So, after Legoland in May, and again at MCM Manchester, R2’s wheels have been scrubbed clean of all tread clear down to the plastic hubs. The first set of Banebot wheels lasted a year so after Legoland I just replaced like for like, thinking they’d last another year.
A lot of other builders use Colson wheels, so I went on a hunt for them. Now I’d got his center omniwheels from Vex Robotics, and they have a whole line of wheels and accessories so I went looking through their website.
What I found there was a system using hex shaped axles, rather than the current round ones. This meant a more even transfer of force from the drive cog to the wheels. With the round shaft, all the torque was through the keyway that was cut into it, but there is no need for that when the shaft is hexagonal.
A quick order online (well, two as I forgot to get new bearings) and a UPS delivery, and the new hardware was here. Everything on the drive shaft had to be replaced, including the cog, to make use of the hex shaft. It didn’t take long to press fit it all together and now R2 has a nice new drive system.
One down, one to go. Also working on a better system for having the battery boxes attached to the foot shell, as it is a real pain to remove them which is needed to get the drives out.
As mentioned in my previous post, R2’s current main upgrade is to the center foot. The main parts to improve are the wheel, the shell, and the ankle attachment to the body. Improving all these should give a much smoother ride.
Originally, the center foot had one large castor that swivelled on a mount. The main problem with this is that a) it has to swivel to change direction, and b) because of that the wheel needs to be smaller to allow the change of direction and not hit the foot shell.
With the new Omni wheels from Vex Robotics, there is no need to have any swivel built in as the wheels can roll in any direction smoothly. This also allows the use of much bigger wheels which gives a smoother ride and makes it easier to get over obstacles. The wheels were mounted into a custom chassis that I made from sheet and square tube aluminium which gave a very solid ride. (See this blog post for more info) This also mounted directly to the ankle to make the whole system more rigid.
The foot shell I had in place was one I received near the start of my build, and was never particularly happy with. Recently a member of the UK Builders Club, Mark Leigh, started making some new steel foot shells for members and I decided to fork out for a set. I’m very glad I did as they are excellent quality and up to club spec.
There are a number of benefits to the new shells. For one, the side panels come off which allows for easy access to the main ankle bolt which was a major limitation of the previous one. Also, all bolts could be tightened up with allen keys or screwdrivers whereas before a lot of them could only be done to hand tight, and even then it was very awkward.
Lastly, the new foot shell is no longer structural, with the shell, ankle, and wheel chassis all being mounted via the same bolt. Previously the castor was attached to the shell, which was then attached to the ankle. When I removed the old foot, there was a lot of wear and potential failures waiting to happen.
This improvement should never really have been needed if I’d done the job properly in the first place. The ankle is bolted to a plate which bolts through the body into the skirt. When I initially did this, I didn’t make sure the plate was a consistent level, and didn’t have all the bolts done up properly. This led to a lot of wobble and eventual failure of one of them, and then a temporary fix.
This time however, I made some decent spacers all the same length, and bolted everything through them to R2’s skirt (a new aluminium one, but that doesn’t really make a difference, would work fine with the old fibreglass one).
After all this, R2 was feeling rock solid, at least as far as the center foot is concerned.
This weekend R2 was at NWCC Bolton which was going to be his first big test on the new foot. The night before the event, the organisers posted a picture of the hall where everything was taking place and it got me a bit worried. It was a fully carpeted venue. The only part that looked like a hard floor was a little bit infront of the bar where they had the arcade games lined up.
With the old foot, this would have been pretty much a show stopper. However, I got there and unloaded R2 into the hall and turned him on for a test.
Wow, what a difference. At his last event at new year, R2 had great issues being on carpet and I had to push him a fair bit. This time however, not a problem at all. I even got brave and tried going over the transition from hard floor to carpet, and he didn’t miss a beat or slow down. Even going over door thresholds with barely a judder.
This has got to be one of the best upgrades I’ve given R2 since I got him working. I’m so pleased with it all and would heartily recommend Omni wheels for any astromech. Infact, I’m currently wondering if I should replace the castors on the main drive too.
Of course, it wasn’t just the Omni wheels that made the difference, a combination of all three improvements contributed, but I do feel that the wheels made the majority of it.
The main issue R2 has at the moment is a rather dodgy center foot. For a start off, the shell is actually structural which I don’t like. The shell is also not the best, with no easy access to remove the center foot without a full dismantle which isn’t easy.
So R2 got some new foot shells made up, and I started work on a new set of wheels to fit in them.
Based on a design by another builder (Youtube video of them in action), the chassis for the wheels is made out of plates of aluminium with some square tubing for spacing. The wheels going into them are 4″ Vex Omni Pro ones, which allow movement in all directions, not just forwards and back. Much better than a caster as it doesn’t have to swivel when changing direction. Also allows for larger diameter wheels which helps getting over bumps.
This chassis will be bolted directly to the center ankle, and the foot shell will more or less just be floating on top. This, coupled with a few other modifications and tweaks, should make for a much more steady ride with less rattles.