Hi there, and welcome to the GameCube-Bot Instructable!
GameCube-Bot is entering this summer's contests! If you like it, I'd be honored to have your vote!
GameCube-Bot is a strange beast. Here's a tour of what's inside.
- Designed and built from the ground up!
- brushless airplane motors with lots of torque!
- custom transmissions made from servo replacement gears from the almighty Hitec HS-805BB servo
- Press-Fit Laser Cut Delrin Chassis
- Magnetically detachable shell
- Easy-to-find parts! (mostly from McMaster-Carr)
- open source hardware!
The driving video is from Version 1. Version 2 is slightly faster and lighter.
(Too long! Don't Read!)
A Quick History and the Driving Thoughts behind this project:
GameCube-Bot V1 was born in the underground machine shops in my last semester of college. Nimble. Bouncy. It was my first leap into building transmissions for mini-battlebots. V1 was machined out of aluminum with a CNC mill. I'm excited to say that V2 (featured here) requires absolutely no time spent crouched over greasy machinery in a fancy machine shop; you can build it (from scratch!) in the comfort of your home using mostly stock parts and hand tools.
Through GameCube-Bot, I'm hoping to help democratize hobbyist robotics with a design that's easy-to-assemble and yet has much higher torque compared to other robots at a similar scale and price range. At the very least, I hope you can take away a few bot-building tricks along the way.
My fellow bot-building companions, I wish you the best as you begin your journey!
Step 1: The Bill-of-Materials and the Tools List
You can almost build it in your livingroom! Here's a list of tools and parts you'll need.
Tools: Chassis-Only Assembly
- safety glasses
- One of these (better to worse): arbor press, drill press, bench vise, or Kant Twist clamp
- Metric Drills: 2mm, 3mm, 5mm
- Imperial Drill: #46 (aka: 0.081 [in])
- Fractional Drill: 1/8th [in]
- Metric hex wrenches
- Imperial hex wrench: 1/16th only
- Dremel Tool
- 90-degree countersink
- soldering iron and solder
Tools: Full GameCube-Bot Assembly (with shell)
- One of these: band saw or dremel tool
- GameCube security screw bit and screwdriver
- Philips screwdrivers
- LiPo Battery Charger
- Gaffers Tape or Duct Tape
- Electrical Tape
All of GameCube-Bots stock parts can be bought from McMaster-Carr and ServoCity. The full list (with part numbers) is in one spreadsheet.
Lego Wheels can be found on bricklink (part nums also on the spreadsheet)
I found all the gears I needed on ServoCity. HobbyKing, though, does sell metal pinion gears, and many other suppliers sell the servo replacement gears.
- 2x sets of Nylon Servo Replacement Gears for the HS-805BB Hitec Servo
- 2x Pinion Gears: 19-tooth, 64 pitch, 0.125[in] bore
If you are laser-cutting with your own laser cutter and your own material, you'll need:
- 1 piece Acetal Delrin Natural Polymer (white or black) 12" by 24" by .09375" thick
- 1 piece Acetal Delrin Natural Polymer (white or black) 3" by 9" (or any large scrap) by 0.125" thick
- 1 piece Acetal Delrin Natural Polymer 3" by 3" (or any scrap) by 0.0625" thick
If you are laser-cutting parts through a laser-cutting service like Ponoko, ensure that they can cut delrin for you at the above thicknesses.
Notes on Delrin: I lean towards Online Metals for Delrin because their orders arrive in flat packages. Other suppliers don't always send material packed flat, and the piece arrieves warped and unusable for laser cutting.
Notes on Other Plastics: Acrylic will not work as a drop-in replacement for Delrin. Parts must be press-fit into delrin, which expands nicely forming a snug fit. Acrylic will crack rather than deform because it's much more brittle.
HobbyKing and HobbyPartz both supply electronics speed controllers (ESCs) that are suitable for this project. An 18[A] ESC is sufficient.
- 2x 18 [A] Electronic Speed controllers (ESCs)
- 1x 2S or 3S LiPo Battery of maximum dimensions 105 [mm] by 20 [mm] by 35 [mm]
- 1x RC transmitter and receiver
- 2x Brushless Motors with M3x0.5 mounting holes spaced at 19 [mm] (diameter less than 1.25"). I'm using Hobby People 2208/15 outrunners. The 19 [mm] spacing is fairly common in this size range.
