Introduction: Land Sailboat
This instructable was created in fulfillment of the project requirement of the Makecourse at the University of South Florida (www.makecourse.com)
This is a land sailboat-- a wind powered machine that, instead of having a hull that floats and cuts through water, has five wheels and glides across land. It is, of course, remote controlled.
Step 1: Print/Acquire Parts
Many parts will have to be 3D printed. However, there are several parts that will have to be acquired through other means:
- 8 mm x 500 mm Carbon Fiber Tubes x6
- Arduino Uno
- Short (~3 in) USB-A to USB-B cable
- Battery (an external lithium ion battery designed for phones is ideal)
- High Torque Servo x2 (The servos used here created 125 oz-in of torque)
- Skateboard wheels and bearings x5
- About a square yard of ripstop nylon
- About 25 feet of string
- Thread and Needle, Sewing Machine, Stitch Witchery, or Sail Tape
- Plastic Strips (~10") x2 (The strips used here came from cutting up a plastic notebook cover)
- Breadboard Power Rail x1
- Wire x10
- Remote Control x1
- RC Receiver x1
- Rubber Band x7
These 3D printed parts can be made in a variety of ways (even out of wood, if no 3D printer is available), however, they should have certain key elements to give them their intended functionality. The parts as shown from right to left:
- The main box. It has two 8 mm holes in the front facing forward to connect to the front wheel, an 8 mm hole in the front facing upwards for the mast, as well as a pinhole just large enough for a string to go through in the back facing upwards. Also has two "nostril" holes in the front that face forward just large enough for string. The steering string is fed through these holes. Two 8 mm holes in the rear facing outwards from each side allow the axles (carbon fiber tubes) to be slotted in.
- The Platform. It has casings built in to hold the servos in place. The size of these will depend on the type of servo bought. They should be measured using a digital caliper or another similar tool.
- The back cover. This closes up the box once the platform is slid into the main box. It also has holes on the inside that can be used to create a pulley system to gain torque or speed for the sail-moving mechanism. It is possible to completely forgo the main box, platform, and back cover shown here in favor of a different system, assuming it has all of the required connectors and space for the servos, Arduino, and RC receiver.
- The wheel cover. The two 8 mm forward facing holes on the main box connects to this piece with two carbon fiber tubes, and this piece has its own set of these holes facing backwards. It also has a cavity large enough for a skateboard wheel on the bottom and a smaller hole that spans the space between this wheel cavity to the top of the cover. Also present on the rear top of this cover is a small hole to which rigging is attached.
- The wheel mount. The wheel is mounted to this. It can be mounted using a 3D printed axle or a suitable replacement. The main body of this is housed in the wheel cover cavity, while the round top piece protrudes through the hole connected to the cavity.
- The bridle. This goes on top of the wheel cover, attaching to the protruding part of the wheel mount. The two lobes have holes to which strings attach. These strings are fed to the "nostril" holes of the main box where a servo inside of it manipulates them.
- The axle cap. The big half of this piece slides onto the axle. The wheel slides onto the smaller half of this piece. A string is tied to the small half before the wheel is put on to hold the mast up.
- The mast cap. Slides onto the top of the mast. It has holes at the top to accommodate the strings that hold the mast up.
- The spreader. It attaches two 500 mm carbon fiber tubes together to create a 1 m tube. Also has a bar running across it which holds the stays away from the mast, increasing support.
- The boom. Holds the tail end (the clew) of the sail out, away from the mast.
Step 2: Program the Arduino
The code shown here includes the main loop in addition to a function to control the sails based off of input from the receiver and a function to control the steering based off of input from the receiver. The main loop's only job is to run these two latter functions.
The setup, before the main loop, initializes the pins used, declares global variables, creates servo objects, and declares the functions. If different pins on the Arduino are used for sails, steering, channel 1, or channel 2 than shown in this Instructable, the last character in lines 3 through 6 should be changed to reflect what pins are chosen.
