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.

 

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.

 

MorpHex MKII

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:

MorpHex

MorpHex MKII:

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As you can see, the sphere sections are reinforced using some T-shaped aluminium 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 aluminium 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 section before I monted 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..

 

 

 

 

 

The FireAnt hexapod robot

A couple of months ago I got the FireAnt kit from Orion Robotics. The FireAnt is based on my A-Pod design and made from red anodized aluminium. My first impression was very good, all parts have a great quality with a fine brushed finish. Assembling the robot was an easy task when following their very detailed assembly guide. One of the major modification I did to the FireAnt was to make a new 2DOF joint for the abdomen (tail). The reasons for doing this was to make the abdomen work as a battery holder and for making the 2 DOF joint more compact and similar to how I did it on my original A-Pod. By comparing these pictures you'll see that the modification only involve one custom made part:

Orion Robotics FireAnt:

fireant_iso_twist_small800600

The modified FireAnt abdomen 2DOF joint:

FireAnt004

Compared to the original A-pod:

A-Pod

Initially, the 2S 2200 mAh LiPo battery was ment to be placed under the mcu boards inside the main body. When it comes to LiPo batteries I like to charge them in a safe area. This mean that it should be easy to replace the battery. By placing the battery inside the abdomen, replacing the battery isn't a problem anymore and you get more free space under the mcu boards for servo wires etc. I've also used some shorter standoffs for lowering the boards. The new digital HV-220 servos are fitted with a very long servo wire and thats a relief when it comes to the tibia servos. That also makes it easy to guide the wires without the need for extending the wires.

I'll take some better pictures of it when I've uploaded and tested the software. I'll post more information about the mcu boards and the servos later.

FireAnt002  

As you can see I'm using two power switches; the rear switch is the main switch for both electronics and servos, the front switch is for the servos. Personally I prefer having a separate powerswitch for the servos.

The mcu boards are programmed through an USB cable, unfortunately the usb port on the DaVinci main board is a bit hard to reach every time you need to update the software. I solved this by using a mini USB roll-up cable that is permanently connected to the board. I placed the roll-up holder inside the abdomen as well:

FireAnt003

FireAnt005

Like I said, I'll give you some updates when I've tested the software for the FireAnt.

Morphex III Becomes Boca Bearing Company’s Innovation Contest Winner

MorpHex

A few days ago I got the great news from the Boca Bearings company that my contest entry won their grand prize! More information about the contest results can be found here. 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.

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 MK2. Or maybe I should call it Mark 3.. 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 the 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 the new brackets here:

MorpHexMkII_04

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 come in the future.

-Zenta, "Having fun with robots".