Intro: GearBot: a Dual Speed, Gear Driven Bot
The GearBot is a simple, single actuator 3D printed toy with a transmission entirely made up of gear mechanisms. This bot includes a working clutch mechanism, along with some other basic types of gears. If you are interested in gear mechanisms, I would suggest checking out this Basic Gear Mechanisms Instructable. I hope you have fun building this, and even more fun designing your own!
Step 1: Why GearBot Works
GearBot is entirely driven by gear systems, which are a type of mechanical transmission. Gears are essentially circular wheels with teeth around their circumference, and the teeth mesh with other gears to transmit power. As gears rotate, their teeth contact the teeth on other gears, thus forcing the other gears to rotate as well. GearBot is a simple system composed of multiple gear systems drive the robot forward.
Step 2: Gather Tools and Non-Printed Components
The first thing you'll need to do is gather all the off the shelf parts that you'll need for this assembly. Here's the list:
- 3 AAA Batteries
- Pololu Universal Hub for 3 mm shaft with 4-40 Holes
- Pololu Micro Metal Gearmotor Bracket
- Pololu Micro Metal Gearmotor 298:1 or 1000:1
- 2 4-40 Socket Head 12 mm Cap Screws
- 3 AAA Enclosed Battery Pack with on/off switch
- 1 foot of .25 diameter D profile rod stock
The tools to assemble this are as follows:
- Small screwdriver
- Wire strippers
- .05" Hex Wrench (comes with motor hub)
- 3/32 Hex wrench
- Solder and soldering iron
- Hack saw or band saw
- 3D Printer
Step 3: Print Out the Files
Of course, the first thing you're going to need to do is 3D print all of the components. I printed out the parts on a MakerBot Replicator 2, on standard resolution. All the parts have been designed to avoid the need for support material. Printed all in one job, it takes about 6 hours in total. For my final version, I printed out different parts in different colors to show which gears were linked together.
The quantities you'll need are as follows:
- Back_Chassis X1: Large piece with a slot for the battery box and two holes for shafts.
- Front_Chassis X1: Smaller piece with two holes on the front face, and two holes passing through each side.
- Clutch X1: Small piece with three teeth sticking into the profile of a hole.
- Spacer X1: Cylindrical piece.
- Hubcap X2: Small, circular pieces with a D-shaft profile
- Bevel_Gear X2: Bevel gear pieces.
- Low_Speed_Driver X1: Small gear with a flat face on one side.
- Low_Speed_Clutch X1: Large gear with teeth extruding from its face
- High_Speed_Clutch X1: Small gear with teeth extruding from its face
- High_Speed_Driver X1: Large gear with a flat face on one side.
- Driven_Gear X1: Large gear with a hub extruding from it.
- Drive_Gear X1: Large gear with four holes in it
- Foot_Left X1: Wheel with feet on it pointing counter-clockwise looking at it from the hub side.
- Foot_Right X1: Wheel with feet on it pointing clockwise looking at it from the hub side.
- Wheel X2: Wheels with a textured rim and hubs extending from their faces.
Step 4: Cut the Rod Stock to Length
You'll need 4 pieces of rod stock for this design. Here are their lengths:
- 2.225 inches X2
- 2.388 inches X2
After your parts are cut, you'll want to file down any sharp edges or burrs and make sure the rod ends are flat.
Step 5: Check the Fit
I designed the 3D printed pulleys to have a tight fit around the shaft and the frame to have a loose fit. The tolerances on the MakerBot I used may be different than the printer you used, so the fit may not be exactly the same. Try sliding your parts onto the D-shaft and see if they fit well. You may need to use a file to widen the axle holes if the fit is too tight, or you may want to reprint some of the parts and scale them up or down by a small amount.
Note: the clutch piece should slide along the D shaft, but NOT rotate. The two clutch gears should rotate freely around the shaft. The clutch piece has a pretty tight fit initially, but once you press it onto the shaft and slide it back and forth a bit it will loosen up. Make sure the flat tooth on the clutch lines up with the flat side of the D-shaft.
