Making a wheeled mobile robot chassis
Date: Monday, June 16 @ 06:58:46 EDT
Due to their small size and lack of carrying ability, our robugs are far from satisfying some visitors' needs for bigger robots for their special projects. Now i've got a newer project for those visitors. A bigger, tri wheeled mobile robot chassis which is able to carry up to 2lb load which can go on many different surfaces.
The DC motors are german made, brand is Böhler. High quaility motors with reduction gear included in a very small package. Internally lubricated metallic gears with long life and precision. Each motor draws around 200mA current when turning freely. Two plastic wheels are made by me on a small lathe at our workshop. Two rubber rings are wrapped around the wheels to increase road grip. As the third wheel, a free turning caster one is selected and used. This can also be found in hardware stores in many varities.
These are the photographs of my first prototype. The design of the back wheel supports are different than the drawings in this article. i've first made that design and found it a bit difficult to produce and weak under load so i've modified the design. You had better make yours according to the drawings below, not the photos. ;)
The two boards that form the chasis are made from 6mm plywood. i've rounded the corners to give it a better look.
first i've made a one storey chassis, then added a second storey. It is possible to add a third one for additional electronics or sensors.
Anyway, these storeys need not to be made of plywood. they can be cut out of plastic boards, plexyglass, fiberglass, aluminium etc. any plain material which is light and durable enough. Below is a modification schema, all the shapes and motor locations are different.. wheels are also bigger. The modification of the design is up to you.
The side wiev of the motor part. The blue lines show the wheel and motor support which will be made of sheet metal. i've used the chassis metal of an old CDROM driver and cut it by using metal scissors. There should be two holes for securing the motor onto it and two bigger holes for the motor axle to pass thru.
The side wiev of the U profile that would be cut out of sheet metal. Blue lines show the sape. The dimensions are in milimeters. The triangle shape on the motor side is a bit wider to enlargen the surface that supports the weight of the motor. The triangle on the other side is smaller and for protecting the motor axle against heavy loads only. Normally it won't be in contact with the axle. The profile of the wheel is also shown.
The front wiev of the robot chassis. The motors are drawn a bit separated from the U profiles. Normally they will be in contact, securely screwed each other. The motor axle will pass from the hole of the side of the U, then thru the wheel and then thru the other side of the U. There will be no contact between the axle and the profile to prevent friction losses. The wheel will be secured to the axle to enable it turn with the axle. To make this i've made some special big screws with small stopper screws on them which holds the axle securely.
The perspective wiev of our robotic chassis which is very suitable for being a robotic vacuum cleaner.
Wiev from the right.
The blue lines show the motor at the right side of the chassis.
The blue lines show the motor at the left side of the chassis. As you see mounting of the motors are not exactly symmetrical. Because the axles of the motors are antisymmetric due to reduction gear inside. This is usually the case with small size DC motors with reduction like these. To enable the wheels be located symmetrycally, the motors are mounted on a bit untisymmetric locations. This won't effect the movement of the robot due the wheels are symmetric now.
You may see this antisymmetry better from the top wiev.