More Chassis for Cheap Robots 1: Battbot

I'm back! Most of you probably aren't going to associate my Instructables with any sort of timeframe, but I just had to say that it's great to be back writing them!

Hi! I'm Jay! I write tutorials for folks trying to get started with robotics, but who get intimidated by the initial investment.

Kits these days are fantastic for beginners. They can teach you a ton, and work well to give you surefire and quick successes to keep you enthusiastic and moving forward. Problem is, they're also expensive, often costing several hundred dollars.

I aim to fix that! My For Cheap Robots series is all about building your own kit, from scratch and on the cheap! Best of all I focus on using stuff you can find around the house or salvage from old electronics! My tutorials are short, and modular, so you can mix and match to customize your robot to suit what you have at hand.

Today I'm excited to show you a fourth robot chassis! Sure, that may not sound like much... Another chassis? But wait till you see it! It's by far the simplest chassis I've made, it uses no cardboard, and it's got the best performance yet thanks to a new type of caster wheel!

Let's get started!

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For more Instructables on building cheap robots, please check out the For Cheap Robots collection page! For more things that I've done, you can check out my profile page, and for more information about Digilent and the Digilent Makerspace, check out the Digilent blog!

For this project, you will need the following:

• Two small gearbox motors with milk carton cap wheels. You can find out how to make these in my Motors and Wheels for Cheap Robots tutorial. You're going to need very small motors for this project, and you can find very similar motors to the ones I use here for about five dollars each. I found these after only a little bit of searching, so they're not necessarily the best choice.
• A battery pack. I pretty much always use four AA or four AAA batteries for my projects because they work well with microcontroller boards like the DP32 or Arduino.
• A DP32. For this project, the DP32 really is your best choice because of its built in breadboard. The one I use here already has my motor controller and line sensor circuits soldered on because I used it in a guest article I wrote for IntoRobotics! Check it out!
• A bead. Pretty much any bead will do, but if you can find one with a smaller hole diameter (just big enough to fit on your paperclip), that'll make it roll more smoothly.
• A paperclip.
• Your most trustworthy hot glue gun!
• A pair of needle nose pliers.

I won't go into too much detail with this step, because the pictures cover it better than I can really. Essentially, you're bending this into a sort of T-bracket that allows the bead to roll along an access perpendicular to the bracket's main face. This will let our castor roll more easily side to side, which might seem strange to you. Wouldn't I want the wheels to roll forward?

To explain, I've added three gifs of the completed robot in action. As you can see, because the robot is constantly bouncing along the left side of the line, the motion that the castor deals with the most is actually a side to side motion. Additionally, the motors have no problem pushing the castor forward. After all, they're both pointed forward! It's much harder for them to push the castor side to side, so the extra help goes a long way.

Once again, this step is really self explanatory, but I'll give you a couple pieces of important advice.

Firstly, I'm starting this step off with a picture of the finished robot because you need to keep in mind how you want to mount your DP32 to the battery case. This will help you figure out which end to mound your castor on. As you can see in picture two, the screw terminals for the DP32 are on its left, so you want to make sure that you put the battery leads on the left as well, and mount your castor to the front.

I also advise you not to spare the glue for this part! This castor has a particularly useful feature that lets you adjust its height by changing the angle the castor sticks out from the base. This can be vital when you're working with sensors whose distance from the ground is important. (Like line sensors!)

However, this does put a lot of torque on the base, in a direction that it's not particularly well equipped to handle. Even after you add a lot of glue like I did, you still will need to be careful. It's best to hold the base down with two fingers when you bend the castor down or up, to keep from torquing the glue too much.

Note: I should apologize for the somewhat obscure reference in the third image, but I think of that line every time I do anything with hot glue now...

Once again, a pretty self explanatory step, and once again use a lot of hot glue! These motors are going to have a bit of torque applied to them because they have to hold up the batteries.

I'm starting this step with a picture of the finished part because it'll help illustrate how close the wheels come to the terminals of my battery case, that's why I glued the terminals to the side of the case before adding the motors.

I was surprised to find out that the glue does not bind well to the metal of the motors. Wrapping them in duct tape will help solve this problem, but you want to wrap it tightly, and all the way around so the tape gets a change to bind to itself. The strips I used were about 1/4 the width of a standard roll of duct tape.

Now, if your motors have a plastic casing (for whatever reason), you might want to skip the duct tape and glue directly to the plastic. Hot glue will bind more easily to plastic that duct tape. That said, your glue might bind too well, in which case it'll be much harder to get it off the motor if you decide to reuse them.

Keep in mind that you do have to be a little careful with these mounts. Duct tape will bond to the hot-glue more strongly than it will the metal of the motor casing, but it still will not be perfect. It's possible to pull the motors off if you're too rough with them. To prevent this, use lots of glue when mounting to give as much surface area and support to the motors as possible, give the glue plenty of time to set, and try not to press down on your robot when it is on its wheels.

Your chassis is almost finished! Lastly we need to add the DP32.

The most important thing to consider with this step is board placement. Picture two shows how I tested out my position before gluing the board on. I wanted to keep that first row of header pins fully accessible from the underside of my robot so I could re-solder components as necessary.

This wasn't as important for my board because I already had the electronics installed, and because we're only using a little hot-glue to attach our boards, it's also okay to detach the board and re-glue it as needed.

Which brings me to my next point for this step. Normally I would tell you to use as much glue as possible to attach your DP32 to the battery case, but it's a little more complicated this time. Because there are long solder leads and thick components on the underside of the DP32, you need to use big dollops of glue to bridge the gap between the board's surface and the surface of the battery case. HOWEVER, you don't want to make those dollops too big, because then you may risk breaking the board when you try to remove it.

Check out picture three of this tutorial to see how big I made my glue dollops. I only used two, spaced about one inch (or two centimeters) apart, and while they were thick, they didn't spread out much which minimized the surface area that actually bonded to the board.

Now you're all done! (With the chassis at least.)

For this tutorial, I used a board on which I had already installed the line sensor and motor controller circuits.
If you're interested in building this completed robot, you can check out the tutorials I've linked above, or check out the article I wrote a while back for IntoRobotics.com! There, I explain a little about what's going on in the circuits and why you need them. I also explain how to program your DP32 (which you can also find in my Getting Started with the DP32 Instructable), and I include code for testing your circuits and the robot code for the final project.

For that tutorial, I used my Boardbot chassis, instead of this one, but the concepts are still very much the same.

This chassis has got to be the simplest one I've made so far, and it's also one of the best performing! It can be a little harder to track down small gearbox motors like the ones I used, but if you're looking to put together a general purpose kit for yourself (or maybe for a class) I highly recommend it!

I hope I've helped or inspired you, and as always I'd love to hear any comments or suggestions you might have for me! If any of you make this robot, please let me know!

Thanks!