Step 6: Put the Batteries in the Battery Box
Before we solder the motor to the battery box, we need the batteries in the battery box so that we can test which direction the motor will spin. Unscrew the screw from the back of the battery box and slide the cover off. Put three AAA batteries into the case and re-attach the cover.
Step 7: Slide the Battery Box Into the Rear Chassis
The battery box should slide right into the back of the Back_Chassis piece. Slide it in with the power switch facing down and toward the back of the chassis. You'll notice on the bottom of the that there is a nice slot to give the switch clearance. You'll also need to keep track of where the wires end up. As you slide the box in, make sure the wires are sticking out of the notch at the back of the Back_Chassis piece. This will prevent them from getting squished or tangled in the chassis.
Step 8: Mount the Motor and Bracket
Place the motor bracket on top of the motor's gearbox (with the top of the Pololu logo toward the motor shaft). The bracket should have come with 2-56 mounting bolts and nuts. Put two nuts into their cavities on the bracket, and slide the bracket and motor into the bracket-shaped hole on the back of the chassis. The motor and bracket should be flush with the back face. Next, stick the two bolts up through the holes in the bottom of the chassis and use the screwdriver to screw them into the nuts and tighten everything down.
Step 9: Check the Motor Spin
We need to make sure that the motor will spin in the right direction before we solder the motor to the battery box. Cut the wires down to minimize the slack, and strip their ends. Looking at the back of the chassis, the motor needs to be spinning counter-clockwise for the robot to drive forward. Turn on the switch on the battery box, and hold its wires against the leads of the motor. Make sure that the motor spins counter-clockwise. If it is spinning clockwise, switch the wires. Remember which wire was attached to which lead for soldering!
Step 10: Solder the Battery Box to the Motor
Now that we know which wire to solder to which lead, feed the stripped wires through the holes in the motor leads. My battery box had multi-stranded wires, so I needed to twist the ends tight before feeding them through. Secure the wires by looping the ends through the lead and twisting the wire around itself. Then solder the wire to the leads. Be careful not to melt the plastic casing on the back of the motor!
Step 11: Glue Axle Ends
Although each pulley has a close fit with the axle, there is still a chance the pulley may fall off the shaft. You'll want to superglue the following pulleys and shafts together to ensure a secure connection:
- Driven_Gear to 2.225" shaft
- Hubcap to 2.225" shaft
- Foot_Right to 2.388" shaft
- Wheel to 2.388" shaft
To glue each part to each shaft, add a drop of superglue inside the axle inset, and slide the D-shaft in, lined up with the axle profile on the part. Make sure the axle is perpendicular to the face of the pulley.
Note: Don't apply too much glue. If you do, it will flow up and onto the shaft above the wheel, and this will make the fit between the shaft and the axle holes tighter and harder to turn, which is not a good thing! Just add a small dab of glue to the bottom of the hole in the gears and wheels.
Step 12: Grease the Shafts
Before you put anything together, you'll want to take some grease and either spray or rub it over the axles and holes for the axles in the chassis pieces. I fed them through their respective holes and slid and rotated them a bit to spread the grease around. The Driven_Gear axle will go through the holes on the right side of the Back_Chassis piece (looking from the back), while the Hubcap axle will go through the right. The Foot_Left shaft slides through the top of the Front_Chassis piece, while the Wheel piece slides in below the battery box enclosure. Greased joints will ensure a smooth rotation once everything is assembled, and prevent anything from catching.
Step 13: Attach the Drive Gear
Now it's time to put your first gear on the bot! Stick the two 4-40 screws through opposite holes on the Drive_Gear piece and screw them into the motor hub with the 3/32 hex driver. Thread the set screw into the motor hub with the .05" hex wrench, then feed the hub onto the motor shaft, making sure to line the set screw up with the flat side of the shaft. Tighten it down and you're good to go!
Step 14: Assemble the First Shaft
Slide the Driven_Gear shaft through the top right hole of the Back_Chassis. After its all the way through, slide the High_Speed_Driver gear on, with the flat, round face away from the chassis wall. Next slide the Spacer piece on, and then the Low_Speed_Driver, with its flat face facing the chassis this time. These two gears will drive the gears on the clutch mechanism.
