# Mecanum wheel drive train School project - HELP NEEDED

We have recently started a project in our course to make a drive train to use mecanum wheels. We have no previous knowledge about this topic apart from our research that we have done so far. We were wondering if there are any types of motors that most recommended since there are thousands on the market but we don’t know which one we need. We are looking for speed instead of looking for torque since using mecanum wheels might make it more complicated since they slide around a lot. Also some coding tips would be appreciated, we don’t have much experience in C or C++ but we do have some knowledge which shouldn’t make it confusing. Are there also anything we have to keep in the back of our mind whilst building/designing the frame of the drive train. We are already aware that the center of gravity is important with mecanum wheels but any other tips or ideas would be highly appreciated. Lastly is there any tips with different parts for example, gear box, actuators any types of electronics that are necessary.

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Mecanum wheels have rollers on them canted at 45°!

I remeber a time when I was teaching my litlle roboteers how to build our first mechanum drive and we banged our heads against the walls for hours trying to get it to work! Let me save you a few hours of headache by learning from our mistakes.

You can have your wheels oriented in sucha way that when looking down on the robot, the rollers look like this: < > but what you really want is the rollers to look like this: > <

You wouldnt believe the amounts of eggs on my face when we realized our errors!!! ahahaha

Yeah, I have no idea how to program it though.

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As far as motors and electronics go, it really depends on your budget, and how big you are trying to make it. As far as programing, there is a great tutorial here Programming Tutorial - Mecanum Drivetrain - Game Manual 0
It is in Java and for FTC, so depending on what electronics you use it might differ a bit, but in general all the math and logic should still apply.

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Welcome to Chief Delphi!

Scope of Project
Firstly, consider what size/design constraints you need for your design. Most of the forum discussions on Chief relate to FRC robotics, but if your course only needs to demonstrate a mecanum drive, you might be better off developing an FTC sized drive train. Below is a size comparison. The smaller one will be much cheaper, safer, and easier to demonstrate in a classroom setting. For reference, the smaller of the two robots has an 18"x18" foot print. This video will give you an understand of size and approximate speed you might expect.

Chassis Motors
The above image/video shows the a gobilda strafer chassis, which you can find here. Regardless of if you buy it or not, the specs on the drive motors should give you a decent idea of what range of torques/speeds you want if you don’t have a decent way of calculating it. Other motors that have been used for FTC Mecanum drives include NeveRest Motors and these from Rev robotics.

Roller Direction

To further elaborate on this, the reason has to do with the ability to turn. Let’s take a quick look at the below video.

We see that the force generated by a mecanum wheel is 45 degrees to the “front” of the robot. If you orient your wheels incorrectly, you can’t generate a rotational force, so your robot wouldn’t be able to turn. This can be fixed by flipping the wheels.

Control System
The common controller for FTC is a Rev control hub. Alternatively though, you could use an Arduino with pwm signels. (Note that if you use motors, not servos, you’re going to need a motor controllers as well. )
Here is a lovely tutorial on how to control servos (or anything that runs on PWM) with Processing, Arduino IDE, and a Game controller.

Programming Algorithm
This below video is epic. Watch it.

Thoughts, Feelings, Emotions
This is a pretty big undertaking, so if you let us know your resources, we might be able to better assist you in your process. Let us know if you have any questions!

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Buy this, problem solved. (this is a joke and you should def do research and stuff cuz this is a cool topic)

This Chassis

This thing if you are using a RC control system.

You will probably not be able to get the FIRST Tech Challenge control system as it is out of stock and only sold to registered teams.

Good luck

Are you sure you cant get it to work if the wheels look like <>? I’m pretty sure you can configure mecanum to either work in an “O” (<>) or “X” (><) configuration, it just depends on your code. Last season iirc our FTC team used O while our second FTC team used X.

I may be mistaken here, that’s just what I seem to recall and what I think I know.

You can do O, but you lose some turning authority with the way the rollers touch the ground

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Hi, thank you for your information. Our project for this school is a collaboration between a FRC team. Meaning that we have to make a FRC-sized drivetrain. We are aware that the size and all other parts of the robot change each year but we decided to settle with a 650mm by 650mm frame. If there are any recommendations for motors and any other electrical devices. Also, do you know if the mecanum mixer is a viable component for a drivetrain of our size?

No there is no possible wat to get <> O to work I tried it myself. The way the rollers work you will sctrinch the carpet if you O and you need to >< X and that will give you a bad time. Trust me. We tried a lot.

You may be misteaken but that’s okay everybody makes mistakes sometimes that’s how we learn! Everyone has those days when we wake up with confidence just to learn it was misplaced and that we don’t know as much as we thought. But that provides such an incredibly wonderful opportunity for growth!

Have a wonder ful day,
Greg

FRC Legal or Not
The first question you should ask is if you want to make this as a demonstration drivetrain, or one that is legal for play in FRC Competitions. I’ll discuss a little of both in the following lines. If you go down the route of making it FRC legal, know that the cheapest option will be to borrow these components from your FRC team.

WPILIB for FRC Robotics
WPILIB is a set of libraries for FRC robotics that allows for easy set up of robotics. is going to be the most comprehensive guide to understanding programming and wiring. It also has an overview of what hardware components you need (you don’t need everything listed here, but most of it). Feel free to ask here if you have further questions.

Motors for an FRC Drivetrain
There are typically 3 types of motors used in Drivetrains for FRC robotics: CIMs, Neos, or Falcons. CIMs are a very common motor type, and are most likely what your team has extra’s of. Neos and Falcons are very powerful and make for wonderful drivetrains, but are not necessary for a drivetrain if you don’t need the extra power associated with them.

Mecanum Mixer

Yes it is, because it’s taking PWM signals and translating them to other PWM signals. Know though that this means you must use PWM and not CAN. Not using CAN limits your options of motor controllers. The video I sent in the prior video has an algorithm for doing the exact same thing in code. This will save you \$30 dollars if you “Do the Math and Save the World”.

Control Systems for Robots that aren’t FRC Legal
If you are just partnering with an FRC team but not creating a robot that will ever go on the field, there are cheaper control system options.
An Arduino Uno is capable of sending PWM signals to motor controllers for \$30 instead of the whooping \$485 of a Roborio 2. I recently made a robotics project myself with the following components:

This is a cheaper option than buying an FRC control system, but a much more expensive one than just borrowing a control system. I wanted to have parts on hand for my graduate research, so I got a lot of this stuff.

Wheels and Gearboxes
Most FRC Drivetrains use 6 inch mecanum wheels. Andymark has a selection of them here if you don’t already have them.
You probably need some sort of gearbox as well. I can go more into detail based upon your needs.

Final Thoughts
In case I haven’t pushed it hard enough, reach out to your FRC team to determine what you can borrow from them. This will reduce your cost significantly.
Let me know if you have any further questions!

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Thank you! I definitely know the value of mistakes lol not too worried about it

O worked for us but it was scuffed, we just never experimented with anything else and in hindsight, that might have been our issue.

Make sure the chassis is flexible enough that each of the 4 wheels can carry roughly equal weight at all times. This may be more important iyou are not aiming to use it in an FRC competition. The surfaces you are likely to be driving on will likely be less flat and smooth than an FRC field.

Unequal weight on the wheels will cause the behavior to be erratic when trying to drive sideways. Work out the forces exerted by the rollers on the 4 wheels under ideal conditions. Then work out the forces with only 3 of the wheels touching the floor.

One team I was on built a very rigid mecanum chassis that had a slight twist in itIts behavior driving forward and reverse was okay. Its behavior driving sideways was unpredictable and changed as different wheels touched the ground.