Drivetrain for precise driving

[EggrollChs]

Is there any type of build you could use for precise driving without the wheel base leaning to one side turning one side over time

[Entropy]

The simplest answer is to highly optimize the friction on both sides and make sure you are using good motors on both sides.

[Connor]

1. It is impossible to have a perfectly straight robot. You can get really close but you’ll never be perfectly straight. However, look at the BLRS wiki for tips on better build quality practices: Drivetrains | Purdue SIGBots Wiki
2. Odometry helps. Once you have the robot driving straight enough, that is it can go across the field in a straight line only shifting less than 3 inches, you can use libraries out there to do odometry, pure pursuit, etc. to course correct while traveling a virtual path.

[u89djt]

@Entropy is right. @Connor is right. But show your robot so we can actively help you. There are lots of builds that are bad for basic reasons that the builder can’t see because of how much work they put into it - they see what they intended, rather than the actual thing in front of them. Fresh eyes on your build will likely find something in that case.

[Some_random_person]

A bit simpler than odometry, you could have a system that adjusts your drivetrain’s motor velocities based on a gyro when the input to the robot is to go straight. (If the gyro senses deviation from a forwards path if travel, the side of the drivetrain which is overpowering the other slows down until there is no more significant deviation).

[TroyWingard1069F]

maybe if your whole robot was just one giant, self correcting, perfectly engineered ball like BB-8 from star wars.

[technik3k]

@EggrollChs

Is there any type of build you could use for precise driving without the wheel base leaning to one side turning one side over time

This is a good question to be addressed this early in the season. Lets see what the field of VexForum archeology could yield us when searching for “Drive Straight PID” (you need to know the right keywords, of course):

@mvas

Using PID to drive straight is a problem that can be solved with a 2-DOF controller (two degrees of freedom)…

@Anomaly

Most everyone struggles with accurate base control in auton. At the highest level, 5225 developed a 3 tracking wheel solution that allowed them to set the world record in programming skills last year, and a handful of teams including 8059 and 139 have replicated their “odometry” based on a document they released last year. Team 5225 Introduction to Position Tracking Document

But at a less extreme level, for people just looking to take a step up from move.relative you may like the base control code I developed this year…

@technik3k

Does anyone have a good reference to a Drive Straight PD loop for encoders? I am new to PID loops in general, so just looking for a basic PD loop that gets the job done. Thanks in advance!

For driving straight the most important thing is to have one PID loop for driving robot forward and another separate control loop for small heading corrections to keep the robot straight, which is exactly what @Doug Moyers code does.

That code could work great if you have perfectly balanced drivetrain and matched motors. However, that is very hard to achieve in the real life. One side will inevitably have more friction than the other. To handle that you will need to cap drivePower coming out of the forward PID loop about 10-15% below the max power that motors could accept.

If you visit above topics there will be actual code samples as well as more discussion and links to additional resources.resources

[EggrollChs]

thank you for all your help i believe i got it now I’m just working on trying figure out if i want to focus on torque or speed this year. Once again thank you for your help on this discussion.