Step 15: Assemble the Second Shaft
Now its time to add the clutch shaft! Slide the shaft with the Hubcap piece on the end through the other hole (top left, looking from the back), in the Back_Chassis piece. After it's through, slide the High_Speed_Clutch piece onto the shaft, with the teeth facing away from the Back_Chassis. The gear should rotate freely around the shaft. Next, slide the Clutch piece onto the shaft.
Note: Make sure you're putting the clutch on the right way. The tooth with the flat internal face should line up with the flat on the D-profile shaft.
After the Clutch piece is on the shaft, slide the the Low_Speed_Clutch gear onto the shaft, with its teeth facing the shaft. Like the other clutch gear, the gear should rotate freely.
Step 16: Attach the Front Chassis
Snap the Front_Chassis piece onto the battery box, with its large, flat face against the Back_Chassis. Make sure thet the two axles slide through their respective holes in the Front_Chassis. There are snap-fit joints on either side of the Back_Chassis that snap into the insets in the Front_Chassis piece. You may need to spread them a little with your fingers as you slide the part on. Once each hook clicks into each hole, the entire chassis should be secure. Note that the movement of the battery is stopped by small chamfers at the front of the piece.
Note: Ensure both gear sets are meshing before clicking the Front_Chassis in place.
Step 17: Attach the Shaft Endcaps
Now it's time to constrain the two shafts so that they don't slide off. Put some superglue in the inset of the second Hubcap piece and fit it onto the drive shaft (the one without the clutch). For the clutch shaft, slide a Bevel_Gear part onto the end, with some superglue around the hole for the shaft. Make sure the teeth are facing out, and the back face of the gear is flush with the chassis wall.
Step 18: Attach the Wheel Shafts
We're almost done! Slide the Foot_Right shaft assembly through the right side of the chassis, like in the image above. As you do so, slip the other bevel gear onto the shaft so that its back face is flush with the right wall of the Front_Chassis piece.
Slide the Wheel shaft assembly through the lower set of holes in the chassis as well.
Step 19: Attach the Left Wheel Set
Put a dab of superglue inside the hubs of the remaining Foot_Left and Wheel piece, and slide them onto their respective shafts.
Step 20: Sliding the Clutch
To work the clutch mechanism and change the speed of your bot. If you haven't messed around with it yet, it is probably on its shaft but not fixed to any of the gears. Note that the holes in the clutch piece match the extrudes on the faces of each clutch gear. When aligned correctly, the clutch piece can slide around the teeth of the clutch gears. Slide the clutch along the shaft so that it engages with the small gear. If you turn the motor on, this will drive the shaft at a 2:3 ratio with respect to the motor (because the ratio from the motor to the first shaft is 1:1), so this is high speed. When you slide the clutch over to the other (turn the motor off before you do this for the first time), larger gear, this drives the shaft at a 3:2 ratio, so it is a lower speed. It ends up that high speed is twice as fast as low speed. You can shift the clutch while the motor is running, but it can sometimes get stuck and stall the motor, so be careful when you do so!
Step 21: Test It!
You're finished with the GearBot assembly! Turn it on and see if it moves! If not, you may want to check to ensure the gears are meshing and nothing is getting stuck. If they do get stuck, grease the axles around their pivots in the chassis.
Step 22: Decorate!
I accidentally managed to put a smiley face on the front of the GearBot, so you can decorate it if you want to! I got some pipe cleaners and googly eyes and superglued them to the chassis to give it some character.
Step 23: Build Your Own!
There are lots of fun ways to make gear-driven bots, and they can have any range of complexity. Make your own GearBot using some of the tools and ideas I've provided. If you want to learn more about other gear mechanisms, check out this Instructable on gears. Have fun!
There are definitely a couple ways I could have improved this design, and there were a few things I wanted to include but I didn't have the time! There's always room for improvement in design! If you have any questions or want to share your own versions of GearBot, please leave them in the comments!