Let's Make Robots!

DIY RC, Moving to Arduino, RasPi, and other questions

I have added more questions to the end of this, so please have a look.

Hi

I sort of started this question on another page, but I thought I'd move it here so I'm not hijacking someone else's page.

2 questions here;

1: I'm looking to move from using picaxe to Arduino. Can anyone give me any pointers on where to start? (I know this question's probably been asked elsewhere on LMR)

2: One of my interests is making RC cars, boats, etc., so I'm considering making a DIY RC transmitter/reciver to give me some extra channels and functions (telemetry, freedom of layout, built-in speed control, etc.) without breaking the bank. I'm looking at XRF modules for the radio side of things, as they're fairly cheap, easy to use, have a decent range, and 2 way transmission. Does anyone have any experience with them, or can anyone asvise anything better?

Also, the XRF modules seem to be based around this chip (pdf warning). Would it be possible/cheaper/better to build up an XRF compatiable tranciver from this chip, so that I can keep it all on one board?

Thanks in advance, and sorry if I've done anything wrong (I'm pretty new to forums)

 

More questions/info on use:

Any radio I use will have to not interfere with standard 27mhz, 40mhz and 2.4ghz equipment, as I'm a member of a RC boat club that runs ocasional pond evenings.

Also (this is probably an obvious point), I want to have at least 4 fully proportional channels (for two 2-axis joysticks).

Extra question: would there be any problem with using a combination of arduino and picaxe, IE an arduino based transmitter and a picaxe based reciver?

Thanks the replies

 

More info in what I'd like, idealy, to make a transmitter to do

 

Sorry if this sounds in any way over ambitious, I was just jotting down features that I'd like to try and put on it when I do it.

Also, sorry if any of it doesn't make sense, as these were notes for myself.

It may be a while until I do any physical work on this project, as I've got other projects (a theremin and a stirling engine) and exams to do before I make a start. This post is mostly to sort out ideas as to how to do it.

Cheap one-way RF / Xbee / cheap RF tranciver (2.4ghz?)
            Reciver:        Picaxe
                    Expandable (via serout/shift register)
                    Digital, servo + serout
                    Expansion port?
                    Shift register
                    AV transmit?
                    Audio recive?
                    Remote reprogrammability?
                    Cheap IR reciver for lightweight/cheap use?
                    In-built PWM control for Speed control etc.
            Transmitter:    Picaxe / Audrino (Rasberry PI?)
                    Screen? (Character LCD/OLED / Nokia LCD (monochrome/colour?))
                    2 joystick
                    Extra anologue channels
                    Xbox finger triggers?
                    Toggle switches / push button / On screen?
                    Mixing Etc
                    Anologue trim (mechanical / Digital?)
                    Use dead transmitter for joysticks, case, arial ETC.
                    PC connectivity?
                    Cruise control on throttle (and all spring return controlls?)
                    Multi-model switching (model ID code at begining of each command)
                    Simple High-res mode?
                    AV recive?
                    Audio transmit?
                    Remote reprogrammability?
                    Lightweight budget IR transmit/recive?
                    Optional +/- or normal ("crawler mode")

Thanks again

 

Yet another question...

If I used some form of USB host module, on the transmitter side, and used a radio that allows remote re-programming, would it be possible to re-program one arduino (the one in the reciver) using the arduino in the transmitter, and code from the memory stick?

This is probably beyond what I can do at the moment, as I haven't even flashed an LED on an arduino yet, but I'd be intrested to know for the future.

Thanks

 

Another possibility...

I recently came across another posibility as to how to arange things, which might be a bit easier as a starting point. I was having a look at these. They are 2.4ghz conversion modules for non-modular transmitters. My thought is to get one of these, and interface it up to a DIY microcontroller-based transmitter. These have the advantage of good range (the 4ch recivers have about 500m, the 8ch ones have about 1.2km), allready availiable recivers, and I know they won't interfere with other people's systems. They are also relatively cheap (transmitter module and reciver), get good reviews, and have serial-based telemetry, for stuff like battery voltage, temprature and location (using GPS). There is also already some stuff on DIY telemetry using this.The connection to the transmitter using PPM, so the thing that I'd need to know is this; How hard is it to get a PPM signal out of a picaxe or arduino microcontroller?

