Introduction: Mechanical Dry Erase Board
Second Prize in the
Instructables and RoboGames Robot Contest
By using a joystick, some controllers, written code, and some elbow grease, you can build yourself a life size, 21st century computerized canvas. This video shows all of the working components.
The difficulty of this project depends on how large you make your board... the bigger... the more difficult. This board is 4x4 feet. It was also built in my dorm room, so precise measurements without a stable table were kind of difficult.
This project was most recently seen at the San Mateo Maker's faire at the Microsoft booth.
*There are a bunch of improvements I am going to suggest that have not yet been implemented onto the board.
Step 1: Before You Start!
Because this was the first prototype and I was forced to build it in a short period of time, I ran into a few unanticipated errors...
I will tell you what I used, and then I will suggest how you should improve/embellish upon them.
1. Not buying a previously mounted dry erase board.
-Because the board was not mounted, or framed, the wooden frame I built warped. This caused an uneven distribution of friction on the board's surface when the pen would move.
- There really is no reason to purchase the board unframed, I did not want to be stuck with a material that limited the range of the pen's motion... I was wrong... buy a framed board.
2. Not doing torque/power calculations on my motors.
-I was just trying to piece together parts without doing precise calculations.
-I was originally only supplying about 2 amps of current to both motors, when they were drawing about 7-10 amps each... yikes. The solution: a lawn mower battery.
-Once I finally got the power right, the motors were not giving enough low end torque, and because the board was warping, the added friction made the pen skip around in certain areas... :(. I'll show you later how we can fix this!
Step 2: Get Your Materials. There Are Alot Needed.
Dry erase board (framed). Whatever size you want.
Two wooden planks 4 inches by X. (X represents any number that is about 8 inches larger than the width of your board) by 1 inch.
2 3/4 inch wooden dowels.(length dependent on size of board add 6 inches to the lenght to accomodate the Y component)
2 1 inch wooden dowels.(length dependent on size of board)
6 three 1/4 inch screws with bolts.
8, 3/4 inch PVC pipe T connectors.
4, 1 inch PVC pipe T connectors.
2 3/4 inch PVC pipe connectors.
4 1 inch PVC pipe connectors.
4 X foot alluminum channels. (length dependent on size of board, you will need two for the X, and two for the Y)
2 X foot steel crossbeams.(more so for design than functionality... but it added some support.)
A bunch of different sized screws, depending on the boards size...
Carbide Bit along with othe sized regular drilling bits.
Spade drill set (depending on the size of the motor you use)
Wallpowered drill... you can use battery powered... but I just hate anything that is battery powered.
Gears: The best website I found for gears and such is https://sdp-si.com/eStore/
This website is unbelievable! If you have any gear or shaft related questions, they place you on the phone with an engineer!
When ordering sprocket gears, stick to metal... I used plastic, they were not meant to be used with applied torque. Order metal gears, with a set screw spot and a hub. (without one you will get slippage.)
Get metallic spur gears with hubs that match the pitch of your selected chain.
The Chain: I purchased the chain from
again... this site has everything!
Get a METATLLIC roller chain that matches the pitch of your gears.
The Motors: I used two brushed 12 volt DC motors. They worked... okay. But I used them for a big board. For a smaller board... they should be perfect... I programmed them to step, like a stepper motor, but they do not provide feedback such as position. To correct this, you could slap some encoders onto the motors and hook them into the controllers.
I bought my motors from:
I got the:
22$ each. They really don't have great low end torque, so my best advice is to scrap these motors, and use Brushed DC Spur Gearmotors... They are pricier... but they will be much better for what you want in the long run. They provide up to 1100 oz of torque-inch! Not bad... but that number depends on the gear ratios. Get the Spur Gearmotors. Stay away from basic brushed DC.
The computer controls: My code is written for the amazing Phidgets! So use them, they are incredibly easy to use!
High current motor controller:
Servo Motor and Motor Controller:
Each one of these comes with setup instructions.
Power: 12V Lawn Mower Battery. Excessive... but neccessary, I dont know why the two little DC motors were sucking so much amperage out of this battery... it does not make sense to me... what am I not understanding?
Speaker wire... or any wire. Speaker wire has a nice gauge, and is easy to work with/strip.
