Zenta Robotic Creations

Advanced hobby robotic designer

MorpHex MKII

Posted on 2 January, 2013

MorpHex Becomes Boca Bearing Company’s 2012 Innovation Contest Winner!

badge-april

A few days ago I got the great news from the Boca Bearings Company that my contest entry won their grand prize!  I do feel very honored for getting a prize like this. I’m also very humble thinking of all the other great projects that was submitted to contest. One of my favorite projects was the human powered helicopter, a very impressive achievement indeed.

 

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As you may have noticed I’ve not had much time for updating my blog lately, its mostly caused by little free time. When it comes to the MorpHex project I’ve done some progress on the next version of MorpHex, called MorpHex Mark II. Or maybe I should call it Mark III.. You see, I’ve had a few setbacks lately. I earlier mentioned that I would try to go for a fully symmetric version and using a completely different leg design. I did some progress on that attempt, but after a while I realized that it wouldn’t work under one critical condition; transforming from ball to hex. Here is a rather low quality picture of a very different coxa with dual femurs I made under this attempt:

 

MorpHexMkII_02

 

 

After a lot of thinking I came to a decision of going for an asymmetric design again. To be honest I don’t think a symmetric version of MorpHex would be very appealing. You see, a symmetric design mean that the upper and lower leg sections share the same coxa servo. So when walking the upper sections always need to follow the lower legs. An asymmetric design where the upper section can keep the half sphere shape is something I really liked with the first version. So this time I’m going for an upper section with 2 DOF. I do hope this will work better.

So far I’m still working on assembling the lower leg sections. I’m using a slightly different coxa design (don’t have any pictures ready for that yet) and a tibia bracket that are going to make the sphere sections much stronger. A picture of some of the new brackets here:

 

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There are still a lot of work left when it comes to hardware assembling, calibration and programming.

Again, I want to thank Boca Bearing for the very generous prize! Hopefully many more robots to come in the future.

-Zenta, “Having fun with robots“.

 


 

Posted 17.03.2014

It has been a while since my last post, actually one year! Ouch..

The reason is that I’ve been occupied with many other projects and family life.

But I’ve got some free time now and then in the last couple of months. So I thought it was about time to make an update about the MorpHex robot. I’m calling the new version MorpHex Mark II (MKII). At first glance the MKII would probably look almost just the same:

 

MorpHex MKI:

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MorpHex MKII:

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As you can see, the sphere sections are reinforced using some T-shaped aluminum brackets for supporting and holding the plastic (PC) sphere sections. This made a huge difference when it comes to rigidity. On MKI I struggled with the fact that the plastic sphere section was to flexible and I had to reinforce the edges with ribs. The problem was the ribs kept getting loose (the PC glue wouldn’t hold), so I had to do even more improvements. On MKII the ribs isn’t really needed, simply because of the aluminum brackets that is shaped to match the inner part of each sphere section perfectly. I did spend some hours in the workshop fine-tuning the bending tool to make the bracket fit.

The main challenge with MKI was that it wasn’t able to roll in a straight line of path, only in a curved direction. I believe the main reason was the constrained motion of the upper sphere sections. Having only one DOF (degree of freedom) or only one servo motor for each of the six upper sections made it very challenging. It might be possible to make a more complex linkage system that gave the upper sections a better motion when rolling. Not sure how though..

I therefore decided to use two servo motors on each of the six upper sections. Having 2 DOF would make it easier to control, so that the upper and lower sections move in a symmetric motion.

A picture of MorpHex MKII pushing out both (upper and lower) sections:

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The challenge was to make the motors fit inside the upper section without getting in conflict with the electronics. A picture of the upper sections before I mounted the plastic sphere sections:

MorpHex upper section

 

 

Compared to the leg section, the femur and tibia sections are mounted very different. One advantage is that the servos in the upper section draw very little energy when holding the ball shape. To make enough space for the upper sections I also had to make new leg sections.

All these hardware updates also made MKII a lot heavier. So I’ve had to upgrade the servos to 24x HSR-5990TG (all femur and tibias), 6x 5980-SG (coxa) and I’m still using the same HS-5645MG (inner body servo).

The code is still a WIP (work in progress), but I’ve done good progress lately. And this weekend I made MorpHex MKII roll again! I’m not 100% pleased with the result but it looks promising though.

Some new pictures:

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As you see, the new upper section has a lot more freedom.

