[modeleng] Re: Where are you all?

Hi Hubert,

I am just building a heavy duty version of a train controller to control the 
speed of a fifteen amp dc motor. If you vary the voltage to the power supply 
you slow the motor but you also loose most of the torque. For the same 
reasons if you vary the output voltage to slow the motor from 12v to 6v for 
instance you again loose most of the torque so the motor can stall very 
easily.

I am building a small electronic controller using a couple of 555 chips and 
large mosfet transistor to pulse the motor. The length and frquency of the 
12v pulses varies the speed without loosing any torque. There were some 
simple plans for one in ME I think last year.

Perhaps the better choice to better control your leadscrew would be a 
stepper motor and controller. Drive directly or gear 2:1 and you shoiuld 
see300-600rpm which is proibably far more than you need for the leadscrew. 
The torque is better on steppers when they are run slower than full speed. 
ArcEuro sell a controller for £28. It can be driven by a simple 555 control 
circuit. Again plans are in ME from within the last 18 month. By coincinence 
I am also building one of these to drive the table on a seig X3 and one to 
drive the leadscrew on my Seig lathe. If I get a chance to get into the 
workshop tomorrow I can find the issue numbers for you if you want or if you 
can wait til I have built them can send u photos and diagrams.


Regards

Julian.
----- Original Message ----- 
From: "Shep" <shep.28@xxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Wednesday, September 17, 2008 3:28 PM
Subject: [modeleng] Re: Where are you all?


> Hello everyone
>
> That's MUCH better!     Four immediate replies, full of most useful
> suggestions!     Thanks chaps!
>
> My detailed replies are below.
>
> Cheers!   Hubert
>
>
> Hi Jeff D
>
> Thanks for your prompt reply.     I never thought of a model train
> controller.    The wirebound rheostats from RS Components were in excess 
> of
> £50!     If my present solution does not work properly, I will certainly
> follow your suggestion
>
>
> Hi Patrick
>
> I did indeed think about sewing machine controllers, but the foot 
> operation
> is rather clumsy for this particular
>
>
> Hi Peter
>
> I did consider the possibility of overheating - and I will knock out 
> several
> of the round discs in the steel container to help with ventilation.
>
>
> Hi Rich
>
> Thanks for your long and informative message.    I know very little about
> these matters!     The use of this drive will be intermittent, and the 
> load
> light.   If the dimmer fails, they are relatively inexpensive.
> I will probably use the clasp nut to disengage the drive, rather than 
> depend
> on the possibly dicey switch.    I have replaced the fuse in the plug to a
> 3A.
>
> I have cut a five-groove poly-vee pulley to sit on the end of the 
> leadscrew
> and a mating one for the motor.   The little lathe is on an old Myford
> stand, on the top shelf of  which is a three-phase motor controlled by an
> inverter.     Once again, a five-groove polyvee, in this case cut directly
> into the mandrel     Thus both motors will be directly below the lathe,
> making a neat drive.    I have not yet tried the wiper motor, but the main
> motor works fine, although the diameter of the 'pulley' on the mandrel is
> only 20mm.      The drive to the leadscrew will be very slow, and if it
> slips, I will have to try a tooth-belt drive.    I have a very old 
> Hardinge
> lathe and the ability to change mandrel speed and cutting feed, while
> actually cutting metal, is magic.
>
> To gain extra length for the gear train (I want to use Myford 
> changewheels,
> of which I have a plethora - bought for the Hardinge, where they fit
> perfectly, saving the HUGE cost of Hardinge gears!).
> I am considering making a tumbler-gear reversing mechanism on the 
> right-hand
> side of the 'wall' supporting the banjo.   This will give me a  couple of
> extra inches of vertical space to accommodate the Myford gears, and will
> obviously give me 'reverse' - but in 'neutral' it will disengage the gear
> train when the wiper-motor is used.
>
> I cut the leadscrew 10tpi Acme (I have at LH tap!).   I used this thread, 
> as
> 10tpi = 2.54mm - near enough to 2.5mm, when cutting fine and short 
> threads,
> to make no difference.   This removes the necessity of a large conversion
> gear.
>
> Good luck with the Hobbymat conversion - let's hear your progress!
>
>
> This is a heavy little beast, carved out of large lumps of cast iron (my
> main product was swarf!).    If any of you wish to see the 
> work-in-progress,
> give me your email address, and I will send you some pics.
>
> Cheers again!   Hubert
>
>
> ----- Original Message ----- 
> From: "Jeff D" <jeffdayman@xxxxxxxxxxxx>
> To: <modeleng@xxxxxxxxxxxxx>
> Sent: Wednesday, September 17, 2008 12:19 PM
> Subject: [modeleng] Re: Where are you all?
>
>
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