Rnet CJSM2 not accurate

[expresso]

i have the Rnet CJSM2 - big nice color -

i recently starting using the chair - i usually use the JS to keep an eye on the miles i used - distance - i clear it each time before i go out

i reliezed - its not accurate at all - on a 40 mile ride - it showed 30 miles - my phone GPS shows 40 and i know the ride since i do it often - its 40 miles give or take

today i seen on a shorter ride - it showed about 5 miles off - 5 miles less shows -

strange - what could this mean - or how to fix it ? i had to unplug it a few times to program - but on my other Rnet chair - never had an issue and was correct the miles -

it was an rnet color JS - older model not the CJSM2 mode

any ideas ?

[Burgerman]

Obviously it cant ever be accurate. That distance and speed thing is a gimmick. Just like the battery gauge.

It doesent measure speed at all. It cant tell wheel speed. It shows how far you pushed the joystick only. And it displays this as speed. Yes its that basic!
Actual speed depends on gradients and load. If it cant tell the speed (no gps, no idea of real speed) then it doesent know how far you really travelled either. Because thats speed x time.

If you drive up to a steep slope or up to a wall for e.g then the chair wont move and the speed will read as whatever you pushed the joystick regardless. It doesent know the wheels are not turning. Or the actual wheel speed due to load. Or are turning slower due to load which they always do unless traveling downhill.

So that if you add weight to the chair. Or drive along a lateral slope like road that is cambered so it drains water properly, then the chair will go slower than the speed reading. So covers less distance over time than the reading says. Conversely on a flat road the opposite happens. So you will cover more distance at the same "speed" showing. The calculations are probably averaged or "fudged" to read something close to correct on average.

You can probably get it closer by changing the "design rated speed" on programming. Increase it to get it to cover more miles... But you cant ever get it correct as it doesent acually measure speed or miles. And varies due to load.

[expresso]

i know the speed isnt correct - i have larger rear tires - and upped it to 24.5V - two over stock - so this chairs feels very nice in speed dept.

its the JS screen Mileage - not correct - not even close -

you suggest i raise the fake speed limit to show a higher speed - ? change it to 10 miles - you think that will translate to a more accurate mileage reading ?

[Burgerman]

As I say whatever you set it to it will VARY due to load. Anyway. So will read different things on different days.

But you can get it closer to give a better average if the thing reads speed more accurately. So drive flat out for 100 yards IN A STRAIGHT LINE in a place where there are plenty satellites visible. Note accurate GPS speed.

Set chairs design speed to the same.
Set display speed to this too.

Then test.

[expresso]

i see - but i dont know of any way to set the display speed -

i can set the speed in the settings section - i can set to 10 - i have to test my speed but its close to 10 if not 10 itself

i am talking about distance - not speed - i know the speed display is not accurate - its the distance display -

[Burgerman]

It NEEDS an accurate speed to guess distance better. SPEED over TIME = DISTANCE.

Design rated speed and display speed right there in programming. Set both to whatever the GPS says is ACTUAL speed on the flat ground in a straight line. Its still never going to be accurate. That depends on load and so on terrain. Even tyre pressures. Will read high or low depending on route or day. Because it doesent ever know the actual speed only the joystick position.

[expresso]

its not about speed display - the speed will always say 8.5 when full speed - i am doing closer to 9.5 - 10

its not the speed i am talking about


its the distance - Miles driven - no speed involved -


the distance shows alot less than the actual distance covered - so i know it takes about 20 miles to get to where i went - one way

it shows i think 13.5 when i got there - i knew it was wrong - my GPS showed it correctly -

when i got home it showed about 30 or 31 miles covered - when in real life it was 40 miles -

[Burgerman]

This is goint to be one of those long threads where nothing sinks in and I repeat myself over and over. In many different ways.

It NEEDS an accurate speed to guess distance better. SPEED over TIME = DISTANCE.

