Lynxmotion Tech Support

I have an extreme quadrapod and would like to add a tail for dynamic stability. I'm not quite sure what parts from the servo erector set I need so I'm hoping that someone can provide some pointers. I want to put a servo in the top plate hole (after turning the plate around backwards of course) for side to side rotation of the tail, then use several servos hooked up together to curl into a circle that can expand and contract in diameter. Ultimately I want to have it in a scorpion configuration where the circle reverses near the tip.

Can anyone let me know which parts would be good for this?

Thanks!

Tyler

some were to start could maybe be a selection of SES parts like this:

http://www.lynxmotion.com/images/jpg/asb041.jpg

parts in this:
1x ASB-04 = Aluminum Multi-Purpose Servo Bracket Two Pack

1x ASB-06 = Aluminum "L" Connector Bracket Two Pack

1x ASB-03 = Aluminum "C" Servo Bracket Two Pack

or something like this with a weight on the end:
http://www.lynxmotion.com/images/jpg/misc/alurod01.jpg

of caurse if you really wanted to build a fully working model you could always google it and see how (robotraptor) from wowwee robotics have done thiers. also look at (pleo).

this sort of design can work with a single motor using pullys etc!

good luck!

_________________
Jonny Poole,
Freelance Concept Art & Animatronics, 3D Art and 3D Modelling, as well as Physical Modelling, Mechanical design, and illustration.
http://www.innerbreed.co.uk/
Create, Innovate, Inspire.

how is the quadruped coming along?

_________________
Jonny Poole,
Freelance Concept Art & Animatronics, 3D Art and 3D Modelling, as well as Physical Modelling, Mechanical design, and illustration.
http://www.innerbreed.co.uk/
Create, Innovate, Inspire.

I have also been experimenting with a quadruped (actually I am making my second) and I am going to try and add a tail.

So far I think your second idea is the better design. If you can take advantage of a pendulum motion for rocking it can help with the balance.

if the only weight the tail needs to support is itself then it could be interesting to use some of the new micro servos and ses brackets.

I think I'd add a head first. Maybe you already have a head?

Alan KM6VV

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Totally agree with Alan, head first!

It looks odd if it goes with a tail, but without a head. Then again, we don't want a head constantly looking left and right all the way

Another method you could use is to mount a servo in the middle, inside the body (can it fit?). The horn is to be secured onto the body, leaving the servo free. That way you could use the weight of the servo as weight.

For additional weight, best to use common steel screw and nuts, attached to the servo. Steel density is about 3x of aluminum. You can save the bracket for the head!

In my experience, the weight of the quad shifts in the opposite direction you are going. So if you are going forwards, your back feet tend to drag because your weight shifts backward. So, while a head is very functional for sensors, I would recommend doing a tail for the balance of a quadruped.

Just my two cents-- I am no expert.

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www.backyardrobots.com

What's your experience?

I can't say that I have any experience.

At best, there is a triangle of support, formed by the three legs on the ground. And the forth (lifted) leg lies outside of the triangle. The COG is often just on the side of the triangle facing the lifted leg. So a slight improvement would be to shift the COG in the opposite direction of the lifted leg. Is that the way you see it? I've been working out a simple two-servo tilt/pan head for my 'quad. Not much weight to it, and I don't see it (currently) making much difference in the COG. I've also struck upon an idea for a simple tail, a single servo (for now) that will wag a BlueSmirf antenna. Mostly for cosmetics!

Alan KM6VV

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Last year I tried putting a tail on two different quadrupeds, Fluff (an old crust crawler kit), and Sterylite, a kind of crazy but powerful quad. In both cases the reason why I tried it was to improve the ground clearance of the back legs. I try to get my quads to have good ground clearance on all four legs, but typically the back legs have worse ground clearance then the front ones.

I think this is because the robots weight shifts a little backwards going forwards and, more significantly, when you start going up an obstacle the body becomes slanted backward and the weight goes to the back legs. That's why I looked into tails instead of heads.

In both cases I created a tail that didn't touch the ground, it was just sort of a counterweight. On Fluffy I put a HS-422 servo in the back with some bolts on it to give it weight as it swung back and forth. On Sterylite, I put another quarter scale servo in the back facing horizontally and down. I connected an aluminum rail (like the ones I use for the legs) to the servo and had it swing back and forth. I taped weights to it to give it mass. Some time I should document this on my web page, it was just one of those things I tried quickly, although Sterylite still has that servo connected in the back, there is just no tail there.

In each case the counterweight tail seemed to help the back legs a little, but not necessarily more then just adjusting the leg height to put the weight of the robot more on the forward legs. I think you could get a much more dramatic effect if you had a really heavy tail, like if you put one of the main batteries in the tail. It also could have more effect if the tail actually touched the ground and became load bearing. That might require more articulation.

I really am just a complete amateur and guessing about these things, but I thought I would mention it because it seems like something I would like to learn about. I didn't see your post until I came back to this forum which I don't visit often.

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Any Pix?

I'm still thinking I need a head first!

Alan KM6VV

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http://tech.groups.yahoo.com/group/HexapodRobotIK/