What exactly sets apart a “good” drive train from a “mediocre” drive train? This is my first year in FIRST, and drivetrains seem to be one of the things that increase the performance of a robot.
Maybe my question can be better phrased as: what are the different elements of a drive train, and how do teams maximize each elements performance.
Ive been checking out some drive train pictures, and I am astounded by some that are machine and look like some kind of rover or something. Another thing that surprised me is that some drivetrains had wheels that were not “aligned”
Sorry, I’m kind of typing out loud
Thank you for your input
The drivers. Hands down. A good driver can take a mediocre drivetrain and make it great. A bad driver plus a really good drivetrain could equal disaster.
The best drive train is one that gets your robot (and other robots your robot might be “kindly escorting”, depending on your strategy) from point A to point B as quickly and reliably as possible. Since 2005, the most successful drive train has been the 6WD (based off of the composition of the championship finals alliances, where 61% of teams since 2005 have used one), usually with a lowered centre wheel. However, as Eric said, driver skill and practice are the single biggest determinant in how well a robot performs (well, next to being turned on, but I don’t think that really counts). Build it simple, build it sturdy, build it with enough speed, build it maneuverable, build it with a decent amount of traction, and most importantly, build it early so the drivers can practice. If you do all of those, you’ll have a very effective drive system.
speed, torque, and controllability all play important roles.
If you cannot control your robot you will fail. If you do not have sufficient speed, you will be lagging and not score as well. If you have too little torque(traction) you will get pushed around.
You can compromise between traction/speed with a single speed gearbox or get both with a shifting gearbox(more expensive and complicated).
Controllability you get from programming and your wheel set up (i.e. if you have a partial omniwheel setup like us (3 sides instead of 4) you will fishtail and not drive straight well).
I think reliability is one of the most important aspects of a drivetrain. If your wheels fall off on the field, you aren’t going to be doing much scoring. Another important factor is operator-frendliness (this includes OI design), the chassis and OI need to be designed to work together so the drivers can easily use the drivetrain as it was intended. You can have the coolest, beefiest swerve drive, but if your drivers can’t control it, you’ll go down like a metaphorical lead blimp.
Drive Trains can be broken down into the parts they include (excluding crab drive):
Motors: There are not too many choices for drive motors in FIRST. Most teams use 2-4 CIM motors for drive, depending on the weight available, and the power needed. Some teams will supplement with geared fisher-price motors. If you are going with a tank-drive style, two CIM motors per side is usually the way to go if you have the weight for it.
Gearboxes: FIRST supplied the AndyMark toughbox gearboxes in the kit this year. These will accept one or two motors stock, and are simple and easy to use. One thing that these don’t provide that many teams desire is more than one speed. To achieve this, you can either go with a prebuilt shifting gearbox, such as those manufactured by AndyMark, or a custom design. AndyMark makes the supershifter model, which can be operated with servos or pneumatic pistons. This is a simple option, but somewhat expensive ($360 each plus pneumatics)Other options are available for single speed, such as planetary gearboxes from banebots or andymark, but they are used much less for drive systems.
Wheel type/arrangement: As mentioned above, the 6 wheel drive with a center wheel offset is the most common system. This has worked extremely well for us, and for many other teams as well. This system is usually paired with a set of traction wheels, either bought or custom machined. One type that has been gaining popularity are the Mecanum wheels. These wheels enable the robot to travel in directions other than forward and backward, through strategically reversing rotation direction. One downside to these is they usually provide diminished traction. Omni wheels are also being used frequently. This would be used on a robot to improve the ease of turning. Like Mecanum wheels, these also provide less traction.
Drivers: The final part of the drive train is the driver. The driver is not what it is all about, but a poor one can make bad use of a great robot. A great drive cannot make a robot good, but a bad driver can sure make a drive train terrible.
We (973) have been using the six wheel drive, center wheel offset design for 4 years now, and it has worked it greatly to our advantage. We custom machine wheels. We have experimented with both one and two speed gearboxes, finally using the AndyMark Supershifters, with pneumatic shifting. We use two CIM motors per side.
