Introduction: Robotic Arm for Autonomous Tank

I recently purchased a robotic arm to mount onto my Autonomous tank project. I was unable to find any real tutorials on how to build the arm so I decided to do one myself.

The frame for the arm can be found on eBay and usually ships from China. It took about a month for all the parts to come in.

The Servo's were purchased from Amazon and can be found here:

An arm kit that includes six servo's can be found here:

Note: This arm build uses only 4 servos and does not posses left to right rotation. This is because the Tank will be doing the rotating. If you would like left to right rotation you will need to buy another servo and set the frame up accordingly.

Here are the links for Parts 2 and 3 of this build:

Robo-TK Tank Chassis Assembly:

Autonomous Tank and Bluetooth Control:

Step 1: Add Bearings to the Servo Brackets

1. Grab two servo brackets, 2 bearings, 2 long screws/nuts.

2. Put a bearing on each screw and insert it into the middle of the hole pattern at the bottom.

As you can see from the picture I added the bearings after attaching the servos to the bracket which turned out to be the more difficult way.

3. Tighten well and repeat for 2nd bracket.

Step 2: Add Servo Horns to U-Bracket

1. Gather the two U-shaped brackets, 2 round servo horns, and 8 servo screws.

2. Hold the servo horn tightly against the inside of the U-bracket and start adding screws from the outside. Be sure that you attach the servo horns to the correct side of the U-bracket.

3. Repeat process with 2nd U-bracket.

Step 3: Assemble the Forearm Frame

1. Gather a Servo bracket w/ attached bearing*, a Servo, the L-shaped bracket, and U-shaped bracket w/ attached servo horn.

*I added the bearings to the servo brackets last as I had no instructions. This is why it is not visible in the pictures above.

2. Using 4 screws and nuts attached the L shaped piece to the servo bracket as shown.

3. Next, grab the U-shaped bracket and secure it to the other side of the L-shaped bracket.

4. The servo can now be attached to the bracket using 4 thick screws and nuts. Be sure the servo is facing the correct direction.

Tighten Everything!

Step 4: Assemble the Wrist Frame

1. Grab the servo bracket w/ attached bearing, the other servo bracket, 2 servos, 8 thicks screws/nuts and 4 flathead screws/nuts.

2. Align the servo brackets as shown and screw together.

3. Then using 8 thick screws/nuts secure each servo into its bracket.

Step 5: The Claw

1. You will need the claw, a servo, a round servo horn, 2 servo horn screws, the gear shaft servo screw, and 4 small flathead screws.

2. Slide the round servo horn in between the two sides of the claw as shown and secure it into place with 2 servo screws. Be sure it is facing the right way up.

3. Next you must turn the servo gently all the way counter clockwise using another servo horn.

The point at which the claw closes should be at the end of the servo's range. This is to ensure the servo isn't put into a high-current state as the servo tries to force the claw past the point of being closed. Also it will allow the claw a wider opening range to pick up larger objects.

4. Press the servo gear into the servo horn attached to the claw and screw the servo into place with the 4 flathead screws.

5. Add the gear shaft screw to secure the horn to the servo.

A more detailed tutorial on how to assemble this claw can be found here:

Step 6: Attach the Claw to the Wrist Frame

1. Grab the Wrist frame, the claw, a round servo horn, 2 servo horn screws, and a servo gear shaft screw.

2. Attach the round servo horn to the servo and screw it into place with the gear shaft screw.

This must be done before attaching the claw or the entire claw will keep falling off.

3. Gently rotate the servo horn to center position

4. Hold the Claw against the attached servo horn with the holes lined up and screw it down with 2 servo horn screws.

Step 7: Attach the Forearm and Wrist Frames

This part will be easy.

1. Grab the Wrist frame, Forearm frame, and a gear shaft servo screw.

2. Be sure that you centered the wrist servo before attaching it to the Forearm frame.

3. Hold the Forearm frame while gently pulling the sides of the U-bracket apart just far enough to slip the bearing and servo gear into place. Do not pull too far or the U-bracket will bend out of shape and the paint will chip off.

4. Secure the servo gear to the servo horn using a gear shaft servo screw.

Step 8: Secure the Base of the Arm to the Tank Chassis

1. You will need a U-bracket w/ attached servo horn and the arm's base.

2. Attach the U-bracket to the top of the base arm with 4 flathead screws/nuts.

3. Bolt the base to the tank frame using 4 flathead screws/nuts. The hole patterns are identical.

Note: This arm was always meant to be attached to my tank chassis. If you only have the arm kit you would screw the two sides of the base together before attaching the arm to it. Also I did not need a servo to rotate the arm from side to side as It was to be mounted on the tank. If you would like left to right rotation for the arm you will need to buy one more servo and change the frame accordingly.

Step 9: Attach the Arm to the Tank

1. First rotate the servo shaft to its center position.

2. Gently pry the sides of the U-bracket open wide enough to slip the bearing and servo shaft into place.

3. Firmly press sides together and add the servo gear shaft screw to secure the horn to the servo.

That's it!


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