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Assembly guide

Javier edited this page Dec 27, 2016 · 47 revisions

This section of the wiki is dedicated to the printing and assembling of the physicall parts of the hexapod. It is divided in three sub section and you can acces them from the links below. You should check the guide in the proposed order.

#Hardware-componentes

##3D printable parts

The parts have been designed in CATIA V5r21 with a full parametric design, witch allows you to easily resize and adapt the model to your own servos or hardware requirements.

Unfortunately, CATIA is not a free opensource program, so if you want to modify it, you will need a license. We would like to port it to a free software solution but, at the moment, it is not posible.

All the parts have been exported to stl format, so you can easily print them.

Recommendations for printing

Part Layer Height Infill Support Number of Pieces Plastic (g) Material
Coxa 0.2 40% Yes 6 189 PLA
Femur 0.25 40% No 6 30 PLA or ABS
Femur simetria 0.25 40% No 6 30 PLA or ABS
Separador 0.2 40% No 6 9 PLA
Tibia 0.2 40% Yes 6 342 PLA
Tapa servo 0.1 50% Yes 18 128 PLA or ABS
Base inferior 0.2 25% No 1 156 PLA
Base superior 0.2 25% No 1 158 PLA
Base superior RPI2 0.2 25% No 1 158 PLA
Separador cuerpo 0.2 40% No 2 19 ABS
Soporte camara 0.2 40% No 1 20 ABS

WARN: To date, Raspberry Pi(RPi) B+ and RPi 2 have been released. We have designed two different cases for the top frame, one called base superior and a second one called base superior RPi2. You have to print ONLY one of the two models depending on the model of RPi you have bought. We suggest you to buy the new model but we support the older one too if ou want to use it.

##Bolts, nuts and washers

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Component Used in Number Type
Bolt M2.5x20 cabeza avellanada Separador femur 12 A
Bolt M3x20 hexagonal head Servomotor 72 B
Nut M4 autobloqueante Tapa modificada 18 C
Bolt 2.2x6.5 autorroscante Horn/Arduino/RPi 80 D
Bolt M4x16 hexagonal head Tapa modificada 18 E
Nut M3 autobloqueante Pi 6 F
Washer M4 Tapa modificada 36 G
Bearing 4x10x4 Femur 12 H

##Vitamins

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Component Picture Number
Towerpro MG996R 12kg Servo Towerpro MG996R 12kg Servo 18
Rubber End Cap D10mm Rubber end cap 6
Lipo Battery (2S or above) Lipo Battery 1
XT60 Connector (Male) XT60 Connector 1
YEP 20A SBEC YEP 20A SBEC 1
Arduino Mega 2560 r3 Arduino Mega 2560 r3 1
Arduino Mega Proto Shield R3 Arduino Mega Proto Shield R3 1
Male Pin Strip 0.1'' Male Pin Strip 0.1 60
DC 7V-24V To DC 5V 3A USB DC 7V-24V To DC 5V 3A USB 1
RPi B/B+ or 2 RPi B/B+ or 2 1
8GB SD Card 8GB SD Card 1
USB Wifi USB Wifi 1

WARN: To date, Raspberry Pi(RPi) B+ and RPi 2 have been released. We have designed two different cases for the top frame, one called base superior and a second one called base superior RPi2. You have to print ONLY one of the two models depending on the model of RPi you have bought. We suggest you to buy the new model but we support the older one too if ou want to use it.

Optional

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Component Picture Number
Raspberry Pi Camera Board Camera Board 1
LiPo low voltage alarm LiPo low voltage alarm 1
PS3 Dualshock controller PS3 Dualshock controller 1
USB Bluetooth USB Bluetooth 1

WARN: The SBEC doesn't alert of a low battery charge. It is highly recommendable to add a voltage alarm to the LiPo battery in order to not damage it.

The Raspberry Pi B has only two USB ports. One of them is going to be used by the serial connection with the Arduino MEGA. This fact leaves us two connectivity options:

  1. Bluetooth
  2. Wifi

If you want to use them at the same time you will have to buy a USB hub with external power supply because the RPi can not power several devices with a high power consumption.

#Assembly

##Servo assembly

In order to increase the stability of the structure, we are going to modify our MG 996 servos turning the old bottom case into a new one. This modification adds a new plastic shaft in the bottom of the servo. This step must be done before we introduce the motor in its corresponding hole in order to make easier the assembly. The first step is to remove the old bottom case.

  1. Remove the four long screws of the servo. You should be able to remove smoothly the bottom case. We are not going to use the old case so you can keep it or you can trow it to the trash.

  2. Insert the new case in his place and thight the screws. Servo AntDroid

  3. Glue the head of E type screw in the hexagonal groove.

  4. The final step is to set in the circular horn in its place. Put pressure on the horn until it reaches the top of the servo's axe and tight the bolt of the horn. Servo horn AntDroid

If you are going to do this step with all the servos at the same time, you should now that is better to only mount six horns. We are going to set in the rest of them while assembling the leg.

