Gearbox For Wheeled Robot : Differentials & Transmission

A dc motor can spin up with quite good rotational speed. But a gearbox can alter the rotational speed to higher torque. Here is a Guide on Choosing the Right Gearbox For Wheeled Robot. Our goal is to make a sturdy design in DIY way to save the cost in long term. Information is provided to avoid various deliberate bad idea distributed by consumer grade websites with a shop beside the blog. We will go towards automobile design to drive the wheels. That is time tested to work on real life on normal plain surface.

Robotics Peoples are quite back dated, they are not RC Car hobbyists. They only add a circuit over 4 wheeled box. Their “gearbox” is not exactly what “gearbox” means in real life. Gearbox means Transmission gearbox. Your car have automatic transmission, manual stick gear etc. & you drive it. If we attack their robot cars with our RC Cars, their automation will break in to pieces. Because our RC Cars are exact minfied form of a real car. We will attack at first gear to give the highest hit & can see via camera.

In very short, we expect that you know zero, your fund is zero, but you will buy metal or parts made of highly durable materials for the creation a autopliot car or rather autopilot robot. That robot will do work.

Choosing the Right Gearbox For Wheeled Robot : Axle wheel Differential Kit

Previously, we have talked about selecting wheeled robot chassis. Regular readers of this website already know the basics – basic way to control a 3V DC motor with Arduino, somewhat advanced way to control a 3V DC motor with Arduino and a basic way to use a LED as sensor. This guide on Choosing the Right Gearbox For Wheeled Robot is important as you may use different DC motor depending on your need. We are taking that the wheels are flat tyre – like those F1 racing cars, two wheels out of total four wheels will be connected to the motor and remembering basic formula (x is used to indicate multiplication) like :

Power = Torque x Speed
FinalTorque = TORQUEofMotor x gearRatio x gearEfiiciency

Choosing the Right Gearbox For Wheeled Robot : Axle wheel Differential Kit

Attaching DC Motors directly to the wheels is fucking bad idea of DIY Electronics stuff selling projects including Arduino, Adafruit etc. Obviously they tell this way knowingly. This method of direct adding is called direct transmission. Small DC motors are not designed to bear any bending stress which is normal in case of directly mounting on a wheel. It is even bad idea to give 50gm over such a design. It can not run 15 mins per day x 10 years unless you are running it on glass or nice floor.

It is done indirectly to make the motors die faster. Easiest way is to design is quite easy like the mechanical spring toys – two wheels would be connected with a shaft and motor’s shaft will be connected to the DC Motor with a simple belt. That is called undirect transmission system. This means that the shaft holding the wheels is on a totally different plane than the shaft of the motor. There will be free movement of the belt if too much load given to the wheels. Indirectly the motor is less likely to face abnormal stress. That is how your car is also designed from mechanical point of view. Otherwise you can not apply brake, there would be no suspension/spring system. This called Differentials in case of a rear wheel drive car.

Now, the wheels will spin at different speeds when turning, total path travelled will be different for each wheels. So, let us break the two wheel connecting shaft in to left and right axles. Add a simple gear at the inner end of each axles, add a ring gear at 90 degree to connect the two separated axels to a virtual one shaft. Now your DC motor-gearbox output shaft should become another long rod which we will say pinion, with a gear end, which we will say pinion gear to rotate the ring gear. We can add two side gears on the ring gear to make flawless. This is called “Advanced Gear Kit” in miniature world or scale model world. That is how all normal rear wheel drive vehicles run. This is how knowledge can reduce the cost – one 3V DC Motor can actually run a DIY basic wheeled robot chassis. Lego actually has this full system in plastic form – Lego Differential Kit. When you’ll search for robotics, you’ll search with “Axle wheel Differential Kit”. This is an animated image from Tamiya’s one RC car :

Part-time four-wheel-drive systems in cars do not have a differential between the front and rear wheels. In normal consumer grade wheeled robot chassis, the design of front wheel drive car is followed.

Choosing the Right Gearbox For Wheeled Robot : Motor and Gearing Combination

For choosing the right gearbox for wheeled robot a motor, one should consider the following points :

What is the typical power needed? Most motors are classified according to their power. Smallest, lightest, most inexpensive motor which meets the requirements should be the choice. Voltage is another important deciding factor as higher voltage need of a battery will demand bigger (and heavier) battery.

