Hypothetical motor/gear ratio question

VEX IQ General Discussion
#1

Lets say you had one motor on a 1:5 torque ratio,
Now you want to make it two motor 1:5, so wouldnt it be twice as fast? while using half the energy?
Meaning you could make it 2:5 with two motors. So would that mean two motor 2:5 torque is FOUR TIMES faster than one motor 1:5?

#2

no

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#3

why not and how come u dont have the 20char rule

#4

yes

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#5

But also, its just not how motors work, you dont just gain extra speed by using 2 motors

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#6

Adding another motor gives you additional torque not speed. You could then adjust your gear ratio to convert that torque into more speed.

Imagine a bicycle with one rider. If you add a tandem rider the bike can’t go twice as fast. However they will have more strength working together and should be able to use faster gears.

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#7

Motors have power. Let’s say one motor has a power of 5, and if you spin it as fast as it can go, it has a speed of 100 and a torque of 100. (This is hypothetical, so the units don’t matter.) If you put one motor on a 1:5 torque ratio and spun it as fast as it would go, the end gear would have a speed of 20 (1/5th of 100) and a torque of 500 (5 times 100).

If you attached another motor to the driver gear, on the same axle as the first motor, and spun it as fast as it could go, it would have a speed of 100 and a torque of 100 (since hypothetical motors are all identical). Now, the input gear would have a speed of 100 (since two motors going 100 does not equal a gear going 200) and a torque of 200 (since it’s twice as hard to stop two motors as one). So logically it seems that the output gear should have a speed of 20 (1/5th the input) and a torque of 1,000 (5 times input), and since I’ve never actually tested it, all I can tell you is it seems logical. This is reasonable, since you only should have either twice the speed or twice the torque with two motors, right?

Now suppose you changed it to a 2:5 gear ratio with two motors. The motors are both spinning at 100 speed and 100 torque, so the input gear has 100 speed and 200 torque. Then the output gear has (100 X 2/5) speed :arrow_right: (100 X 2 / 5) :arrow_right: (200 / 5) :arrow_right: 40 speed. And the output gear has (100 X 5/2) torque :arrow_right: (500 / 2) :arrow_right: 250 torque.

So now we have a little table:

               | Speed | Torque |
---------------------------------
One motor 1:5  |  20   |  500   |
---------------------------------
Two motor 1:5  |  20   | 1,000  |
---------------------------------
Two motor 2:5  |  40   |  500   |
---------------------------------

This makes sense, because why would doubling the number of motors quadruple the power? “Because the world is strange.” Ok, so yeah, I’m not positive this is how it works, but it makes sense. Hopefully it makes more sense than

and

He probably did something like <ThisTextWouldBeHiddenIfIDidntHaveABackslashBeforeIt>

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#8

Just to clarify, theoretically what is mentioned above is correct. But the practical standpoint it’s slightly different. I totally agree in a perfect system with no load. If one motor yields velocity of 100 , than 2 motors should still yield velocity 100 with more torque or acceleration.

However, if the system is put on some load as with building VexIQ robots for the challenge, the weight or load of your robot plays an important role.

So you build a robot with 2 motor drive. You code max velocity to be 100 but since there is some weight to the robot, the motor is actually only yielding a true velocity of 75 let say. Now you add two motors to the robot to have a 4 motor drive. Now with this system, there is less strain on each individual motor and your code for max velocity of 100 now reaches say a true velocity of 90.

So yes, in theory adding more motors shouldn’t increase velocity since the motors are designed to spin at a given fix max velocity. But adding load or strain to the motors, will reduce the max velocity output of the system (slowing the motor down). So in a practical situation, adding more motors would give you more speed assuming you haven’t reached max velocity with your robot because of the load but it can’t give you more velocity than the theoretical max motor speed free of load. I.e. can’t go faster than the max velocity of 100. Unless of course the robot is going down a ramp. :stuck_out_tongue:

I hope that helps.

Cheers.

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