Developing a hexapod with your own hands from scratch (part 1)
Hello! Not so long ago I began to study programming for microcontrollers. At first, writing simple programs for flashing a light-emitting diode and even two was no longer fun and getting bored. And one evening sitting in meditation on what to do with his head, he decided to find more complex projects. On the Internet, I saw a lot of things that people create, but most of all I was surprised by a six-legged robot or hexapod.
Inspired by the pictures and video, I decided to try my hand at it. The development of the body, electronics and software will be conducted from 0.
tomnewmann kindly shared with me the drawings of his project, for which he thank you very much.
Having estimated the sizes of the future details and having thought a little of all the received information began to throw the drawings of the case. I figured it would be wiser to start with the design of the legs, since they are the most difficult part of the hull.
After several hours of reflection, the first model of "Coxa" appeared (as it is customary to designate a knot that connects the leg to the body). The node tried to make it as compact as possible. The servo drive will be completely inside, so do not forget (which is the first time I did) about the hole for the output of the wires.
Detail 1 - The axis to which Femur will be attached (the second leg part). It is assembled from a screw M3x1? washers and nuts M3
Detail 2 - Screw M3x20
Detail 3 - Rack for PCBs M3x20
Part 4 - They are a kind of retainer of the servo drive, to prevent its movement along the vertical.
The height (A) of this node should be such that the servo drive can fit into the inside, which will stand on the frame.
Then you need to do "Femur". The detail was the simplest of all and I think it does not need any comments.
Detail 1 - Screw M3x20
Detail 2 - Plastic sleeve 3x10 (I did not find the long rack, I had to look for other solutions)
Detail 3 - Rack for PCBs M3x30
The next detail is "Tibia", the last part of the foot. With her problems should not be and its length depends on the height, which is planned to understand the robot. I have it 130mm from the axis of the servo, I did not do it anymore, since the load on the servo drives, especially the servo in Coxa, also increases with increasing length. On the second side, I made the second hole under the axle so that you could turn the servo and reduce the length of the lever, if suddenly the servos will be hard.
Next on the turn comes the frame - the biggest part. It is she who determines the configuration of the feet of the future robot. There are several variants of the location of the legs, but I stopped on the variant with the letter Ж (when viewed from above it looks like).
At the first stages of designing, the question arose: "At what distance should the legs be located from each other?". In search of an answer to this question, I realized that there are no recommendations on this matter. Studying other people's projects and gait variants concluded that the distance is selected based on the desired maximum angle of rotation of the limb. The greater the distance between the legs, the greater the angle can reach the limb while walking.
In the solution of this question, drawings helped. tomnewmann , of which I took the distance between the legs, since the dimensions of the robots were quite similar (mine is slightly smaller). A few hours later, the upper and lower parts of the frame were born:
At the bottom of the frame is a cutout under the battery and its mountings. By the way it will be attached to the Velcro, which are used on quadrics when attaching the battery to them. Rama turned out pretty big. After sitting another evening and making the intermediate parts in the form of supports between the parts, I decided that it's time to make the assembly of the frame with the installed servos. The result did not take long:
Since all the necessary components we already have, we can make a complete assembly of the case:
In the center of the case, between the plates, the power supply for the servo drives was planned, a 3S Li-po battery from the bottom, and the control board (Arduino Due) from the bottom. In accordance with this, I changed the frame assembly:
The board on top is the Arduino Mega model with some kind of shild. It is used simply for a view and has similar dimensions as the Due.
It does not look very nice, but taking into account the wires that will stick out will be even worse. In addition, the body seemed to me very thin. I decided to cover up the electronics as much as possible without damaging the appearance and come up with a name for my offspring.
The solution to the first task was to cover the top and bottom, covering the battery and control electronics. These are the only parts to be assembled with glue. Later the model of the bottom cover was born.
If there were no problems with the first task, then with the second task there were difficulties for 2 days. Yes, it took me so long to just think of a name for him. Randomly remembering the movie "Terminator" decided to call it "Skynet" and cut the name on the top cover. Also added cutouts for HC-SR04.
As a result of the addition of just two roofs, the chassis significantly changed the appearance for the better:
The result I was very impressed and the appearance is quite attractive. In the second part, I will tell you about the assembly of the hull and the rake, to which I was advancing.
Drawings do not hide and I am ready to share them with anyone who wants to.
I will be glad to any criticism and is ready to answer any questions within the framework of this material.
It may be interesting
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