I designed a bigger, stronger, and longer version of the "meArm" robotic arm. Robot arms are fun to watch and more fun to play with. This design gives you the added bonus of building your own robot arm. Using a 3d printer and parts from the hardware store I was able to increase the lifting ability and strength of the original "meArm" kit. I added a few new features to correct issues I had with the original kit.
To view the original "meArm" check out his project at Pocket-Sized-Robot-Arm-meArm-V04 . I purchased his kit from adafruit.com/products/2012 and had fun putting it together and trying it out. I love the design it looks like a robot arm in a factory. The original "meArm" is a good kit but a little weak for any real use. So I fired up SketchUp and warmed up the 3d printer. Time to make it bigger, stronger and longer! I doubled the scale, added bearings to the joints for smother movement, and bigger servos to help move heavier objects. I had some issues to overcome and have more improvements I would like to make but I am well on the way to a successful project.
Download my files from thingiverse.com
Check out my web sight at engineeringwithjazz.com
Special thanks to:
My dad's boss Jimmy without him I could never have made this project. His help with measuring, tolerances, and using his 3d printer made all the difference. Thanks!
phenoptix for releasing this project as open source. I have learned so much!
Step 1: Parts List
- 18 ~ 5/8" long M4 screws
- 1 ~ 3/4" long M4 screw
- 3 ~ 1-3/4" long M4 screws
- 22 ~ M4 nuts (I used the ones with nylon inside)
- 3 ~ Small washers
- 12 ~ Bearings 624ZZ 13mm OD x 4mm ID amazon.com
- 12 ~ Small screws for servo horn
3D Printed parts:
- Bace Center Strut
- Center Beam
- Center Beam Top
- Grip Arm
- Long Arm
- Servo Arm
- Short Arm (Two of these)
- Stand Lid
- Support Arm
- Tri Support
- Pilips screwdriver
- 3d Printer
- Grinder (to shorten some of the screws)
- 3 ~ Servos (4 if you want a active gripper) polou.com
- 3 ~ servo extension cables adafruit.com
- 1 ~ Micro-controller I used Arduino adafruit.com
Step 2: Assembly of the Stand
After you print the required parts t is time to start assembly. Lets start from the bottom up. Insert the nuts into the bottom of the stand then screw the lid on with the servo hole closest to the servo cutout in the stand. The stand is where I made my first improvements. In the kit the servos have a little wobble in the holders mine are nice and tight with mounting holes to make them even more secure. The second improvement is the nubs on the lid. They help prevent the arm from tilting when something heavy is picked up.
Step 3: Assembly of the Base
The base will need a servo horn screwed into the bottom. There is also a center strut that will need 4 nuts press fit into it. The center strut is mounted into the base using four screws. You may need to remove the center strut latter in the build to insert the locking screw into the side servo horn. That is why I made it removable.
Step 4: Assembly of the Arm (Elbow)
Now to start on the arm. First lets attach the parts for the elbow. The long arm will need a press fit nut. Then the short arm will require two bearings. The bearings press in and hit a stop. The stop is the side that attaches to the long arm. Insert the screw into the bearing and attach to the nut on the long arm. Attach the servo horn to the servo arm. Then the servo arm will require another nut and will attach to the other end of the short arm.
Step 5: Assembly of the Arm (Center Beam)
The center beam is in two parts (Center Beam & Center Beam Top). The top will require four nuts press fit. A servo horn will also need to be screwed onto the Center Beam along with one press fit nut. This is where I made a mistake designing the part in 3d. This servo horn will need to be screwed on upside down from the other two. This will not affect the arm strength in any way. Now connect the two parts using the 1-3/4" screws. I noticed my mistake after I printed the part and adjusted all other parts to fit the mistake. If I were to redesign I would fix this error. You print you learn.
Step 6: Assembly of the Arm (Attach Elbow)
Insert a bearing into the middle of the long arm. Then screw to the center beam on the opposite side from the servo horn on the center beam. When complete the servo horn gear holes should both point away from the center beam.
Step 7: Assembly of the Arm (Build Shoulder)
This can be a little tricky because the arms look the same but each one is a little bit different. You will need the tri-support, one of the short arms, the support arm, and the gripper arm. The gripper arm is a little thinner on one end. The support arm has both of the bearings holes on the same side. Press fit the two nuts into the tri support. Then attach the support arm to the long end of the tri support using a bearing and screw. Next attach the short arm into the other nut on the tri support. The gripper arm and the tri support will require bearings. Be careful which way you put the gripper arm onto the tri support. If you put it on upside down it will not attach properly to the gripper head. The bearing side on the opposite end should be facing down. Use the 3/4" long screw and place washers in between the two bearings on the tri support and the gripper arm. This will screw onto the center beam in the next step.
Step 8: Assembly of the Arm (Attach Shoulder)
Now screw the shoulder onto the center beam. This will attach to the center beam on the same side as the servo horn. If you notice in the photo I have the gripper arm on upside down (See note). So if yours looks like mine in the photo you will need to flip it over. Otherwise move on to the next step.
Step 9: Assembly of the Arm (Attach Gripper Head)
The gripper head requires three nuts press fit. Three bearings are also need to be put into the arms and all attached using screws.
Step 10: Assembly of the Arm (Attach Arm to Base)
The arm is ready to attach to the base. First attach the support arm to the base. This nut is the one sticking out from the back of the base. Then attach the arm to the center strut on the base using a bearing and screw.
Step 11: Assembly of the Arm (Insert Servos)
The servos slide into the holes in the side of the base and with some careful fidgeting of the servo arm into there respective servo horns. This part requires some patience. Then insert the servo into the stand and attach the base.
Step 12: Final Thoughts and Improvements
When assembled the arm is super strong and stiff. All the joints move easy and will not where out. The original had a 7" reach mine is 14". I added some steel legs for ballast and it looks mean. Some people compared it to a evil spider. I do not have a active gripper like the original because I am using a electromagnet. If I would use a gripper I think I would change the design to have more fingers or use the DIY Universal Robot Gripper.
The servos I have pictured are from adafruit.com and have a extra wire for position feedback. I was going to use them for a learning arm (Move it by hand and it would record the movement and play back). But the servos were not strong enough to move the arm when fully extended. So I switched to some high torque ones from polou.com that I put on the parts list. They have not come in yet so I am excited to see how they will do. The trade off is they do not have feedback so no learning arm for me. I think if I removed some of the plastic from the center beam the original servos might work.
Changes I would make if I build another:
- The base limits total travel so I would remove the front and back sides.
- Update the radius on all parts so they match (cosmetic)
- Interchangeable gripper head to hold different grippers
- Wire management built in to model
- Stronger legs on the stand
- LED's just because
- Reduce weight of all parts by adding holes (triangle shaped)
- Some kind of cord keeper to prevent the wires from twisting when it rotates
- I think using stepper motors with gears could add to the weight capacity and give 360 degree rotation at the base. (Might be a bad idea I don't know)
Many more small changes I have yet to discover