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Author Topic: Hexapod project (newbie)  (Read 801 times)

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Offline HerantTopic starter

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Hexapod project (newbie)
« on: December 17, 2013, 07:10:19 AM »
Hi,

After i came across a video of hexapod  "Dmitri" http://m.youtube.com/watch?v=CVHd2_NUgIs on youtube i got bitten by this robotic desease and now i want to build a hexapod my myself. My main problem is the lack of knowledge about electronics and coding/programming which i trying to work with but choose to consentrate on one task at a time. I bough myself a 3d printer and already started to design legs in solidworks(as i learn solidworks aswell now), its abit time consuming task but i like it so far. Servos that i choose for this project are going to be http://www.hobbyking.com/hobbyking/store/__27213__tgy_1270hv_metal_gear_digital_servo_w_heat_sink_40kg_18sec_170g.html not really expansive but pretty solid as i see it. (Allready fryed one as i was experementing with arduino ).
So the idea is that i want to build a hexapod which can be controlled with a ps3 controlled (maybe even ipad through bt) which earlier mantioned servos and a camera. I want to control servos through arduino and  camera with raspberry pi.

So my question is which electronics do i need for this to work? I allready got Arduino kit with alots of different components aswell as i got raspberry pi b.
I would really appreciate if you guys could help me with this one.
« Last Edit: December 17, 2013, 11:08:35 AM by Herant »

Offline jwatte

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Re: Hexapod project (newbie)
« Reply #1 on: December 17, 2013, 11:19:24 AM »
That looks like a strong servo!

The main problem is going to be to generate enough stable servo control signals to drive them all. An Arduino, or Raspberry Pi, can't do that on its own.

I would recommend the Axon 2: http://www.societyofrobots.com/axon2/
Another option would be the Pololu Mini Maestro: http://www.pololu.com/product/1356
I would probably use the RPi or the Arduino for sensors and control, and use the Axon or Maestro only for servo control, to make sure the output is stable. Both of them can receive commands from USB or serial port.
The Axon, additionally, has enough I/Os and easy enough development that you could do the robot with that alone, too (if you don't need the amount of power that an RPi gives you.)

Offline waltr

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Re: Hexapod project (newbie)
« Reply #2 on: December 17, 2013, 12:01:14 PM »
Or use one of Adafruit's I2C to Servo boards controlled from the R-Pi.
http://www.adafruit.com/index.php?main_page=adasearch&q=servo

A hexapod is a big project. You are better to start with a simpler project or at least many of Adafriut's tutorials so you can learn many of the pieces required for the hexapod.

There are also many threads in the SoR forum on hexapods that you should read and click on the "Robot Tutorials" on the upper right corner of this web page for lots of good basic info on building bot.

Offline bdeuell

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Re: Hexapod project (newbie)
« Reply #3 on: December 17, 2013, 07:12:59 PM »
I am also in the process of designing my first hexapod robot.

Having not built one I cant speak from experience but I have been researching what other people have built. I have seen a lot hexapods with

BotBoarduino (http://www.lynxmotion.com/c-153-botboarduino.aspx) or Bot Board II (http://www.lynxmotion.com/c-66-bot-board-ii.aspx)
and
SSC-32 Servo Controller (http://www.lynxmotion.com/p-395-ssc-32-servo-controller.aspx).

I am planning to use the ARC32 (http://www.basicmicro.com/ARC32_p_141.html) because space is a major concern in my design.

As for the controller I havent seen anyone use PS3 controllers but PS2 controllers are quite common.


Offline HerantTopic starter

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Re: Hexapod project (newbie)
« Reply #4 on: December 18, 2013, 03:06:37 PM »
I am also in the process of designing my first hexapod robot.

Having not built one I cant speak from experience but I have been researching what other people have built. I have seen a lot hexapods with

BotBoarduino (http://www.lynxmotion.com/c-153-botboarduino.aspx) or Bot Board II (http://www.lynxmotion.com/c-66-bot-board-ii.aspx)
and
SSC-32 Servo Controller (http://www.lynxmotion.com/p-395-ssc-32-servo-controller.aspx).

I am planning to use the ARC32 (http://www.basicmicro.com/ARC32_p_141.html) because space is a major concern in my design.

As for the controller I havent seen anyone use PS3 controllers but PS2 controllers are quite common.


Could u please link me a list of components that you use for your project so i know what a hexapod built of, kinda want to know so i can start planning the body  ;)
« Last Edit: December 18, 2013, 03:10:58 PM by Herant »

Offline HerantTopic starter

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Re: Hexapod project (newbie)
« Reply #5 on: December 18, 2013, 05:12:04 PM »
Btw thx for the heads up. I'm going to keep designing mechanical parts for hexapod simply because i already got a 3d printer with shitloads of filament :) but i'll definitely wait with buying electronics until i know how to program and use them :) plus it might be a good idea to spend alot more time planing/designing and less on building.

Offline HerantTopic starter

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Re: Hexapod project (newbie)
« Reply #6 on: December 19, 2013, 04:35:54 AM »
So if i understand this correctly the list of electronics parts are:

1. Servo controller (a board with 18- 32 outputs)
2. Something that can carry coding for servos (arduino, raspberry pi etc)
3. Communication chip which will be connected to "arduino or raspberry" (wifi, BT, or radiocontroller)
4. Battery pack for servos and battery pack for electronics
 
Camera (optional):

1. A camera
2. Something that will send live picture through wifi (raspberry)
3. Separate servo which can move camera either way (controlling by Arduino)
4. Maybe even one more battery pack

Correct me if i'm wrong but i seriously need to draw a picture of every part connecting together so i know what i need on board which may help me to calculate space that i need and ofc weight.

