3D Printed Folding RC Land Yacht - MUSHU

This instructable goes through the process of creating a folding RC land yacht through 3d Printing.

This project fits into the IRCSSA class 1 rules (http://ircssa.org/class-standards/) which is a development class of RC land yacht using a box rule (all of the vehicle must fit within 750mm length x500mm width x 1000mm height) This land yacht is designed as a fun simple project to get into RC sailing and 3d printing, not as a regatta leading race machine. 

I will walk through the steps of designing this yacht, the principles of which can be applied to custom designing your own land yacht. Feel free to do this if you have the CAD knowledge or take my parts and print these as they are. 

For simplicity I have used a mast and sail from an easily accessible RC yacht class. The parts for this could be replaced by a cheaper home built assembly but lightweight and quality masts and sails will make for a better performing boat. The only part that would need to be modified is the mast step which currently accepts a 5mm tube.

The name of this design 'MUSHU' came in part from the rig. The mast and sail are from a Dragon Force 65 (DF65) RC yacht. This project is for the land though, so the first land dragon that came to mind was Mushu from Mulan that has been a regular at my house with a soon to be 3 year old running around.

If you have any questionsn about the project feel free to message me or comment on this instructable.

TOOLS

• 3d Printer or access to someone with one. 
• Scissors
• Lighter or matches
• Hacksaw
• Drill and bits
• Files
• Sandpaper
• Adjustable Spanner
• Phillips head screw driver

MATERIALS

• 3d printer filament (approx 300g used)
• Superglue
• Aluminium bar 10mmx3mm section approx 1m needed
• Dyneema cord 3m - https://www.hobbywarehouse.com.au/joysway-881204-df95-0-6mm-dyneema-cord-10m-length.html
• 6x 4Gx9mm screws (to attach servos)
• 2x 8Gx16mm screw (rear wheels)
• 8x M3x20mm bols (to join hull parts and Aluminium bars)
• 6x M4x10mm bolts + nuts (to join Aluminium bar to hull)
• 2x M5x30mm bolt (for Front wheel assembly)

PURCHASED PARTS

• 608 Bearings - https://www.kogan.com/au/buy/acosecommerce-10x-608rs-skateboard-roller-scooter-sealed-ball-longboard-skate-bearings-wheels-dks-sk8-wheels-10x/
• Sail Servo - https://www.hobbywarehouse.com.au/joysway-83014-servo.html
• Steering Servo - https://www.hobbywarehouse.com.au/dynam-17g-servo.html
• On/off switch - https://www.hobbywarehouse.com.au/joysway-881529-dragon-force-65-v6-switch-rod-with-rubber-bellow-and-switch-connector-set.html
• Bowsies - https://www.hobbywarehouse.com.au/joysway-881210-df95-bowsies-pack-of-10.html
• Trasmitter & Receiver pack - https://www.hobbywarehouse.com.au/joysway-880515.html
• Battery Pack
• Reusable batteries to fit above + Charger
• DF 65 B rig assembly - https://www.hobbywarehouse.com.au/joysway-880563-df65-v5-complete-b-rig-assembly.html
• DF 65 B rig Sails - https://www.hobbywarehouse.com.au/joysway-881510-dragon-force-65-v6-b-printed-mylar-sail-set.html?gclid=Cj0KCQiAjc2QBhDgARIsAMc3SqThDtDNUXOsHUjNt05B7USZmftN0spW6BOD--vNNPlIB6P5TDnDolAaAoU2EALw_wcB

The first step in designing this land yacht was assembling all the required RC gear. This really dictates the layout and physical size of your land yachts ‘body’ 

For a functional land yacht you only need a very basic RC setup:

• 2chanel transmitter & receiver
• 1x battery pack
• 1x servo switch (on off switch)
• 1x steering servo (i used a 17g servo) 
• 1x sail control servo (I used a 37g servo)

If your like me you wont be able to resist plugging everything in and seeing how they move… Go for it. This will help you see what your servo’s range of motion is. 

