Some of you may have noticed that for quite a while SparkFun has been listing a "UAV Development Platform - ET312 + IMU
" that's always been out of stock. I backordered one out of curiosity last year, and pretty much forgot about it. Then, last week, SparkFun called and said that they'd "finally got it working" and it was now available for backorder customers. Did I want one? Sure!
It showed up today and it's going to take me some time to figure it out properly, but here are some first observations:
- It's a "development platform", not a fully-featured working autopilot. Although there is firmware available for it, it's designed to be a standard hardware package around which you can develop your own autopilot code.
- The firmware comes pre-loaded, and works pretty much as advertised. I tested it on the ground, so it was hard to tell how well it actually stabilizes a plane, but the elevator seemed to respond properly to tilting. The rudder didn't, but that was probably because it was trying to turn the "plane" to a destination and I wasn't playing along ;-)
- That firmware is written in assembly, so good luck to you! It seems to do pretty much the basics of what you'd want an autopilot to do (and I mean basics--there's no provision for waypoints, and it's just a "fly home" autopilot at the moment), but if you want to tweak it you'll have to do learn PIC assembly (not super hard, but still: what's wrong with C?!)
- It includes a 4-degree-of-freedom IMU: two gyros and one two-axis accelerometer.
- As the two-axis configuration suggests, it's designed to control just two channels: elevator and rudder. A third channel is used to turn it on and off.
- It's got a good SiRF III GPS module on board, although you'll need to add your own antenna through the included SMA connector.
- At $299, it's not cheap. But when you consider that a simple set of accelerometers and gyros will set you back $109, the addition of GPS and a PIC processor, all nicely integrated on a board, is probably worth it. But it still seems about $100 overpriced to me.
- You need some additional hardware to work with it: the main thing is an ICD2 interface to program the onboard PIC chip and for debugging. That will set you back another $120.
- The documentation looks excellent, with a lot of theory on control and aerodynamics as well as a lot of help on PIC assembly language and development suggestions for the platform.
- Bottom line: this looks like a good, albeit expensive, way to learn about IMU-based autopilots. It's not really an autopilot itself yet, but could be made into a relatively low-featured one pretty easily. I think it's accurately described as a "development platform", so if you're in the market for that and can afford a $300 lesson, I can recommend it as a unique and well-made way to get started.