Monday, October 13, 2014

Motors for Arduino Labs

This week I went through many of the SparkFun Inventor's Kits that we use in our CoderDojo Arduino labs and realized that the kids have been loving our little DC mini-motors to death.  As you can see in Figure 1 over half of the wires had broken off!

Figure 1: DC Motors with most connector broken off

The ones supplied in the SparkFun Inventors kits have small delicate wires on them that break off easily. Since the motor circuit lab is a popular lab we need reliable DC motors!

It was pretty easy to solder the wires back on.  However, I wanted to make sure they didn't get pulled off again.  So I have replaced the old thin wires with some thinker 22 gauge stranded wire. I then use heat shrink and some cable ties to bind the wires to the case of the motors. You can see the heat shrink just before I applied the heat in Figure 2.

Figure 2: DC motors with heat shrink

Next I used some small cable ties (see Figure 3) to firmly secure the wires to the motors.  So if the kids pick up the motor by the wires it will not strain the solder joints.

Figure 3: DC with cable tie

Viewing Motor Direction (Optional)

I also realized that some of the motors don't have gears on them so it is difficult to tell what direction they are spinning.  In our labs (not in the Sparkfun Inventors Kit) we need to show both clockwise and counterclockwise directions in the labs. The direction of rotation is used in the motor labs that use the motor driver H-bridge chips like the popular L293D. So I have added a small drop of hot-glue on the end of the motor spindle and then added a Golden Spiral sticker to help the students see the direction of rotation. I also put a ring of hot-blue around the base and then used a felt pad so that the motor could stand upright.

Figure 4: Motor on base with Golden Spiral label on motor spindle.  The wires are multi-stranded 22 gauge but have a 1/2 inch solid gage at each end to work with the breadboard.

Figure 5 has the artwork from the Golden Spiral Label. This is one of may favorite designs.
Figure 5: Golden Spiral Label to indicate rotation

As an aside, some of you may know that spirals are painted on jet engines like in Figure 6 to indicate that the engine is rotating and give the viewer some indication of direction.

Figure 6: Golden Spiral Graphic painted on jet engine to show motion

A discussion of the golden spiral is also a change to discuss the beauty of mathematics. A PDF file that can be used print out the designs on sheet of labels is here. Let me know if you want the source PPT file. I am not artist and others might have a better spiral design. An SVG image might be a bit smoother.

So some of you might be thinking that this is a lot of detail for a just one lab! You would be right! However, I think that the care and attention to detail we give each of these labs help the kids get quickly to the next level. This principal helps us apply the theory of Constructivism to our labs. Once kids know they can change motor direction directly from within their Arduino code they can then make the logical next step to seeing how they can turn a robot car direction by having one wheel motor go backwards. Each of these are small logical learning steps we need to keep kids coming back to our STEM classes.

In a busy noisy class with 20 students jumping around we don't want to have to search through 20 kits looking for a motor that has the wires attached. This takes time away from our learning objectives.

With a good solid supply of motors that will last through a year of labs like in Figure 7 you will be ready to help all your students get to the really fun parts - building their own Arduino powered robot!

Figure 7: Motors ready for the kids!

We will hear more about this and the learning steps to building robots in future blog posts.



Eric said...

There is a great supplier of shrink wrap in quantity on ebay. Large rolls cheap. Let me know if you want to know the supplier's name. I will post it here.

Dan McCreary said...

Yes, I would like to know. I need to order some for the LED light strips. - Dan

Dan McCreary said...

I just had someone let me know that I am not the first to use cable ties as strain reliefs on motor connectors:

Eric said... This is less than 1cent / inch

It arrived in a few days. 3MM is the size I use the most.