Let's Make Robots!

ShC v1 (Simple hexabot Clone version 1)

hexapod Clone

 ShC v1 (Simple hexapod Clone version 1)

 
Description.

This small hexbot its based in the simple three-servo hexapod robot using the Pololu Micro Maestro.
This version uses an ATMEL with ATMEGA32U4 and small  shield to connect sensors and servos.

arana-vfs.jpg

arana-mf.jpg

ara-f2.jpg

aranv11.jpg

 arana-prev.jpg


Note: Each square is 2.3 x 2.4 cm

cuadro.jpg

 

 

1 Circuit Design


1.1 T(ee)nsebo and Brain

The brain of ShC uses a Teensy 2 (Figure 1.1.1) with ATMEGA32U4. Advantages of this board are: the size, price and code compatibility with Arduino. For better usage its designed a shield which support : 4 Analog sensor inputs, 2 Digital Inputs and 6 servos inputs. The PCB design of the Tnsebo its shown in figure 1.1.2. At this moment its only assembled: 2 Analog sensor inputs, 2 digital Inputs and 3 servos inputs (Figure 1.1.3). Finally the Tnsebo its mounted at the back of ShC (Figure 1.1.4) .

tensi.jpg

Figure 1.1.1 -
Teensy 2, wit ATMEGA 32U4 .

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Figure 1.1.2 - Tnsebo Version 1 PCB.

tsebo.jpg

Figure 1.1.3 -
Assembled Tnsebo Version 1.

arana-bav11.jpg

Figure 1.1.4 - Tnsebo v1 mounted on the ShC v1.


1.2  LDRs for light following

For the LDRs its used a basic configuration using potentiometers to calibrate each eye, the base value is between 2.1 - 2.6 volts. In figure 1.2.1 its shown the PCB. In figure 1.2.2 its shown the ShC with the mounted PCB.

ldr-pcb.jpg

Figure 1.2.1 - LDRs PCB.

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Figure 1.2.2 -
Eyes of ShC.


2  The ShC design

2.1 Basic Design

I was reviewing the manual of the hexapod from Pololu, which is a great reference to built this clone. In figure 2.1.1 its shown the original design of this nice hexbot. The main differences are: battery and battery base, cable compartment, processor, sensors and legs. Making this changes the clone was born, which is shown in figure 2.1.2,

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Figure 2.1.1 - Original hexapod design.


arana01.jpg

Figure 2.1.2 -
ShC design with plastic legs and base.


2.2 Parts of ShC

In figure 2.2.1 its shown the parts of ShC, all plastic parts are from old toys packaging. The acrylic base is cut from an old CD case.
The long pots are from Chocolate pops :)  (Figure 2.2.2).  TG9e small servos supports 1.5 kg of torque, and the old 3.6 V battery as power supply. 

    In Figures 2.2.3 and 2.2.4 are shown the construction of the leg, both are glued and screwed. Finally in
figure 2.2.5 its shown the assembling of the motors based in Pololu´s Manual,  and both legs are mounted.

arana-03.jpg

Figure 2.2.1 -
Parts of ShC.

arana-parts.jpg

Figure 2.2.2 -
Parts for assembling ShC.

pata-part.jpg

Figure 2.2.3 -
  Parts of the leg.


pata1.jpg

Figure 2.2.4 -
Creating the leg.

arana-4p.jpg

Figure 2.2.5 -
ShC with 4 legs.



3 Testing the ShC

3.1 Basic Walk Cycle

The first step, is to test the walk cycle of the hexbot. For that reason a simple program its design. This version takes via serial communication several characters that indicate a movement to each leg. On this way its possible to change the movements and see how the behavour is. In table 3.1.1 control and angle changed are shown.


Table 3.1.1 - Legs and control characters

    Leg 1 Leg 2 Leg 3
    +10      a     b     c
     -10      d     e     f


For cycle movements the following table can be generated (Table 3.1.2). This based on figure 3.1.1 and Pololu's online manual.


posc-f.jpg

 

Table 3.1.2 - Secuence using control characters

  Frame 0   
  Frame 1    e a c
  Frame 2    d f d f   
  Frame 3    b b
  Frame 4    a c a c


With the code (TestSerMot.) for Teensy, we can send the complete string as follows:


        eacdfdfbbacac


3.2 Testing

Taking the data below, another program is design to test two walk cycles. Using angles table 3.2.1 is generated, and is possible to move the hexbot as shown in video 1.

Table 3.2.1 - Angles for walkcycle based on Table 3.1.2

    Leg 1   Leg 2   Leg 3
0     80      80      80
1     95      65      95
2     60      0        60
3     0        95      0
4     95      0        95
5     0        65      0

 

 

 

 

 Figure 3.1.1 - Movements for walkcycle.

 

The basic cycle could be written as:

Init:    Initiate (0)
    Start (1)
  
Cycle:  Move1 (2)
    Move2 (3)
    Move3 (4)
    Move4 (5)
    Go Cycle    



3.3 Follow me

 3.3.1 Base Algorithm for  ShC

The Follow me program consider a base algorithm designed to take several condition using a binary action table.  For each eye we initialize with the ambient base light obtained as follows:

nAmb1 = analogData
nAmb1a = nAmb1 + 50
nAmb1b = nAmb1 - 50

Then, its created all the thresholds areas for each action according to a previous calibration on LDRs.

nAmb1s = nAmb1a + 63
nAmb1r = nAmb1s + 63

nAmb1c = nAmb1 - 205
nAmb1d = nAmb1c - (nAmb1b - nAmb1c)


For each cycle its obtained a new light value saved as: AAmb1,  evaluating:

if (AAmb1 < nAmb1a) & (AAmb1 > nAmb1b)
    -1
if (AAmb1 > nAmb1a) & (AAmb1 < nAmb1r)
     0
if (AAmb1 > nAmb1d) & (AAmb1 < nAmb1b)
     1

For real values its evaluated using a binary table:

01  02
 0    0     Backwards()
 0    1     Turn 1()
 1    0     Turn2()
 1    1     Forward()
 0   -1    Turn 1()
-1    0    Turn 2()
 1   -1    Turn 2()
-1    1    Turn 1()
-1  -1     Stop()

Those functions contains the basic cycle for each movement.


In Video 2 its shown how ShC reacts to light. First obtains ambient light, the it reacts to the low light (shadows), and begins to turn arround, when the lamp shows up, we can see different reactions, until the ShC follows it. And again, it finds low light and try to avoid it turnign arround.

 




 

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That looks like a nice design; I like how you managed to reuse parts from so many different things.  What is the scale - I guess it is bigger than mine?  Is it really going to work at 3.6V?

I hope to see more details and a movie soon!  Can I post a copy of your picture at the end of the original build instructions page?

-Paul

No problem man, the hexbot I hope to fineshed next week, I´m waiting the processor to arrive, It could work at 3.6, the line follower works with that small battery , but only for less than 5 minutes.  The idea I have in mind, is to use a small lamp and the hexpod will follow the light.
These little bots are awesome. I think I might have to make one.
Give it a try ¡¡¡ :)