Thanks

Offline jwatte

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Re: Hexapod project (newbie)
« Reply #7 on: December 19, 2013, 11:51:01 AM »
Yes, you absolutely need to start drawing out your system parts! Design and planning is what makes a successful robot.

Btw: You can probably use a single high-quality LiPo battery for all the things, assuming your servos are OK with a fully charged 2S LiPo at 8.4 Volts.
Also, sometimes the servo controller and the "code" microcontroller can be the same thing -- for example, the Axon II can be both the Arduino and the Controller in your list.

For camera, it may be easier to use a camera with built-in WiFi (these are easy to find; you'd just have to hack off whatever little plastic stand they come with.) Or use a "FPV camera" with separate analog transmitter from the RC plane/copter area. I'm using a CCD camera with a 5.8 GHz transmitter for video, which is a bit smaller and lighter than needing a separate computer/board for processing the video on the bot itself.

Finally, if you have a receiver for commands (Xbee, Bluetooth, RC receiver, whatever) then you need to also have something not-on-the-bot that sends those commands. Typically, this is a radio control remote for RC receivers, or a computer for Xbee/bluetooth, but it could be a custom controller such as the Arbotix Commander: http://www.trossenrobotics.com/p/arbotix-commander-gamepad-v2.aspx

Finally, if you just want a working hexapod and don't want to do all the planning and mistakes and re-work yourself, consider a kit, such as the PhantomX from Trossen: http://www.trossenrobotics.com/phantomx-ax-hexapod.aspx

Offline bdeuell

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Re: Hexapod project (newbie)
« Reply #8 on: December 19, 2013, 08:04:30 PM »
Herant,

My BOM is not complete yet but this is what I have so far:

http://www.orionrobotics.com/Intelligent-PS2-Remote-Control_p_300.html
http://www.basicmicro.com/ARC32_p_141.html
http://www.robotshop.com/en/gws-pico-std-servo-motor.html

Notes:

One of my objectives to design a very small robot.

To help with the software development I am planning to use the phoenix code developed by several members on the lynxmotion forum as a starting point (available here https://github.com/KurtE/Phoenix-Code). This played into my selection of a controller.

I am going the PS2 controller route over the Xbee because I wanted to concentrate on the robot and wanted an off the shelf controller solution. The one I listed however is not directly compatible with the phoenix code but I selected it for size. I have heard that some PS2 controller brands can be more difficult to interface with.

I am planing to purchase one of the servos to do some testing before purchasing them all. Power specs were not available for the servos so I am waiting to spec out the power system. However I am planning on using a LiPo pack, a charging board from sparkfun and boost converter (if i can make it work with my current requirements).

many of the mechanical components will be 3D printed as well (unfortunately I do not own my own) so I will have to outsource that. Still working on the design so I have not listed any of those parts.

I will likely add an IMU and maybe a camera eventually.

Offline jwatte

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Re: Hexapod project (newbie)
« Reply #9 on: December 19, 2013, 09:21:24 PM »
That looks like a 4.8V-6V servo. It would be unhappy with 1S LiPo (too little) and 2S LiPo (too much.)
You can drive it with a UBEC, but then you'd need a large number of UBECs for a large number of servos.

Also, the torque on the side is bad: 0.7 kg / 10 oz is not a torque specification. Let's assume they mean "kg.cm" and "oz.in" Let's say your longest lever on a small robot will be 6 cm, and that there will always be 3 legs on the ground. That means your robot body can, at most, weigh (0.7/6*3) == 0.35 kilos, which is not a whole lot. You may wish to consider stronger servos.

Offline bdeuell

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Re: Hexapod project (newbie)
« Reply #10 on: December 19, 2013, 10:43:56 PM »
I am aware of the voltage concerns, that is why I am planing on a boost converter. I don't want to hijack the thread but any advice on this would be appreciated.

The units are kg-cm and oz-in. As you pointed out the weight may be an issue and if necessary I could go with a larger servo but I would really like  keep this as small as possible. Some other solutions would be to preload the arms with springs or to use a gait where only one leg is off the ground at a time.

At this point I have no idea how much power these servos draw so I cant size the battery and the mechanical design is still in its infancy so I don't have a good weight estimate there yet either. My plan right now is to buy one servo to play with and continue the design and see where it goes. I may need to back off on my size constraints to make the design feasible but I like the challenge ... its what makes engineering fun.


Offline HerantTopic starter

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Re: Hexapod project (newbie)
« Reply #11 on: December 21, 2013, 05:16:09 AM »
Thanks for your help guys, atleast i know now which of the components i need onboard which will let me start designing the body :)
Btw does any of know about some good and strong servos with more "robotic" mount features which are not too costly and not so big like mine?

Offline jwatte

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Re: Hexapod project (newbie)
« Reply #12 on: December 21, 2013, 12:09:17 PM »
Here are some low-end robotic kinds of servos:
http://www.trossenrobotics.com/dynamixel-ax-12-robot-actuator.aspx
http://www.roadnarrows-store.com/products/move/servos/servo-herkulex-drs-0101.html
http://www.hobbyking.com/hobbyking/store/__27556__Turnigy_TGY_S901D_Metal_Gear_Digital_Robot_Servo_13kg_0_14sec_58g.html

They are not super small -- there is a size/performance trade-off where the really small stuff can't develop sufficient torque to be interesting for robots. The first two use some kind of serial communication (TTL UART) and also support feedback, whereas the last one uses regular RC-style PWM pulses for control.

They also are built to take a second "idler" horn on the back, so that you get better strength and not so much shearing force, which is mechanically important for robotic linkages.

Finally, the smallest robot servos I know about aren't quite on the market yet, but look like the best match for what your requirements are: http://www.robots-dreams.com/2013/10/robotworld-2013-robotis-posed-to-disrupt-robot-development.html

 


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