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Hexabot: Build a heavy duty six-legged robot!

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introHexabot: Build a heavy duty six-legged robot!

This Instructable is going to show you how to build Hexabot, a large six-legged robot platform that is capable of carrying a human passenger! The robot can also be made fully autonomous with the addition of a few sensors and a little reprogramming.

I constructed this robot as a final project for Making Things Interactive , a course offered at Carnegie Mellon University.



Typically, most of the robotics projects I've done have been on the small scale, not exceeding a foot in their largest dimension. With the recent donation of an electric wheelchair to the CMU Robotics Club, I was intrigued by the thought of using the wheelchair motors in some sort of big project. When I brought up the idea about making a large-scale something with Mark Gross, the CMU professor who teaches Making Things Interactive, his eyes lit up like a kid on Christmas morning. His response was "Go for it!"

With his approval, I needed to actually come up with something to build with these motors. Since the wheelchair motors were very powerful, I definitely wanted to make something that I could ride on. The idea of a wheeled vehicle seemed kind of boring, so I began thinking about walking mechanisms. This was somewhat challenging since I only had two motors at my disposal and still wanted to create something capable of turning, not just moving forwards and backwards. After some frustrating prototyping attempts, I began looking at toys on the internet to get some ideas. I happened to find the Tamiya Insect . It was perfect! With this as my inspiration, I was able to create CAD models of the robot and begin construction.

During the creation of this project, I was stupid and didn't take any pictures during the actual construction process. So, to create this Instructable, I took the robot apart and took pictures of the assembly process step-by-step. So, you may notice that holes appear before I talk about drilling them, and other little discrepancies that wouldn't exist if I had done this right in the first place!

Edit 1/20/09: I discovered that, for some reason, Step 10 had the exact same text as Step 4. This discrepancy has been corrected. Step 10 now tells you how to attach the motors, rather than telling you how to machine the motor linkages again. Also, thanks to Instructables for saving a history of edits, I was simply able to find an early version with the right text and copy/paste it in!
Hexabot: Build a heavy duty six-legged robot!
hexabot.JPGhexabot_2.JPGinsect.jpg
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step 1CAD Model

Using SolidWorks, I created a CAD model of the robot so I could position components easily and determine the location of holes for the bolts that connect the legs and linka…


step 2Materials

Here's a list of the materials you'll need to construct the robot:-41 feet of 1" square steel tubing, 0.065" wall-14 feet of 2" x 1" square rectangular steel tubing, 0.065"…


step 3Cut and drill the metal

After procuring the metal, you can begin cutting and drilling the various components, which is a pretty time consuming task.Begin by cutting they following quantities and l…


step 4Machine the motor linkages

After cutting and drilling the metal, you'll want to machine the linkages that connect to the motor and transfer power to the legs. The multiple holes allow for changing th…


step 5Weld the frame

Unfortunately, I did not take pictures of the process I went through to weld the frame, so there are only photos of the finished product. Welding itself is a topic to deep …


step 6Add holes for motor mounts

After welding the frame, some additional holes need to be drilled for secure mounting of the motor. First place one motor into the frame, and add a bolt through the front m…


step 7Prepare motors for mounting

After drilling the holes for the motor mounts, the motors need to be prepared for mounting. Locate one motor, along with an aluminum motor linkage, the set screws for the…


step 8Prepare the legs for moutning

The Legs cut in Step 3 need some final preparation before they can be mounted. The end of the leg that contacts the ground needs a "foot" added to protect the robot from da…


step 9Begin the assembly

With the previous steps completed, the assembly of the robot is ready to be completed! You'll want to prop the frame up on something when you're assembling the robot. Milk…


step 10Mount the motors

Take one motor and put it into the frame (like you did when marking the mounting holes for the U-bolts). Add a 4 1/2" 12-13 bolt and lock nut, and tighten everything so tha…


step 11Add the leg axles

With the motors mounted, the leg axles can be added. Add the front axles first. The front of my robot is indicated in the first picture below. Take a 5" 3/4-10 bolt and ins…


step 12Add the rear leg and linkage

These next three steps will be performed on one side of the robot.Locate a Leg and a Linkage. Place the leg on the rear bolt, and add a 3/4-10 nylon lock nut. Do not tighte…


step 13Add middle leg and linkage

Locate another Leg and Linkage. Add the leg to the drive bolt over the first linkage, with the wooden foot pointing towards the ground. Add the first linkage to the front a…


step 14Add the front leg and linkage

Locate a third Leg and Linkage. Add the leg to the front axle, with the wooden foot pointing toward the ground. Add the linkage the drive bolt, then connect it to the top o…