Design rated speed and display speed right there in programming. Set both to whatever the GPS says is ACTUAL speed on the flat ground in a straight line. Its still never going to be accurate. That depends on load and so on terrain. Even tyre pressures. Will read high or low depending on route or day. Because it doesent ever know the actual speed only the joystick position.

How in hell do you suppose it knows how far you travelled?
It DOESENT!!!
It only knows how long you hold the joystick FORWARDS. It uses this INCORRECT forward speed on your display multiplied by time, to guess the distance travelled.

So if the SPEED displays inaccurately. Then the distance also displays inaccurately. Please read this properly before replying that you dont care about the speed... Only the distance!!!

[expresso]

you are saying that the speed is not correct - distance is tied to the speed so it will be off also

my older Rnet was pretty much accurate - you have the same JS - try it on yours one day - just to see

Ok - i raise the speed in the settings and test - if its closer to the correct distance - then i just play with the speed

[Burgerman]

Over and over...
I dont need to try it!

The R-Net system has absolutely no way to know distance.
It doesent have GPS. It only knows the JOYSTICK POSITION. It doesent know how fast a motor turns, wheel size, or anything else.
So YOU TELL IT how fast the chair goes at full speed by setting the chairs SPEED in programming.
It then thinks the chair travels at that speed when you push the joystick fully forwards. It doesent, it varies due to many things. But this is all it knows.

So if you set it to 6mph, it knows that at HALF stick you should be doing 3 mph. And at full stick 6mph. So if you hold it at say full stick for 1 hour then its covered 6 miles. THAT is how it determines distance. Thats ALL it knows.

Please read this because it is all that matters and you are not getting it!

So set your SPEED to whatever the GPS says is correct. Because until you do it will display distance covered WRONGLY!!!

THESE 2:

[expresso]

i have to only set the Max display speed - leave the rated speed alone ?

i am curious for you to try it to see if its that much off also - not to confirm what you are saying

my other chair JS older style - small color screen JS rnet - was pretty much on the nose -

next time i use it - i will see what the GPS tells me about the speed - and set it there - then test on a ride -

[Burgerman]

Ok - i raise the speed in the settings and test - if its closer to the correct distance - then i just play with the speed

No. SET IT TO THE GPS READING.

Because it will NEVER read accurately. The actual speed varies due to load, slopes, camber of road, hills, your weight, tyre pressures etc It will be as much as 25% out plus or minus on different days. You cannot fine tune that because thats it inbuilt level of "accuracy". It only knows JOYSTICK POSITION! One day it will read high. Another low. Theres no "correct" or correction possible other than adding the correct GPS speed on the flat.

[Burgerman]

i have to only set the Max display speed - leave the rated speed alone ?

i am curious for you to try it to see if its that much off also - not to confirm what you are saying

No BOTH!!!
As shown in yellow on the screenshot, and all the above posts telling you to do both...

my other chair JS older style - small color screen JS rnet - was pretty much on the nose -

Its not possible for this to be consistent. So it may read "on the nose" on one trip. And be 25% wrong on a different one. There IS no way to improve this.

will try 10mph and see what that does -

Again. SET TO WHATEVER THE GPS SAYS IS MAX SPEED - no hills, no turns over a long distance of say 100 yerds or more. NOT some arbitrary guesswork number. That wont work as the accuracy isnt adequate to do it that way. As different destinations will give different results.

[terry2]

i have to only set the Max display speed - leave the rated speed alone ?

i am curious for you to try it to see if its that much off also - not to confirm what you are saying

my other chair JS older style - small color screen JS rnet - was pretty much on the nose -

next time i use it - i will see what the GPS tells me about the speed - and set it there - then test on a ride -

Mine has a built in speedo in the rear wheel hub that talks to the R-Net controller.
It matches the GPS to a tee.

You could buy a bicycle speedo and fit that.