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I’ll probably make an optional rolling feature using this posture:

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Hopefully I’ll soon post some new videos..

 


Posted 18.03.2014

MorpHex MKII video

Yesterday I made a new video for demonstrating some of the new features of the MorpHex MarkII hexapod robot. Like I wrote in my last post I’m still working on the code. I’ll try to post more info about the code later.

Meanwhile I hope you enjoy the video.

 

 


Posted 13.04.2014

MorpHex MKII, a short outdoor test

Five days ago, we (I and two of my youngest kids) did our first outdoor test on a basketball court. It worked fine and I was able to control it very well, rolling straight, to the left and right!  It’s just like driving a RC car.

Compared to the MKI the rolling method by pushing out only one section didn’t work very good. The reason was that the sections are a bit heavier on MKII, so when pushing out one section the “ball” tends to roll towards the opposite direction as I want, this method work for rather slow rolling though. But the best approach was to push out the opposite sphere (the other side of the globe) at the same time to sort of keep the ball in balance. This method proved to be more effective, it moves more like a tread, kinda..

Still some tuning to do on the code.

I gave my 8 year old son my phone to shoot a short video of MorpHex for you on the forums, so it’s a bit shaky. It’s live sound this time and unlisted. I want to make a better video when going public on youtube though.


Posted 17.04.2014

Outdoor footage of MorpHex and a servo failure

Two days ago I did a second attempt to make a new video of MorpHex outdoor. This time I wanted to see MorpHex rolling down a short slope. I think this is the first time I’ve ever seen a hexapod robot rolling downhill. The outer sphere sections protects the inner parts of the robot very well.

To be honest, not everything went ok during the filming. 5 seconds after 3:31 on the video the inner body servo broke down!

 

I’ve had a bad feeling for this servo for a long time now. I did think of replacing it when I made the MKII version, but for saving time I didn’t.. sigh..

This was a major set-back since my plan was to demonstrate some other features as well. Currently I’m home alone, because my wife and our 3 kids has already left for Easter holidays. I’m going to join them tomorrow though. This meant I got much free time for playing around with the new Teensy3.1 on a breakout board designed by Kurt Eckhardt. I’m thinking of using this board on several of my robots in the future. The Teensy3.1 feature the latest ARM Cortex M4 processor. Also having connectors for the Robotis servos, a holder for XBee RF communication and a speaker make this board just perfect. Thanks Kurt! You can read more about Kurt’s Teensy 3.1 breakout board on the Trossen Robotics Forum.

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FYI, I’m not using the new board on MorpHex yet..

Instead, I had to spend about 10 hours in my workshop for resurrecting MorpHex.

On this picture (from the bottom side of the body) I’ve removed the LiPo battery holder and marked the white Nylon gears just to be sure..:

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Removed the “body-arms”. As you can see, the screws that hold the Hitec HS-5645MG servo is a real pain to reach:

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After removing the servo, I opened the servo case just to confirm that one of the brass gears was broken:

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Luckily, I have several spare Hitec HSR-5990TG servos. They are much stronger and feature gears of titanium. FIY, the Hitec HSR-5990TG servo are discontinued. Some years ago, I bought about 40 of them, used but in good shape and for a very good price.

The new servo in place!:

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So far so good? No. At this point, I found another problem. You see, the main reason for why the servo broke down was that one of the screws that hold the pairs of “body-arms” loosened after a while. To improve this I had to remove all the arms again and remove the upper sphere section and the ARC-32 mcu board. Believe me, this made me very frustrated. What a mess!

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As you can see from the picture below, the screw marked with a red circle became loose and came in direct conflict with a fixed part of the inner body. On the head of the screw you can see some scratches, actually this was more visible on the fixed body part of aluminum (no pictures of that). The solution was to use inset screw (the red arrow) and using Loctite this time:

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I do not think I’ve explained this before. The upper section are mounted to the inner body part using only three 4M screws (marked with arrows and a circle on the next picture). All in all, it’s a pretty simple task to mount.

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After assembling and recalibrating the inner body servo, I only had to do some minor changes to the code and MorpHex was working fine again!

My next upgrade might be the new Teensy3.1 board. However, that require a lot of work on the code, not sure if that is my priority #1. I’ve some plans for a new robot too..

 

End of page. Read more on the MorpHex MK III page.


 

 

 

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