step 15Tighten the bolts and repeat 3 previous steps

Now that everything is attached, you can tighten the bolts! Tighten them so that you can't spin the bolt by hand, but they spin easily with a wrench. Since we used lock nut…


step 16Electronics time

With the heavy-duty construction out of the way, it's time to focus on electronics.Since I didn't have budget for a motor controller, I decided to use relays to control the…


step 17Wire it all up

I used a Proto Shield from Adafruit Industries to interface the everything with the Arduino. You can also use perfboard, but the shield is nice because you can drop it righ…


step 18Mount the electronics enclosure

With the wiring completed, you can mount the enclosure to the frame. I drilled two holes in my enclosure, then placed the enclosure on the robot and used a punch to transfe…


step 19Add batteries and safety features

The next step is to add the lead acid batteries. You'll need to mount the batteries in some fashion. I welded some angle iron to the frame to create a battery tray, but a w…


step 20Route the wires

Once the batteries, fuse, and emergency stop are in place, route all of the wires. Neatness counts! Run the wires along the frame and use zip ties to secure them.


step 21You're ready to rock!

At this point, the robot is ready to move! Just upload some code to the microcontroller, and you're good to go. If you are powering up for the first time, leave your robot …


step 22Add a chair

To make the robot more rideable, add a chair! I could only find the plastic seat to a chair, so I had to weld a frame to it. You certainly don't have to make your own frame…


step 23Add a joystick

When you're sitting on your robot, you may want to have some means of controlling. A joystick works great for this purpose.I mounted my joystick in a small box made of shee…


step 24World Domination!

You're done! Unleash your Hexabot on the world!


step 25Epilogue

I learned a lot in the process of building (and documenting) this robot. It's definitely the proudest accomplishment of my robot building career. Some notes after having …


step 26Credits

This project wouldn't have been possible without the assistance of the following individuals and organizations:Mark Gross Professor of computational design in CMU's schoo…


82 comments
1-50 of 82
Oct 19, 2009. 4:14 AMdemonsonic1 says:

Is there any way to make it faster?
 


Oct 19, 2009. 6:53 AMrpantaleo (author) says:

Faster motors or altering the step size. My motors are 24V but I'm only running them at 12V, so upping the voltage would make it faster too.


Oct 19, 2009. 6:07 AMMr Slippy Fist says:
That is so cool! Now you just need to make one thats bigger, with lasers, and a fireball cannon, and tesla armor . . .glavin.
Sep 17, 2009. 4:27 PMocto137 says:
yo, i'll buy one of those.
Sep 8, 2009. 9:07 AMMajor Fuchs says:
Hey i have a question. how much did this cost you. parts wise.
Sep 17, 2009. 3:22 PMrpantaleo (author) says:
This cost me about $150. But, I had the wheelchair motors, batteries, and steel for the frame donated. If you had to buy everything, it would run you at least $500 if not more.
Sep 3, 2009. 12:07 AMboy says:
sweet, man!!
Jul 31, 2009. 3:22 PMbobtet says:
how long does it take and whats the cost?
Jul 31, 2009. 7:28 PMrpantaleo (author) says:
It took me about a month to build it working mostly on weekends and occasionally during the week. With enough determination, it could probably be done in a week.

Cost-wise, you're looking at ~$500 for materials. I was fortunate enough to have the more expensive stuff donated (motors, steel tubing), so I spent about $150 on it.
Jun 16, 2009. 6:17 PMRichiepoo says:
Epic! I might do this for a science fair project.
Jun 13, 2009. 1:11 PMthefunktopus says:
Road legal?
lol
May 28, 2009. 9:40 AMsrikanthafdo says:
can dis tin turn? da video dsnt show any movements lik dat, so i guess t jst goes straight. anyway good work dudes. i am goin to build dis myslf :)
Jun 1, 2009. 1:31 PMrpantaleo (author) says:
It can turn. The drive is skid-steer, like a bulldozer or tank.

If you watch the video more closely from 2:00-2:12, you can see the robot executing some turning movements.
May 28, 2009. 11:10 PMDon.Jambo says:
The automotive relays are have 4 pins or more?
Jun 1, 2009. 1:28 PMrpantaleo (author) says:
5 pins
May 12, 2009. 2:46 AMDon.Jambo says:
Hey man...
What is the exact position(or coordinates) of the motor axle as you look the frame from one side?
I have a different type of motor, and I have to build for it a different motor mount for it, and depending on the position of the axle I have to weld some extra tubes to the frame!
Thanks!