If your transmitter does not have a "signal mixing" feature, you'll also need
- 1-2 packs of Sugru or other filler
- 1/16th [in] by 1/16th [in] by .25[in] B114 square magnets from K & J Magnetcis
Step 2: Laser Cutting
Depending on your situation, there's a number of different paths you can take here. To try to save you some work, I have a couple varieties of the same design files.
- Original design files
- Offset design files (0ffset by 0.003[in])
I have a laser cutter nearby; let me cut my own parts:
Awesome! If you can play with the setting on your laser cutter, download the original files, and offset those files to the kerf of your laser cutter. Don't forget--it's better that holes come out slightly smaller rather than slightly bigger!
I don't have a laser cutter, but I'll use an online service:
Sounds good! Go ahead and send out the offset design files. The file names specify which thicknesses to cut them out from: 0.0625[in], 0.09375[in], or 0.125[in].
How do I pick which files to cut??
Laser cutters trace the path of the vector graphic file that they are cutting. In that sense, they will actually burn away a small amount of material slightly bigger than the width of the laser. This feature is called the laser cutter's kerf. If we cut the files with the exact dimensions, our parts will actually come out with slightly altered dimensions. (Holes and pockets will be slightly bigger; outer edges will be slightly smaller.) To compensate for the kerf, we need to offset our design file slightly such that the laser cutter cuts out a part that matches the dimensions we wanted in the first place. This isn't too difficult to accomplish with many vector graphics programs, but I've included pre-offset versions of these files if you'd like to skip doing the offsets of the original design files.
If you can't determine the kerf of your laser cutter and don't know how much to offset by--don't worry! I'd suggest using the pre-offset version. It's offset by slightly more than necessary so that the individual holes can be widened manually with a drill bit of the intended size. In the case for this project, it's better that holes are slightly smaller than slightly bigger so that they can be widened manually with drill bits or reamers.
Step 3: Touching Up Delrin Plates
Did the laser cutter cut out parts in the perfect dimension you needed--me neither! From the last step, we cut our parts so that holes and pockets are slightly undersized. Now let's go in and adjust some important dimensions manually.
We're going to make two adjustments to the main plates. We've got four identical main plates.
- 2 of the 4 main plates get a countersink feature
- the other 2 main plates get their holes widened.
The images above show where these features get added.
For the hole widening, just run a 2[mm] and 3[mm] drill through the laser cut holes by hand until they can run back-and-forth.
For the countersink feature, use a countersink and either a hand drill, drill press, dremel, or.. by hand to create the countersink features.
Important Note on the Countersink:
For the countersink feature, the side of the plate matters! Take a close look at the two main plates, and put the countersink on the side that was laser cut to have the wider edge. For more details, see the zoomed in picture with notes.
Why does the side that we countersink matter??
When we sandwich these plates together later, they'll have to hold a ball bearing between the plates. It's much easier to do this if the thinner edges are put together. (The green outline has a picture of this.)
We're touching-up certain features in these parts because we want certain types of fits: some snug press-fits, some loose slip-fits. When we press-fit a dowel pin into the part into the delrin, we're actually apply a stress on the plate that forces it to expand. This stress squeezes back on the pin, holding it in place!
Step 4: Press-Fit Dowel Pins Into Plates
Now that our hole dimensions are just as we want them, let's press-fit our dowel pins. These pins are the key to holding the gears in place.
With an arbor press, drill press (UNPLUGGED), bench vise, or Kant-Twist clamp, press the 2mm and 3mm dowel pins into the two main plates so that they are flush with the bottom of the plate. Ensure that the parts don't get pressed in at an angle, or you'll have a grinding gears that don't mesh well.
Step 5: Press-Fit Dowel Pins Into Bearings
Using the same technique as before, press-fit the 8mm long dowel pin into the ball bearings with 5[mm] inner diameters. The image above has the pin sticking out past the bearing, but you can push yours in until the pin is flush with the bottom of the bearing.
Make two of these.
Step 6: Widen the Smallest Gear's Bore
The smallest gear's bore is slightly undersize.
With a 0.081[in] drill bit (aka: #46), widen the gear's bore by running the drill bit through the bore a few times by hand. (No drill needed!)
Step 7: Assemble Transmission
Add the 19[mm] standoffs with 2 countersunk M3 screws and 2 normal M3 screws. Now, let's build up the transmission:
- Press-fit the other ball-bearing into the spacer until it's flush with the delrin plate.
- Insert the nylon spacer and brass bushing into the 3mm dowel pin.
- slide the smallest gear into the 2mm pin.
- Add the middle gear
- Insert the Large output gear
- Add 3 more brass washers
Step 8: More Press-Fits
Press-fit the 5[mm] dowel pin into the inner plate. (smallest plate.)
