I haven’t done many updates on Droid 2 for a while. Besides the Q85 drives, the work has mostly stalled due to other projects. However, I realised I haven’t done a post about the frame/leg kit I’m using and the extras that I’ve installed.
The basic styrene frame kit is from a UK run of the Media Conversions eggcrate frame. Its a very easy to put together CNC cut system, with slots to easily align everything. You can do a dry fit of the frame in a couple of hours, and then just apply DCM to solvent weld it.
Following the instructions wasn’t enough for me tho, and from looking at a lot of droids over the years I have come to know where the weak spots are on a droid. These are the ankles, shoulders, and especially the center foot. Styrene droids especially suffer from delamination at the shoulder on the leg. I wanted to make sure I combated these issues as much as possible.
To do this, I have inserted aluminium plate and extrusion in key areas. Nothing fancy or CNC’d, just something that can be cut out by hand if you wanted to. I used my bandsaw to cut everything.
To start with, the frame. First issue was that I wanted to do was use a set of aluminium skins that I had. Unfortunately with a styrene frame the skins are structural and stop the substantial twist that occurs without them being bonded to the frame. So I needed something to stiffen it up. I use aluminium extrusion for this, which also does double duty as a holder for my electronics board.
Also, when the center foot hits something and stops, then a lot of stress is sent up through the ankle into the frame as you have pretty much the entire weight of the droid concentrated at that point. To help with this I installed a large aluminium plate at the bottom of the frame, and attached it to the aluminium extrusion. This helps transfer the load quite nicely.
With the ankles, its less about the stresses of the droid (tho there are still plenty) and more to do with the wear that happens on the pivot points. Especially with the outer ankles. The standard styrene build uses many layers of 3mm styrene layered on top of each other to create the right thickness. So I took two layers out and replaced it with a sheet of 6mm aluminium, cut to the same size.
Shown here is the center ankle, but the same applies to the outer ankles which are part of the leg structure.
As well as strengthening the ankles, this has an added benefit of improving the center of gravity, adding more weight down low. Coupled with steel foot shells and heavy drives it should make the droid pretty stable.
The shoulders are still an area I need to improve on. Currently the best plan I have is large washers to help spread the load out a bit, but ideally I would’ve added something more substantial if I’d thought about it before constructing them.
All in all, I’m very happy with the strengthening. There is zero twist in the frame even with no skins attached, the ankles feel super solid, and the whole droid has a nice low center of gravity. I just need to find time to finish it now!