Misunderstanding of PSCU-BS2e communication

bhaskarghsh4 · 2013-10-30 00:49

I used the following program to move one vehicle continuously in forward & backward direction upto a certain distance.
I am using 2 servos (180 degree rotation) with the two wheels which is controlled by BS2e through PSCU.
When I am running the vehicle with the following program the wheels are rotating at different speed.
I am not getting how this is happening with this code. I will be thankful to you people for helping me to sortout what the problem is with the code.
By the by I measured the speed for both of the wheels with tachometer.
Thanks.

path_tracing.bse

Gadgetman · 2013-10-30 05:00

Can't really tell what's wrong as I don't know the PSCU, but...
(Are there any difference between the servos? Have you tried switching them around?)

I do notice that you have a few of these:

IF err=0 THEN
   Do something
ELSEIF err=1 THEN
   Do something else
ENDIF

This is 'not good' programming.
Sure, in this case err can only have those two values, but...
That means you could have used:

If err=0 THEN
  Do something
ELSE
  Do something else
ENDIF

In fact, if you turn the jobs around, it can be shortened a bit more:

If err THEN
  Do something else
ELSE
  Do something
ENDIF

(I think that should work. Haven't programmed a BS2 in 'a while')
Any test like '= something' takes time to execute after all. And it fills up the program memory, too.

bhaskarghsh4 · 2013-10-30 12:11

thanks Gadgetman

Chris Savage · 2013-10-30 22:53

Are the servos calibrated such that a 750 to both servos causes them to stop moving (not move)?

bhaskarghsh4 · 2013-10-31 02:52

Thank u sir for ur kind attention.
But for ur kind information i need to say that my vehicle is moving but the wheels have different speed.
Even as per my view it should not be different according to the code. I have measured the wheel speeds with tachometer.
So please help me to find out why this happens.

Thanks

Gadgetman · 2013-10-31 04:10

This probably happens because no two servos are alike.

Try experimenting with changing the speeds of each servo a bit.

Chris Savage · 2013-10-31 12:36

My question about calibration was directly related to your problem. If the servos aren't calibrated it could cause this very issue.

bhaskarghsh4 · 2013-10-31 22:23

Thanks sir .
But I am a newbie in bs2e (basically all parallax devices).
So I am not aware about this CALIBRATION process of servo you are talking about.
Is this done through the proper instruction in PSCU or by something else.

Gadgetman · 2013-11-01 00:35

To calibrate = to adjust, to correct...

What we mean is that you measure the difference in speed between the servos, then adjust the program to compensate.
One motor too slow? Just increase the 'Ramping' on it.
One motor doesn't stand still after initialisation?
Adjust up or down from 750 until it does.

If you look at a RC remote, there's always a set of sliding adjustments around the sticks, used to adjust the neutral position.
Servo motors use a simple comparator circuit to decide the position they're in and whether or not to move. This circuitry is of course made of the cheapest available components...

Chris Savage · 2013-11-04 13:30

In the context I intended I was referring to how our Continuous Rotation Servos have an adjustment potentiometer on them which adjusts the center (stop) position. If that potentiometer is not adjusted properly then the servo can exhibit many weird symptoms such as moving faster in one direction than the other or only moving in one direction and not the other.

Misunderstanding of PSCU-BS2e communication

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