X would mark the exact position of the axle:
_ _ _ _ _ _ _ _ _ _ _ _ _
| _ _ _ _ | X _ _ _ _ _ _ |

PS I'll send you some pics with a how far I'm at with a replica of you robot!
May 12, 2009. 7:47 PMrpantaleo (author) says:
The axle of the motor should be in the middle of the frame. Looking at your sketch, you need to move it towards the center.

I'll try to get a pdf drawing posted.
May 12, 2009. 2:47 AMDon.Jambo says:
Can you mark it exactly in another sideview.PDF with SolidWorks?
May 11, 2009. 6:15 AMDon.Jambo says:
Please explain:
-The the phase of the rotation between the two motors affects the robot's ability to move around. It seems that adding encoders to the motors would allow for better control of the gait.
May 9, 2009. 2:01 PMzascecs says:
Hold On! It's gonna be a bumpy ride!
=)
Really cool! 5 stars!

Apr 21, 2009. 5:23 AMDon.Jambo says:
a new issue has come up: the wall thickness of the rectangular tube.

I went this weekend to buy the "iron" needed, and I told the guy there that i want a the 1in by 1in tube for a frame, and that I will weld it together, and the guy told me that it's better to use the rectangular tube with 0.078" wall (2mm), not the 0.065" wall (1.65mm).

after you welded the frame and used the robot for a while, did the rectangular tube have any cracks in the area where you welded? The the store the 19.6ft, 0.065" wall tubes seemed very flexible, not that robust as the 0.078" wall.

last thing would be the weight of your frame. did you get to weigh it? If between the 0.078" wall frame and the 0.065" wall frame is a very big difference, I'll stick also with the 0.065" wall. Please post!

Apr 24, 2009. 7:43 AMrpantaleo (author) says:
I inspected the frame yesterday and could not see any cracks in the welds.

I have never weighed my frame, but some quick calculations make it about 50 lbs. This includes the legs and linkages. If you made the frame from 0.078" wall tubing, then the weight would be about 60 lbs. This increase in weight should have little effect on the overall performance of the robot.

You can use either 0.065" or 0.078" tubing and the robot will work just fine.
Apr 24, 2009. 4:21 AMDon.Jambo says:
Could you please weigh or approximate the weight of the frame?!
Apr 23, 2009. 5:12 AMsoeinegaudi says:
This is simply awesome !!!!
I mean.... not that I would be to lazy to walk on my own, but this must be fun !!!
thank you sooo much to share your knowledge
Apr 14, 2009. 3:15 AMDon.Jambo says:
If I use 1.18" (3cm) square steel tubing in stead of 1" (2.5cm), and 2.36" (6cm) x 1.18" in stead of 2" x 1" with same wall thickness that you used will it make the frame a lot more robust, but too heavy?? Is it worth it?

Or it's ok to go with 1" and 2" x 1"? I don't know how robust your frame is. If it's good enough I won't go with thicker square tubing (it's the same wall thickness).

please reply, and also specify if I might mess up the power-to-weight ratio!
Thanks


Apr 15, 2009. 10:18 PMrpantaleo (author) says:
You shouldn't need larger tubing, but using it shouldn't mess up the power/weight ratio too much. The frame I made is very robust; it could easily support a 300kg stationary load. Of course, the actual capacity of the robot is limited by the strength of the motors and the axles that support the legs. The dynamic forces transimmted through the robot's joints during operation make the estimated 'safe' operating load about 100kg.

So, if you desire a stronger robot, you might experiment with larger axles, specifically the ones that connect to the motors and drive the middle legs.
Apr 6, 2009. 4:58 AMDon.Jambo says:
And about the joystick: any joystick is good (PC gaming, alarm systems, toys, machinery) or you have to use a wheel chair joystick?
Thx
Apr 6, 2009. 7:17 AMrpantaleo (author) says:
Any joystick is fine, provided you know how to wire it to the Arduino to get it to do what you want. I used one that is commonly found in arcade gaming machines http://www.allelectronics.com/make-a-store/item/JS-5/JOYSTICK/-/1.html .

Apr 6, 2009. 4:52 AMDon.Jambo says:
Which Arduino mircocontroller did you use?!
the Arduino Mega or the Arduino Duemilanove? I cannot see that in the pics, and you didn't specify what model!

Please let me know as soon as possible, cause I want to order it!
Thanks, and Great Project!
DonJambo
Apr 6, 2009. 7:10 AMrpantaleo (author) says:
I used the Arduino Diecimilia (the Duemilanove and Mega weren't out yet when I started the project), but the Duemilanove would work just fine since it is the next generation Diecimilia.
Mar 28, 2009. 5:23 PMkfinkel1976 says:
Great project!! Now you just need to add some suspension to the chair to cancel out the jostling around and put some better traction on the feet, you'll have a viable road vehicle.
Mar 21, 2009. 9:50 AMalejandrina says:
Hey!

