AscendRobotics/AscendData · Datasets at Hugging Face

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Example drivetrain CAD
Another type of drivetrain is the X-drive. This drive has more maneuverability, but reduced torque and pushing power relative to the standard tank drive.


Photo credit: Team 1619Z
While the increased maneuverability does offer an advantage in niche scenarios, X-drives are very weak against defense by others teams. For example, out of the 20 teams that won their division during Spin Up Worlds (i.e. top 20 teams in the world), all 20 of them used a tank drive.
There are another couple types of drivetrains, but these are not competitively viable in VEX Robotics.

Overall, the recommended drivetrain for both new and experienced teams is the standard tank drive.
Design Guidelines
Let's assume you're going with the tank drivetrain (please do!). Here's a few general guidelines to keep in mind while designing it.
* Smaller is generally better, but don't make a drive so small that it can't fit other mechanisms on the top of the robot
* Don't use any more gears than is absolutely necessary, to reduce friction
* Have the wheels as far apart as possible, which makes it harder for the robot to tip over
* Use 2-3 cross-braces, and have them as far apart as possible. This keeps the chassis from bending under heavy defense
Here's another example CAD that follows these guidelines. Always CAD the drivetrain before building it!


Over Under drivetrain CAD from 96504C
Additional Resources
Here's two videos on how to square the chassis--this is very important for having consistent autonomous and a low friction drivetrain.

Screw Joints
Screw joints are an advanced build technique that reduces friction and increases structural stability on the drivetrain, compared to using axles on the wheels.
Here's one type of screw joint:


Layout for one type of screw joint
Here's how to attach the gear to the wheel for this type of screw joint:


And here's another type of screw joint using a 2.75" wheel with a 48T gear:
Boxing
No, not that type of boxing
Boxing is an advanced build technique that improves the stability of a connection. The basic idea is to prevent a C-channel from bending by supporting it at two points rather than one. This is done with a long screw and 7/8" of spacing on the inside of a C-channel.
Here's an intake before and after boxing. In the picture to the left, the C-channel bent under heavy defense. It was fixed in the picture to the right by boxing, and the C-channel never bent again.

We also recommend boxing the cross-braces on the drivetrain as shown below. This prevents the drive C-channels from bending and makes the robot more durable.


Note that only the corner screw needs boxing
Bearing flats
It turns out that the square holes in vex metal pieces aren't a great fit for a rotating axle. Yes, they technically work, but the axle is highly unstable, and the friction is egregious.


Note the shape of the hole in the metal
The solution? Bearing flats! Bearing flats are essential for having low-friction drivetrains, and also for other mechanisms on the robot. They keep shafts aligned to the center of the hole, preventing it from touching the metal (which adds friction) or wobbling.


Bearing flats should be used on either side of an axle to support it and reduce friction. However, a motor also supports the axle, so there is no need for a bearing flat right next to a motor:


On the drivetrain, bearing flats should be used for both axle and screw joints (as possible), since they do reduce friction. For example, in the drivetrain below, the motor shafts have one bearing flat on the outside to keep the motor axle stable.


Note the zip ties. Yes, this works, and it works well!

Fixing Friction
Not this again...
Friction on the drivetrain can be caused by any number of issues.
Testing Friction
Luckily, it's relatively easy to test drivetrain friction. Attach all of the gears and wheels, but not the motors and motor cartridges, like so:


Then, give the drivetrain a good spin with your hand, as fast as you can. The drivetrain should keep spinning for at least:
* 3 seconds, if you have axle joints
* 5 seconds, if you have screw joints
This is called the freespin time, and it's a great way to test the friction on the drivetrain. The longer the freespin time, the less friction there is.
Fixing Friction
If the freespin time on the robot is longer than acceptable, there is friction somewhere. Here's a few potential sources of friction:
Bent axles
If the drive axles are bent, then nothing else can really work. To test if an axle is bent, press it against something you know is flat and look for a gap between the axle and the flat surface. Do this for all four sides of the axle.


