It is relatively easy to find gears in many mechanical pieces. We have to be carefull when dismounting them in order not to destroy the potentially useful pieces

Many of the gears are made of plastic, but sometimes it may be important to consider using metallic discs in our design

A typical situation where a piece of metal will improve the way the motor moves is when willing to make the motor move in soft movements, the extra wheight of a metallic disc over the motor's shaft will give a certain inertia to the movement that will make it much softer

(in the picture, a complex gear used in a toy)

 

 

The other issue regarding the mechanical characteristics of a haptics control is the use of gears to reduce the speed the control presents to the user

As mentioned earlier, the consideration of something moving quick or slow depends on the case. Sometimes we need to reduce the speed our device will present to the user and the motor characteristics make impossible to reduce the speed any further through the use of the PWM signal. In that case we can use a set of gears to do so. In the picture you can see a very cheap set of gears we mounted on a powerful motor. The gears were part of an old printer, and would reduce the speed to a factor of 1 to 10. This means that if the motor spins at 1000 rpm, the final wheel spins at only 100 rpm

On the other hand, the use of gears is also affecting the amount of information the encoder produces. If we reduce the speed in that factor, it means that the final wheel of the gear will be having as many count points as 10 times the original value. So if our original encoder was having 500 points in resolution, the final resolution is of 5000 points. This is not affecting the speed that our microprocessor will count, but in a way shows that if we plan to use gears, we can from the start use encoders with smaller resolution values

Commercially it is possible to find gears that reduce the rotation in factors of like 30 or 50 in sets of already mounted wheels. Those are very expensive and, at the same time, tend to offer a pretty high physical resistance to the rotation, what makes them uninteresting for the specific application of haptics