##Leg assembly

Coxa

Servo coxa

Insert one of the custom servos in the hollow of the coxa. Be aware of the orientation of the servo. You can check it by looking at the groove that the coxa has to make easier the insertion of the servo's wire. This servo is one of the six in which you should have set in the horn.

Coxa servo assembly AntDroid

The space for the servo is quite small so be carefull to not broke the plastic or the servo putting to much pressure. You can file the inner hollow to do easier the insertion.

Once you finished, tight the four B type bolts with the allen key.

Servo coxa 2

Insert another servo in the other hollow. This servo shouldn't have the horn assembled. As we did before, tigth four B type bolts. Three coxas should have the servo pointing in one direction and the other three opposite them.

Servo coxa 2 Antdroid assembly

We have finished with the coxa. You can leave it apart for the moment.

###Tibia

Servo

Insert one servo in the hollow of the tibia. Tight 4 B type bolts and remember to not assemble the horn. As it happened with the coxas, three servos should be pointing one direction and the other ones should be assembled opposite them.

Tibia servo assembly

Foot Remember to add the rubber end cup to the end of the leg.

###Full assembly

Femur

Put pressure on the 4x8x4 bearing to introduce it into the hole of the femur. Put one femur in its correct place as indicated below. Set in the horn and tight it with the provided screw. Tight the two or four (as you wish) D type bolts in the horn to join the femur with the horn.

femur assembly Antdroid

Use two G type washers to ensure the union between the femur and the tibia. Put one in one side if the femur and other in the other side. Tight the four pieces with a F type nut.

The orientation of the servos is extremely important in order to not damage the servomotos in the first boot of the robot. If the central positions of the servos are to away from the desired point, the leg can collide with itself.

Legs assembly 3

Femur and separator

Join the separator with one A type bolt to the femur you assembled in the last step and put to other femur in its place as seen below. We recommend you to brush up the holes of the separators with a 2.5 drill.

Femur assembly Antdroid 2

Put pressure on the 4x8x4 bearing to introduce it into the hole of the femur. Join the femur with the horn with two or four D type bolts and tight the screw of the horn to the servo's axe. Use one A type bolt to join the separator with the other side of the femur.

Use two G type washers to ensure the union between the femur and the tibia. Put one in one side if the femur and other in the other side. Tight the four pieces with a F type nut.

##Body assembly

###Bottom case

Separators and Arduino

Insert the two body separators in their respective holes. It is highly recommended to sand de top and the bottom of the pieces if you have to do to much pressure to put them together . Tight six D type bolts.

Upper case

Protoshield

Join the protoshield with the Arduino. This step should be completed when you have finish the wiring of the protoshield. For more information go to this link.

protoshield

Upper case

Tight two D type bolts. The Raspberry Pi's USB should be facing the same side that the Arduino's USB.

Raspberry assembly

###Legs

Legs

Join one leg with the upper body setting the horn of the servo in the groove that the case has for it. Tight two D type bolts for each leg you attach.

Legs assembly

The orientation of the servos is extremely important in order to not damage the servomotos in the first boot of the robot. If the central positions of the servos are to away from the desired point, the leg can collide with the body.

Legs assembly 2

Bottom case

Assembly the bottom case to the body. Insert the plastic axes in the holes that the case has for them. As we mention before, tight one E type bolt in the hole of the axe to increase its resistance. Use a G type washer.

full assembly

The battery can be allocated on the upper case.

battery

#Electronic parts

The electronic system is made up of the following components

  • LiPo battery
  • DC/DC converters
    • SBEC
    • USB converter
  • LiPo alarm

The next schematic shows a general overview of the electrical system of the Antdroid:

A USB hub was involved in the first assembly in order to allow us to connect the WIFI and the BT dongles (one of the Raspberry Pi's USB ports is used by the Arduino). The RPi2 and the RPi B+, which have 4 USB ports instead of 2, fixed that problem. Nevertheles, the robot can be operated using just the WIFI connection.

##LiPo battery

Minimum requirements:

  • 1x 3 cell battery
  • Current rating of at least 10 A.

##LiPo alarm

There are two ways to plug the alarm in, which are shown below:

Due to its simplicity, we recommend the first wiring.

##Arduino The Arduino MEGA has a protoshield which makes easier connecting the servos to the microcontroller. The protoshield integrates 18 triterminal connectors welded directly to the PCB, one for each servomotor. The Arduino MEGA has a A-B USB wire wich connects the microcontroler with the Raspberry Pi.

The shield has a negative and a positive track to power all the servomotors. So, one of the pins of the triterminal connector has to be welded to the negative, a second one to the positive and the last pin has to be connected to one of the digital pin outputs of the Arduino. Usually, the red wire of the servo has to be connected to the positive, the brown wire to the negative and the orange wire is for the signal, so be carefull while welding the power tracks to the triterminal pins. A wrong connection may destroy your servomotors.

The protoshield and the servos are powered by the 20A SBEC. It is highly recommendable to unify the ground of the SBEC with the ground of the Arduino. The MG996R works fine with a 6v input, so the SBEC can be set to this voltage thanks to its jumper.

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