I think what AllanLane5 means is that "differential drive" really means different things at different times:
- in an automobile, differential drive means that both wheels on an axle can be "driven", i.e., powered, at different speeds, but both in the same direction. For example, when you are turning a corner, the inside drive wheel needs to turn slower while powered than the outside wheel
- in robotics and motion control, differential drive is used to refer to a platform that has two independently powered wheels on the same axis -- so that if both wheels go forward, the platform goes forward. If one wheel goes backward and the other goes forward, the platform turns/spins. Etc. The platform needs to be either self-balancing or be balanced by casters, ominwheels, etc. I have read that the true term for this kind of setup is "differential steering", not "differential drive", but robotic hobbyists use them interchangeably. The Boe-bot is a differentially steered platform.
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When the going gets weird, the weird turn pro. -- HST
And in electronics, differential drive refers to one line driving in one direction while the other in the pair drives the other direction, such as in an RS-485 network.
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If you are referring to "differential drive" in terms of motor drive, then the purpose of the "differential" is to balance the amount of power by re-distributing the drive
shaft energy to each wheel proportional to the wheel load. You can do this electronically as well as mechanically.
A simple hands on visual concept experiment: Take two identical electric motors and connect them in series to one another. With the remaining motor leads (One
from each motor) connect them to your power source (Battery). Both motors should spin and reach an equilibrium speed that is roughly the same for both motors.
Now with one of the motors, apply resistance to the shaft (<--with a small motor use your finger), the other motor should start spinning faster. This is similar in
principal to an electric car/robot taking a corner. The inside wheel of the turning radius will be slower (introducing more resistance) than the outside wheel (this
wheel will need to turn faster to makeup the radial distance) of the turning radius.
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IC Layout Engineer
Parallax, Inc.
Comments
- in an automobile, differential drive means that both wheels on an axle can be "driven", i.e., powered, at different speeds, but both in the same direction. For example, when you are turning a corner, the inside drive wheel needs to turn slower while powered than the outside wheel
- in robotics and motion control, differential drive is used to refer to a platform that has two independently powered wheels on the same axis -- so that if both wheels go forward, the platform goes forward. If one wheel goes backward and the other goes forward, the platform turns/spins. Etc. The platform needs to be either self-balancing or be balanced by casters, ominwheels, etc. I have read that the true term for this kind of setup is "differential steering", not "differential drive", but robotic hobbyists use them interchangeably. The Boe-bot is a differentially steered platform.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
When the going gets weird, the weird turn pro. -- HST
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
If you are referring to "differential drive" in terms of motor drive, then the purpose of the "differential" is to balance the amount of power by re-distributing the drive
shaft energy to each wheel proportional to the wheel load. You can do this electronically as well as mechanically.
A simple hands on visual concept experiment: Take two identical electric motors and connect them in series to one another. With the remaining motor leads (One
from each motor) connect them to your power source (Battery). Both motors should spin and reach an equilibrium speed that is roughly the same for both motors.
Now with one of the motors, apply resistance to the shaft (<--with a small motor use your finger), the other motor should start spinning faster. This is similar in
principal to an electric car/robot taking a corner. The inside wheel of the turning radius will be slower (introducing more resistance) than the outside wheel (this
wheel will need to turn faster to makeup the radial distance) of the turning radius.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.