Rhex

Let's Make Robots Robots
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I definitely want to build a 6 legged Rhex robot. Below are some drafts I made today with Sketchup. 6 standard servos HS-325, a LiPo battery, two Sharp IR distance sensors and a tilt switch. 2011.2.14I thought about how to synchronize the legs of my Rhex robot. I want to use servos, no kind of

This is a companion discussion topic for the original entry at https://community.robotshop.com/blog/show/rhex
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Would servos be fast enough

Would servos be fast enough for this? 

3

Nice looking! I have a

Nice looking! 

I have a question though, won’t you need simple encoders for the servos to be able to stop them when the tip of the “leg” (what is the proper name for that?) is nice on the ground, like in the pictures? Or to make sure the legs are sincronized?

Make sure you waterproof the beast, then you can have it cross the pond and climb over the rocks on the other side… That would be cool!

4

They are just turning around

They are just turning around like wheels, no encoders or synchronization planned yet. I’ve an idea how this could be realized with a special modified servo.

Here is an interesting video with slo mo leg movement: http://www.golem.de/1101/80988.html

Always 3 legs are synchronized.

 

5

Prototype This!
A show that aired in the US for about 8 episodes attempted almost the exact same design w/o success. I believe part of the problem was speed and position.
http://dsc.discovery.com/videos/prototype-this-six-legged-atv.html
I believe they modeled their attempt after a version about the size of what you are attempting and I am pretty sure it functioned. I would not know where to find a link to a video for it though.

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I think you would be better

I think you would be better off with using stepper motors. It seems to me that speed is crucial to get the foot back into position for the next ‘step’.
With stepper motors you have absolute control of speed and position. I would take it even further and see if there is a way to link three ‘feet’ with timing belt. This would give you absolute synchronization of three by three feet running from two steppers.

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Hi Geir,Yes, I also thought

Hi Geir,

Yes, I also thought on a belt connection, but also with stepper motors only you have no absolute control of position. You need a kind of feedback regarding the current position. Even with a stepper motor the position could be unintended changed (for example if one leg hit an obstacle).

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You could probably get away

You could probably get away with only one mark on the encoder to recalibrate the stepper and do a recalibration on every rotation. I would place the encoder mark on the very top position of the rotation, then you will be in control again for the next foot down.
With the belt configuration your legs will still be in sync.

9

Rhex is a great inspiration for locomotion experiments

For anyone who is not aware of the original Rhex that inspired Markus, I highly recommend a visit to this page and this one and of course wikipedia.

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The main properties that inspired me are:
- legs are compliant (they are springy): the compliance has been methodically tuned for their purpose;
- one motor per leg;
- one rotational, absolute encoder per leg;
- gait (leg synchronization) controlled by central brain;
- gait dynamically changes with circumstances and mission;

I'm speculating that a different kind of sensor (flex instead of rotation) would be advantageous to the energy efficiency of the gait. But if it would be easy (or even doable), I'm not sure.

10

I have always wanted to make

I have always wanted to make one of these. I will have to see what you come up with :).

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** Collaborative project?**

Hi Patrick,

I also will have to wait till DAGU manufactured my servo. This will make it mutch easier to build a Rhex. Are you interested in a collaborative project?

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**intersting rip off **

Hi guys im new here and havn’t even made my first robot yet :frowning: anyhow I began this new interest when i was looking at the boston dynamics website and my jaw hit the flaw when i saw what these guys are doing and loved the rhex! Anyways i stumbled across a kids robot kit thats isn’t realy a robot but its a rip off from the rhex! maybe you can even hack this thing and save some time! It has more like an s shaped paddel that it walks on maybe this is to solve thoes timing problems you guys ae talking about, anyhow heres the link…enjoy

oh and i would love to here about any developments you guys have come up with on this thing…love it, so simple but effective!

https://www.robotshop.com/roboxplorer-multi-terrain-robotic-toy-vehicle-2.html

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RHex Legs

can anyone tell me, where can i Buy these legs. I need them urgently to finish my project. Please Help.