Re: Re: Whoooosh..thud..oh bugger

[Simon Pawson <SimonP1234@xxxxxxxxxxxxx>]

I tried this reply last night but haven't seen it yet...

Coming totally from a strange direction....

could you do something with a reversing sensor system for a car. The bar
graph of LEDS could be converted to opto-isolators driving relays with
build in resistors to slow the travel.

Might be hard getting a reliable bounce if wall/frame mounted. Easier
spotting the wall from the door but not so elegant. Could be set up as a
safety measure as well. Child in the way stops (or even beeps).

Sorry just an odd thought - back to the merlot.

Simon


In message <461A91D0.8000200@xxxxxxx>, Martin Howell
<martin.howell@xxxxxxx> writes
>Hmm, this unit from RS gives the 'soft start' I'm looking
>for, but not the 'soft stop, which is where the real problem
>  lies.  I agree with your analysis of the drive train
>issues, but I'm concerned that strengthening the cables and
>applying more tension will just move the force to the next
>weakest part of the drive - the cable fails at present
>because of a joint, inserted partly to prevent breaking a
>more difficult to fix part of the drive.  I'm looking at a
>more simplistic system of forcing a slow down at each end of
>the movement, watch this space to see if it works, or if the
>whole contraption bursts through the wall into the garden :-)
>
>Martin
>
>David Cole wrote:
>> Martin
>>
>> Sounds to me like you need a PWM (Pulse Width Modulation) drive to
>> efficiently control the speed of the motor.
>>
>> Something along the lines of 510-1209 at RS should do it, this
would
>> give the acceleration and deceleration whilst also limiting the
>> current if the door jammed. Alternatively google for PWM DC drive
>> circuit
>>
>> You want to ensure that your drive train (cables) are as stiff as
>> possible, this is why industrial applications usually use rack and
>> pinion drives. This may mean increasing the diameter of the cable
to
>> ensure that you don't have any stretch which causes jerk. It
sounds
>> like you have a lot of inertia in your system it may help if you
add
>> additional gearing which will reduce the speed, increase the
torque
>> but also decrease the amount of reflected inertia seen by the
motor.
>>
>> Hope this helps
>>
>> Regards
>>
>> Dave
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
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--
Simon Pawson