Circle Drawing Machine

This is a basic drawing machine that creates circles. It is based on a ruler and a 3D printed marker slider. The machine pulls the marker around a weighted center pivot to create a circle. By repositioning the marker along the length of the ruler you can draw circles of different sizes.

This was created to help support a 5th grade curriculum, but surely can be used at other grade levels. See the attached lesson plan for how you might use it in the classroom to explore measurement.

If you are looking for a machine for older students that demonstrates more complex mathematical and engineering principles, check out the Torus Drawing Machine.

Step 1: Materials

(x1) Continuous rotation servo (modified for direct drive)***
(x1) 12" Ruler
(x1) 3D Printed Marker Bracket
(x1) 3D Printed Wheel Hub (not pictured)
(x1) 3XAA Battery Holder
(x3) AA Batteries (not pictured)
(x1) Sharpie marker (not pictured)
(x1) 76mm Skate wheel
(x1) 3/8-16 x 3" Bolt
(x1) 3/8-16 Nut
(x20) 3/8" x 2" Fender Washer
(x1) 5.5mm male screw terminal power plug
(x1) 5.5mm female screw terminal power socket
(x4) Rubber adhesive feet
(x2) Self-adhesive zip tie mounts
(x3) 8" Zip ties
(x2) 4" Zip ties
(x1) Large sheet of paper (at least 12" square)

*** See Step 3 for more details about modifying a servo.

Step 2: 3D Printed Parts

For this project you will need to 3D print marker bracket, and a set of parts to create one wheel hub. You can download the files from the Tinkercad website by clicking through on the parts shown above.

Step 3: Modify the Continuous Servo Motors

You will need to modify one continuous rotation servo for direct drive. The full instructions for modifying the continuous rotation servo motor for direct drive can be found in the Instructable for Removing a Servo Controller.

Step 4: Create the Center Pivot

The center pivot consists of a bolt with a stack of fender washers and rubber feet for support. The weight from the pivot keeps the machine in place and prevents it from drifting.

To build the center pivot, slide 25 two inch fender washers onto a 3/8-16 x 3" bolt. Lock the washers in place with a 3/8-16 nut.

Finally, place adhesive rubber feet on the bottom of the stack of washers to help keep the whole thing upright.

Step 5: Attach the Motor

Place two self-adhesive zip tie mounts on the front-facing edge of the ruler without the pre-drilled hole.

Using two zip ties (one for each mount), attach the motor the end of the ruler with the shaft pointing outwards.

Step 6: Attach the Batteries

Put the batteries in the battery holder.

Attach the batteries to the ruler using the adhesive zip tie mounts. Slide a zip tie through both mounts and fasten the battery holder in place on top of them.

Step 7: Insert the Wheel Hub

Insert the part of the hub with the stem through the skate wheel. Slide the ring onto the stem from the other side to complete the hub.

Step 8: Attach the Wheel

Remove the servo horn (the plastic bracket) from the servo shaft and using the horn's mounting screw, attach the skate wheel instead.

Step 9: Wire the Circuit

Strip 1/2" of insulation off the end of both the battery holder and motor wires.

Insert the red battery wire into the terminal labeled with a + sign on the male plug and tighten the set screw to hold it in place. Insert the black battery wire into the male plug terminal labeled with a - sign and fasten that in place as well.

Next, the motor wires need to be attached to the female plug. Once again the red wire should go to the terminal labeled with a + sign and the black wire should go to the terminal labeled with a - sign.

Step 10: Slide on the Marker Bracket

Slide the marker bracket onto the end of the ruler of which the motor is not attached. It should easily slide right on.

Step 11: Insert the Marker

Insert the Sharpie marker into the hole on the marker slider.

Step 12: Draw Your First Circle

Place the weighted pivot in the center of a large sheet of paper (at least 12" square)

Position the marker 5" from the free edge of the ruler.

Next, attach the plugs together to power it on. Once you do this, the wheel should start turning. If it does not, check your wiring and try again.

Finally, using the ruler's hanging tab, slide it down upon the weighted pivot and let the machine go free. The machine should now draw a perfect circle around the pivot point.

Step 13: Make a Donut

Now that you have made one circle , let's try making another one!

Lift the machine so that the wheel is not making contact with the ground, slide the marker so that it is not 3" from the edge of the ruler, and then place it back down on the pivot. It should now draw a smaller circle inside of the larger one.

You should be left with something that looks like a donut. You can now keep experimenting and drawing more circles or quit while you are ahead and decorate your donut by adding toppings and coloring it in.