ex-Gooserider wrote:I would agree w/ Lrobbins about the easiest method being to mimic the joystick.
I'd also point out that while I am not sure what is available for the VSI series (which are pretty much the 'lowest grade' controllers for use on low-end chairs, w/ 50A being really low-end) there are a lot of existing alternative input devices available for the better series of controllers like R-net, etc....
While possibly interesting as a 'learning exercise' I'm not sure how practically useful this would be as a project.... It seems likely to me that a CP (or other disability) user with enough functional challenges not to be able to use a regular joystick is probably going to be needing a more sophisticated (i.e. multiple seating controls) rehab chair than the very basic sort of chair the VSI series controllers are designed for.
ex-Gooserider
I was also wondering how to hack the controller as we are replacing it with another control.
greybeard wrote:Maybe tell your polytechnic not to waste its cash on this chair and buy one that's more likely to be currently in everyday use. That way somebody might actually benefit from your research.
Burgerman wrote:I cant help and I doubt anyone can. They dont publish such things.
I can tell you though that any powerchair with that controller is going to be unsuitable for a user with CP. Or in fact any serious disability.
This part baffles me.I was also wondering how to hack the controller as we are replacing it with another control.
Then do exactly that. Throw it away its a toy. Fit something better. What is it about that that needs "hacking"...?
What does one doing digital and one doing analog mean?
All controllers are pulse width control of current to motors since halfway through last century. And most mobility controllers use dc and analog for joystick input. What EXACTLY are you trying to do?
And why are you wanting us to do your homework for you?
Burgerman wrote:If you are not careful, you may be the one to leave!
You were already told how to do that alternate input above by several others. Many here have done it in order to drive by radio control etc including myself. You wont get hold of any better information as it doesent exist outdside of PGDT. And they certainly wont give you it.
What you need already exists. Including the four button switch input. Its called the R-net omni. It allows digital, or analog external inputs,very customisable programming inc latched etc, and is designed for exactly what you are doing. Theres also an IN/OUT module. For similar external custom control systems. You are reinventing the wheel. And trying to do it to the wrong low end control system. The easiest solution and the best in the end is to explain to those that chose this wheelchair that its the wrong one. And to select one that uses a R-net control system so that an external custom controller such as your 4 switches can be easily integrated. And have far greater programability with the controls too. And adequate power to boot.
What you want is one of these. http://sunrise.pgdrivestechnology.com/m ... 813-07.pdf It does exactly what you need. Already. Only with 20 years development and refinement built in. Theres a pilot plus Omni, an Rnet old style omni and a newer very compact one. All plug and play alternative inputs.
foghornleghorn wrote:The newVSI controller pictured is an all in one brain and joystick pod. No talking backwards and forwards from it to a separate controller.
I'm guessing you are in Singapore where this appears to be the commonly used control.
The simplest version of what it sounds like you want to achieve is 4 buttons:
1. Forward - both motors forwards
2. Backward - both motors backwards
3. Rotate the front of the chair to the right - left motor forwards
4. Rotate the front of the chair to the left - right motor forwards
I would have all buttons only work by themselves. Push one for a command to happen. Push two or more and nothing happens.
It may be better to have the left and right aiming send a time limited burst of power to the motor so one click turns 5 degrees for example rather than having the chair rotate forever if the button is held down.
One thing you need to be very aware of in an example where the driver doesn't have full ability is that an electric wheelchair can exert a lot of force on the person in a situation where they catch their leg against furniture or the wall. Broken bones happen very fast and heal very slowly.
LROBBINS wrote:No, you don't need to use RC. What you have to figure out are the X and Y voltage swings of the joystick pot inside the controller and make a circuit that mimics that. (One exception to this that I know of is the Dynamic Shark series which uses an digital rather than analog joystick pot.) That will be MUCH easier than trying to hack the serial digital signal (which may be of any one of a number of different protocols with a proprietary "dictionary" for the messages).
Burgerman wrote:I might add that once you figure out how to immitate the stock joystick dc voltage swings, reference voltage etc, to be able to control the chair without the joystick. That you will need to be able to interface with the your new control system, then you will come across several new problems.
