So i found this gps-rtk board. Im considering ways to accomolish my next project. I have a machine that i want to automate. It has 2 hydrolic powered wheels. A simple valve opens and closes to make it move. I can attach servos to them to run them from an arduino. It needs to be able to remember the same path every time. I would first put the code in a "record mode" where i would run the machine manually as it records the positions every, say, half second. And then i can put it back to the start position, put the code in a "play mode" and then every half second it tells the servos to go to those same positions it recorded.
In theory it would travel the same path.
Here are some isues to overcome.
My tollerance would need to be a few inches.
When the servo is on its not moveable. So i can not move the machine manually. Im told there are servos that i can power down and move manually but still get feedback on its position. This is preferable but i do not know how to find that kind. Other options im told are to lower the power enough that i can overpower it and force it to the positions i put it at and read the feedback. The 3rd option is simply attach my own potentiometer to the shaft and try to line it up with the internal sensor. If i can find a servo i can at least start buildingthe concept.
Wheel slippage. I have no way to detect if a wheel slips. Thus i would not know if the machine is going off course. For this i can monitor a compass. And while thats a good double check, its not perfect. Thats where the board in the link comes in. If i have a strong enough signal it can give me accurate gps coords. I can translate those into where it shoule be and make corrections.
Another problem that i have is that recording positions, compass direction and gps location every half a second would be quite a bit of data. Probably too much for an arduino. But maybe i can use an sd card. My other option would be to use a pi.
GPS is not quite good enough to tell if you're on the street or in your front room. Car GPS units cheat by having a map and forcing the car onto the streets mapped. (Try driving off-road, it tends to stick to the closest road until you are a long way off.)
As for the servos, it should not be too hard to open them up and find the feedback potentiometer. Even "digital" servos have analog pots inside them. Measure the voltage at various positions while the servo is powered. It should be something like 0-5V but you may get 0-6V. You can run this straight to the Arduino's analog input, with an appropriate voltage divider to match the Arduino's voltage.
While you have the servo open, see if there's an easy wire to cut and install a relay to disable the motor. You need the servo powered on to get a voltage from its feedback but you don't want the motor driving while you are in 'teach' mode.
MorganS:
GPS is not quite good enough to tell if you're on the street or in your front room. Car GPS units cheat by having a map and forcing the car onto the streets mapped. (Try driving off-road, it tends to stick to the closest road until you are a long way off.)
As for the servos, it should not be too hard to open them up and find the feedback potentiometer. Even "digital" servos have analog pots inside them. Measure the voltage at various positions while the servo is powered. It should be something like 0-5V but you may get 0-6V. You can run this straight to the Arduino's analog input, with an appropriate voltage divider to match the Arduino's voltage.
While you have the servo open, see if there's an easy wire to cut and install a relay to disable the motor. You need the servo powered on to get a voltage from its feedback but you don't want the motor driving while you are in 'teach' mode.
That would probably work. But I think it would be less work for me to attach a potentiometer to the output shaft and just ignore the built-in potentiometer. I wouldn't want to ruin the warranty I would have on the part
The thing is, I was told that there was a kind of Servo that would let you read the potentiometer after you power down the motor. But I have not been able to find one.
As far as GPS, the RTC function of GPS is a tower that is set up locally to give GPS a one-to-two centimeter accuracy. The Michigan Department of Transportation has some set up for people to use, I'm just not sure how much of a signal I have in my town. There may also be private ones that I can subscribe to.
But i am still trying to find ways to do this without gos. I cant seem to find any kind of sensor that will help