Motor Speed controler

 

The circuits shown below are a few of many suggested circuits as published by SCR and TRIAC manufacturers and cannot be construed as beeing the exact application for your requirements and I cannot be held responsible for their use and end results . 

click to enlarge

It is suggested that the subject of TRIAC and SCR as well as motor drive control systems be researched before making a final decision as to the application of these control circuits .
For satisfactory and safe results, knowing the exact type of motor you wish to control is of prime importance and all data available should be obtained before you contemplate to add any drive control circuits . Mount all SCR's and Triac on heatsink . Use current rated stranded wiring as required .

If you cannot find the SCR's and TRIAC's suggested in the circuits you may be able to find a substitute following this link Cross References

Some links to SCR's,TRiac's and motor control application notes:

Thyristors
Application Notes
Triac Data
NTE Triac Selection
NTE SCR Selection

You can use a transformer with up to 12 amps output current with corresponding fuse value . Use No.12-14 stranded wiring to battery connection with heavy duty clips .
Mount Rectifiers and SCR's on heatsink . You can use a mA meter with a shunt resistor . See Metering a power supply .

Note The rectifiers and SCR's value as quoted can be changed to lesser values as required for lower current output .