ONE of these is that that in order to travel in straight lines and go where intended, rather than influenced by where the casters are pointing or need to change position, or influenced by carpet pile, or lateral slopes outdoors for water drainage on footpaths and roads, that you will need either a finely tuned gyro system, or a wheel encoder setup. Because it certainly will not go straight just because you tell it to do so. The stock motor load compansation algo isnt capable of this. The R-net system you should have started with, already has all required modules and firmware/software available to do this as part of its more advanced system. These are very much required if your system is to be any real help to an end user with only 4 buttons and no ability for steer correction in the usual way. Dont believe me? Try using a MANUAL wheelchair along a road edge. And THEN you will understand the problem. Right now you dont.
https://www.cw-industrialgroup.com/Prod ... ions/R-net System.
https://www.cw-industrialgroup.com/Prod ... -Interface omni for your speciality input control system.
https://www.cw-industrialgroup.com/Prod ... der-Module encoder module for accurate straight line tracking regardless of obstacles and wheel load.
https://www.cw-industrialgroup.com/Prod ... yro-Module gyro, acomplishes much the same thing.
All the settings and programming of these parts (modules) is built in to the system and can be configured with the OEM level programmer.
This is one of the many reasons that you are starting with the wrong system... Just for information. Your project has rather a long way to go to match what you should already be using as a starting point. I suspect a lot more than a couple of years at school as a project will accomplish.
Dan wrote:I think we need to accept that this is just a learning project for students rather than an attempt to find a solution to the problems a person with Cerebral Palsy might have when trying to use a powerchair.
nani13, you are trying to make something that already exists. There is already a full system for people with restricted movement. That R-net system has been here for a long time.
He has been tasked with creating a new interface to replace the joystick on the P&G VSI 50A controller. So what exactly does the joystick do? How does it create an output that can be used by the power module? How can that joysticks output be emulated?
Those questions have already been answered in this thread? Once you get it all figured out you should be able to hook up your emulator to use electroencephalography.
What do you mean I am starting with the wrong system? I am starting with this controller as it is BUILT IN and either way I am replacing it with my teammate's DIY control switches. So you recommend me getting this R NET System for steer correction? Is getting this system a must?
Burgerman wrote:Its unlikely he knows what motor load compensation is or why its essential in what he proposes. He has a plan. And only 2% of the required knowledge and understanding needed. That was one of many reasons I said that its not the right chair. Or controller!
LROBBINS wrote:That chair probably also has small, low power, 2-pole motors that might not withstand 120A draw and will not produce enough torque at currents they can stand to give good motor compensation (with or without an encoder). That was certainly the case with Rachi's original anemic Fracmo motors, even with caster angle sensors added. Once I'd changed the motors to much better ones, motor compensation worked well even with the sensors removed and even though it's front wheel drive. Turn in place remained a problem because it has far too much weight on the rear casters.
To see what the joystick pot does you have to open the case and find the wires that go from the joystick to the circuit board. If it's an analog joystick pot it will have one that's + supply, one that's ground, one (or two) that's a center tap half way between those, one (or two) for X output and one (or two) for Y output. The "or two" is because some pots have duplicate outputs that are used as a safety check that it's functioning correctly. Some fancier pots also have a separate output that is switched on when the stick is centered. Each output will = the center tap voltage when the stick is neutral and have a swing above and below that when the stick is moved. If there are two outputs for X (and for Y) they may swing in the same direction or swing in opposite directions. Chances are that this controller has the simplest pot available with just 5 wires: +, -, center, X and Y. In any case all you need to find out is a half-way decent voltmeter (and great care not to short anything when you are figuring it out). If there's actually a label on the pot you can search using the label information and probably find a data sheet which will tell you everything you need to know without even doing that. Then you have to design a switch interface that will produce the correct X and Y voltages.
LROBBINS wrote:The VSI almost surely uses one or another serial protocol to communicate with the rest of the system and hacking that may be a tall order. It may be much simpler to make an adapter that connects to the same leads as the joystick pot and mimics the joystick output. Do a search here for postings by woodygb to see how he's done that for using RC controllers to mimic other joystick controllers - yours will be similar. Years ago I had done something similar just using 4066 ICs connected to head and foot switches to select among a set of simple voltage dividers, but Woody's way is a much more flexible solution.
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