An Update on Keith Cameron's Lift

The Model is based on a design by Keith Cameron published in Constructor quartely No 7 march 1990 and is a simple example of the application of the Motorvator. This really complements my tram model as in the latter case this was an example of how the Motorvator could considerably simplify the automatic operation of a model without user intervention, whereas the lift model demonstrates how the Motorvator can considerably simplify a model requiring user intervention. I have seen a lift model wth a very complex circuit involving numerous relays to do the same job.

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The model is accurate at floor levels to about +- 3mm max.and more usually to +- 2mm. It might be possible to improve on this with further tweaking. The problems are motor overrun , positioning of the rotation counter when it stops and possibly the rotation counter missing a pulse ( I don't think this happens although it might). I have used a Meccanisms 107rpm motor which seems just right for the job. Of course a stepper would give exact positioning and I might modify the model to test this.

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On the model, selecting ground or 5th floor will re register the position and can always be selected if a sgnificant position error is noticed although in practice I have rarely found an error greater than 4mm. Andrew has suggested that greater accuracy might be obtained by slowing the motor to reduce overun as the lift approaches floor level and I am experimenting with this.

Note that the limit switch in the photo IS the ground floor switch: it is triggered by the counterweight which is of course at the top when the lift car is at the bottom!

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The Consul of lift call buttons is made of standard Meccano and Electrikit parts. the connection to the motorvator is to OnOff 1(two wires), OnOff 2 to 4 (+ive pin only), Timed 1 (centre pin only) and timed 2 (centre pin only). The ground is connected at the consul to all 6 inputs.

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The inputs from the model are the rotation counter connected by two wires to Timed 4 (ground and centre signal pins), the limit switch for ground and fifth (two switches one connection to timed 3) and the motor connected to motor port B.

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I have used the Director socket extension board but I imagine that the Analogue inputs on the Motorvator could be used instead with a small change in the program.

As you can see the program consists of a simple loop which tests for a button press for each floor in turn.

The Consul could be considered as a model specific "Director" and the idea could be extended to much more complex models.

Here is the code for the MotorVator


Begin Program
Declare Byte Counter=0
Declare Byte Totalcount=0
Declare Byte Stoptb=0
Declare Byte Ground=0
Declare Byte First=0
Declare Byte Second=0
Declare Byte Third=0
Declare Byte Fourth=0
declare Byte Fifth=0
Declare Byte DiffCount=0
Declare Byte StartCount=0
Declare Byte Finalcount=0
Declare Byte AtFloor=0
Declare Byte Speed=50
Disable Events
SetEvent 19,rotationcount
Enable Events
Call Initialise()  ;This initialises the program and takes the lift to the Ground floor
Loop
    ground=readOnOff(1)    
    if ground=1 then
        AtFloor=0     ;This variable prevents any action if the lift is already at the floor for the button pressed
        Call Initialise()  ;also reregisters position
    end if
    first=readOnOff(2)
    if AtFloor<>1 then
    if first=1 then
        call  GoToFirst()
        Atfloor=1
    end if
    end if
    second=readOnOff(3)
    if second=1 then
    if AtFloor<>2 then
        Call GoToSecond()
        AtFloor=2
    end if
    end if
    third=readOnOff(4)
    if third=1 then
    if AtFloor<>3 then    
        Call GoToThird()
        AtFloor=3
    end if
    end if
    fourth=readtimedstate(1)
    if fourth=1 then
    if AtFloor<>4 then
            Call GoToFourth()    
            AtFloor=4
    end if
    end if
    fifth=Readtimedstate(2)
    if fifth=1 then
        Call GoToFifth()     ;Also reregisters position
        AtFloor=5
    end if
End Loop
    
End Program

Declare EventHandler RotationCount()
    counter=ReadTimedState(4)
    If counter=1 then
        TotalCount=TotalCount+1
    End  If
    DisplayNumber Totalcount
End EventHandler

Declare Function Initialise()
    SetMotor 2,backward,speed
    Do
        stoptb=readtimedstate(3)
    Until stoptb=1
    Do
        SetMotor 2,backward,speed
        counter=ReadTimedState(4)
    Until counter=0
    Stopmotors
    totalcount=0
End Function

Declare Function 

GoToFifth()
    SetMotor 2,Forward,speed
    Do
    Stoptb=readtimedstate(3)
    Until Stoptb=1
    ;displayNumber totalcount
    Do
        counter=1                     ; An attempt to move the counter to a standard position
        displayNumber counter
        SetMotor 2,forward,speed
        counter=ReadTimedState(4)
        displayNumber counter
    Until counter=0
    Stopmotors
    totalcount=120
    stoptb=0
End Function

Declare Function 

GoToFirst()
    If TotalCount<=24 then
    Do
        SetMotor 2, forward,speed
    Until totalcount=26
    totalcount=24
    End If
    If TotalCount>24 then
    StartCount=totalcount
    Do
        SetMotor 2, backward,speed
        DiffCount=Startcount-totalcount  ;calculates the position relative to the last count
        finalcount=Startcount+DiffCount
        Until finalcount=30
    TotalCount=24
    End If
    StopMotors

End 

Function

Declare Function 

GoToSecond()
    If TotalCount<=48 then
    Do
        SetMotor 2, forward,speed
    Until totalcount=48
    End If
    If TotalCount>48 then
    StartCount=totalcount
    Do
        SetMotor 2, backward,speed
        DiffCount=Startcount-totalcount
        finalcount=Startcount+DiffCount
    Until finalcount=53   ;In an ideal world this would be 48 but changes were made to allow for motor overun. 
    TotalCount=48
    End If
    StopMotors
End Function

Declare Function 

GoToThird()
    If TotalCount<=72 then
    Do
        SetMotor 2, forward,speed
    Until totalcount=72
    End If
    If TotalCount>72 then
    StartCount=totalcount
    Do
        SetMotor 2, backward,speed
        DiffCount=Startcount-totalcount
        finalcount=Startcount+DiffCount
    Until finalcount=76        ;see note above
    Totalcount=72
    End If
    StopMotors
End Function

Declare Function 

GoToFourth()
    If TotalCount<=96 then
    Do
        SetMotor 2, forward,speed
    Until totalcount=96
    End If
    If TotalCount>96 then
    StartCount=totalcount
    Do
        SetMotor 2, backward,speed
        DiffCount=Startcount-totalcount
        finalcount=Startcount+DiffCount
        DisplayNumber finalcount
        Until finalcount=101
    End If
    TotalCount=96
    StopMotors
End Function