Introduction: Motors and Wheels for Cheap Robots
When I was little, and just getting started out with robotics, I had very little in the way of funds or patience for ordering robot kits online. Back then the selection was more limited than today and pretty much all the robotics kits were built for Windows users, which my family and I very much were not (and I was not as adept at finding things for myself online).
Left to fend for myself, I had to get creative. You might even say I got "crafty". I used cardboard for my robot chassis, cardboard for my wheels... cardboard for pretty much everything, with bottle caps, duct tape, and other bits and bobs thrown in. While I had some success, my very restricting resources, combined with my childlike lack of motivation without immediate results, proved to be my downfall.
More often than not, my biggest stumbling block were wheels. Here I intend to aid the childhood of my not-so-distant past, and in doing so aid the childhoods currently in progress.
This tutorial is actually going to be several different tutorials sandwiched together to show you three different ways of adding motors and wheels to your robot.
Let's make some wheels!
For more info from Digilent on the Digilent Makerspace, check out the Digilent blog!
Step 1: Chocolate and Peanut Butter, Motors and Wheels
Before we consider wheels, we have to consider our motors. Motors come in all shapes and sizes. They have different torques and speeds. Most importantly, some will have gear-boxes, and some won't.
When choosing wheels for your first robot, chances are you're going to need to choose your wheel based off the motor.
I will explain what sets these motors apart later on when I explain their preferred wheel type. For now it's enough to know that the types of motors I cover are servos, gearbox motors, and direct drive motors.
For the more well educated out there, you'l notice I've left out stepper and/or brushless motors, because those honestly deserve an entire Instructable to themselves (also because I haven't played with them nearly as much).
Step 2: The Golden Standard: Servos and Kit Wheels
If you're getting into robotics for the first time, and you've got the money, your best choice would be a couple of continuous rotation servos and kit wheels like those pictured above. Continual rotation servos are like normal servos, but instead of going to a specific position and staying there, they move at a specific rotation speed.
Kit wheels, like the one above, are very cheap compared to the servo price, so if you're getting the servos, why not get some wheels to go along with it? Digilent has continual rotation servos and kit wheels that you can buy for a good price (along with a nice metal robot platform), and a number of verygoodtutorials on PWM and servos that can get you started, and they're a very good starting point for newcomers to robotics.
Step 3: What? No Wheels? Introducing the Cardboard Servo Wheel!
If for some reason, you don't want to, or don't have, the kit wheels that attach to your servo, there's a quick and easy way to make your own that will actually perform fairly well themselves.
These wheels' performance relies greatly on your ability to cut smooth, round wheels out of cardboard, and then find the center of those wheels. If you can do that, they should be able to reliably travel a fairly straight line!
Step 4: What You'll Need
AS A WARNING, in this project I only make one wheel, so keep that in mind when gathering supplies. I would also recommend reading through it once before actually doing anything.
What you'll need is:
- A largeish piece of good cardboard. No bends or kinks, and definitely not tears or strips of packing tape.
- A glue stick. (optional)
- A glue gun. (not optional)
- Something with which to make circles. (a compass would work the best, but so long as it traces a good, round circle, you're golden)
- Something with which to find the centers of circles. (I used a ruler, but mostly eyeballed it)
- A rubber band. (a nice wide one works best)
- Servo stuff.
- The servo.
- A servo arm attachment. (any of them work, but the cross or round ones work best)
- Servo arm attachment screw. (don't lose this! I almost did!)
Step 5: Cut Out Your Wheel-Halves
This step is fairly self explanatory, but I'll spell it out anyway.
Use your circle drawing utensil to mark a circle out on a good patch of cardboard.
Cut said circle out.
Repeat once more so you have two circles.
I will also offer some additional advice. Cut the square with the circle off the cardboard first, then do a rough cut to get the corners and such off, and then do one final cut around the rim, getting as close as you can do your line, but don't go over! This method cuts the wheel in to progressively more manageable chunks, and has always resulted in smooth, equally sized circles.
Don't worry if you can't cut perfectly round wheels. Do the best that you can, and check out my note after the next step.
Step 6: Glue Your Two Wheel-Halves Together
There's a somewhat important trick to this step.
Cardboard is very strong when you try to bend it one way, but very weak when you try to bend it the other way. This is because of something I like to call the grain of the cardboard. In the second picture, you can see how the corrugation inside the cardboard causes ridges on the surface of the cardboard. The direction of these ridges is similar to the grain in wood. If you bend against the grain, wood is strong. If you bend with the grain, it breaks more easily.
If you make sure to glue these two wheel-halves so their corrugation directions are perpendicular, you can use the strong direction in one half to strengthen the weak direction in the other, and vice versa. This makes for a much stronger wheel in all directions.
My friend starshipminivan (who is by far a more accomplished crafter than I) has pointed out that if your wheels are not perfectly round, you can take a bit of sandpaper to them to wear off those bumps. If you have that problem, I would recommend doing that after this step, when both your wheels are glued together. That will make sure your wheels are even and smooth.
