September Blog Post - Exciting Developments on SR-6 and T-wist

Hi guys,

This is a dev blog post to let you know what I’ve been up to the last week or so. I’ve got a quick update on the SR-6, and news about a very satisfying upgrade to the T-wist.

SR-6

I’ve been pressing forward with work on the SR-6 prototype. This is a clean sheet design that works quite differently from the OSR2+, and quite complex too, so I’ve been been keen to make sure I have the arrangement right.

I don’t have any images to share yet, but this machine will have a receiver ring like OSR2 and use 6 servos. It will be a 5+ axis design, which means that this robot will be able to take a fleshlight and not only lift up and down, roll left and right and pitch forward and backward, but it will also be able to slide forward and backward, and slide left and right. The option to add a twist receiver, very similar to the one designed for the OSR2, will enable the full 6-axis experience.  

I can report that I have been able to run the full six servo arrangement with my VaM plugin, and I was very impressed with the way the design performed. IssacNewtongue’s original “Paper Love” lap dance scene has become my go-to test sequence for such things. With this new design I was particularly impressed by the the side-to-side movements, which I have never managed to reproduce before. I am always amazed how much extra nuance I get from a robot when I add an extra degree of freedom, and this time has been no exception!

T-wist

In the meantime I am very excited about this coming month’s release, which is the third and final, for a while at least, version of the T-wist for the OSR2. During the last few weeks one of my patrons alerted me to the existence of a special servo built by a company called parallax: the 900-00360 Feedback High Speed 360° Servo.

This servo has two big advantages over the generic continuous rotation servos used on the existing versions of the T-wist.

First, it rotates at double the speed of most continuous rotation servos - 120 RPM, which doubles the rotation speed of the twist action to 38 RPM. This means that with this servo the T-wist will go from +90° to -90° in less than a second, which is excellent performance.

The best thing, however, about this new servo is that it also has an extra wire coming off. This wire allows the servo to send a feedback signal, using pulse width modulation, back to the Romeo telling it what position the servo is in. 

I was really excited when I realised this, because it meant that with a little bit of programming it would be possible to do away with the L-bracket and potentiometer that are the current means for the T-wist to tell what position it is in. Not only do these features look ugly, but they also make the receiver top-heavy and add a lot of complexity to the assembly, so I am happy about being able to do away with them.

The new servo and the extra wire plug neatly straight into the Romeo, with no soldering or even wire extensions required. The feedback process works more or less the same way as the servo receives commands from the Romeo: The Romeo listens to the wire for when the voltage goes from low to high and then high to low, and can tell by the length of the pulse what position the servo is in. From there it’s simply a case of counting rotations, as the servo and drive gear rotate on a 28/88 gear ratio with the ring gear.

I’ve written the code to drive this and it works really well. The only downside is that because I’ve had to use the Romeo’s hardware interrupt function the extra wire has to plug in to digital pin 2. This displaces the left arm servo lead from pin 2 to pin 8 (or 7 on the v1.1).

The only other thing I found was that this new servo, whilst nominally a standard size servo, is slightly smaller than a generic servo. For whatever reason it’s not quite as tall. I will therefore be releasing a new T-wist receiver body and base, sans L-bracket mount, in a week or so as the October release, as well as the new Arduino sketch to drive it.

My main effort in October will be getting the SR-6 into a state where I can share a sneak peek. It really is next level stuff and I really can’t wait to show you guys what it can do.

Thanks again, as always, for your support. You guys are the best!