what's your most important drive train advice?

Technical Technical Discussion
#1

Hello all. I’ve been preping a workshop/seminar for WRRF teaching teams’ students about drive train, and I thought “why not ask the people on CD about this?” This way I will make sure I don’t leave anything important out.

So, if anyone can help out with this, it will be great!

Please answer these two questions:

What’s the most important advice you can give to teams about drive train? If you are only allowed to give 10 advices about drive train, what would they be? (please don’t limit your reponds to 10 if you have more advices :wink: )

How do you come up with a drive train most sutiable to the game? In another word, how do you pick through the many many designs you have from your experience/learned from others and choose the perfect one that you think is best for the game/your robot?

Thanks!

#2

My only piece of advice

Break the darn thing as soon as you get it running. (Not Maliciously)

By doing this, you know where your drive train needs work, by fixing this during the build time, this lowers the risk of your team rushing at competition to fix something.

Our team uses the drive train from the previous year, but we make additions and changes to improve our weaknesses…

Not much help there, we’re riding in our groove when it comes to drivetrains

#3

Well, I don’t know if I can come up with 10, but I’ll give it a shot.

#1: Simplicity is best. Don’t spend too much time building an overly elaborate drivetrain. If it’s the greatest drive system ever, but it doesn’t work, you’re going to be stuck. Whatever you build, make sure it works. A basic drill drive that works is better than a 12-motor drive that doesn’t.

#2: Make sure what you build is suitable for the game. Design your drive based on what you need to do in the game, not what would be cool to do. If speed and maneuverability are key, swerve drive might help. If pushing power matters, though, you might want to go with treads or basic 4-wheel drive.

#3: Make sure your drive is suitable for your robot. Like rule #2, if your drive doesn’t fit your robot’s overall plan, you won’t be as successful.

#4: Don’t spend too much time on drive. The drive system is the most important piece, but don’t wait until the last week of the build season to build the rest of your robot. If you follow Rule #1, this should be a piece of cake.

#5: Plan everything out first. If you’re doing something really simple, this doesn’t take much, but if you’re going to be a little more ambitious, a good plan (in CAD, Inventor, or the like) is a must.

#6: Keep yourself open to all ideas. Some of the best drive systems ever (71’s walking bot comes to mind) were totally different from anything ever seen before. Keep Rule #1 in mind, but don’t rule out anything just because it is different.

#7: When designing your drive system, remember what resources you have available. If you don’t have what you need to build your ultimate drive system, it’s not going to happen.

#8: Watch your costs. If you’re team is on a small budget, you don’t want to break the bank by having all your gears custom made and your housing cut on a waterjet. You can do a lot with stock gears and basic machine shop equipment. One hint: look at automotive parts, like drive shafts and such. Sometimes, you can salvage a very good part from an old car drivetrain.

#9: Watch your weight. Try to minimize the size of your drive; it’ll give you more room for other “fun” stuff.

#10: Finally, after viewing all of the above, refer back to Rule #1. It has to be simple to succeed. You don’t have to limit yourself, but rather control yourself. Think: “Is what I’m doing possible to accomplish in six weeks, with my current resources and expertise?” If you answer yes, go for it! If you answer no, go back and think about what you can do to solve any feasibility issues. You’ll be satisfied with the results, and it will save a lot of time and frustration later on.

Guess I made it to 10 :D. I hope this helps you out. This is, in a nutshell, how we plan out our drive system. If you follow all the “rules,” you can’t go wrong.

#4

When you get your drive train built, you can only see if it really works if you do these three things:

  1. Attach weights to it so that it weighs close to 130 pounds (if this is what the maximum weight is next year). We ususlly use cable ties or duct tape to tie down a box of spare bolts or some steel plates to the drive train frame.

If you drive your new drive train around without weighing it down, then you will get a false sense of security that it works just fine. Weighing it down will expose it to what really will happen once you get the rest of your bot finished.

  1. Drive it on the playing surface that we will be competing on. I assume that this will be carpet next year, since the past 11 years has been carpet… but FIRST may change this. A 130 pound robot drives differently on carpet than it does on concrete, that’s for sure.

  2. Like DJ said above… break it. Don’t maliciously damage the robot, but put it through at “road and track” test early. Try to drive it like you would during a match in the elimination rounds. Breaking your robot early in the build cycle will make you fix your weak links and give you more experience for what needs to have preventive maintenence.

Andy B.

