Getting started with RCAP2

[CrashingDutchman]

Ok, I am about to buy the RCAP2 kit or completely built kit (depening on funds), but I have some questions before jumping into this.

I have a Garmin GPS12 that I plan to use with it. This GPS has the possibility of storing 500 waypoints. Enough to get started with, I think :rolleyes:. Only negative of this, is that it's quite heavy, actually, it is the 4 AA size batteries that make it heavy. I have found out that pfrank (http://www.pfranc.com/) sells plugs for the Garmin. It seems that I can power the GPS12 through the plug. The plug has 4 pins (power, data-in, data-out, ground). So, I should be able to get rid of the heavy batteries and find another power source. The 4 x 1.2V AA batteries provide the gps with 5 volt (or 4 x 1.5V = 6V), so I guess I should stay in that range. I think I can use a 2cell lipo with a voltage regulator to power it. I have sent pfranc an e-mail about this, waiting for their answer.

Then the questions:
1. Anyone with a (better or other) solution to power the GPS12?
2. Once I switch the RCAP2 on, how does the plane hold it's altitude?
3. On the RACP2 site (http://scalerobotics.com/store/catalog/), I saw that also a 'Horizon and Attitude dual axis tilt sensor Kit with PCB, IR sens' is available. Do I need that to get started and do these even work together? (Might answer question 2)
4. If I buy the RCAP2, will it contain the new PIC with bootloader, or should I ask this question somewhere else?

Might very well be that your answers arise new questions. I will put them here!

Thank you in advance!

CD

Ps. I have a U-blox (http://www.u-blox.com/products/sam.html) with 100k datalogger module that I bought about a year ago. It's still new in the package. I might decide to sell this to fund RCAP2. In case someone is interested, let me know.

[CrashingDutchman]

I just found out that the GPS 12 needs 5-8 VDC, so I guess a 2s1p lithium with a regulator will do.

Other suggestions welcome.

[radiohound]

Hello CD,

It has been mentioned that the GPS-12 sends out nmea updates every 1 second, rather than every 2 seconds like most others. This would be a bit of a plus, but yes, there is the added weight factor to consider. This largely depends on the size of your plane. If you want a smaller gps, the etrex versions are a bit lighter, but they want 3 volts or so. The geko versions 201 and 301 are very small and light, but they are more expensive.

The RCAP2 currently relies on you to set the throttle to a position that will keep your model at altitude. A barometer altimeter is being developed, but it will take some time to get tested and ready for use.

The tilt sensor I sell gives an analog signal out, but has not been implemented for the RCAP2. There are analog inputs available on the RCAP2 that could take these analog signals and do something with them, but mostly it would be something to keep your plane level, not at a certain altitude. Currently, this sensor is just for people that want to experiment with using the sensor, or impliment their own code with the RCAP2 for it. So the short answer is, no, the do not work together.

It is recommended that the RCAP be used with an FMA co-piliot type device to help keep your plane stable. However, if you have a very stable trainer type, high wing aircraft, you might be able to get by without the FMA Co-pilot.

RCAP2's that are currently being sold are being shipped with the bootloader installed and version 1.6 firmware = Version 1.6B. This will allow anyone with a PC and serial port and null modem adapter, to program new firmware (as it becomes available) into the RCAP2. Sure is nice not having to pull the chip in and out to program it.

Let me know if you have any more questions.

Walter

More info on the RCAP2 http://www.uavs.net/rcap.html

To purchase: http://www.scalerobotics.com/store/catalog

[CrashingDutchman]

Thank you Walter, that really helps.

How do people in general power their RCAP2? Would it be possible to get the power for the GPS device from the RCAP2, I mean, is there some point where I could get (preferable) 5-8vdc from the RCAP2 for powering the GPS?

CD

[twinturbostang]

Walter, how many analog inputs does the RCAP2 have? This sounds like great news, as I did not know it had any inputs. It sounds like the tilt sensor kit that you sell could be incorporated into the RCAP2, which would be cheaper than buying an FMA co-pilot. All that needs to be done is wire up the inputs and write some code. I am getting closer to purchasing one of these, and I have some special requirements, so I probably will be digging into the code anyway.

[radiohound]

Thank you Walter, that really helps.
How do people in general power their RCAP2? Would it be possible to get the power for the GPS device from the RCAP2?

The RCAP2 comes with a 150mA regulator. I think most gps's use about 90ma to 100ma or so. You could test yours to see what it uses at 5v. If it uses close to 90 or 100ma, I would say you are too close to it's max output. The RCAP2 usually uses about 25mA, but can peak higher at times. You could replace the regulator with a more powerfull regulator. Just make sure it does not overheat, and take a look at the data sheets to see what kind of capacitors are recommended.

I think most people are powering their GPS's from the gps's batteries, but I could be wrong. I can see why you would want to power it differently, since yours has 4 double A size batteries.

[CrashingDutchman]

The manual says:

Power consumption: 1 Watt

[typicalaimster]

I think most people are powering their GPS's from the gps's batteries, but I could be wrong. I can see why you would want to power it differently, since yours has 4 double A size batteries.

I'm powering my GPS from the GPS batteries. I'm then powering the RCAP from a regulated 6v power source.

[radiohound]

Walter, how many analog inputs does the RCAP2 have?

It sounds like the tilt sensor kit that you sell could be incorporated into the RCAP2, which would be cheaper than buying an FMA co-pilot. All that needs to be done is wire up the inputs and write some code.

