January 30, 2015

Vario-F, NOT an alternative to SBS01-A

Since my previous post on the Vario-F I've been testing the device some more. In fact, today I took it for its for flight. And I noticed two things; the variometer is not reporting correct values and the e-fuelgauge had stopped.

Only getting the Vario-F to work wasn't easy. Registering the device in the remote (I'm using a 14SG) didn't work. It wasn't even close to working. While I was reading the Futaba manual I discovered that Futaba claims their sensors come with a default slot setting and if that setting works for the installation then no device configuration is required. I figured it was worth a shot and it turns out it works. Simply select SBS01-A on slot 3 and the numbers start coming in.

The Vario-F acts as a Futaba SBS01-A. The Futaba sensor reports both relative altitude and variometer, which is rate of ascent and descent. The variometer is most useful for detecting thermal effects on a glider aircraft. This is not important to me but it's worth mentioning that the Vario-F does not report a correct value for the variometer reading. Looking at the telemetry log it seems as if there's some random number between -1 and 1 reported.

In the aircraft I was testing the variometer in there is also an E-fuelgauge. This device has been reused a few times and I think it is now in its third craft. To my surprise, it wasn't reporting an increasing mAh count while I was flying. At first I thought I broke it but it turns out that if I disconnect the Vario-F from the bus the e-fuelgauge is working as it should.

This seems kind of scary. It is possible that the Vario-F does not implement the SBUS2 protocol correctly and causes other sensors to malfunction. This is a big issue since the SBUS2 is a multi-master bus. A multi-master bus uses the notion of gentlemens agreement in terms of occupying the bus and the introduction a non-compliant devices causes other devices to malfunction.

If someone was to put critical things like a servo on the SBUS2 port together with the Vario-F? Well that would probably not end well.

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