Playing around with different layouts for the parts early on helps get an idea of what the body shape could be to accommodate all the RC gear. The second image in this step with multiple assembled layouts shows a couple of different options I played with before settling on the compact option at the bottom.

Once I had all the parts assembled I arranged them roughly where I thought they could go and measured the overall dimensions. This became my guide for the body (see plan view sketch image). with key internal dimensions.

My final shape looks a lot more refined than the orange box shown in the images. However these early prototypes were really helpful to see the RC parts inside this box. This showed me which areas had heaps of extra space, where wires could run etc and from that I was able to remove some of this empty space and create a more curvy design (See sketch and two part image)  

While this shape worked and everything fit inside nicely, I wasn't happy with the amount of support material needed to print the hull. I changed the model and turned the two part hull into a three part hull. This meant that very little support material was needed for the print, but the model now could be printed with a coloured middle section adding a bit more interest to the project. Win win! (See CAD images)

Figuring out how to join the main hull to the wheels was relatively straightforward. I had some Aluminium 10x3mm solid section spare from another project that I wanted to use. I designed the additional parts to accept these with small bolts used to hold them in place. There was a lot of trial prints to get all of this right. The final image shows a bunch of the bits and peices that I printed on the way to the final design.

For the Wheels I made my own hubs to take some bearings in an attempt to get them running a bit smoother. The sizes of some of these parts will vary depending on what wheels etc you have on hand. I made my wheel hubs fit these tires - https://www.amazon.com.au/gp/product/B09D3NNGKJ/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

Feel free to use whatever wheels you can get your hands on. I have read a lot of guides on roller blade wheels being ideal for RC Land yachts. 

If you are going to design your own parts then you have quite a few hours of fun ahead of you. Otherwise use the parts attached here that I have designed and you have quite a few hours of printing ahead of you!

Most of these pieces have been designed to print without support. See below at the end of this step for quantities, support and infill settings that I used. Feel free to play around with these settings as you see fit. I haven’t had any breakages from the parts on this prototype to date. 

Clean up any of your prints that need it with a bit of sandpaper or files. I have left most of mine as they came of the printer as i’m not too worried about the print quality. I printed my parts on an Anycubic Mega Pro with only minimal tuning to date - One day i’ll get better print quality but i’m happy with this for now.  

Check all of your nuts fit into the allocated holes on the printed parts, as well as your mast and any bolts. 

Most of the nuts should be a bit of a pressure fit but if you want to make sure they always stay in place feel free to take some superglue and fix them in place. 

Printing quantities and support:

All parts .16mm layer height. .2 infill.

Hull bottom - 1x. Needs supports for where the steering servo goes only.

Hull middle - 1x. No supports

Hull top - 1x. no Supports

Rear wheel axle - 2x. No Supports but print vertically

Fron twheel attachment point - 1x. No Supports

Front wheel bracket - 1x. No Supports

Front Wheel Axle - 1x. No Supports

Front wheel lock nut - 1x. No Supports

Wheel Hub - 3x. No Supports

M4 Lock nut - 3x. No Supports

Take your Aluminium bar and cut two lengths at 227 mm long and one length at 400mm long

Give the ends a bit of a sand or file to clean up any scrappy bits your hacksaw may have left. 

Dry fit the Aluminium bar into each of the parts that join together and mark holes using the 3d printed parts as a guide to mark where your holes need to be drilled. (check the images later in this instructable if you arent sure where these parts need to line up)

Use a punch and make a point on the Aluminium to help center the drillbit when drilling out holes in the bar. This step helps stop the drill bit from wandering off your mark and leaving your hole drilled out of place.  

Drill out each hole and test the fit with your 3d printed parts and nuts and bolts. If need be drill the holes larger to fit everything together. 

Firstly before fitting all the RC gear and bolting the hull parts together, attach nuts inside the base of the hull. Use a little bit of superglue to hold these in place. You won’t be able to access these later in the assembly. 

