In our last post we discussed expanding on the HTC Vive’s default configurations by incorporating additional base stations, controllers and systems. In this post we took apart a Vive controller to get a better understanding of its impressively accurate tracking and haptics.
Inside the controller we found the two grip buttons are actually one tactile switch. The grip buttons are arranged so the button switch is mounted on one half of the grip and depressed by the other.
Notably, we were surprised that the controller was operating a single haptic motor, right below the touchpad. The device’s construction was purposely rigid so that the haptic vibrations would properly spread throughout the device.
The Surprisingly Elegant Trigger
The button trigger on the bottom of the controller is a Hall-effect sensor instead of an optical rotary encoder or potentiometer. It detects a moving magnet instead of detecting a beam of light being interrupted, or the drop in voltage across a wire changing. This is surprising because Hall-effect sensors are typically used for building speedometers, whereas the others are generally used for positioning in the case of traditional joysticks and computer mouses.
The trigger also has another button directly underneath it, but the use of it does not follow standard button behavior. In the developer tool OpenVR, you receive a “button pressed” signal when the trigger has been pulled past a certain threshold (approximately 95%), regardless of whether the button has actually been pressed. If you do pull the rest of the way to press the button, it forces the trigger pull to go all the way to 100%. This is a neat hack to get around the fact that it can be very difficult to calibrate analog devices to read a full 0-to-100% range.
The use of a button under the trigger also more accurately simulates the feel of using a real firearm. The trigger pull in real guns usually has a little play in it before hitting what is called the “sear”, the part that holds the striker back from igniting the primer in the back of the bullet. Pulling the trigger further releases the sear, with a distinct “click” or “snap” feeling, to drop the hammer. With the Steam VR controller, the click of the button at the top of the trigger pull feels very similar to the click of the sear releasing.
Past & Future
Interestingly enough the first controller prototypes had flat surfaces with a similar wand grip that is present in the current Vive controllers. We believe the circular design is comparatively more ergonomical. First, this design lets each individual sensor stand out and distributes the sensors for enhanced tracking. If the sensors were all on the same plane, the device would have more difficulty in figuring out where the controllers were. The controller design also has wings protruding from the bottom of the donut to get the sensors off of the plane of the circle. Secondly, the design reduces weight, with each controller weighing in at 10.9 ounces.
We’re patiently anticipating the next controllers HTC is releasing, especially because they are noticeably more compact and resemble the Oculus Touch controllers.