Step 7: Find the Center of Your Wheel
Because I did not use a compass to make my wheel, I needed to find the center myself. There are some pretty cool ways to find the centers of circles, but honestly some guessing (aided with a ruler) will do you just fine.
Step 8: Punch a Hole in It!
Place some scrap cardboard underneath your wheel (I recommend at least two layers), and punch a hole in the center using your pen. Push it pretty far through so the hole gets big, but be careful not to hurt yourself or tear or bend the cardboard.
Step 9: Glue Your Arm Attachment On
Stop for a moment and plug in your glue gun to get it heated up. Make sure to place something underneath the tip so the drips of glue don't end up ruining something important.
I'll also take a moment to advise that you place the wider side of your hole against the servo arm attachment. This is because we can widen the side that isn't attached to the arm, but we cannot widen the side that is, and that cardboard could get in the way when you screw your attachment arm onto the servo in the last step.
Use the hot glue to attach your servo arm attachment. Make sure the center of the arm is sitting squarely over the hole you just made. Press the arm on firmly, and let it sit for a little so the glue can dry.
Step 10: Put the Rubber Band On
Again, this is self explanatory, but it can take a couple tries to get right. Make sure the rubber band isn't twisted anywhere, and that it isn't slipping off the side anywhere.
Step 11: Attach the Servo
The last steps are pretty straightforward as well.
Widen the hole in you cardboard enough to put the screw in (but don't just yet). Press the servo arm onto the servo. You'll know it's snug when you can turn the wheel and hear the gears in the servo buzzing inside. (Don't turn too hard or it could break!) Finally, screw the arm onto the servo, and you're done!
Step 12: The Cheaper Alternative: Gearbox Motors
Servos are expensive. Really good servos can be as much as $30 for just one, but that buys you an integrated motor, gearbox, and speed controller all in one. No muss no fuss!
There is, however, a much cheaper alternative, and I would honestly recommend this over servos for a number of reasons. Servos are very simple, and they'll get you up and running right off the bat, but they do quite a lot for you because they include a speed controller. If we cut that out, you can get a cheaper integrated motor and gearbox combo.
These can be much cheaper than servos. For example, you can find similar motors to the one on the left for approximately five dollars each.
They can also be just as expensive as servos. You can buy the motor on the right from Digilent for $20, but in addition to being powerful and high quality, it also includes a built-in odometer. That odometer is very cool because it'll let you program your own speed controller later on, which can teach you quite a lot that a servo cannot. (You can buy kit wheels for it as well.)
Step 13: Thirsty for Adventure! Milk Carton Cap Wheel
If you've managed to get your hands on some gearbox motors, then there's a very simple little wheel you can make that attaches right on. I used caps from the brand of milk jugs my roommate and I buy, but you can do this with any sort of lid, so long as it's bigger than the diameter of your wheel! For the motors I chose soda-bottle caps would have worked quite nicely (and I may have actually preferred them for the faster Digilent motor to slow it down a little), but you could also do this with lids as large as Pringles can caps.
Because these wheels don't rely on your ability to cut round objects, they perform just as well as, if not better than, the cardboard servo wheels, and will travel in a fairly straight line on their own.
Step 14: What You'll Need
The supplies for this are even simpler than the first. You'll need:
- A rubber band. (the smaller the better)
- A thumb-tack
- A glue gun. (your best friend)
- Your gearbox motor.
- A plastic bottle cap of some sort.
- Your trusty, sturdy pen! (alternatively you could find a nail, but pens offer a nice large cone-shaped tip to gradually widen your hole)
Step 15: Poke a Hole in It!
Use the thumb-tack to poke a hole in your plastic lid. I like plastic lids like this because they'll usually have some small divot or something that gives away where the center is. On this one, I had to look very closely (and guess a little) but it was there!
Also, be VERY CAREFUL that you don't stab yourself with that thumb-tack. Keep track of where your fingers are before applying pressure.
Step 16: Widen the Hole a Bit
Use your sturdy pen to widen the hole a bit and then put the cap on the motor. Be careful that you don't widen it too much though. If you get it just right, you'll just barely be able to slip the cap over the end of the motor shaft.
Here's something cool. Plastic has very high elasticity, meaning it'll stretch out a bit before permanently deforming. This means that after your pen stretches the hole wider, it'll actually try to close a little. See if you can get the hole just wide enough that it slips on and then tightens a little! It's hard, but not necessary.
Step 17: Glue It On, Add Some Grip
Use your hot glue gun to glue just around the tip of your shaft poking out from the cap. After you glue, you'll have a bit of time to fiddle with it. Use this time to make sure the cap is level, so it won't wobble when the motor turns. Once you're happy, just hold it a little while until the glue sets, and then stretch the rubber band around the rim!
Step 18: The Bare Necessities: Direct Drive Motors
How can you get cheaper than a gearbox motor? How about just a motor? Regular motors don't have any gearboxes on them, but that makes them even harder to use in your robot.