Liquid mix Epoxy
Dry Erase Makers, Twisty Markers
4 Roller Casters, that fit the width of the aluminum channel.
4 smaller wheels that fit the width of the aluminum channel.
Step 3: Getting Started.
Draw blue prints. They don't have to be perfect, but get some grid paper, a ruler, and mechanical pencil... It will pay off in the end. My final design changed slightly from the original drawing... but the drawing served its purpose.
Step 4: Building the Y Component.
It is hard to describe this process and it can definitely be better understood visually, so I will make a blue print for you guys to follow.
Just look at the diagram, do not screw anything in yet, because you will need to add the moving pen piece later.
After you frame everything, add an aluminum channel to both dowels. Mount them using some epoxy and some screws. Don't completely screw in the end screws; this will stop the pen from flying out of the track.
Now you can make the pen component. I did this by taking a 6 inch 3/4 dowel, and drilled a hole, that was the size of the thickest part of the marker. Onto this, I mounted four small wheels that slide into the aluminum channel. A picture diagram explains.
I used epoxy putty to keep the wheels in place.
Step 5: Building the Z Component.
Onto the Pen component (the 6 inch rod) you are going to mount the servo motor. The motor is to be mounted so that the body is parallel with the rods body, and so that the shaft is facing the rod.
You will need to take the twistable pen apart (linked to on the materials page) and replace its ink with the ink from a dry erase marker. You can also saw off the bottom of the pen if you find that easier. Use an ink color that matches the color of one of the 6 markers provided. Place the dry erase marker ink in, shake, and wait for the ink to absorb into the twistable markers tip.
Once you have built your marker, your going to want to make a ring out of the roller chain, and slide it down the shaft of the marker, the exact distance will change as this distance depends on how close you want the marker to the board.
Place one of the gears onto the servo motor, and fasten it with some putty epoxy (putty epoxy is not great for torque, but it worked okay).
Look to diagram for mounting instructions, also watch the video to see how the motor should be mounted.
To raise the motor up, I bought these flexible metal things, not sure what you call them. I wrapped them around the rod and it held the servo motors in place.
Step 6: Putting Together the Y the Z, and the Motor.
You can now put the pen component, into the Y frame built two steps ago. Make sure you leave enough room for the wheels to glide in the channel. If youâre having gliding issues, use WD40.
Once you put the pen component in. You can now mount the motor.
I took a four by four inch block, and drilled a 1 and 1/4 hole into it. 1 and a 1/4 was the diameter size of my motor. If you over drill, you can always tape up the motor, so that it wedges into place, so it doesnât slip. The Motor should fit tightly in between the four T components. Take the motor, wedge it into the wooden block, and screw them both down onto the PVC pipe and rods.
I mounted the gears onto the Y component. In order to transfer the energy to the gear on the bottom of the motor, I had to make my own gear shaft. I did this by buying a little aluminum shaft, and gluing two gears to it. It was slipping, so I fixed that by cutting a pen in half and using the body to slip over the shaft. I then used putty epoxy and it held in place. I recommend you look for a gear shaft that mocks this.
The size does not need to be exact because you are given some play with the motor placed in the block, you have about 5 mm of freedom. I chose to have my chain go to the left... so from the motor, I placed the custom shaft about 3 inches away, and then at the bottom of the Y frame, I placed another gear of equal size exactly below it. This made a nice little gear system.
Now you will hook the pen component onto the roller chain. This was done using, putty epoxy, two small aluminum rods, and zip ties.
Onto the pen component, take an aluminum rod and putty epoxy it on. Then epoxy the other end onto the roller chain. Now, take a zip tie and fasten it all together. Make sure the zip tie does not get in the way of the aluminum channel... we don't want to have any additive friction. Repeat this step again, so that the pen component is fastened in two places.
Step 7: Add Wheels and Wire Hiders.
I placed the Roller Casters into the 3/4 inch T connectors... they fit nicely. To reinforce them I slathered them in putty epoxy, so that they would not move. Place the casters into each T connector so that side with more wheel exposed is facing upward.
Flip the Y component around and repeat.
Once this is done, place some wire hiders over the Y components rods... It gives it a nice effect... I also added a small coupler in between the top T connectors, it adds some stability and it gives it some aesthetic value.
Step 8: Frame the Dry Erase Board!
You really should use a level in this step; it will save you time and effort.
