Aluminum Frame Hexapod based on Phoenix design

Aluminum Frame - Phoenix like - Hexapod

Introducing GOLLIAT the Ecuadorian hexapod

Quito - July 2017 -----> It has been a VERY long time since i wrote my last blog entry, sorry for that!, but i will ammend it with this exciting project - currently a work in progress - related to hexapods...

One of the biggest challenges i have found is to learn Inverse Kinematics, im still in the long learning curve, reading, investigating, watching videos, tutorials, etc... whatever that can help me to not only understand the concepts behind IK, but also a clever and effective way to apply it to a real hexapod system.

This time, i have built and aluminum frame based hexapod, bought from e-bay, this hexapod design is based - after researchnig in the internet i found it out - in a very famous design called the Phoenix hexapod which is a very well designed.

And here is a link to a instruction guide in PDf format:

Assembly guide

Construction

Following the documentation provided in the previously link, i ended up building my hexapod, the only difference so far is i used chinese - basically because of the price - servos of the model MG995 also bought on e-bay at ~ USD $ 5.0 each.

So here are some pictures of the process:

The kit consist of several aluminum pieces, servo holders, femurs and body plates.

It also has the main body upper and lower parts as well as a set of nuts, screws, flanged bearing, etc.

All you need to assembele, is - of course - the set of servos - and a screw drvier, some other tools maybe and a LOT of time and patience.... is very fun actually.

After some couple of hours of fun, you can see it start to take shape.

Please note and pay attention to the servo orientation everytime. Double check. Always.

Once you start attaching the legs, you start to realize the real imponent aspect the hexapod start to take, also the real dimesnion of it, is very imponent, cool looking hexapod!.

Once it's finished, you will feel very happy (ike i was), its a stuning hexapod, nice constructed and with a very cool look. enough from now, take a rest and lets talk about the electronics used for this project.

Electronics

For this projects i have used and /or plan to use (i have to see results beofre i decided or change something) so far:

1 x arduino mega clon:

1 x arduino mega servo shield:

1 x 2s lipo battrery 1200/ 2100 Mah

Also dont forget to use a lipo buzzer to not over-discharge and damage your lipos:

And of course a lipo-balance charger:

1 x 9 v ni-mh battery

1 x Wii nunchuck + breakout board for arduino

18 x MG955 servos - I picked up these ones because of the price, if you can afford the HITEC, go for them, they should be more precise than the MG955 but in my case they are far my budget. I bought the MG955 at ~ USD $ 8.00 each

18 x Metal Servo Horns - Found them on e-bay.

Update 06/October/2017

Im still in a very deep inverse kinematics learning. Searching the web and reading all the documentation i found related to it. Also about the different gaits, etc, etc...

In the meanwhile i have been playing with the servo controller creating sequences, i also have fried some of the resistances of my Arduino Mega Clon....

This my Arduino Mega clon.......

This is a close-up view of the two fried resistors just below the USB port..... they burned one at a time, so that means i have two incidents so far... but still working thank God!......................

Also i have asked a friend to help me getting some wii nunchuck with the arduuino adaptor and a pair of mini arduino mega and a pair of key estudio megas which actually looks really great in the case i finally completely fry my mega clon, ehich actually looks has a 'bug' which i will show you right now:

As you can see it has TX/RX pins missplaced!.. you have

14 - TX3

15 - RX3

16 - TX2

17 - RX2

18 - RX1

19 - TX1

20 - SDA

21 - SCL

Looks really crazy don't you think?!/....

And the Key Estudio looks really nice:

It comes in a NICE packaging....

And the colours are really nice, also when you connect it, the leds are oragne as well!.

When everything is set-up and completely secure i will use this one for the final set-up, just to avoid damaging one of these.

Ok, so far its just an update... i will post very soon expecting to make the IK engine to work.....

Update - 18/October/2017

I have put everything together inside the hexapod, enough testing so far.
Also i put a voltage regulator (switching regulator) like this one:

Because i dont want to fry or burn my board again. Also i have split the power sources, one 2s lipo for the servos through this votalge regulator, being set @ 6.0 volts, and a 9 V battery for the Arduino.

I also found that delvering the 2s lipo full votage and with the spider trying to actually walk on the floor supporting its total weight, the regulator gets REALLY hot, so i put an RC car fan ii have as spare:

Apart from looking cool, it does it job flawlessly.

