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Motor control in my radio control car
Still finding it difficult to find the I/O details of my radio control receiver and my electronic motor speed controller. What is on those three wires (white, red and black) between the receiver and the ESC?? Also what is the information format on the three wires (blue, red and black) between the receiver and the servo?
RC receiver: FUTABA FP-R122JE am 2 channel BEC
ESC: NOSRAM Tomahawk Reverse 93050
motor: MABUCHI RS-540RH/SH
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I have done a lot of work on Autonomous control of RC cars, helis and airplanes. My applications have mostly been on stabilization and waypoints for aircraft using in inertial measurement unit (IMU) board. On the RC car, I ripped out the simple RC controls and replaced them with a Specktrum RX.TX system. I used a PIC processor to convert the throttle PWM signal into something the existing H Bridge motor controller understood and replaced the steering servo with a standard RC servo. I have a camera on a servo controlled pan and tilt servo system, and added things like the Parallax PING sonic distance sensor, and compass module and a GPS (but this only works outside). There are a lot of things you can think of adding.
Looks like you already have a real RX/TX system with a BEC/ESC to a motor. The signal going from the RX to the ESC; Red/Black/Blue(sometimes different color) are +V/GND/Signal. Signal is a Pulse Width Modulated signal whose width tells you how much throttle to apply. Typically this signal will be 3.5v (or so) and a width of 1.2 to 1.8 usec, depending on throttle setting.
Autonomous control will depend on what you want to do and what sensors you need to accomplish it. Waypoints won't work indoors with a GPS, but you can memorize a track, detect obstruction, follow a wire or tape track, lots of things.
A very sophisticated version of indoor automony is a laser scanner that basically maps its environment, but very pricey. You could try a sonar version of this using the PING sensor, lots of math and geometry involved.
Good luck and have a lot of fun with your students.
John
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Getting somewhere...
Thank you, John for answering my questions. I am out here in the middle of Massachusetts. Is there a robotics club around?
My RC car is not the correct one for this job. It has 4 wheel drive and hence a drive belt down the middle where I would mount the PIC. I refer to it because that is all I have. If this idea takes wings a new car can be purchased.
My first thoughts for autonomous control sensors is simple sonic proximity detectors. If they looked to the right and to toward the front, I'll bet I could program the car to follow a wall (close on its right side) until it found an opening (in a corner). Or something....
I need to pick a PIC. I've been told that VEX uses Microchip's 18F8520. Our local technical high school has some VEX kits, but I do not have access to play with them. Any suggestions would be greatly appreciated.
I am a retired digital hardware and software designer. I still have my Texas Instruments 7400 Series TTL catalog. I have not done hardware design since the early 1980's. I am way out of touch.
Ken
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Hi KenOriginally Posted by Kenjones1935
I'm out in Colorado, so don't know much about clubs in Mass, but you do have MIT there and they are well known for their work in robotics. You might see if you could connect with them. The laser scan I mentioned was at MIT. Here is a link you might enjoy:
http://diydrones.com/profiles/blogs/...ter-with-laser
I don't really know about VEX, but I have chosen my PICs based on numbers of hardware PWM channels, ADC channels etc...so depends on application. I never found I taxed the speed of the processor.
One thing I started, but never really finished was to put a PING on a servo so I could rotate it left and right. I took a left/right scan and stored the distances to detected obstacles, basically making a map. I could then make decisions on where to go next. You can't really scan very fast though due to a couple of things. The first is that you need to make redundant measurements to filter noise out at each setting, and then the servo is constantly moving and can limit it's lifetime. So this isn't useful for a fast moving car, but maybe a crawler. I like the idea since it requires some math and algorithm development as a learning project.
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What a great video!!
John,
Thank you for the pointer to the quadcopter video. It is spectacular.
I am a member of the Cardinal and Gray. The alumni organization for those who graduated from MIT over fifty years ago. I have been looking unsuccessfully for an alumni robotics club.
