Any idea how to make a drivetrain this smooth and fast?

VEX V5 General Discussion
,
#1

I’ve always had trouble making a robot that doesn’t shake forward and backward when changing direction or driving quickly. I recently saw this video and I was intrigued on what 606X used to create their drivetrain. My question is what methods should I use to create a smooth, fast, competitive robot? 2 or 4 motor drive? Gears or sprockets? What motor type(Red, Green, or Blue)? Where should I place the motors(two in front and two in back, two in the middle next to each other on both sides, etc.)? Also, what is the best place to put the electronics(brain, battery, vex net) and end effectors to have the best balance and not have to add a counterweight?

Lastly, what are PTO’s and what are they used for? Sorry for so many questions. :slight_smile:

Here’s the video I saw: 606X Spin Up | Intake Explanation - YouTube

2 Likes
#2

From my understanding, smooth drivetrains have nothing to do with the build it’s to do with the coding. I assume they they have allowed their robot to coast somehow with their code. Otherwise robots would jerk to a stop when you take your hands off the controls. Also if you are very aggressive with your driving that will also have an effect.

#3

To create a fast, smooth competitive robot you would need a:
4-8 motor drive (never use 2 unless you absolutely have to)
Gears have less friction than sprockets and take up less space so they are better for a DT
You should always try to minimize slop so you should use blue cartridges in pretty much all drives, unless you don’t have the correct spacing and gearing for them. (4” generally require a green cart, otherwise for 3.25 and 2.75 you should use blue carts)
You should pretty much always keep your drive symmetrical, and motor placement is usually determined by what kinds of mechanisms that you want your robot to have.
The best place to put electronics really depends on your bot, I usually put the brain + battery on one side and balance it with pneumatic reservoirs, or brain and battery deadmass and the reservoirs spaced out.
A PTO is a transmission that uses pneumatics to share motor power with different parts of a robot - basically a switch (EX: 6m drive cata bot using a pto to draw power from its other 2 motors to essentially make it a 8m drive cata bot)

4 Likes
#5

For my robot we are using 4(600rpm) motors geared 3:8. It is smooth fast and does not overheat quickly. Honestly I don’t know where to put the brain (I just quit it where ever I have space). A PTO is where you use a ratchet or a piston to move power from one source to another. This way two different mechanisms can be powered from one motor.

#6

Smooth drivetrains are partly programming but build quality is important too. I would recommend 4-6 motors for the drive. If you do not have pneumatics, 4 motors would be better.

2 Likes
#7

Build characteristics that will help the appearance of smoothness and retention of control while whizzing around include 1) a low centre of gravity, 2) wide and long wheelbase assessed in terms of where the wheels contact the ground and 3) rigid construction.

#8

Are the 4 and 3.25 and 2.75 inches the diameter of the wheels or gears?

#9

Can you provide an example of a code that would create such a smooth drivetrain?
Here’s the code I have right now:

while (true) {
    leftFront.setBrake(brakeType::coast);
    leftBack.setBrake(brakeType::coast);
    rightFront.setBrake(brakeType::coast);
    rightBack.setBrake(brakeType::coast);
    leftFront.spin(directionType::fwd, Controller1.Axis3.position()/1.25, pct);
    leftBack.spin(directionType::fwd, Controller1.Axis3.position()/1.25, pct); 
    rightFront.spin(directionType::fwd, Controller1.Axis2.position()/1.25, pct);
    rightBack.spin(directionType::fwd, Controller1.Axis2.position()/1.25, pct);

I’m not sure if setting the brake type in the beginning has any use…

#10

Also, do you think that a gear ratio for more speed is necessary for the drive train, or is a 1:1 gear ratio on 4 blue motors good enough? And what size of wheels would you recommend for the drivetrain that I want?

#11

Wheels

#12

If you are using a blue cart, you generally need to gear it down unless you want to run a 600 2.75 (very fast)
And if you are using a green cart, you usually need to gear it up unless you are running a 4m 4” drive

1 Like
#13

Also both 3.25 and 2.75 are good wheels, 4” ones generally have tipping and space issues. Recommended drive setups/rpm combos: 3.25 - 360 on 6m or 2.75 - 450 on 6m
**if you want to be competitive you will most likely need to use a 6m drive

1 Like
#14

@Orange_L, check out these resources:

4 Likes
#15

One more question: is there a good way to put on bearing flats for motors and shafts? Like is it best to keep the shaft in the middle of the bearing flat, or on one side? Especially for motors, because my motors always seem to get loose and are wobbly after some time and I’m unable to retighten them because I can’t get a good angle.

#16

For a smooth but fast drive you might want an exponential drivecode.
This can be done with math, and the one I’m using right now is to set the motor velocities to the [(axis_position)*abs(Same_axis_position)]/100
Here’s a screenshot of the code to show it better:
Split arcade steering:

image
image768×308 67.7 KB

Tank steering:
image
You will have finer control at lower speeds but still be able to reach the max speed

1 Like