PS: This is by no means my final decision on how I'm doing things, and it will still be a while before I get round to doing anything, due to other projects and exams.

 

More thinking...

Still haven't got around to doing anything on this, I'm afraid, as I've been busy redecorating. I have, however, got my hands on a raspberry pi, so I've been thinking; Would this be any good for a transmitter? Is it quick enough to put out a real-time signal, or not? Would I need a secondary microcontroller to handle some stuff, like PPM encoding? Is it worth using a raspberry pi for, or would I be better off with a standard microcontroller?

If I used the pi, how hard would it be to strip back the OS to just do the RC stuff? I woulden't need anything for networking, etc. and I might not even want any video output, so how much could I strip back linux to get it booting and running as quickly as possible?

Another question (a bit seperate) is this; is it possible for two microcontrollers to share memory? EG can one write a value to a space on an EEPROM, and then can that be read by another microcontroller? My thought here is that one microcontroller could handle the PPM encoding, and run really quickly, and the other could handle the inputs, throttle curves, mixing, etc. I'm not sure if this is worth doing, as an arduino might be able to run quick enough anyway.

I also found this arduino library; http://sourceforge.net/projects/arduinorclib/

I can't seem to find out all that much about it, and I have absolutely no expirence with libraries, so has anyone here used it?

PS; Entirely unrelated, but i've written my first instructables, and entered them into a competition. This is partially to show why I haven't had time to get started on this yet. If you want to have a look, here they are;

How to make a corflute roller-shutter (or any other curved shape)

How to make a Hi-Fi cabinet

If I shoulden't have posted them, I appologise.

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When I tested the small modules outside with my Rover I could drive it to the end of my garden (20m) without losing connection. I have one on the other end of my house with several brick walls between them and they never drop any packets. They can sent and receive but not at the same time. I sent data from my Rover back to my remote and display that data on an lcd. I'm very new to microcontrollers and programming but got them to work pretty easily.

As far as I know you can not use them to remote program an Arduino as the nRF24L01 can only be an SPI slave.

thanks for the info

What's the range like on the cheap ones?

If its not to good, is it possible to add a DIY amp and preamp?

Thanks

you have a couple of options. You can get a set of the really inexpensive RF transmit/receive pairs that are typically 433mhz or go with something like the xbee or its ilk. It boils down to how much data you need to move quickly, and, whether or not you need bidirectional communication.

If you were to consider something like the fetaduino, why not just get it and make use of it? Someone has already done the work to get everything to fit neatly together in a small package.

I would like to have bi-directional communication, as I'd like to be able to do a bit of telemetry (battery level, temp, etc), so I'd rather go for something like an xbee (although not an xbee, as they're a bit on the pricey side, and I want to keep costs down). Also, with bi-directional transmission, I might be able to rig up remote re-programming (I know that you can with the XRF modules, I'm not sure about others).

I was considering the fetaduino, but I prefer designing and making my own circuits and boards

Thanks

the fetaduino that ChristheCarpenter is selling on his rocketbrandstudios.com site. Add a couple joysticks and you should be good.

I did origeonally ask some questions on the fetaduino page on LMR, as it looked like it would probably do the trick, however I would rather custom-make my own board to do the job.

I don't know much about RC stuff. But I have a bunch of nRF24L01 modules that I use to control my Rover 5 and I'm using them for a home automation project. These modules are 2,4GHz and do 2Mbps. You can find these modules on ebay for 3$. I have 2 with amp and preamp that have a very big range (+1km), these cost a bit more (20$ a piece). They are well supported by Arduino, there are 2 libraries for them.

I had looked a little at these, but I wasn't sure of the range, and they seemed more expensive than the xrf modules

Could you post a link to the ones on E-bay? I've only come across the 20$ modules.

Also, would this cause any problems with other 2.4ghz radios?

Thanks for the help.