My impression is that the RC cars world (no microchip) and the VEX school competition world (both RC and autonomous but mostly RC) and the robotics world are completely separate. Then of course there is the land of production machine control.
The RC cars motor can draw up to 80ampere. These cars have a 7.2 volt battery pack that feeds directly to the ESC which in turn gives a dribble of power to the RC receiver. If the micro proto board which has its own battery pack were to provide the PWM signal to the ESC might I not have a power problem?
Really my problem is getting started. I thought the micro controller could be the middle of the car. The RC receiver gives it a low power PWM signal as per usual. When under RC control the micro interprets then passes this signal onto the ESC. If that were the design, the micro could take over control on its own without a command from the human.
I need to pick a microcontroller either a fully packaged one like the VEX, the RCX or the NXT or a proto board. In my past I programmed in machine language and on RISC. More recently it was C, C++ and some higher level languages. That was alll in the work office environment. At home I am starting from scratch. If this looks promising I am pretty sure I can get some help. I need a basic design.
Ken
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Ken
You probably need to decide if you want the flexibility of a bare PIC or a package that is already programmed. I went with the PIC since I can basically make it do anything I want.
There is a price to be paid to get in that game however. Perhaps you already have all the infrastructure, if not you will need a programmer to write to the PIC, and then decide on the language. Since you are on this forum, you may have PICBasic. If not, you can go assembly (free), C (also free from MicroChip without optimization), or some other language (maybe free, maybe not). There are a lot of programmers out there. MicroChip has some, but other vendors too. I use an ICD2 clone from Sparkfun and PICBasic Pro for smaller PICs and the MicroChip C30 C compiler for dsp chips. I also program in asy, but I can get a lot more done with Basic or C.
If you go the PIC route, I would just use a proto board to build up your circuits.
I typically use an 11v LiPo battery to a BEC to get 5 volts for the board. You can actually take the power off the RX on the Red and Black wires of any channel. This is very low power drain compared to the motor and servos.
Just a suggestion, but I would use an RC car or truck that has a very slow speed option. Fast isn't good when you are trying to debug sensors and code.
One way to switch between manual RC and Auto is to use a channel of the RX that the PIC reads. If it is high, then manual, low then auto for instance. but you need a spare channel. I use a Specktrum DX-7 TX/RX with 7 channels for all the goodies I need to control. This approach is useful if the Auto goes nuts, you can switch to manual with the flick of a switch.
This can get a little expensive to start, but if you plan to stick with it and do similar projects, I think the basic building block approach gives you the most fun....but then again I don;t know what the VEX etc are. And I do a lot of this on many different platforms.
Did I understand you were involving students? It's a great learning project.
John
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autonomous ex-RC car that goes around the block
The Tech Junkies have this video. They removed the RC control and made the car completely autonomous being guided by the gps satellites.
Their Arduino proto board has a voltage regulator. It produced a 5 volt supply from the 9 volt battery. This would allow me to keep using the 7.2 volt battery pack. I was hoping to keep the speed capability of the RC car.
Ken
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You wrote:
"One way to switch between manual RC and Auto is to use a channel of the RX that the PIC reads. If it is high, then manual, low then auto for instance. but you need a spare channel. I use a Specktrum DX-7 TX/RX with 7 channels for all the goodies I need to control. This approach is useful if the Auto goes nuts, you can switch to manual with the flick of a switch."
Is that as easy as flipping a double pole double throw switch under PIC control?
I have not chosen a PIC. Is the PICaxe Starter Kit for fifty bucks what you would recommend? It does not have any spare proto space. Are pretty much all the sensors I might need directly connectable? Will I need additional off board interface circuitry for, say, a servo or a simple on/off motor? Microchip sells a PIC18FXX20 Demo Board. It contains their 18F8720. I think VEX uses their 18F8520.
I gotta purchase something and get started. One more thing. I have both Windows and Linux PC's at home. I assume that most everybody uses Windows.
Ken
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