Drive Trains

[Rick TYler]

KISMIL: Keep it simple, make it last.

[MrForbes]

Originally Posted by neoshaakti

what are the different elements of a drive train, and how do teams maximize each elements performance.

Leaving the driver aside for now....

The first element is the motors. A fast, powerful robot will use at least two CIMs per side, or if it's a Mecanum or Omni drive it will have one CIM for each of the 4 wheels. For added power some teams add a Fisher Price motor to each side also.

The second element is the transmissions. They need to be strong, reliable, and provide the correct gear ratio(s) for the way you plan to play the game. Multi-speed transmissions will give both good low speed pushing ability and maneuverability, and high speed for moving quickly across the field. Designing and building your own transmissions is quite a challenge, some teams meet this challenge well, but most decide to either use the kit transmissions or buy good quality transmissions such as AndyMark offers. Maintenance is an important issue, gears need lubrication, bolts need to be kept tight, etc.

The third element is connecting the wheels to the transmissions. Some use direct drive, some use gears, most teams use chains, and a few use belts or "tank treads". The drive system needs to be well made, have the correct ratio to play the game well, include necessary tensioning methods, and be easy to repair if needed.

The fourth element is the wheels. The kit wheels are good enough for many teams, but there are also many different styles and sizes of wheels available from different sources. Many teams that have CNC machining capability design and make their own wheels. Important considerations are wheels strength, tread friction and life, and maintenance. Good wheels will provide high traction and the tread will last at least for an entire regional event, and the wheels won't break or come loose or otherwise fall apart. Also there are several types of omni and Mecanum wheels available, and some teams make their own wheels.

I won't talk about crab or swerve drives, they are a special category and require quite a bit of research to figure out how to make them work well.

[Shadow503]

I loved our drive train this year. It was simple and always the fastest on the field! We have a rear wheel drive powered by 2 cims in direct drive for each wheel. We have powered ackerman steering in the front and software differential in the back. It is innovative yet simplistic XD

I have yet to see a robot out-drive us.

[dtengineering]

Originally Posted by BigJ

Also, have the programmers work with the drivers to make the controls more comfortable. The programmers can make the controls more or less sensitive (depending on how they are already).

This is an important comment that should not be lost amongst all the other valuable tips on the mechanical aspects of the drivetrain. The human-robot interface can make a good driver great.

Although we have used the "default" KOP joysticks and mixing code in the past, this year we knew we would have to have a much higher-performance drive system than in previous years.

We put a gyro on the robot and used it to make sure that the robot went straight when it was told to. Then our programmer re-mapped the turning axis to provide exponential response (very little near the "centre" but full-bore near the extreme edges). Finally we invested in a USB dongle from IFI, and hooked up a logitech game controller. Now the driver controls forwards and backwards with one thumb and left-right with the other. This is an advance over a single stick, as there is no chance of telling the robot to turn when you want it to go straight.

Most of this was accomplished using an older robot in the first two weeks of build, while the new drive train was being built.

Strangely, we found our new drive train performed well, and were really pleased with our driving.... even though mechanically we have almost the simplest drive train possible (modified KOP frame, four CIMS, two toughboxes, driving two IFI traction wheels at the front with two AM omnis free-wheeling at the back.)

People always tend to think of the programmers when they see a great auto/hybrid mode... but behind every great driver is some great drive code.

Jason

[MrForbes]

Good point Jason, this year we were playing with Ackermann drive and so we connected an R/C car control to it (the type with a small 2" diameter steering wheel and trigger throttle, all in a pistol grip) and it worked very well. Then we had an "aha!" moment and asked the programmers to make the new controller work with last year's 6wd drivetrain...and the result is an intuitive way to drive a skid steer robot. And a Rockwell Automation Innovation in Control award!

[BornaE]

Originally Posted by squirrel

Good point Jason, this year we were playing with Ackermann drive and so we connected an R/C car control to it (the type with a small 2" diameter steering wheel and trigger throttle, all in a pistol grip) and it worked very well. Then we had an "aha!" moment and asked the programmers to make the new controller work with last year's 6wd drivetrain...and the result is an intuitive way to drive a skid steer robot. And a Rockwell Automation Innovation in Control award!

That is what we did to test out our driving system with our 2007 bot to simulate ackermann drive that is on our 08 bot for testing hybrid. the code was also used on our back wheels as the electronic differential.