MorpHex part 1
Posted on 19 November, 2010
A new project called MorpHex
This is a project I’ve been thinking on for a very long time. Shortly explained this is a sphere shaped hexapod that I plan to give the following features:
- Roll freely like a ball
- Have different sort of locomotion for moving in any direction
- Variable inner-body dimensions
- Transform from a sphere shape into a hexapod and vice versa
- Walk like a hexapod
Before I started to make any exact sketches or started building anything, I shared my ideas with my friend Jeroen Janssen (Xan). We talked about this project when I visited him in Netherlands this summer. At first I was thinking of using a fixed sized inner body with 6 x 4 DOF legs, similar to what I used for the T-Hex hexapod. Another problem was finding a sphere shaped material that I could use. Jeroen and I went to a local toy-shop and I just asked him to look for ball-shaped object. After a little while Jeroen had found a globe! At that moment I got the feeling that using a globe could actually work. After a few months and some searching in different book and toy-shop’s I found a 28cm in diameter globe from Toysrus. It was also cheap and the plastic material seemed to be relative solid (about 3mm thick).
I’m cutting out 12 identical sphere parts. Using a simple handsaw and cutting along the lines of the Longitude every 60 deg. The line of equator was made of 1mm thick dark blue plastic band and was very easy to remove, that resulted in a perfect clean edge too! Here are some pictures of the sphere parts:
The map coating was very easy to peel of. The trick was to preheat the surface carefully and then start in one corner and just peel off the whole layer. To the left is the original part. The middle part has the globe/map layer peeled off and the right part is sanded by hand.
As you can see the material is very transparent, I do have some future ideas of mounting several LED’s for some cool lighting effects:
The principle is very simple. I’m using one digital 5645 servo in the centre of the body, the servo holds two delrin gears:
I’m using 7x of the LPA gear sets from Lynxmotion. One gear with SES holes is mounted to each of the 6 outer body sections.
This construction makes it possible to adjust the body dimension by about x2 using only one servo.
The main reason for making the body like this is to hopefully make some more free space for each leg when the robot are in the walking mode. Even with the increased body size, the legs are still going to be highly restricted in free motion caused by the large sphere parts, but I think it will work 😉 I’ve already done some changes to the body section, like replaced the 1.5 mm aluminum parts used on the 6 outer sections to 2mm for more strength and stability. In addition, some more stuff like a holder for electronics.
There is still a lot of work left and I’m currently working with assembling all the legs. In total there will be 31 servos, 12* 5990 + 19*5645.
I’ll post more info when I’m finished with all the legs and have some photos.
To make Morphex being able to curl up into a ball shape, I’ve decided to go for a little special leg design. Actually, MorpHex is a sort of dual hexapod, where one leg share a common coxa part with two femur and tibia parts.
I’m using standard SES brackets, but pay attention to the ASB 15 v2 bracket that holds the two femur servos. The v2 bracket is just perfect for attaching the ASB-04 coxa bracket.
5990’s are used for the femur and 5645’s for the tibia and coxa.
Notice that the 5990 wires are guided through the 8 mm bearing/SES hole between the ASB-15 v2, LPA lexan spacer and the ASB-04 coxa bracket.
Since my first post about this project I’ve replaced the outer body parts from 1,5 mm to 2 mm thick aluminium, mainly for increased strength and stability (less flexing):
Making sure that every gear is aligned correctly was the hardest part when assembling the body section. I solved it by carefully placing one gear at the time and mark the 4 SES holes on each outer bodysection, remove the section, drill the holes and mount the section onto the inner body section again. I repeated this process for all the 6 sections.
Instead of using 3mm steel hex screws for holding the 12 ball-bearings onto the inner body I’m using 3mm threaded rods. The rods make it much easier for mounting a holder for battery and electronics.
Finally, all the six legs complete, the next step is to mount them to the body:
MorpHex, taking form
I know it looks kinda messy right now, but I do have plan, LOL. This picture show all legs mounted to the body and the upper part have their legs curled up into the ball shape position.
Another picture illustrate MorpHex in the walk mode position:
I’ve fixed some sphere parts with velcro just for giving you a little hint of how MorpHex are going to look like with all the sphere parts mounted:
I might have to modify the feet a little bit (using smaller end caps and modify the ends of the tubes) so that they can be aligned even closer in the curled position. But these pictures illustrate how it’s going to look like at the end:
This is one of my favorite pictures, it kinda remind me of the unfinished Death Star from Star Wars, LOL:
Its been awhile since I posted anything about MorpHex. I’ve not got much time for it either. Sadly this has to be a longterm project.
Anyway, I just wanted to post some minor updates. I’ve added two decks (acrylic, I’m not sure to be honest) that are going to hold the electronics on one side and the battery on the other side:
Still a lot of work left. But that’s kind of good thing since I’m strongly considering to build a humanoid using the 5990’s, meaning that I’ve not wasted too much time.
It’s much easier to work on MorpHex when you have a strong stand:
One big challenge was to guide the power wires from the battery from one side to the other due to all the gears and the outher (variable) body parts. I solved it by carefully drill a hole through the battery-deck and inserting two brass tubes:
The power wires are going to be guide through these brass tubes. The tubes protects the wires from being crushed between all the gears. That would be very messy using LiPo power.. 😆
Picture of the battery-deck:
First teaser video of MorpHex
Recently I had to make a hard decision. I’m not ending the project, but there are some issues that has bothered me for a while. The fact is that I’m afraid MorpHex is just a little bit too heavy while being in sphere mode. Another thing is the wires; a total of 36 (x3) servo wires gets a bit too crowded in the center of the body. For reducing total weight, I’m using a simple 3 DOF leg not the double femur/tibias. Instead, I plan to mount 6 servos on the top deck for manipulating the six upper half spheres. At this moment, I’m using 5990’s on the femurs and 5645’s on the tibias. The 5990’s are directly power by the main 2S (7,4v) LiPo battery. The other 13 5645’s are powered using one Turnigy 8amp (max 15 amp) switch regulator. I’m also planning to use 36 Starlites from BasicMicro as background light inside the sphere. The Starlites require an additional regulator; I’m using a 3 amp switch regulator (also Turnigy).
I’ve also decided to go for one single ARC-32 board from BasicMicro for commanding the servos. Also a XBee module and a Razor 9 DOF IMU running AHRS code for getting accurate orientation in sphere mode.
Here is a short teaser video of MorpHex (not yet completed). The main goal of this video was to demonstrate the morphing body part.
For making the hexapod work with a variable sized body there are some math to do, simple trig (law of cosine). The input value to the math algorithm is the angle of the inner body servo. Then you’ve to calc the new bodyradius and a new coxaoffset. When you have the body radius its pretty easy to find the new body dimensions (coordinates) for a circular body.
After that, you need to adjust the positions of the feet corresponding to the new body radius. In the walking gait you can re-set the initial positions when the leg is lifted.
Next step is to work more on the code (sphere mode) and start mounting the actual sphere parts.
End of page. Read more on the MorpHex part 2 page.