Then i found the robot was falling down one side after a few steps on the ground so i tought it would be a electrical problem or a servo problem, so i started to raise the power on the voltage regulator up to 7.2 volts, but nothing happened, the problem persisted, so i tought maybe it was because of the cheap servos, but in faxct they are powerfull, delivering - as stated on its specifications - a torque of :

9.4 kg-cm @ 4.8 V
11.0 kg-cm @ 6.0 V

So with that being check, i started to observ the leg movements of the hexapod.... and finally found the problem, the 0, 1 and 2 femur and tibia were moving inverted, so i had to unassemble and put back again in the opposite direction, so now the full body looks like this:

As you can seem the both sides of the hexapod are not like a mirror, now it looks like every leg is assembled exactly the same way in a clock-wise direction, please refer to my first pictures on this entry so you can found the difference.

After that change - took me like 1.5 hours to change everything back, i connected the nunchuck and started testing again, this time i set up everything nice , arranged and clean on top of the hexapod, like this:

The 2s lipo is a 2100 Mah, and is connected to a voltage beeper, and secured with a wrap to the body, on top right.

THe 9V battery is feeding the board, and is on the Top Left, is a Ni-MH rechargeable battery.

And on the bottom, is the voltage regulator, with the Cooling FAN on top of it, the cooliing fan is connected to any of the GND and VCC pins on the Arduino mega servo shield.

NOTE: Always make sure to set the voltage regulator to something the servos can handle, so far i have burned 4 servos..... i always set it up to 6 volts max.

First Steps

So far i have been able to make it erratically walk:

Cost - without taking into account burned stuff ;) :

New cost break down (Updated @ Jan 10 - 2018):

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Update on 28-11-2017
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OK, so finally i found a problem on my design, the buck down module is strong enough just to handle a max of 3A, which at certain point drivers the hexapod to fail as the current security shutdown activates because of the temprature increase of it because of the actual servos current draw.

I found that after using the hexapod for some minutes, it fails and shutdown, then i found the buck down voltage regulator got very veru hot.... so i started to invetigate.

I found that servos (the MG's 996/996R specifically) power consumptions are more/less these ones:

Specifications

• Weight: 55 g
• Dimension: 40.7 x 19.7 x 42.9 mm approx.
• Stall torque: 9.4 kgf·cm (4.8 V ), 11 kgf·cm (6 V)
• Operating speed: 0.17 s/60º (4.8 V), 0.14 s/60º (6 V)
• Operating voltage: 4.8 V a 7.2 V
• Running Current 500 mA – 900 mA (6V)
• Stall Current 2.5 A (6V)
• Dead band width: 5 µs
• Stable and shock proof double ball bearing design
• Temperature range: 0 ºC – 4.8 V a 7.2 V – 900 mA (6V) double ball bearing design 55 ºC

So, assuming a tripod wal which uses 3 legs at the same time, assuming 900 mA per servo gives us:

3 x 3 x 0.9 A = 8.1 A

Now, frrm the 9 servos, 3 are horizontal (coxa) ones so they wont use the 100% current draw... so it shall be less than 8.1 Amp..... So... i bougth an 8A UBEC form hobbywing.. like this one:

The beauty and advantages i found on this are several:

1.- It has an integrated lipo 2s-3s voltage indicator, this means i don't need my lipo buzzer anymore.
2.- It has a power switch. It means i dobnt have to implement one.
3.- It has a Y split output so i can power the arduino circuit and the servos with the same batrery input, that means i don;t need the 9V battery anymore. Simpler design.
4.- It has a 15A peak so it should be powerfull enough....

So...... if my calculations are correct, i should validate it after installing it, which i did yesterday, and it does it job flawlessly.... it barely gets warm works like a charm, now i can use my hexapod until the baterry draing totally with no electrical problems.

THe last improvement i made to my hexapod is to replace the wired nunchuck with a wireless one, like this one:

So now with this, the hexapod is almost complete.... i will post pictures of how it looks now later, now that everything is under the hood, it look much clean, the onyl thing on top is the battery!.

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FINAL -> Update on 08-12-2017
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Ok, so far, the Hexapod is complete and my job is finished, finally!!!!!!!.

NOTE: Just make sure you use 8amp capable cables from the output of the UBEC to the Servo Shield (arduino servo shield), because a lot of current is passing through it and the cables got really hot, they got so hot that mines melted and caused a short-circuit that cost me 4 burned servos i had to replace!.
Now i have replaced the cables with stronger one filament ones they get more less hot but they dont overheat, also i have put them separated from each one so in the case they get really hot they wont cause a short circuit.

Now it looks like this: