Motor Movement!

Well, the connectors didn’t turn up on Saturday, but they did turn up today! So after a bit of crimping, and a bit of soldering (and a few mistakes, but we won’t go into that) I had a couple of cables made up to allow me to connect the Q85 motors to the ODrive.

Here is one of the sets of cables. They consist of the red wires in the back that go to an MT60 connector that carries the main signal to the motors, and then another bunch of wires that come from the hall effect sensor that is embedded in the motor. This tells the controller where the motor is in its cycle, so that it knows which coils to energise.

Also needed were some capacitors across the sensor terminals to cut down on some noise. Instructions for doing this are here: https://discourse.odriverobotics.com/t/encoder-error-error-illegal-hall-state/1047/7

With all that in place, I gingerly powered it all up and set about calibrating everything. I followed a guide on the main astromech forum, along with the odrive guide for hoverboards (same principal as driving an astromech it seems). It took a bit of trial and error, that I’m hoping to iron out into a proper tutorial at some point, but the motors were eventually running!

The mixing that I’d done in software all looks like its working as intended. I can also bump the speed up incrementally, as I can with R2, but with a lot more control and accuracy.

I do need to change the ramping settings on this, which I may even make changeable on the fly from the controller. Also the multiplier may need some tuning to set top speed, but that will require some testing in situ. I need to push my changes back into github, and make sure that R2 still works with the new code.

I think this brings the electronics to a good resting place for now. Just going to tidy up some of the cabling and add a volt/current meter. Its time to concentrate on making the actual droid. So this weekend it will be time to don the breathing mask and start glueing everything together.

Droid number 2 on its way

I’m going to have to give it a work in progress name, but its a bit difficult without even knowing what dome I’m doing!

But anyway, I picked up the CNC’d styrene kit at R2UK this weekend, and decided to get a picture of everything I’ve gathered so far:

So here you can see:

  • Styrene kit, which includes:
    • Frame
    • Skins
    • Shoulders
    • Legs
    • Ankles
    • Skirt
  • Motors (Q85), tyres, and Speed Controller (ODrive)
  • Power distribution (fuses, wires, switches, relays)
  • Amp and speakers
  • Raspberry Pi
  • DC-DC power convertors.

I’ve also bought cells for another battery, which will be identical (a little more capacity) to R2’s current one. That way they can be switched.

Hopefully I’ll be able to make a start on something this weekend. My first main jobs will be:

  • Motor conversion – The Q85s have to have their clutch frozen and rims turned down
  • Electronics mount – I want all the electronics to be removable for ease of maintenance
  • Frame – Actually put the frame together

So, watch this space for which I decide to do.

Upgraded foot drives

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.

Nope.

Drive is stripped down to make repairs. Note the lack of rubber on the wheel.

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.

Omnis and center foot

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.

Wheels

Assembled set of wheels
Assembled set of wheels

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.

See the build gallery for more pictures

Foot Shell

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.

Center foot assembly

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.

Ankle

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).

Conclusion

After all this, R2 was feeling rock solid, at least as far as the center foot is concerned.

R2's previously worst nightmare - carpet
R2’s previously worst nightmare – carpet

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.

Looking forward to the Northern Builders Day in a couple of weeks to show him off a bit more.

Working on the new center foot

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.

Center foot chassis
Center foot chassis

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.