Note the gap between the wooden table and the axle
If it is bent, then simply replace the axle and throw away the old one. There's no reason to keep bent axles around.
Tight spacing
On either axles or screws, too much spacing can cause friction issues. That's because the spacers rub against the drive C-channel, which adds resistance and extra friction. The wheel should be axle to wobble back and forth on the axle/screw by about 0.25 mm. If it can't wobble a little, then likely the spacing is too tight. Remove some of the spacers and replace them with shorter ones.




In the images above, there isn't a small gap anywhere along the axle. Thus, the spacing is too tight; this will cause friction issues. In this case, removing a washer would be the best way to fix it.
Misaligned drive C-channels
If the drive C-channels are even slightly misaligned, then that can cause friction because the axles won't be perfectly perpendicular to the inside face of the drive C-channels. Make sure to square your chassis before you start building the drivetrain to resolve this problem.
Extraneous shaft collars
Shaft collars are essential in VEX Robotics. However, there should never be shaft collars on the outside of the drive C-channels--they only cause extra friction. One shaft collar on the inside of an axle is enough to lock it in place.
Bad bearing flats
Sometimes, bearing flats go bad or can become misaligned with the holes in C-channels. If a bearing flat seems to be causing a problem, try replacing it.
Bad motor cartridges / motors
Make sure to test each motor before putting it on the drivetrain. Ideally, each motor (with the motor cartridge in) should not draw more than 0.1 - 0.2 watts of power at max speed. Use the "devices" screen on the brain to test the motor, and if it draws more than 0.2 watts of power, try to find a different motor with less internal friction. Additionally, make sure to test each cartridge as well. Bad motors and cartridges ruin a good drivetrain.



450 RPM on 2.75"
The best drivetrain
In this tutorial, we'll show you how to build a 6-motor 450 RPM on 2.75" drivetrain, one of the best in the world. This drivetrain is fast, low-centered, and easy to build on.
We'll start with the wheel assembly. We used 1.5” screws, ¼” spacers, and nylock nuts to connect the 48T gears to the 2.75” wheels as shown. There are two screws that go through opposite sides to balance the weight.

Example drivetrain CAD

Another type of drivetrain is the X-drive. This drive has more maneuverability, but reduced torque and pushing power relative to the standard tank drive.

Photo credit: Team 1619Z

While the increased maneuverability does offer an advantage in niche scenarios, X-drives are very weak against defense by others teams. For example, out of the 20 teams that won their division during Spin Up Worlds (i.e. top 20 teams in the world), all 20 of them used a tank drive.

There are another couple types of drivetrains, but these are not competitively viable in VEX Robotics.

Overall, the recommended drivetrain for both new and experienced teams is the standard tank drive.

Design Guidelines

Let's assume you're going with the tank drivetrain (please do!). Here's a few general guidelines to keep in mind while designing it.

* Smaller is generally better, but don't make a drive so small that it can't fit other mechanisms on the top of the robot

* Don't use any more gears than is absolutely necessary, to reduce friction

* Have the wheels as far apart as possible, which makes it harder for the robot to tip over

* Use 2-3 cross-braces, and have them as far apart as possible. This keeps the chassis from bending under heavy defense

Here's another example CAD that follows these guidelines. Always CAD the drivetrain before building it!

Over Under drivetrain CAD from 96504C

Additional Resources

Here's two videos on how to square the chassis--this is very important for having consistent autonomous and a low friction drivetrain.

Screw Joints

Screw joints are an advanced build technique that reduces friction and increases structural stability on the drivetrain, compared to using axles on the wheels.

Here's one type of screw joint:

Layout for one type of screw joint

Here's how to attach the gear to the wheel for this type of screw joint:

And here's another type of screw joint using a 2.75" wheel with a 48T gear:

Boxing

No, not that type of boxing

Boxing is an advanced build technique that improves the stability of a connection. The basic idea is to prevent a C-channel from bending by supporting it at two points rather than one. This is done with a long screw and 7/8" of spacing on the inside of a C-channel.

Here's an intake before and after boxing. In the picture to the left, the C-channel bent under heavy defense. It was fixed in the picture to the right by boxing, and the C-channel never bent again.

