The Back Scratcher

The Back Scratcher is made for scratching away itches on the back. It is a brush on a stick that moves by means of a servo. The brush has an adjustable speed and an adjustable angle over which the brush moves back and forth. You can adjust these two variables using the rotary knobs close to the handle. This way you can set a different setting for each possible itch!

Things you’ll need:

Materials

• Small bottle brush
• Standard servo
• PVC pipe
• Klein tasje met rits
• Arduino
• 2x Potentiometer
• (Bicycle) rubber handle
• Something to fill up the space between the PVC pipe and rubber handle;
• For example tape.
• Battery
• Adhesive paper for decoration
• 9 Jumper cables
• Shrink wrap

Tools

• Hairdryer / hot air blower
• Soldering station + Solder material
• Battery charger
• Saw for the PVC pipe
• PC / Laptop for programming

For this project you don't need any extra printed circuit boards, you can plug everything directly into the Arduino. Be careful with connecting multiple wires though, it is strongly recommended to use shrink wrap on the wires that you soldered together to prevent short circuits.

Before you start to solder, make sure to read the first part of the Construction step to save yourself some hassling!

This is all the code you'll need for the back scratcher!

I have also uploaded a .txt file with the code for if you wish to copy n paste the code.

Before you start soldering, make a hole in the PVC tube for the servo. Then clip the servo into that hole and secure it with duct tape. Then pull the wires through the PVC tube towards the handle and make a small hole to pull the wires through. Then take your bag and make 2 holes at the top and bottom close to one of the sides and then put the stick through the bag.

After that you can start soldering according to the schematic in step 1: Showing The Circuitry. After you have soldered everything correctly, you have two potentiometers that are now loose. For the potentiometers, make two holes for the potentiometers and put them through the bag so you can turn them from the outside of the bag. Then fasten the potentiometers securely with nuts. Also take a piece of shrink-wrap and put the shrink-wrap around the Arduino, it's a fabric bag and this prevents static energy from reaching the Arduino and it also makes sure that all pins remain in place.

I used a zippy 500 battery for my back scratcher because it is small and fits easily in the bag. You can clamp the battery between the PVC tube and the bag, you don't have to attach it so that you can easily charge it later.

The last step to get the back scratcher working is to put a servo horn on the servo and screw it on. Attach the brush to the servo horn, take the brush stick and place it parallel to the horn. Then you can grab some shrink wrap and attach it to both sides of the horn.

After that you can work on the layout of the back scratcher, for the handle I used a rubber bicycle handle. The PVC tube was just too narrow for my handle so I cut open an empty toilet paper roll along its length and wrapped it around the PVC tube. Then I stuck it firmly with duct tape and a few more wraps of duct tape over the toilet paper roll to get the right thickness for my handle. Then I pushed the handle on and the handle was firmly clamped. Because the handle is over it you can't see the toilet paper roll and the duct tape so it still looks neat.

And then finally slide the bag all the way against the handle. I used masking paper to wrap over the PVC tube so that it stays firmly in place and give the stick of your back scratcher a nice pattern. You can easily wrap the adhesive paper between the servo and the bag. For the servo, I measured exactly the circumference from the top of the servo to the other side of the top of the servo with the tube in between to stick a piece of masking paper exactly over the PVC tube and the sides of the servo. This way you can no longer see the hole in the PVC pipe. For the top of the PVC tube I cut a circle in the adhesive paper and made cuts up to the edge of a smaller circle in the large circle, the radius of the small circle should be exactly the radius of the PVC tube. The dotted line in the picture is the fold line and the dashed lines are the cut lines. Then you can fold this circle of adhesive paper around the top of the PVC tube and stick it to close the top. Now you'll have a neatly wrapped back scratcher!

And there you have it! The Back Scratcher for all your scratching needs!

I quite quickly knew that I wanted to use a brush instead of the standard 3 hooked back scratcher, because I was pretty sure I could vary more with a brush than with 3 hooks. My first idea was to spin it by means of a motor. It was also my idea to be able to move the head to the left and right to get into all the good places on your back.

I drew the dimensions of the servo, motor and Arduino so that I could make them in a 3D program to experiment with a housing for the back scratcher.

After that I experimented on paper how exactly I was going to spin the brush. I soon ran into problems that I couldn't get the head to move properly when I wanted to tuck the rotor away a bit. I thought about rubber bands, but if you turn the head you get one tire very tight with a lot of resistance and the other tire is very slack and therefore has no grip. The only option would be to have the rotor visible or to have a whole piece of the stick rotate with it.

Then I came up with the idea to simplify it: instead of the brush being perpendicular to the PVC pipe, I let the brush run as an extension of the PVC pipe. This would allow me to move the head a lot easier, I thought. But when I started brainstorming how I was going to actually get that done, I found out that this was going to be quite difficult as well.

At this point I also experimented a lot with how well the dc rotor worked to spin the brush. I tested it with an elastic rubber band. This worked very poorly because the rubber band had to be stretched very specifically, too short was too little grip and too long was too much resistance for the rotor. I then tried to attach the brush directly to the rotor, but this caused the brush to spin in a cone shape instead of rotating properly.

After this I deleted the idea of running the brush with a rotor, because a rotor was not going to work properly. I thus started looking to have the brush move back and forth by a servo. That worked much better because the servo could have quite a bit of resistance. When I switched my design to a servo instead of a rotor I saw an opportunity to change the speed with buttons and I managed to make the option to change the angle with a potentiometer. I choose for potentiometers to make the changing of the speed and angle more smooth.

For the back scratcher's stick I wanted to keep it fairly simple, my idea was to make it a stick with a handle on one side and the brush on the other. I wanted the Arduino close to the handle for the buttons.

With this project I learned to simulate my ideas on paper through sketches, which saved me a lot of time instead of actually building it and figuring it out the hard way. And then after I think it'll work on paper I actually test it to see if my theory is correct. I also learned that it is important to ask for help when you get stuck, because i was quite stuck after my rotor idea failed.