Electric motors are almost always paired with a gearbox. This is because they spin very very fast, but they don't have much torque behind them. That means that if you attach a wheel directly to an electric motor, it'll spin way too fast to control, and won't be able to push much weight!
Worse still, while most motors will have a small gear attached to the shaft , many don't have anything attached at all! The tiny little shaft coming off the front of these motors is usually very hard to grip onto, which makes it difficult to attach our craft wheels.
So how do we do it? It's really hard to attach a wheel, and even if we do they're too weak and they spin too fast!
Step 19: The Simplest, Cheapest Wheel of All! Duct Tape!
Duct tape, properly applied, can solve a surprising swath of difficult problems.
Here, we can use it to not only stick to our slippery motor shafts, we use it to widen them slightly so they can act as wheels themselves. Driving robots directly by using the tiny motor shaft instead of a complex gearbox is a commontrick in kitrobotics. The only difficult thing about it is getting your motor to an angle where the shaft hits the ground, but not the motor.
This quick tutorial will show you how to get your motor's shaft or gear wrapped up in nice grippy duct tape.
These wheels are the most erratic of all three craft wheel types. They cannot travel in a straight line at all! Thing is, many robots won't need them to! many simple line-followers, object-avoiders, or wall-huggers just rely on one motor turning the robot one direction, and the other motor turning it the other direction, and not on precise directional control. If you just need a wheel to get your robot moving, these may be what you're looking for!
Step 20: What You'll Need
- Duct Tape
Step 21: Tear Off a Strip, Tear It in Half
I've seen half-width duct tape for sale in places, but I never seem to have it on hand. It's a little tricky, but I usually just tear my strips of duct tape in half with my hands. If you're less dexterous than me, you could also use a sharp knife (like an x acto) to cut it in half lengthwise on a cutting board. I wouldn't recommend using scissors unless you're prepared to try taming the two ends while you cut the main piece in half.
You're only going to use the one piece for this next step, but if you stick the second to the edge of your table, you'll have it for when you make a second wheel, and this way they'll both be the exact same diameter!
Step 22: Thin Shaft Wrapping
First, I'll show you how to wrap your thin shafted motor.
Start by lining the end of your duct tape up to the shaft of the motor. Make sure the straight side (the one you didn't cut or tear) is on the motor side. You'll also want to make sure you leave a little space between that edge and the motor itself, or the wheel will rub against your motor.
VERY CAREFULLY begin wrapping. You want to avoid getting any wrinkles in your wrapped wheel. Most of your roll to the left of the wheel hangs off the end of the shaft and will be cut off later, so keep in mind that it's alright if that side gets a little wrinkly and mis-shapen. You can use this to maneuver your strip of tape to keep it both in-line and smooth.
Once you are done with wrapping, the side of your wheel facing the motor should actually taper away from the motor a little bit, but not too much.
Once the shaft is wrapped, if you squeeze it, you should be able to feel where the shaft ends and the duct tape just hangs off. Take some scissors and cut this off. Then use your scissors to roughly bevel the edges by cutting corners off. The end result should be a little rounded.
Step 23: Thick or Geared Shaft Wrapping
The method for wrapping a thick shaft, or one with a thick gear, is exactly the same as with a thin shaft, but is less strict and fiddly than a thin shaft. You should still end up with a roughly rounded wheel.
Step 24: Using This Wheel
Most wheels have to be larger in diameter than the motor itself, so the wheel can roll without dragging the motor, but not this one. That's because in order to use it, you have to mount the motor at an angle, so the wheel hits the ground but not the motor. To test this wheel, I created a simple A-frame chassis which did the trick. I'll show you how to make one later in another Instructable for cheap robot chassis.
Step 25: Additional Reading and Inspiration
I am, of course, not the only person trying to make good wheels out of cheap supplies. While I was researching these methods, I found a number of good tutorials that inspired me, and I'd like to share the best ones with you so you can get inspired too!
Poor Man's Robot Base: In this clever Instructable, Wehrdo shows you how to turn a couple of cheap walkmen (walkmans?) into a set of gearbox motors! This robot base could easily have a couple of cap wheels attached to it in lieu of their lucky-find plastic wheels.
Starting with robotics (Arduino): Here, vonPongrac and their friend purgec build a simple and versatile robot platform using a couple of continual rotation servos mounted to jar lids. They had the clever idea of using rubber gloves for traction instead of rubber bands!
Grippy robot wheels: For those of you with a little more resources and expertise, Instructables user kenyer can show you how to create some very high quality, rubber robot wheels with lots of grip.
This is just the first of a series of tutorials I aim to create geared towards creating cheap robotics projects for kids and adults looking to get into robotics, but without the trappings and expense of kits. There are plenty of useful and versatile construction materials everywhere in our homes and offices, if we just get creative enough, and draw on some old school arts and crafts. I hope I've inspired you to start looking at the castaway bits and pieces around to in a new, and more crafty way!
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