We can optimize the design for maximum efficiency in converting electrical power to mechanical power, to save electrical power. Motors are usually most efficient at converting electrical power to mechanical power at high speeds. Gearboxes with larger gear ratios generally have lower efficiency than gearboxes with smaller gear ratios.

Efficiency in converting electrical to mechanical power is usually not a concern.
Some of the mechanical power created by a motor goes to accelerate the rotor of the motor itself, and some of it goes to accelerate the load. Next, we need to choose a gearbox for the motor so that we can achieve the speed plus torque combination.

We can divide gears in to certain types – Spur Gears, Rack and Pinion, Bevel Gears, Helical Gears, Worm Drives, Planetary Gears, Ball Screw/Lead Screw and Harmonic Drive Gears. Three types of gearing are common in robots – Harmonic drives, Planetary drive and Cyclodal drive.

Choosing the Right Gearbox For Wheeled Robot : Dimension Characteristic of DC Motors

It is quite important to know the terminologies related to the dimension characteristic of DC motors and the key factor the terminologies play to really drive a wheeled chassis with load. They are –

Speed in RPM, Torque, Voltage, Current, Efficiency, Audible Noise, Electrical Noise, Mass and Dimension. It is beyond the scope of this article to discuss the points.

Choosing the Right Gearbox For Wheeled Robot : DC Gearhead Motors Are Over Simplified Solution

Gearhead motors have a separate chamber, with a visible form as either a rectangular box or a cylinder in front of the DC motor. The whole unit is sold for the consumer grade DIY robots. Gearhead is too simplified and probably great.

Cheap DC Gearhead Motors are sold with terminologies like “DC Geared Motor”, “DC Gear Motor” on Ebay, Amazon etc. They are usually of 100-150 RPM range and come with a price tag of $2 – $10. Great for basic works. We do not thing you are even thinking about this option as you have understood the basic.

Choosing the Right Gearbox For Wheeled Robot : Real 5 Speed Gearbox

An ideal rear Wheel Drive 4 wheeled robotic car will have real wheel differential, 4 speed gearbox with way to control the gear to select the right ratio in appropriate situation like a real stick gear car and a separate front wheel steering system. Yes, Lego has gearbox – Lego 5 speed gearbox! Tamiya also has like Lego. Yes, things will go towards scaled model cars. Radio controlled (or RC) cars have everything. Electric RC Cars are taken as “bad” (lol), kids play with them. We are elderly person, we should have 4 stroke engine with good brake.

There is dog gear shifting & other ways to change the gear.

Choosing the Right Gearbox For Wheeled Robot : RC Car Robotics

From many points RC Cars are best for building wheeled robots. From tires, suspensors – all has replacement supply, RC Cars are not for kids, serious adults talks about them on few hundreds of online forums. People there will joke you if you suddenly ask about how to add a DC motor skipping the fuel powered engine. You have to learn yourself to build from the chassis. If you search with “Tamiya Type-S Chassis Kit”, you’ll get the idea of the real 4 wheeled robotic chassis.

Your original intention was to create a wheeled robot which is perfect. Instead of donating money to the DIY electronics manufacturers who also manufacture gears, it is more reliable to depend on a RC Car company with large user base. If the wheel of that DIY electronics manufacturers’ body’s robot breaks, you have two option – buy the full thing or buy a set of 4 wheels. But a RC car sells everything as an individual part like a car seller plus there are third party parts manufacturers. It will easily stay for more than 2 decades with good maintenance.

Additionally the suspensors/springs & other detailed parts will ensure longevity of the Board & other electronic kits. You’ll work in a way so that you may take out the board & use it for other projects. You are not seeing it, so it is a flexible matter. Even paying $10 for a plastic gearbox is factually useless. With high load the teeth may break. RC Cars are made for handing the odd situations in real world.

Joking Robotics Peoples is just for fun. Definitely they know more about the electronics part. The discussed topic is about really working stuff which has durability. Being gears individually is for learning gears,Lego’s level is up to learning. If you buy a metal gearbox as electronics matter, you’ll not know how to maintain with which lubricant. Tamiya is just one name, there are lot of good companies. HPI Racing is another company which you may like. Tamiya 4WD Chassis Kit cost quite less if you want something at lesser budget – $30. They have specification like real car :

You need not to think about many mechanical matters.