Metal Skull Robotics Hexapod Project

Hexapod Robots

Metal Skull Robotics Hexapod Project

Postby MetalSkullRobotics » Mon Jun 09, 2008 11:55 am

I decided to start my own topic about the hexapod I'm planning to build. Will start from the beginning.

I'm a 18 year old boy from the Netherlands who's interest in robots started at young age. Since my 13th I'm very active in a other robot hobby, the combat robots. I have build lots of there and the past 2-3 years I started making parts/designs for other people and made money with this. (Metal Skull Robotics (MSR) will soon be registered as official company) The combat robots aren’t really robots the way I look to it, its just a big remote controlled "thing".

For quite a while I have been thinking of building a hexapod. This was only limited by the amount of knowledge I have about electronics and programming. The past couple of months I have been busy with electronics itself, mainly programming AVR's and making small circuits with their chips. I think my knowledge about the electronics and programming is sufficient for the hexapod itself (it’s the electronics what concerns me, not the mechanical part).

Like I said the robot I'm building will be a hexapod. Six legs with each 3 servo's. The servo's I will be using will be "standard" 3kg at 4.8V servo's. My calculations tell me it will be just enough for the robot to lift itself. If not I don’t really care, the standard cheap servo's (3 dollar each) give me the opportunity to figure out the programming. If I can simulate the basic movements of the hexapod I'm willing to invest in the more expensive powerful servo's.

I'm planning on making the electronics myself by using a total of seven AVR's. One for each leg and one to control the others. I want to have preprogrammed routines in the individual AVR's that will be activated by the main AVR. This way the main AVR gives a signal to take one step forward, and the other six AVR's will make a loop in which the leg makes the appropriate movement.

The design itself is inspired allot by other people. Especially from what I have seen on this forum. The main frame and the servo coupling will be machined from 6mm aluminum. The other leg parts will probably made from 3mm carbon, this because its easy for me to cnc-machine where as the aluminum parts will need to be cut by a sponsor of mine. The whole robot will be like 30*30*17cm's and weighing around 1.8kg's (including a 7.2V 3000mAh Lipo battery).

Last but not least some pictures of the design I have so far. Please comment!

Image
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Re: Metal Skull Robotics Hexapod Project

Postby Matt Denton » Mon Jun 09, 2008 9:49 pm

Interesting coxa design. I presume you plan on mounting your battery on top?
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Re: Metal Skull Robotics Hexapod Project

Postby MetalSkullRobotics » Mon Jun 09, 2008 10:00 pm

Nope, the battery will be mounted under the robot against the bottom circuit board. I'm planning on keeping all the electronics inside of the main chassis.

Here's a detailed picture of the Coxa.
Image

I also made some minor changes to the design of the Femur and Tibia.
Image
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Re: Metal Skull Robotics Hexapod Project

Postby MetalSkullRobotics » Mon Jun 16, 2008 9:52 am

Yesterday evening I was bored so I grabbed some components and start building something. Came up with the MSR-Bug.

[youtube=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/lmYjNWCDYUQ&hl=en"></param><embed src="http://www.youtube.com/v/lmYjNWCDYUQ&hl=en" type="application/x-shockwave-flash" width="425" height="344"></embed></object>][/youtube]
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Re: Metal Skull Robotics Hexapod Project

Postby MetalSkullRobotics » Sat Jun 21, 2008 3:13 pm

After some redesign and programming I came up with this robot.
[youtube=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/k2Ng76VI3Ho&hl=en"></param><embed src="http://www.youtube.com/v/k2Ng76VI3Ho&hl=en" type="application/x-shockwave-flash" width="425" height="344"></embed></object>][/youtube]
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Re: Metal Skull Robotics Hexapod Project

Postby MetalSkullRobotics » Sat Jun 21, 2008 7:01 pm

I just made a video where the robot is walking.
[youtube=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/rp_ZWkBIOcc&hl=en"></param><embed src="http://www.youtube.com/v/rp_ZWkBIOcc&hl=en" type="application/x-shockwave-flash" width="425" height="344"></embed></object>][/youtube]
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Re: Metal Skull Robotics Hexapod Project

Postby robotguy » Sat Jun 21, 2008 8:29 pm

MetalSkullRobotics wrote:Nope, the battery will be mounted under the robot against the bottom circuit board. I'm planning on keeping all the electronics inside of the main chassis.

Here's a detailed picture of the Coxa.
Image

I also made some minor changes to the design of the Femur and Tibia.
Image

I basically like your leg design and the fact it can use standard servo horns. I would have oriented the hip horizontal servo to where the long side with servo horn points inward toward the body. I like a bit more length for legs. I need to design legs for my octapod.

8-Dale
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Re: Metal Skull Robotics Hexapod Project

Postby paulp » Sun Jun 22, 2008 2:05 am

MetalSkullRobotics wrote:Nope, the battery will be mounted under the robot against the bottom circuit board. I'm planning on keeping all the electronics inside of the main chassis.


A note of caution. I had an incident with a bad charger and an exploding cell a while back. Unfortunately, like yourself, my design had the cells mounted close to the underside of a PCB and it burnt a hole through the PCB. I always make sure now that there is a layer of 2mm Polycarbonate over any exposed PCB area now. It will stop the damage and also helps protect against clumsy handling.

My next design had a screen of PolyCarb all round the battery pack but that only served to keep the heat in when charging and dis-charging. Ventilation is a must.
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Re: Metal Skull Robotics Hexapod Project

Postby Tony » Thu Jun 26, 2008 7:54 am

The whole robot will be like 30*30*17cm's and weighing around 1.8kg's (including a 7.2V 3000mAh Lipo battery).


When I was at your age, I don't know windows, robots, even now I don't know what is AVR :lol: Good work, share my experience with you...

Mine is at same size, weight is 3KG, I do not use futaba servo by replacing a much cheaper one with 9KG/cm torque, after I change power cable and 6V 4500mAH battery, it could only make it stand up. I tested the servo torque and no problem found, so no problem on servo, on power, on cable... but Paulp's hexapod even can jump from the table with 6KG servo and approx. 2.5KG weight. Matt's hexapod can lift with only 4-5 legs, I don't know where the problem is but, I am sure your 3KG servo can't make 1.8KG hexapod lift. you can test it your program.

Wait... is the problem on Lynxmorton PCB power connection?
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Re: Metal Skull Robotics Hexapod Project

Postby cyberdead » Thu Jun 26, 2008 11:49 pm

Hy Metal,
I'm working on my own robot (octopod), and i'd like to know how can the 3kg servo lift the robot? How did you calculate? I'm asking because, after my calculations with 3 kg servos and with the robots 1 kg total weight, the needed torque is almost at the limit. So i'd like to know if my calculations are bad, that would be good news for me (used inverse dynamics, on a simple modell) :)
Yeah, it's far from the final state:P

Pete
Last edited by cyberdead on Fri Jun 27, 2008 5:42 pm, edited 1 time in total.
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