Introduction: Build a Modular Robot Chassis Using Actobotics

From my early childhood I have loved robots. The first movie robots I remember ever really liking first, where the three bots from "Silent Running" (still one of my favorite movies!) Those goofy little walking boxes peaked my interest in robots and robot building. Over the years I have planed many bot builds, but only executed a few. I had one major problem, I am all thumbs when it comes to mechanics!

I have never had issues with coding or even building the computer or controller back when that was your only real option for a brain, no I just could not put a good chassis together or one I liked, that was really any good. Now, that did not stop me from building and trying, just not getting good results in mobility.

Enter the building block kits, and modular parts sellers. Companies like Actobotics, Vex and others have nice bots, kits and pieces to help people like me make a decent foundation to build a robot on. In this tutorial, I will go over the basic pieces you need from the Actobotics line of robot building parts to make a robust, modular and easy to assemble chassis. It will allow for many mounting options and will not cost you a arm or a leg.

When looking at websites like Vex or ServoCity, it can be a bit daunting at first glance. So many parts and options to know where to start. I will present the minimum of what you need to have a chassis that you will enjoy to work with and the can be added to and built upon.

Step 1: The Parts - Actobotics

The list given will not be a stead-fast rule, but a guide for you to use while buying. You may pick different sizes, or even other part options.

The chassis I made, uses only eight (8) parts from the Actobotic line. They are as listed:

  • 9.00" Aluminum Channel (585450) - x2 (The main structure f the chassis)
  • Flat Bracket F (585592) - x1 (Used for the sensor tower)
  • Hub Spacer (545384) - x1 (Ties the two 9" channels together)
  • 90° Single Angle Channel Bracket (585424) - x1 (used to mount the sensor on)
  • 37mm Aluminum Clamping Motor Mount (555116) - x2 (the motor mounts!)
  • 90° Quad Hub Mount C (545360) - x1 (used to mount the tower to the chassis)
  • Arduino Channel Snap Mount (585008) - x1 (holds the controller on the chassis)

Step 2: Parts: Other - 1

That is it for the Actobotics parts needed, as I use motors and a rear caster had already. And they list as the following:

  • 100rpm 12v motor with gearbox - x2 (you can get similar ones off eBay)
  • 1” Steel Ball-bearing castor from Harbour Freight (ServoCity has one as well) - x1
  • 2” 8/32 pan-head screws with 3 washers and 3 nuts per screw. From a local hardware store - x2 sets
  • 6/32 1/4” (.250”) screws socket head or pan head - x20 (A good online source is here)
  • 11cm Wheels - x2 (Or your wheel choice. ServoCity has wheels as well as other vendors)

Step 3: Parts: Other - 2

Now I will list the electronics, but you probably have your own already. If not, then here is the list:

Step 4: Parts Sourcing Information

Now that we have all the parts that makes up the chassis, let me talk a bit about sourcing the non Actobotics parts. When building my chassis, I did a bit a playing around before I decided on the final design. I wanted to use as many parts that I already had, so made sure the Actobotics mounts, channel and brackets would fit them. If you have motors already or will get them from other places like eBay etc., please make sure you have the motor dimensions before you order mounts. If your motor already has a mount you may be able to forgo those pieces and just bolt them to the directly to the Actobotics channel. If you need motors, ServoCity has several options as does Pololu, Sparkfun or even eBay. Feel free to shop around!

For the electronics, you can check your favourite place to buy, Pololu, Sparkfun, eBay, etc... The choice is yours.

Step 5: Assembling the Chassis

The build is relatively strait forward:

NOTE: All screws are 6/32 1/4" unless otherwise noted

Bolt the 2 nine inch channels together with the .5” aluminium spacer. The top channel with be open side up on top of the spacer in the middle if the bottom channel. and the bottom channel is top side on the other side of the spacer. The two channels will form a letter ’T'. Use four (4) screws on each side of the channel/spacer, with the first screw in the middle hole from the edge of the channel.

Step 6: Adding the Motor Mounts, Motors and Wheels

Now bolt the two motor mounts to the top side of the ’T’ going in the opposite direction the other beam is.

Once the mounts are on, add the motors. Make sure they are an equal distance in the mount on both motors. Position in mount the way you like, making sure they fit securely and the bot will drive fine in that position. After that is done, mount the wheels on to the motors. The pictured wheels have a built-in set screw. Position the screw on "flat" side of the motor shaft and secure. Repeat for other wheel.

Step 7: More Helper Pictures for the Previous Steps

Step 8: Sensor Tower

Take the 90° Single Angle Channel Bracket and the Flat Bracket F and bolt the 90° bracket to one end if it. This will form a letter 'L'. Now place the sensor bracket on the 90° with a screw or double sided sticky tape, then add the HC-SR04 and wires. You can use zip-ties to mount the sensor to the acrylic mount.

Step 9: Conneting the Sensor Tower to the Chassis

Now take the 90° Quad Hub Mount C and bolt the other end of the F bracket together to it using four (4) screws. Make sure the side holes of the 90° Quad Hub Mount are on the left and right side if the F bracket.

After this is done, you can choose the location you want to mount it on the top chassis channel. I chose about the middle of the forth (4th) hole from the rear. Use two screws on each side to secure it.

Step 10: Adding the Ball Rear Caster

Take the 1" ball caster the two (2) 8/32 2" bolts, six (6) washers and six (6) nuts. Place a washer on the first screw then slide it in the caster with the ball facing down and the bolt pointing up. Now place another washer on the screw then a nut and thread it all the way to the bottom of the screw. Then take the second (2nd) nut and thread it down around 1/4" then add a washer, place the screw in the underside of the top beam on the chassis and add the last washer and nut. Hand tighten only. Do the same for the second screw on the caster and then adjust the nuts at the top and underside to level the chassis out. Tighten all the nuts on the caster assembly now.

Step 11: Adding Your Controller Boards

Take the Actobotics controller mount and place the two ends on the top chassis channel in the position you want it in. Afterwards, place the controller (Arduino, RPI etc. ...) and snap it in place on the mounts. Add your motor shield or motor controller and wire it up as per your robots needs.

Step 12: Adding More to the Chassis and Conclusion

As the chassis stands, it has a lot of room and mounting options. You can add extra brackets from the Acrobotics line or from other vendors. Adding other sensors, batteries is super easy with this bot. I have a few pictured to give you a few ideas. First is a bracket and beam combination to allow for easy mounting of line following sensors. You can also add other sensors (like IR proximity), batteries, servos, etc. with zip ties or mounts for easy removal or as a permanent solution.

The addition of more levels would be easy to add as well. You have a world of options available with chassis!

For even more ideas, have a look at what other users of Actobotics beams, brackets and channels on the web. I am only just starting with them and love the parts a lot so far.

Step 13: The Video!