Thunderborg on DiddyBorgV2 movement variability

Unfortunately there is no way for the DiddyBorg V2 to measure how far it has really gone, all we can do is try and improve on the movement itself.

Given that the first move is correct my first suggestion would be to try waiting for a short period once the motors have been turned off after each move. This will given them an opportunity to stop between commands and may improve the consistency.

Look for the PerformMove function in the script:

# Function to perform a general movement
def PerformMove(driveLeft, driveRight, numSeconds):
    # Set the motors running
    TB.SetMotor1(driveLeft  * maxPower)
    TB.SetMotor2(driveRight * maxPower)
    # Wait for the time
    time.sleep(numSeconds)
    # Turn the motors off
    TB.MotorsOff()

All of the moves use this function to actually set the motor speeds. What you want to do is add another sleep at the end of the function for a fixed time like this:

# Function to perform a general movement
def PerformMove(driveLeft, driveRight, numSeconds):
    # Set the motors running
    TB.SetMotor1(driveLeft  * maxPower)
    TB.SetMotor2(driveRight * maxPower)
    # Wait for the time
    time.sleep(numSeconds)
    # Turn the motors off
    TB.MotorsOff()
    # Wait for the motors to fully stop
    time.sleep(1.0)

If that does solve the problem you can try reducing the 1.0 second delay between moves until it starts becoming unreliable again. If it does not improve things at all then this is not the problem and we need to try something else instead :)

My DiddyBorg V1 uses rotary encoders, repurposed mouse scroll wheels, running on the middle wheels, one each side with a simple mathematical "differential". The results are not perfect but are better than the "dead reckoning" method that you are using.
I also have an XloBorg which gives compass bearings which I use to get reasonably accurate angular movements.
I also work with a low "throttle" (maxpower * 0.6), the slow speed allowing the software time to work it all out, especially when using a camera and OpenCV to find and move towards a target.

I did post some photos on the forum a year or so ago but I can't remember where! Things have moved on since then anyway, I'll sort out some new ones soon.
Oleah, everything is based on modified PiBorg code and what can be found on Google, I can't claim much originality. The compass is on the PiBorg XyLoBorg but I had to work at the software to correct the output for variation and deviation. It was some time ago I did this and although I use the resulting code frequently to "aim" Diddy my brain struggles to remember the details.
The same is true for the rotary encoders, both the compass and the encoders run in separate threads. I'll try and publish some de-cluttered scripts in a few days.

Yes, thanks PiBorg, I remember them now. These are as Diddy is now, it looks pretty much the same but the webcam is now fixed rather than on a servo. The four ultrasonic sensors are now all arrayed on the front rather than two each fore and aft. The Gertboard has gone and I use a stand alone Darlington transistor array to switch the torches on and off.
Diddy's current task is to head towards a target (a coloured light) set at the same level as the webcam while avoiding low obstructions (empty coffee tins which the webcam can see over) using the ultrasonics. The compass is used to calculate the approximate bearing of the target if it gets out of sight after taking avoiding action so that Diddy knows which way to turn to get back on course.
I'm now working on the next task which will to identify an object or picture at the target. This will use the Pi camera.
The rotary encoders are now better and more reliably mounted than previously.
Software is mainly modified Piborg scripts in Python 2.7 with OpenCV 3.3.0 for dealing with image recognition and shape following. The Os is Rasbian Stretch and the brain is a Pi 3b. Manual control is by a PS3 controller and Diddy is set up as a WiFi access point and is run headless via VNC, either to my Windows 10 laptop or my "PortaPi", the latter made up of a Pi 2B, an official 7" screen, 2 BattBorgs and a Kano wireless keyboard.
If there's any interest I can post examples of my code for dealing with the compass and the rotary encoders.