rollbar, Upright.stl", .15mm layer height, 20% infill, no supports.
• One "Tie Rod.stl", .15mm layer height, 20% infill, no supports.
• One "Wheel, Gear.stl", .15mm layer height, 20% infill, no supports.
• Three "Wheel.stl", .15mm layer height, 20% infill, no supports.
• One "Windshield.stl", .15mm layer height, 20% infill, no supports.

This is a high precision print and assembly using at times very small precision 3D printed parts in very tight spaces. Prior to assembly, test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on you printer, your printer settings and the colors you chose, more or less trimming, filing and/or sanding may be required. Carefully file all edges that contacted the build plate to make absolutely certain that all build plate "ooze" is removed and that all edges are smooth. I used small jewelers files and plenty of patience to perform this step.

The model also uses threaded assembly, so I used a tap and die set (6mm by 1) for thread cleaning.

To wire and install the motor, switch and JST connector, I performed the following steps:

• Soldered the JST red wire to the motor "+" terminal.
• Soldered the JST black wire to the switch center terminal.
• Soldered a black wire from one switch outside terminal to the motor "-" terminal.
• Slipped the JST connector and switch through the motor mount then through the outside the rear hole in the cam support ring on "Chassis.stl", then pressed the motor into the motor mount such that 5mm of the motor shaft extended from the outside of the motor mount.
• Pressed the switch into the chassis switch hole near the left rear wheel mount such that the switch face was flush with the underside of the chassis, then secured the switch in place with a small dot of thick cyanoacrylate glue.

To install the gears, I performed the following steps:

• Pressed "Gear, Motor.stl" onto the motor shaft until the gear was flush with the motor shaft.
• Positioned "Gear, Worm.stl" between the worm gear towers on the chassis assembly and secured in place with "Gear, Worm, Drive.stl" (on the motor gear side) and "Axle, Gear, Worm.stl".

At this point, I secured the battery to the chassis assembly using double sided tape, plugged the battery into the JST connector, then turned on the switch to check for smooth operation of the gears and for a current draw of around 18MA. I then turned off the switch and disconnected the battery from the JST connector.

To install the steering, I performed the following steps:

• Secured "Bellcrank, Right.stl" to the right bell crank tower on the chassis assembly using one "Bolt, 3mm Shoulder.stl".
• Secured "Bellcrank, Left.stl" to the left bell crank tower on the chassis assembly using one "Bolt, 3mm Shoulder.stl".
• Secured one end of "Tie Rod.stl" to the right bell crank using "Bolt, 3mm Shoulder, Long.stl".
• Secured the remaining end of the tie rod to the left bell crank using one "Bolt, 3mm Shoulder.stl".
• Slid one end of the extension spring onto one "Bolt, 3mm Shoulder.stl".
• Threaded the bolt into "Mount, Spring.stl".
• Secured the spring mount assembly to the chassis assembly using one "Bolt.stl".
• Slid the free end of the extension spring onto the long 3mm shoulder bolt.
• Adjusted the spring mount assembly along the slot such that there was a small amount of pre-load on the spring, just enough to hold the steering assembly in the left position.

To install the tires and wheels, I performed the following steps:

• Slipped one O-Ring onto each of the four wheels.
• Secured one "Wheel.stl" to the right bell crank using one "Bolt, Wheels.stl".
• Secured one "Wheel.stl" to the left bell crank using one "Bolt, Wheels.stl".
• Secured one "Wheel.stl" to the right rear wheel mount on the chassis assembly using one "Bolt, Wheels.stl".
• Secured "Wheel, Gear.stl" to the left rear wheel mount on the chassis assembly using one "Bolt, Wheels.stl".

To install the cam gear and a cam, I performed the following steps:

• Positioned the hexagonal plug on "Cam, Ovals.stl" into the hexagonal socket in "Gear, Cam.stl".
• Positioned the cam assembly onto the chassis assembly cam support ring, centered over the threads in the cam mounting tower.
• Secured the cam assembly into position using one "Axle, Cam.stl".

At this point the chassis is complete and ready to run!

And that is how I 3D printed and assembled "Robotic Cam Steered Vehicle".

I hope you enjoyed it!

Oh, but there's more...

I operated the chassis for a few days using the various cams to entertain family and friends, and while I enjoyed the model "as is" (I enjoy watching the mechanisms operate), others suggested I needed to add a body. So if you are interested in adding a body, proceed to the final step.

The body is optional and requires supports to 3D print. At the settings I used on my printer, the print time for "Body, SUV.stl" was around eighteen hours and required 98g (12.45m) of filament. After 3D printing the body components, I performed the following assembly steps to prepare and attach the body:

• Glued "Bumper, Front.stl" (flat side down) to the front of "Body, SUV.stl" using small dots of cyanoacrylate glue.
• Glued "Bumper, Rear.stl" (flat side down) to the rear of the body assembly using small dots of cyanoacrylate glue.
• Pressed "Rollbar, Upright.stl" into the front two holes in the cargo area of the assembly.
• Pressed one "Rollbar, Support.stl" into one of the rear holes in the cargo area of the assembly, held it against the rollbar upright, then glued the support the the upright using small dots of cyanoacrylate glue.
• Pressed the remaining "Rollbar, Support.stl" into the remaining rear hole in the cargo area of the assembly, held it agains the rollbar upright, then glued the support to the upright using small dots of cyanoacrylate glue.
• Secured the rollbar assembly to the body assembly using small dots of cyanoacrylate glue.
• Pressed "Windshield.stl" into the holes in the hood of the body assembly and secured in place using small dots of cyanoacrylate glue.
• Placed the chassis assembly into the body assembly then threaded one "Bolt.stl" through the rear body mount horn on the chassis assembly and into the rear body mount tower.
• Threaded one "Bolt, 3mm Shoulder.stl" through the left front body mount horn in the body assembly and into the left body horn on the chassis (removing the front wheel makes this easier).
• Threaded the remaining "Bolt, 3mm Shoulder.stl" through the right front body mount horn in the body assembly and into the right body horn on the chassis (removing the front wheel makes this easier).

And that is how I 3D printed and assembled "Robotic Cam Steered Vehicle" with a body.

I hope you enjoyed it!