Earth Globe Rotating With Arduino Or Raspberry Pi Controlled Stepper Motor using arduino
This instructable describes how to upgrade your globe to a motorized version. It looks amazingly better on the shelf when it is slowly rotating, and any demonstration with your kids (to explain the day/night cycle or the seasons) will gain in interest. No need to rotate the globe by hand while painfully holding the flash light with your teeth.
The instructions correspond to the various parts I had at my disposal so they may have to be adapted to yours. The needed parts are:
- a globe, the one I used is this one ($30) http://www.amazon.com/Elenco-11-Desktop-Political…
- a stepper motor + driver. This one is great because it is geared down conveniently for the kind of torque/speed we want ($6) http://www.amazon.com/gp/product/B00DUSYEWY
- an arduino or raspberry Pi (see link bellow)
- some axle + wheel from a lego box or such. The axle I use is ~1/4″ diameter and was a left over part from a kit, http://www.amazon.com/Thames-Kosmos-665068-Solar-M…
- various tools, such as a saw or knife, a drill, glue (hot glue is optional),…
- but you do want a very strong epoxy JB-Weld that sets in 4 minutes (explanations in step 4), such as this one http://www.amazon.com/J-B-Weld-8276-KWIK/dp/B0006O…
I will not describe the operation of the motor since it is very well done in this instructable: http://www.instructables.com/id/BYJ48-Stepper-Moto… you might want to check it out first since some of the steps bellow are better carried out if the motor is powered and rotating.
Step 1: Flush the globe axis with the rotating plate
This globe, rests onto a plate that can be taken out. Take it out. The large axis that protrudes has to be cut so that the plate will be flush with it when resting on its position. After you cut the axis (leaving 2-3mm of protrusion), place the plate back on its stand. It should rotate freely. If not, shave the small plastic fibers (left over from the cut) with a knife.
Step 2: Drill the base of the arm for your wheel axle
The globe axis that we just cut is actually hollow on this globe. But the hole is not circular and to small anyway for the wheel axle I have.
Find a drill bit with a diameter that corresponds to the wheel axle you have. If you have another one, slightly smaller, use it first. You want the drill to be well guided by the existing hole, and using the smaller drill bit may help you in this task. Also, be careful to not damage the plastic part by going to fast.
The most important part is to stay on axis. Do not drill if you are forced to be off axis. Prefer to drill from the top by bending slightly the globe arm away, it might actually guide you since the top part of the arm is precisely on the rotation axis.
Step 3: Glue the wheel in the plate
Set the wheel on its axle. then fit the axle into the hole through the plate. It should rotate freely, without much play.
At that point, you can glue the wheel in the plate. I used hot glue, just in case I would want to take the wheel back out, but a few drops of epoxy would do it.