Step 9: Secure Set Screws Into Standoffs
Tighten down 12 set screws halfway down into all twelve 35 [mm] standoffs.
Step 10: Assemble That Delrin Sandwich!
At last! Mate the inner plate with the main plate, and fasten it down with some M3x0.5[mm] screws. Using 6 of the 35[mm] standoffs with set screw, connect the outer plate of the transmission with 19[mm] standoffs and set screws.
Step 11: Insert Shafts, Spacers, and Motors
- With a .125[in] drill bit, widen the shaft holes by hand until the bit can slide freely.
- Slide the .125[in] dowel pin into the shaft holes and press-fit it through the (undrilled) last shaft hole in the inner plate.
- Add the .125[in] and .0625[in] spacers. These should fit snugly.
- Screw down the motor through the 19[mm] spaced holes using M3x0.5 screws.
Step 12: Assemble Your Wheels
Press-fit three captive nuts into each of the four hubs and assemble each wheel. The order is..
- 3 4-40 screws
- hub gear
- Lego wheel + tire
- hub with captive nuts inserted
Step 13: Secure Wheels
- Press-fit the spline gear onto the nylon gear. I doubled-up and added a second gear. If you do so too, just be sure that the teeth line up.
- Slide the wheels into the shafts until they reach the spacer, and secure each wheel with another spacer.
Secure both wheels down with another spacer, and fasten the outer plate with M3x0.5 screws.
Keep in mind that each wheel should spin freely on the shaft until it connects with the spline gear. If it doesn't, use a 0.125[in] drill bit to widen the holes in the delrin hubs.
Step 14: Duplicate the Half-Chassis and Call It Good!
Great! You're done with a half-chassis! Now go back and make a duplicate, and connect the two together with the long standoffs!
Step 15: Pack in the Electronics
There's no beloved glory in this step. Just cram the ESCs and wiring into the two spots in the front and back of the chassis. The battery fits in the middle.
Secure it all down with electrical tape or Gaffer's Tape. Tape down loose wires! Take a quick look at the wiring diagram to make sure the connections are correct before powering it on.
If your transmitter does not support "signal mixing," add the V-Tail mixer between the ESC cables and the receiver.
Hook up the battery and take it for a spin. You've come a long way!
Step 16: Part II: GameCube Revival
Old GameCubes are cheap! I picked up 3 busted 'Cubes from ebay for $15!
Let's take that beloved childhood companion off our shelves and give it some new life!
With the security screw bit, remove the four security screws on the bottom, and open the 'Cube.
Step 17: Shelling
Remove all of the 'Cube's internals until you have just the outer shell (4 pieces).
To access the bottom plate, these screws have to go!
Step 18: Touch-ups
Cut down the four "standoff" tabs until they'res flush with the center rim. (Two are shown in the image.) In most cases, you'll want to use a Dremel or some other rotary carving tool.
Trim down the lid tab so that the 'Cub can open once after our robot modification.
Step 19: Handle Adjustments
Remove the handle, and trim down the two handle tubelets so that they too are flush with the inner rim of the cavity where discs go. Be careful not to take off too much! (We'll put it back on later.)
Step 20: Coring It Out
Those wheels have got to go somewhere!
With a band saw or dremel tool, carve out the bottom piece until you're left with only the walls. A thin 1/8th [in] space on the front and back is optional.
If you use a band saw, you'll have to enter into the center with the blade starting from the outside. I'd recommend entering from the small band in the back corner.
Step 21: More Tab Removal
Chop off the last of the tabs in these plates too!
Step 22: Try It on for Size
Go ahead and reattach the handle. Reattach the front and back plates (but not the bottom plate) with Gaffer's Tape.
Go ahead and try the top shell on the GameCube for size. It should rest on the main Delrin plates via the groove from the disc drive. (Move around wires if needed to get this fit.) Feel free to add some sugru filler for a tighter fit.
Step 23: Bringing It All Back Together With Magnets
Yes, our GameCube-Bot has a magnetically-removable outer shell!
Note: If you don't want this feature, you can also use tape. Shh! No one will know!
Attach 4 magnets to the upper shell's corners and 4 magnets to the lower shells corners. (Sugru or Gaffers Tape works here!)
Step 24: The Beginning of Your GameCube Fleet
If you've come this far, shoot me a message! I'd love to hear how it went.
I wish you the best in your future bot-building projects, and thanks for joining me on this one.
...Now only 7 more until you ride through the city streets with a chariot pulled by minion GameCubes!