Use the diagram as your blueprint. I mounted the wooden planks on top of the board... you could do it behind it, but I liked the look. I fastened it down to the board using screws and bolts.
To drill through the board, you will need to use a carbide bit. I drilled through pretty slowly, and it turned out fine. Try to keep your rpm low so that you don't get hit with metal fragments.
Onto the horizontal rods (x bars) I mounted the aluminum channels and steel cross beams. The steel was more of an aesthetic approach, but added some stability as well.
Connect the 3/4 inch rod, with the two 3/4 T connectors, hammer them in, or sand them so that they have a nice snug fit. Make sure that the T connectors are inline with each other. Once this is done, mount the aluminum channels and steel cross beams. Screw them in on opposing ends; to fasten the middle use liquid epoxy.
Use a level to make the X bars, if they are not perfectly aligned, you will run into huge problems. Match the bars up, and make sure that they are mirror images of each other.
Once you have made sure that they are identical, mount one of them onto the middle of the bottom wooden plank. Do this by drilling through the middle of each T connector, and screwing them in with a long enough screw to pierce the plank.
At the end of each channel, slightly unscrew one of the screws, so that the Y component won't fly out of the channel.
Don't add the top x bar. Until you mount the Y component. That will be next.
Step 9: Mount the Motor, Set the Gears, Mount the Y, Close It Up.
- I explain how to make the gear shaft in the following step.
Across the board on the other side I mounted another gear, at the exact same height on a duplicate of the 8 by 4 block. I attached the gears with a very long roller chain; about 10 feet.
Before you mount the Y, you want to make sure that you run speaker wire through the bottom X bar. This will be attached to the Y component motor. Flip the Y component around, so that the motor is on the bottom, slip the speaker wire through the bottom of the X bar, and attach it to the Y motor.
In order to harness the Y component to the X roller chain, I used a similar method to the pen component mount. I nailed 2 gears to the back of the Y component and made sure that they did not move, ie. used some epoxy putty.
I then placed the Y onto the bottom X bar, and let the gears on the back of the Y rest on the X roller chain. I then used putty epoxy to harness them to the roller chain.
Make sure that the x bar gives you enough room so that you can properly connect the Y component to the roller chain, I was within a 2 mm of the board... be careful.
I took pictures after I painted it...
Once you get the Y hooked up, and the wires threaded through, place the upper X bar onto the board. Do this by placing the board flat on the ground, and moving the Y component to the middle of the board.
Fit the upper X bar on top of the casters, use a level, mark off where the T connectors come in contact with the board, and drill them in.
Step 10: Gear Shafts and Controller Board Setup.
I did not mention this before, but I made my gear shafts by using a nail shaft that was slightly smaller than the bore of the gear. I slipped the gear onto the nail, tapped the end of the nail and then nailed it into either the wood, or the pvc pipe. I drilled into the pvc pipe before nailing. The tape was used to add grip.
To hook up your phidgets controllers, use the product manuals. The program I wrote is a console based app, and is designed to work with the phidgets controllers. In order for this to work properly, the motor from the Y component must be screwed into the motor 0 slot. Hook the battery up by connecting speaker wires from the positive of the battery to the positive in the HC motor controller. Do the same with the negative.
Step 11: The Software
I used Visual C# 2008 Express Edition, the software works great and was very easy to use.
My source code can be found at http://blogs.msdn.com/coding4fun.
When the code is published I will provide the exact link.
A full explanation of the code is explained in the comments.
Tweaks and calibrations are also hidden within the comments.
Program files added.
Step 12: Drawing With the Device
Because I made some calculation and mounting errors, the pen did not move as I hoped. With the motors I suggested, and the new improvements, your rendition should work pretty well if not perfectly.
By using the joystick, my software allows for you to have both motors running at once, so it is possible to draw a circle and curves. The joystick also has a toggle switch, so when you push down, it causes the pen to either move up or down, as described in one of the earlier steps.
I was able to write Hello, kind of... haha, it is fun to use though... I just wish I ordered motors with better low end torque.
If you want to take the Y out, you can either unscrew one of the X bars, or you can take out one of the stoppers, and slide it out.
Enjoy building and good luck!
Step 13: Makers Faire!
I got to meet the creator of Instructables, Eric! That, along with the South Park laser etching made me extremely excited!
We have a be nice policy.
Please be positive and constructive.