Step 3: Wire the Arduino to Two High Torque Servos and an RC Receiver
The servo in the right of the picture attaches to Arduino pin 9, while the leftmost servo attaches to pin 8. Channel 1 on the RC receiver attaches to pin 5 while channel 2 attaches to pin 6.
The 5 v and ground pins on the Arduino should be attached to the power and ground rail on the breadboard, and the power and ground on both servos and the RC receiver should also be attached to their respective rails.
Step 4: Attach a Battery to the RC Receiver
The external battery should fit above the breadboard if the wires coming from the Arduino are bent to be flat. The unit used here was a 10,000 mAh Anker battery.
To keep the lithium ion battery healthy, it should be kept at around 50% capacity and removed from the device after use so it doesn't wear down to 0% after extended periods of time. Keeping the Arduino powered by it indefinitely will kill the battery.
Step 5: Create the Sail
There is lots of freedom in constructing the sail. Professionals use cambered boards and lay multiple sheets of sailcloth over the boards before sewing them together to give them a nice curve. However, most people, including myself, do not have the knowledge or resources required for this. For this application, cutting a sail out of the ripstop nylon will suffice. For a more downwind oriented sail, make it wider (low aspect ratio). For upwind, make it narrower (high aspect ratio). If it's going to be used in a place with high winds, make it smaller, and if it's going to be used in a place with lighter winds, make it bigger.
No matter the size and shape of the sail, the leading edge (the luff) should have a slight convex curve to it. This gives the sail a slight camber, even if it wasn't made with a camber board and multiple sheets of cloth like the more professional sail makers do it.
Also, there should be a seam allowance on the leading edge of the sail to allow it to be folded over the mast. This edge can be sewn over by hand or with a sewing machine. Professionals often use sail tape as it allows a more streamlined finish to the sail. In this project, a product called Stitch Witchery, which is basically a heat-activated fabric glue that comes in strips, was used.
The rear corner of the sail (the clew) should have a loop sewn on and through the hole on the end of the boom. This will bind it to the boom.
Step 6: Put It All Together
This is the last and hardest step. Depending on the precision of the 3D printer used, the pieces may require sanding to fit. Super glue or epoxy should be used to fit the pieces together. The platform with the servos on it should be slid into the main box before the back cover is placed. However, before the platform is inserted, all of the strings controlling the steering should be rigged.
The steering strings are tied to the bridle at the front, go back through the "nostrils" on the main box, loop through the servo horn on each side of the steering servo, and then tie to a hook that can be hooked on and off of the rear hole of the wheel cover. This system allows the detensioning of the system when needed for disassembly, as well as extra range of movement for the steering wheel as it amplifies the servo's movement as a pulley system would.
Before the back plate is put on, the strings controlling the sails should be rigged. To do this, make sure the battery is removed, and then feed a string through the hole on the top of the main box, into the hole on the back plate, through the end of the servo horn, and then back to the hole on the back plate where it should be tied. This, like the steering, allows for a larger range of movement at the cost of torque. Once the mast and sail are in place (which should be done later), the other end of the string hanging out of the hole on the main box should be fed through the hole on the end of the boom, wrapped around the mast several times, and tucked into a rubber band wrapped around the base of the mast.
Rubber bands should be placed on the base of the mast to keep the boom from falling too low. They should also flank each wheel to keep them in place. Two wheels slide onto the axles about an inch away from the main box; the other two go on the ends over the axle caps (but a string should be tied to the axle caps before the wheels go on). The front wheel goes into the wheel mount, which is then inserted into the wheel cover. The bridle is glued to the part of the wheel mount protruding from the wheel cover.
The last part is the standing rigging. A string should be ran from the rear hole on the wheel cover where the steering is hooked up to a hole in the top of the mast. Additionally, a string should be ran from each axle cap, through the hole on the spreader on the respective side, and to the top of the mast. A dot of super glue should be placed on each spreader hole to keep the string in place. All of the strings that end at the top of the mast should be tied into the holes on the mast cap.
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