We also recommend boxing the cross-braces on the drivetrain as shown below. This prevents the drive C-channels from bending and makes the robot more durable.

Note that only the corner screw needs boxing

Bearing flats

It turns out that the square holes in vex metal pieces aren't a great fit for a rotating axle. Yes, they technically work, but the axle is highly unstable, and the friction is egregious.

Note the shape of the hole in the metal

The solution? Bearing flats! Bearing flats are essential for having low-friction drivetrains, and also for other mechanisms on the robot. They keep shafts aligned to the center of the hole, preventing it from touching the metal (which adds friction) or wobbling.

Bearing flats should be used on either side of an axle to support it and reduce friction. However, a motor also supports the axle, so there is no need for a bearing flat right next to a motor:

On the drivetrain, bearing flats should be used for both axle and screw joints (as possible), since they do reduce friction. For example, in the drivetrain below, the motor shafts have one bearing flat on the outside to keep the motor axle stable.

Note the zip ties. Yes, this works, and it works well!

Fixing Friction

Not this again...

Friction on the drivetrain can be caused by any number of issues.

Testing Friction

Luckily, it's relatively easy to test drivetrain friction. Attach all of the gears and wheels, but not the motors and motor cartridges, like so:

Then, give the drivetrain a good spin with your hand, as fast as you can. The drivetrain should keep spinning for at least:

* 3 seconds, if you have axle joints

* 5 seconds, if you have screw joints

This is called the freespin time, and it's a great way to test the friction on the drivetrain. The longer the freespin time, the less friction there is.

Fixing Friction

If the freespin time on the robot is longer than acceptable, there is friction somewhere. Here's a few potential sources of friction:

Bent axles

If the drive axles are bent, then nothing else can really work. To test if an axle is bent, press it against something you know is flat and look for a gap between the axle and the flat surface. Do this for all four sides of the axle.

Note the gap between the wooden table and the axle

If it is bent, then simply replace the axle and throw away the old one. There's no reason to keep bent axles around.

Tight spacing

On either axles or screws, too much spacing can cause friction issues. That's because the spacers rub against the drive C-channel, which adds resistance and extra friction. The wheel should be axle to wobble back and forth on the axle/screw by about 0.25 mm. If it can't wobble a little, then likely the spacing is too tight. Remove some of the spacers and replace them with shorter ones.

In the images above, there isn't a small gap anywhere along the axle. Thus, the spacing is too tight; this will cause friction issues. In this case, removing a washer would be the best way to fix it.

Misaligned drive C-channels

If the drive C-channels are even slightly misaligned, then that can cause friction because the axles won't be perfectly perpendicular to the inside face of the drive C-channels. Make sure to square your chassis before you start building the drivetrain to resolve this problem.

Extraneous shaft collars

Shaft collars are essential in VEX Robotics. However, there should never be shaft collars on the outside of the drive C-channels--they only cause extra friction. One shaft collar on the inside of an axle is enough to lock it in place.

Bad bearing flats

Sometimes, bearing flats go bad or can become misaligned with the holes in C-channels. If a bearing flat seems to be causing a problem, try replacing it.

Bad motor cartridges / motors

Make sure to test each motor before putting it on the drivetrain. Ideally, each motor (with the motor cartridge in) should not draw more than 0.1 - 0.2 watts of power at max speed. Use the "devices" screen on the brain to test the motor, and if it draws more than 0.2 watts of power, try to find a different motor with less internal friction. Additionally, make sure to test each cartridge as well. Bad motors and cartridges ruin a good drivetrain.

450 RPM on 2.75"

The best drivetrain

In this tutorial, we'll show you how to build a 6-motor 450 RPM on 2.75" drivetrain, one of the best in the world. This drivetrain is fast, low-centered, and easy to build on.

We'll start with the wheel assembly. We used 1.5” screws, ¼” spacers, and nylock nuts to connect the 48T gears to the 2.75” wheels as shown. There are two screws that go through opposite sides to balance the weight.