SparkFun Forums

[ninjablademaster]

I'm trying to find a GPS module to enable position holding of an autonomous helicopter. The craft can already control its tilt but it gets pushed around by the the slightest breeze.

I've read a few old posts about low cost receivers (sub $200) with position updates >1Hz and I would like to know if anyone is aware of new modules in this category. I would like to use a Sparkfun module with built-in antenna, battery, etc. but I think their update rate will be insufficient for a tight position hold.

A lot of new cellphones are including GPS so there must be some new small, low-cost modules available. Does anyone have more info? The U-Blox 5 series looks interesting but will not be available until sometime '07.

I'm currently planning to use the U-Blox LEA-4M which has a 4 Hz position update.

[NleahciM]

I'm trying to find a GPS module to enable position holding of an autonomous helicopter. The craft can already control its tilt but it gets pushed around by the the slightest breeze.

I've read a few old posts about low cost receivers (sub $200) with position updates >1Hz and I would like to know if anyone is aware of new modules in this category. I would like to use a Sparkfun module with built-in antenna, battery, etc. but I think their update rate will be insufficient for a tight position hold.

A lot of new cellphones are including GPS so there must be some new small, low-cost modules available. Does anyone have more info? The U-Blox 5 series looks interesting but will not be available until sometime '07.

I'm currently planning to use the U-Blox LEA-4M which has a 4 Hz position update.

Even a high accuracy high update rate GPS ain't enough for a position hold - really for that you need a full 6 axis IMU.

[ohararp]

I'd agree on this comment. With my data logger I have noticed drift of 50-100 m when the logger stays in one spot. You are much better of with gps and some osrt of dead reckoning technique.

[ninjablademaster]

I'm trying to find a GPS module to enable position holding of an autonomous helicopter. The craft can already control its tilt but it gets pushed around by the the slightest breeze.

I've read a few old posts about low cost receivers (sub $200) with position updates >1Hz and I would like to know if anyone is aware of new modules in this category. I would like to use a Sparkfun module with built-in antenna, battery, etc. but I think their update rate will be insufficient for a tight position hold.

A lot of new cellphones are including GPS so there must be some new small, low-cost modules available. Does anyone have more info? The U-Blox 5 series looks interesting but will not be available until sometime '07.

I'm currently planning to use the U-Blox LEA-4M which has a 4 Hz position update.

Even a high accuracy high update rate GPS ain't enough for a position hold - really for that you need a full 6 axis IMU.

I'm already using a kalman filtered Sparkfun IMU 6 Degrees of Freedom (v2 with ADXRS401) for attitude sensing and a PID loop for attitude correction. It's working well to keep the craft level.

The Maxbotix EZ1 ultrasonic range finder doesn't seem to be having any trouble finding the ground despite the prop wash so I'm working to add the height above ground to the control loop. Next I plan to add a compass to correct the yaw axis gyros. I will also use a SCP1000 pressure sensor to help determine the elevation. When those components are working properly with the control loop the craft should be able to stay level, face the correct direction, and maintain a constant elevation. Seems like I will still need GPS to fix the position with respect to lat/lon.

The Garmin GPS 18 5Hz has a 5Hz position update and comes in a nice package. It looks like a lot less work than building a solution based on a U-Blox module. I wish I could get my hands on this U-Blox reference design.

Any suggestions?

[ohararp]

I'd think about doing some testing to determine the validity of the gps lock. You can use the DOP values to help with this.

[NleahciM]

I'm already using a kalman filtered Sparkfun IMU 6 Degrees of Freedom (v2 with ADXRS401) for attitude sensing and a PID loop for attitude correction. It's working well to keep the craft level.

The Maxbotix EZ1 ultrasonic range finder doesn't seem to be having any trouble finding the ground despite the prop wash so I'm working to add the height above ground to the control loop. Next I plan to add a compass to correct the yaw axis gyros. I will also use a SCP1000 pressure sensor to help determine the elevation. When those components are working properly with the control loop the craft should be able to stay level, face the correct direction, and maintain a constant elevation. Seems like I will still need GPS to fix the position with respect to lat/lon.

The Garmin GPS 18 5Hz has a 5Hz position update and comes in a nice package. It looks like a lot less work than building a solution based on a U-Blox module. I wish I could get my hands on this U-Blox reference design.

Any suggestions?

The GPS should be used to correct your IMU data - but for accurate latitude and longitude position holding you'll still be decidedly better off using data the combined data from the IMU, rather than data straight from a GPS.

As for what GPS to use - I personally think the U-Blox LEA-4S looks quite attractive at only $100. The Garmin unit is more integrated of course and has a slightly higher refresh rate (5Hz vs. 4Hz), but it also uses less satellites and is quite large and heavy. Additionally, the Garmin unit doesn't support EGNOS or DGPS.