Ditto. In addition to this, it NEEDS to be easy to work on. My most recent system that was featured on the 114 bot could have an entire side of the drive base removed with 6 bolts. Each of the 4 corner wheels (the middle was static) could be tensioned simply by turning a bolt.
The key is robustness, speed, and efficiency in a reliable, easy to work on package. I’d say work on one or two of those at a time, starting with reliability. It may be the most genius drive base to ever hit the floor of a FIRST competition, but if it doesn’t last, you’re doomed.
I was the driver for 2207 this year and I really liked our drivetrain. We had mecanum wheels and they were very helpful with easily moving around the field and getting around obstacles since we could move sideways. I also got us out from being tangled up with a robot that fell on top of us and having the mecanum wheels helped alot. They also helped in making a very easy Hybrid mode as we could move sideways to cross the second line, since we don’t have to turn it was very easy from a programing point.
Any ways Drivers are a key along with the drive train and wheels. We used the AndyMark 8" wheels with the AndyMark Toughbox gearboxes on all of them
The more time spent on the scoring mechanism the better.
How do you think 121 finished their robot so fast? You think they spent hours and weeks designing some crazy three-speed transmission? No. Just a kit-frame with some simple upgrades…
Well there’s a lot of factors that determine this…
First and foremost, it’s driver ability. You can have a godly drivetrain, but drivers who don’t know the controls, and it’ll get you nowhere.
The rest differ from game to game.
This year, we decided that speed and maneuverability where foremost. We looked into many different drive systems, and decided that they can all be fast. Next, we looked into maneuverability, and decided that swerve drive would give us the best maneuverability possible.
Other factors to consider are “what human resources are avalible?”, “how much weight should we allot to the drive?”, and “do we have the time to do this?”. When we decided to undertake swerve drive, much of our resources went there. We used our 6 most powerful motors, as well as the 2 globes on the drive. When we were building the rest of the robot, not having those motors to use was a big loss.
In the end, it’s whatever your team likes and can do.
We like to keep things simple and the kitbot + the old IFI or new AndyMark transmissions have been our standard for the past few years. Tweak the sprocket gearing a bit, bump the middle wheel up or down, and voila, we are usually up and running by the first weekend. Then we can spend lots of time working on a game piece manipulator while the kids practice driving.
From a software standpoint, if you are deciding to go with a holonomic system (i.e., mecanum or all-omni), your programmers better be ready to learn some physics :).
Team 1675 used a mecanum drive for the second time this year, and the programmers have a blast with it. I had so much fun last year just figuring out the way the vectors could change the direction. This year, we worked with the students to develop an algorithm based off an article about all-omni systems in SERVO magazine.
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).
I’d say the drive performance you see on the field is 75% driver and 25% the details and craftmanship of the drive.
I’ve seen 6WD perform amazingly, and terribly.
I’ve seen Mecanums/omnis do the same.
Same for crab, same for tank tracks and so on.
End all, I think a well built 6wd is what lower resource teams should shoot for as the standard; It performs great and is the most applicable to most games. When 2nd picks come around, often times teams just desperately need a 3rd robot with a decent drive, and most often there isn’t one available.
But, no matter what, if your driver is driving the current robot for the first time at the regional, you won’t be preforming great. I’d highly recommend a practice robot (or at least a base) for driver practice at home.
Almost none of the specific details of a drive train are relevant to its performance on the field. In 99% of circumstances, wheel type, speed, or torque are inconsequential.
A successful drive train is reliable – it functions well all the time. If it breaks or malfunctions, it can be repaired quickly and easily.
It is efficient – it is well lubricated, quiet, and makes good use of its weight and power. It turns.
It is no more or less complex than it needs to be – it needs to work for your gameplay strategy. Adding bells and whistles that are beyond the scope of your strategy is a sure-fire way to shoot yourself in the foot.
That’s it! It’s more easily said than done, of course, but very little else about drives matters if you haven’t yet mastered these three things. Once you’ve got this stuff down cold, you can start to think a bit more about the dynamic operation of the system and what changes and improvements can be made to make the most of that remaining 1% of circumstances when power, speed and torque matter.
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.
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
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.
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!