I just wanted to thank you for posting this awesome instructable!
Beautiful. The simplicity of this design was a total lifesaver. I'm trying to build a walking robot and your leg links were so much simpler and cheaper than the rotary-to-linear motion designs I was looking at. I'm a fine arts student at Concordia University in Montreal so I always struggle with the mechanics and coding aspect of any project. I'm still in the midst of building and testing sensors, since I want my creature to talk too. This image is missing most of the skin and all the circuitry. I've never used an Arduino before, just Basic Stamps. But your leg design has saved me tons of work. Thank you!
Beatriz
trivia_one.jpg
Mar 24, 2009. 8:55 PMrpantaleo (author) says:
Thanks! Though I certainly can't take credit for the mechanism, I just adapted it for my project.

Nice robot! Hope to see some pics/video when it's done.
Feb 19, 2009. 2:47 PMthepelton says:
I recall being at a Fantasy Science Fiction Con in late January, and talking with a lady that was getting around in a electric wheeled cart. It was good for moving across flat surfaces, but couldn't negotiate stairs. I recall saying to her that I had imagined something like this in an unpublished Science Fiction story. You need to build one capable of crawling up and down stairs, and capable of holding three hundred pounds (137 KG). Force fields, teleportation and other Science Fiction stuff would be nice, but probably not possible yet. 8>)>
Jan 9, 2009. 1:06 PMmeanbean says:
yeah, it's cool, but how practical is it? how much can it carry and how far? is it all terrain? and most importantly, DOES IT GO ANY FASTER?!?!? so slow
Jan 12, 2009. 10:04 PMrpantaleo (author) says:
Definitely not practical, at least with the leg mechanism. The frame is rock solid, so slap some wheels or treads on it and you have a pretty robust platform.

The way I have it set up currently, the 'safe' load is about 200 lbs. As far as range, I can't say for sure, but the batteries lasted for about 3 hours of intermittent use when I presented at an expo for the class. The batteries were running at ~12.8 V. After those 3 hours, the batteries still were reading ~12.3 V, but it seems that when the batteries get below 12.5 volts, the motors draw more enough current to blow the 30 amp inline fuse.

The step size is pretty small right now, so the robot is not really that suited for all terrain travel. Increasing the step size will make it more suited for offroad travel, but a larger step size = more load on motors which reduces carrying capacity.

Feb 2, 2009. 5:23 PMmusicalbee2003 says:
*ahem* Try this for your mechanism!

Feb 2, 2009. 5:23 PMmusicalbee2003 says:
Inventor's Site

Feb 2, 2009. 5:27 PMmusicalbee2003 says:
So Scatterbrained. I'm sure this guy recognizes it

Jan 30, 2009. 5:41 PMA good name says:
So are the batteries rechargable? If not it seems like it would be awfully expensive to maintain...
Jan 30, 2009. 10:10 PMrpantaleo (author) says:
Yes, they are. They're lead acid, like car batteries, so you can use something like this to charge them.

Jan 31, 2009. 12:32 PMA good name says:
Oh okay. It would have been awfully wasteful to have a 3 hour battery time...

Jan 31, 2009. 1:46 PMreywolf says:
you could add felt pads to the legs for traction and " no floor damage"
Jan 25, 2009. 12:31 PMMr. Halloween says:
If it had rubber feet instead of wooden ones, it would in return have more traction and control
Jan 8, 2009. 12:58 PMimshanedulong says:
Cool! About how much does it cost? I cold probably get some parts at a local salvage shop, but how much did it cost you?
Jan 8, 2009. 2:38 PMrpantaleo (author) says:
I probably spent about $150 on the various hardware (bolts, washers, nuts, etc), electronic components, the Arduino, and the aluminum bar used to make the motor linkages. I was fortunate enough to have the steel tubing, batteries, and motors (the most expensive component) donated.

That being said, I'd guess it would cost you about $400-$500 if you had to buy everything and got a good deal on the motors (The cheapest I've seen is about $50/motor)
Jan 11, 2009. 11:59 AMimshanedulong says:
There are huge motors at the salvage shop for $5-$10. Plus I know of a way I could make it without arduino!
Jan 8, 2009. 4:58 PMbombmaker2 says:
thats cheap
Jan 10, 2009. 9:11 PMMeroki says:
hi there, this priject is very interesting

im going to try to build one, but instead of legs im going to try to use tank treads, and use dual stick controlls

maybe you could help me with a design and where i could fine/maek tank tracks?
Jan 10, 2009. 5:44 PMbudsiskos says:
How do you charge the batteries?
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