I need a strong torque motor which move slow. However, I don't want to use gear train because gears will be damaged easily by the strong torque. Please give me some suggestion.
The cheapest and most common thing you will find is a stepper motor. You can salvage a few of those from old printers and scanners. And if you use microstep control, you can make it very slow and accurate (below the fundamental step of the motor). The problem with steppter motors is that they consume lots of current regardless of speed.
In any case, there are gears that can take a lot of torque. The gearbox in your car does a good job, for instance.
Did you know about these motors :
I think the industry name is direct drive motors or torque motors , these are AC or DC servo motors that are wound and designed for High torque and low speed . Their main purpose is replacing a geared motors ( higher efficiency , better inertia , faster response , zero backlash ) there main application is rotary tables in 5Axis CNC machines and anywhere slew drives where used previously.
Some manufacturers are :
A gear reduction or pulley reduction would likely be your best option to get increased torque and reduced speed. However, this would restrict the working speed to the exact ratio between the input and output gears or pulleys. Therefore, the solution would be a variable pitch pulley that would provide a wide range of ratios to arrive at the desired speed. There are variable pitch pulley sets that use a belt or a metal belt. The metal belt would likely not be practical for a custom-made device, but there are currently variable ratio transmissions in some automobiles. Check out the transmission in a new Nissan