Monday, September 2, 2013

Simple Arduino Robot Arm from 9 gram servos

Greetings once again. I just wanted to take the opportunity to introduce you to my new robot arm. It doesn't have a name, but it is made from house insulation foam and 9 gram servos. I won't do a full tutorial on this because frankly it isn't required. There are tons of this sort of thing out there. Use mine as a starting point for your own design based on what you have sitting around. This is just one example of something that works.

For this project you will need a few things.

The first is an Arduino or other microcontroller. I suppose you could use an RC receiver or some other sort of signal generator, but I will be using an Arduino Mega2560 r3.

Next you will need two HXT900 9gram servos (or similar). These can be purchased  from (what I recommend), or you can search for 9 gram servos on Ebay. They are common and cheap. I will say that the one's from HobbyKing are pretty decent quality (for a $3 servo). They aren't without fault, but you could do much worse.

For the arm's physical construction I will be using half inch house insulation foam. It is also cheap, but you will probably need to buy a full 4x8 sheet of it. You might be able to use styrofoam or foam board as well. Just make sure it is light. These servos aren't very big.

Last you will need some sort of hinge bracket. I use a part off some old plastic blinds for the base and then just a plain screw for the elbow.

First, cut two lengths of foam about 6.5" x 1". This is about the maximum length that I would use. Beyond that the servos start to get overtaxed when fully extended. Next cut the center cross beam. It is about 1.25" x 1". Basically, make it big enough that your servo and hinge will fit in between the first two pieces.

Next we are going to glue it together. Make sure your servo horn is pointed in the right direction, and hot glue it in place as shown. I use the servo itself along with the plastic blinds bracket as the joint. Again, if you are using a bracket completely dissimilar to mine, you may need to modify this. The spirit of this arm is use what you have.

Next we are going to make the other arm segment. This is about 5" x 1". I cut two of them and then glued them together to make one solid arm.

Next I screwed a screw into the center of the arm about a half inch from the end. This works as my other hinge. The metal on foam is actually pretty fluid.

Next we need to mount the elbow servo in the 1st arm segment. I cut a nice slot in the arm and slid it in. A little hot glue, and it was secured. This is a good time to go ahead and make sure your elbow servo horn is in the correct position. This is important. It will be hard to change later. Place the horn to achieve the desired range of motion.

Now cut a hole in the 1st segment opposite of the servo to create the other side of the hinge. Insert the screw of the 2nd segment and glue the horn in place once you get it straight. You should now have a completed arm without a base.

Go ahead and cut a base. I used a 5" x 5" slab of the same foam. Now just hot glue the servo of the first joint to the base, and you are good to go. Your arm is now done!

The keen eyed observer may not that this arm can't really do much. It can't rotate or pick up things. About the only useful thing I have done with it is tape a sharpie to the end. That is not the point. The point was to build a tool with which I could explore inverse kinematics. That goal is achieved.

Inverse Kinematics is another post; however, you can test your arm with either the sweep or knob example programs. Note that if you have problems, try powering the servos from an external power supply. It is entirely possible that your Arduino just isn't providing enough current.

Maybe this post inspired you. Maybe it didn't. If not, wait around for inverse kinematics(now HERE). That will be more interesting.

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