Assemble the RC gear inside the hull. It’s a good idea before you screw the hull together to test the RC gear is all working as desired, Which port on your receiver will determine which control on your transmitter is used to adjust it. Check your transmitter/ receiver manual for information on what to plug in where, also for info on how to ‘bind’ your transmitter to your receiver. Make sure you do this!

With 4xM3x20mm bolts assemble the three parts of the hull together. The fit is tight enough that no nut is needed on the end of these bolts. 

Fix the servo’s in place using 4g x 9mm screws. Pan head or countersunk head both work here. 

Flip the hull over and attach the long Aluminum bar to the front of the hull, and the shorter pieces to each side. You can tighten the front two bolts as this won’t move again but make sure the bolts on the arms are firm but not overly tightened. These two bolts as shown are the pivot points when the arms are to be folded up. 

Attach the last two points with your M4 lock nuts (See the last image). These are designed to be large enough to screw together by hand. These bolts unscrew to allow the arms to fold in for transport when the rig is off.

Both back wheels use identical parts and should be assembled as shown (First image). Take the wheel bearing and press this into the tire hub. The inner ring on the bearing will fit over the round part that attaches to the aluminium bar (axel bracket). Fix these in place using a 8Gx16mm pan head screw as shown. Fix the axle bracket to the aluminium bar using a M3x20mm nut and bolt. (You can use smaller bolts in some parts or cut these bolts down but for this instructional i've tried to keep the different sizes of bolts to a minimum) 

Assemble the front wheel assembly as shown (Second image) The front wheel uses two M4x30mm bolts, one as the wheel axle and one to attach the steering pivot point to the front bracket that attaches to the Aluminium bar. 

Attach your steering arm to the steering servo and attachment point at the front wheel assembly. This might need some fine tuning to get the right amount of turn out of your servo. To get started I used two steering servo arms with attachement points like the one shown here. Then i Taped the two bars together with some duct tape as a temporary hold. This allows you to make some adjustments if need be.

Turn your RC gear on here and let the steering servo center. Unscrew the servo arm and re-attach this in place with the front wheel centered. You should now be able to turn the wheel in both directions an equal amount. 

When we get sailing you may find that you need a longer arm on your servo or to use an attachment hole on the front wheel assembly close to the pivot point to get more turn. My turning circle was quite large at first but with some adjustments i'm happy with the turning now.

Using some fine string (dyneema cord that is used for many model RC yachts is ideal) Attach a jewelry clip or similar clip to both the back aluminium bars and the front aluminium bar. These serve as attachment points for the stays that hold the mast in place. 

Tie a reef knot https://www.youtube.com/watch?v=aprfVTaxkk0 to attach this little bit of string and burn the ends of the rope to avoid fraying. Dyneema cord will burn easily so go careful with your lighter here. 

Take your Donor mast from your DF65 or similar and fit it into the attachment point on the hull. Attach a forestay and two side stays. And pull them both back to where they attach near each wheel. Tie a loop in the end of one making sure that you are putting a bit of tension on the mast (pulling it backwards) when this loop attaches to the jewelry clips. Pull both stays back to the centre of the boat and tie the other stay at the same length as the first. This will help ensure the stays pull the mast symmetrically backwards. Clip both of the stays into place. 

Attach a bowsie to the lower end of your forestay and tie this off so that you can put tension on the mast. Attaching cord to these bowsies can be a bit tricky and needs a nice clean cut on the tip of your cord. If you are struggling with these check out some YouTube videos on tips and tricks for bowsies. 

For the final rigging step attach another bowsie to some cord tied to the end of your boom. Attach the other end of this to a jewelry clip or similar and tie a loop of string onto the end of your sail control servo. Make sure to give enough play when fitting the bowsie that your sail can be pulled tight when the servo arm is pulling as tight as it will go as shown in the below image. 

All off your rigging is now complete and can be quickly assembled and disassembled by loosening the bowsies and unclipping your jewelry clips.

All that's left to do now is go sailing!

I will be working on a box for my boat to safely store the sail away from damage. Two pieces of cardboard and some tape will do for now!

Hope you have enjoyed this intractable and I welcome any comments or feedback.