[Burgerman]

Thats an encoder. They are designed for connection to 2 motors or two wheels to give the r-net system better data for wheel speed for increased control. Esp on weird setups like stered casters/front drive. The module is an encoder module. They can be very accurate if configured correctly. It might also allow a more accurate speedo. I am not sure thats the case though. The speedometer/miles may still work in the same way expressos does.

https://www.cw-industrialgroup.com/Prod ... der-Module

[terry2]

Thats an encoder. They are designed for connection to 2 motors or two wheels to give the r-net system better data for wheel speed for increased control. Esp on weird setups like stered casters/front drive. The module is an encoder module. They can be very accurate if configured correctly. It might also allow a more accurate speedo. I am not sure thats the case though. The speedometer/miles may still work in the same way expressos does.

https://www.cw-industrialgroup.com/Prod ... der-Module

Mine is plugged in to the Can Bus\power control box with other things.

It has a magnet in the rear wheel hub. So the manual says.
But it's as near as one can get to telling the speed.

My smart shunt tells my the AH\Volts on the go with a graph if needed.
And that's nearly spot on with the PL8 and BG-8S battery go

[expresso]

i will do it in the settings and see how that works - or else i have to get used to the wrong display and work it that way

i know more or less what i can with the chair - it wont get drained enough to be a problem it was just accurate on my other JS

now brand new CJSM2 and its worse - older one worked better

[biscuit]

If it were down to me to design a wheelchair odometer I would rather not get involved with speed and time, it sounds far too complicated. I'd start with drive shaft rotations and move on to drive wheel diameter.

No doubt it would all come unstuck because nobody would ever go in a straight line.

[Burgerman]

And when you have the wheel diameter, and a revolution counter how do you determine speed? You multiply your revolutions (distance travelled on each revolution) by time = mph...

If it were down to me to design a wheelchair odometer I would rather not get involved with speed and time, it sounds far too complicated. I'd start with drive shaft rotations and move on to drive wheel diameter.

And your wheelchair has no way to count wheel revolutions. And it does not know wheel diameter.

[biscuit]

If I were counting wheelchair shaft revolutions I would want the shaft to see each time it pointed up and tell that to the controller. And I would want the wheelchair driver to tell the controller the wheel diameter so that the controller could do the arithmetic and display the distance.

I don't think that is a totally stupid idea.

Controllers are sent out to users with an actual time lag between the joystick movement and the wheelchair turning. That is a totally stupid idea.

[Burgerman]

True. And then it doesent stop turning when told so thats even more stupid. And EVERY chair does this. But you can fix this with an oem level programmer that they wont sell you!

[ex-Gooserider]

Thats an encoder. They are designed for connection to 2 motors or two wheels to give the r-net system better data for wheel speed for increased control. Esp on weird setups like stered casters/front drive. The module is an encoder module. They can be very accurate if configured correctly. It might also allow a more accurate speedo. I am not sure thats the case though. The speedometer/miles may still work in the same way expressos does.

https://www.cw-industrialgroup.com/Prod ... der-Module

No idea how R-Net handles encoder inputs, but the encoders will count wheel rotations to the accuracy limit of the encoder, which can range from as bad as 1 pulse / revolution, to tiny fractions of a revolution per pulse, they can also determine direction of rotation as long as there are 2 or more pulses / rev...

Pedal bike speedos are based typically on a single pulse / rev signal, and as such can't determine direction, so they may get slightly confused if one is doing a lot of tight maneuvering where the tracked wheel is reversing a lot. On a straight ahead run they will be pretty good but not perfect.

Assuming an encoder that can determine direction on each wheel, then it is pretty straightforward to get an exact count of revolutions, and then the accuracy of speed and distance reporting will be limited by the resolution of the encoder and how precisely the wheel diameter has been specified.

ex-Gooserider

[Burgerman]

Maybe. But I dont think the R-Net uses the encoder to determine speed or miles covered. Just to increase control accuracy similar to the gyro module. At least thats all it claims to do. And it doesent ask for wheel diameter anywhere.

[Scragger7]

Have tested my new q700 and its accurate with my GPS.

[Burgerman]

Is it 4, 6 or 8mph variant?

The 4 and 6mph ones are all using the same 6mph motor. Only the programming changes. (Theres some 8kph, 5mph HD options too but unlikely to have those).