Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: ashour on August 21, 2010, 11:47:57 AM

Title: Decrease motor speed without gearbox?
Post by: ashour on August 21, 2010, 11:47:57 AM

Hi, i'm trying to build the 40$ line follower robot , i've finished the electronics part , but i'm having so hard times with the mechanical part because none of the parts metioned in the tutorial are available with the same specs in where i live so i have to improvise , and i have a question about DC motors : i found a 6v DC-Motor but i think it have a very high RPM than the 100 rpm mentioned in the tutorial , i can't buy gearboxes even here , because that would be very expensive for me and geared motors available only as used parts from old copy machines !! so they are very big and miss axes usually !

So someone have any method to decrease the motor speed?
I've tried before adding resistors of 6.8 Ohm to the circuit and its not very nice idea

thanks

Title: Re: Decrease motor speed without gearbox?
Post by: waltr on August 21, 2010, 01:29:29 PM

This will be difficult to do electrically. I'll guess that your motors have a shaft about 5-10mm long and less than 1mm diameter. You can get a mechanical reduction when driving the wheels by having the motor shaft against the tread of the wheel. A little more description:
1- mount the wheels on an axial so the wheels are free to rotate.
2- mount the motor so the the motor's shaft is parallel to the wheel's axial and the motor's shaft is pressing against the wheel tread.
3- this gives a reduction ratio of motor shaft diamete divided by the wheel diameter.

  Her's a picture of my first Bot's motor drive:

Title: Re: Decrease motor speed without gearbox?
Post by: amando96 on August 22, 2010, 09:31:02 AM

^^ cheapest and simplest way.

A gear box doesn't simply slow the motor down, it transforms some of that speed into torque, which is necessary to move anything, without torque your robot wouldn't move.

Title: Re: Decrease motor speed without gearbox?
Post by: voyager2 on August 22, 2010, 06:14:42 PM

Thats a good idea Waltr,
I've got lots of those little 6-7.2v motors from toys I've "examined", but all hope of using them in a proper robot failed when I tested the tuque...
Mind you, if you are willing to pull apart a VCR or too you can get a pancake motor with lot's of tuque for it's size.

I wish i had sudden brain bursts like that....

Voyager

Title: Re: Decrease motor speed without gearbox?
Post by: waltr on August 22, 2010, 08:02:01 PM

I can't take credit for the idea since I borrowed it from someone else many years ago. I did think it is a great idea for getting something working with junk box parts.
Have fun.

Title: Re: Decrease motor speed without gearbox?
Post by: Soeren on August 24, 2010, 08:05:26 PM

Hi,

Velo Solex has used a similar method for transferring the motor power to the (front) wheel - a roller covered with something akin to sanding paper for grip (needles to say that the tires wear out relatively fast - and that it steers like *Censored* due to the front hinged motor that you lower to the tire for starting).