I thought I should share my latest project on Matt's forum too.
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 aluminium parts used on the 6 outer sections to 2mm for more strength and stability. And also some more stuff like an holder for electronics.
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.
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. 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.
All the six legs are finally assembled, 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, . 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:
Just for visualization:
This is one of my favorite pictures, it kinda remind me of the unfinished Death Star from Star Wars, 8) :
There are still a lot of work left but I'll try to keep you posted.