The RCAP has 4 analog input ports available. PortA,0 portA,1 and portA,2 , and portA,5. These are analog inputs, and are tied to the onboard 10 bit A/D converter on the Pic16F876a device. It is relatively easy to get values from the conversion.

Yes, all that needs to be done is write some code ... but the control of the servo's to maintain a level airplane could be a bit tricky. Your right though, it is definately possible. Some care would have to be made so that it makes small adjustments to elevator and ailerons, and remain stable.

I would welcome anyone to give it a go. Right now I am concentrating on the barometer/altitude hold, so I do not plan to work on the tilt sensor in the near future, but it would be a great addition. The barometer hold will not use the analog input pins, it will use a separate 15 bit A/D converter. So yes, they are definately available.

There are also plenty of other digital input or output pins, serial input or output pins available to use. Read http://www.uavs.net/rcap.html and it shows that:

J5:
Analog in port (not used) PortA,0

J6: This jumper allows you to power the unit from the DB9 connector. This is better left to the + and - pads, so I suggest you leave the jumper out.

J7: Debug port as documented in RCAP PicBasic Pro code. (Not used) PortA,5

J8: Future use servo/receiver port. PortC,5

A1: Aux servo - future use PortB,1
A5: Aux servo - future use PortB,0

Unlabeled 6 pin header above J5: This header is made up of spare pins from the board that are currently unused by the RCAP. Pins from left to right: PortC,4 PortA,1 PortA,2 PortC,0 PortC,2 PortC,3

[CrashingDutchman]

I'm powering my GPS from the GPS batteries. I'm then powering the RCAP from a regulated 6v power source.

Long time ago, I learned some electronics. My GPS consumes 1 Watt, so Amps = 200 mA at 5 volt (I = P/V, right) or 166 mA at 6 volts. That is more then Walter said that is good. I have to use an external power supply.

I think I can power the RCAP2 and the GPS from this 10W Step down adjustable switching regulator (http://www.dimensionengineering.com/DE-SWADJ.htm) in parallel from a lipo battery.

I think it's better to use a seperate battery for this, right? Not the battery I have for powering the plane itself.

CD

[CrashingDutchman]

Anyone who can confirm on the above?

I also would like to know what the disadvantage would be of using the altitude data that is comming from the GPS? Is it that in an area with mountains, a barometric sensor would be better? I live in The Netherlands and it's pretty flat. It wouldn't be too much of a problem here if that is the case.

CD

[radiohound]

I also would like to know what the disadvantage would be of using the altitude data that is comming from the GPS? Is it that in an area with mountains, a barometric sensor would be better?

The gps altitude just isn't accurate enough to control the elevator and keep the plane at a very stable altitude. You may be able to do it, as long as you kept the altitude at a comfortable height, but your altitude would probably vary a lot, and your plane may look a bit eratic trying to maintain an altitude as it is getting +/- 30 meter readings from the gps.

A barometric reading is much more stable, and can indicate changes in half a meter or so of altitude change.

Some GPS's (like the Geko 301) have a barometric pressure sensor inside them. I believe you have to read another NMEA sentence to get this info, but it would be very accurate, though a bit expensive.

A sensor add on board will become available for the RCAP2. The A/D conversion code has been written for a 15bit A/D converter. Now the rest has to be written ... but it is coming, and will be affordable.

[CrashingDutchman]

I always thought that gps accuracy is +/-15 meters. The operator of the satellites (US Government?) can ajdust this. The manual of my GPS 12 says that it handles DGPS which brings accuracy to 1-5 meters, but I am not sure about availability of DGPS here.

Let's say I want to keep my plane on 150 meter high. Either if accuracy is 15 or 30 meters, isn't it so that the GPS will also show an altitude of 150 meter +/- 15 meter (or 30 meter). In that case, it will stay between 150-15=135 or 150+15=165meter?

If the update rate is once or twice a second, the plane won't go 15 meter lower or higher within the update rate. It will descend or go up slowly to get to the altitude I want to have it. The change in altitude isn't 15 meters in between 2 updates, right? It might be some kind of wobbly road the plane is flying?

Is that correct, I hope to learn something here.

I am a computer programmer for profession. Have never programmed any PICS, but have a programmer for PICS. I have looked into the code and seem to understand it (besides the servo steering in the servo.inc file).

Regards,

CD

[Tuner]

Test it out thats the only way you will know.
Yes averaging out the data point and creating a smooth control response is a no brainer how hard and reliable will it be good question?

[radiohound]

I always thought that gps accuracy is +/-15 meters. The operator of the satellites (US Government?) can ajdust this. The manual of my GPS 12 says that it handles DGPS which brings accuracy to 1-5 meters, but I am not sure about availability of DGPS here.


I looked around, and got different answers on the web. Here is one that talks about SA being turned off (which it currently is). See:
http://gps.faa.gov/FAQ/faq-gps.htm#5

"Without SA, SPS accuracy would be of the order of 25m (2 drms, 95%) in the horizontal plane and 43m (95%) in the vertical plane. "

Vertical accuracy is not as accurate as horizontal. It may be better than this 43m, but it is not very accurate in my experience.

You may be right. It may be do-able. It could be much smother with higher sensing (like a 12 bit or higher barometer sensing). If you had more sensing range (every two feet or meter) then you could have different levels of response to adjust to keep altitude. Perhaps only add 1 or 2% throttle if you dropped 3 meters, but if you dropped more, you could add 5% throttle, etc...

I agree. Try it, and see what you come up with. If it works for you, then you saved some money, and learned more about programing PICs!

Walter