#5

Some of the things that helped us out over the past few years

1.Start now, get the ball rolling on the different types of drivetrains. Same as what has been said, if you are a new team to first try 4 wheel drive with chains and sprockets, make it robust. Next move on to multi motors, maybe a tank. Finally step up to full gearboxe transmissions and swerve.

If you can have a fully working base by week 2 or 3 then you can drive the heck out of it for 4 weeks and find out the weakness.

Many teams have a ‘shelf’ of proven designs that they can call upon as soon as the game is announced.

Pay attention to details when you build a gearbox, taking a little extra time to get the proper meshing will save in headaches. We found that using shoulder bearings oir oiled bushings let the drivetrain move freely with little drag. We found that welding all the gears to the shafts as well as yokes for dissimilar metals proved to be indestructable with no failures on the drivetrain for the season and post season. Keep that as an option.

And, ask the forum for help if you need a specific answer on ratios or materials, the answer will probably show up by the end of the day

#6

After seven competition seasons and countless pre-seasons builds it has taken us years to perfect drivetrain designs.

#1 – rookies should concentrate on simplicity. two or four wheel designs offer plenty of mobility for most teams. teams that use swerve or omni-directional designs have usually spent lots of time between seaons perfecting the systems. don’t try to over complicate a drivetrain. if its your first season i suggest the most simple design that satifies your needs.

#2 – treads look cool but are often hard to get working properly. four wheels can almost always do as good a job as an entry level tread system. (team like the technokats have years on you newbies.)

#3 – pins and set screws are a no no. always try to use couplers that are more robust like keyways, of hex shaped shafts.

#4 – finish it early. if you settle on a simple drivetrain, get it built soon. Have it running by the end of week two or three. the most successful robots in FIRST are usually a product of great drivers. students who have had four weeks of practice time on simple drivetrains can do things that others with less practice and more advanced systems can’t match.

good luck! and remember, don’t be discouraged by complex systems that look polished and refined…our new drivetrain ideas have been on the drawing board for months now, and many other teams have had them for years!

Anthony Lapp
Team 221 --> 857
Superior Roboworks

#7

Don’t use set screws. Use keyed shafts and keyways

#8

From an electrical standpoint…

  1. Make it efficient so as to use less current.
  2. Make sure the motor leads are tight, solder when you can, which should be everywhere.
  3. Dress the leads so that they won’t get caught in the drive train or be run over.
  4. Make it efficient so it won’t overheat.
  5. Dress the leads so they won’t be bent or pulled when the robot steers to left or right.
  6. Make the wiring as short as possible so you can minimize the resistance and therefore the voltage drop.
  7. Make it efficient so it doesn’t burn up the motor or the speed controller.
  8. Test, Test, Test. check the current delivered to the speed controllers under all conditions, especially turning.
  9. Make it efficient. (Can you tell I like this one!?)
  10. Make it easy to repair or replace the motor, else make the system modular and have replacements.
    Good Luck
#9

Just some basic tips…

  1. DO NOT USE SET SCREWS!!! (as ajlapp and wysiswyg said)

  2. If you use a chain drive don’t foget the chain gurds. you wouldn’t want your bot to just sit there and spin in a circle do you.

  3. Again if you use chain drive the chain will loosen as it wears in. Use a peice of solid delrin shaft with an off center hole so as the chain loosens all you have to do is loosen the screw on the shaft give it a turn and tighten it down. This will pickup the slack in the chain and keep it tight.

  4. If you burn or cut lines or nubs on the rubber wheels for traction make a few extra sets. From what I have seen it may help with traction a bit, but once you start pushing something and your wheels start to spin they will wear down really fast.

  5. Don’t overcomplicate it. (KISS) You don’t want to spend most of you build time on the drive system. (what good is you bot if all it can do is move around on the floor?)

  6. My favorite tip of all to remember DON’T USE SET SCREWS!!!

#10

Ooo yeah one more thing don’t use the wheels that come supplied with the kit if they are the same ones that they have given for the past two years.

#11

support all axles with bearings from both sides of the shaft.

don’t use direct gears driving off the motors

expect the unexpected

WC

#12

Maybe make a test Drive System so its easier to make one during the build

KIS (Keep it Simple)

Prototype then build the real thing

Just my 2cents

#13

*Originally posted by Wayne C. *

don’t use direct gears driving off the motors

WC

Wayne, what do you mean by this one, all of our gearboxes were interfaced to the pinions of the motors and worked flawlessly.

See picture of swerve ‘Modular’ drivetrains that we had great success with. Modular is the word that I think Al mentioned. Make the drivetrains swapable in the even of a failure

The plans for this gearbox are in the WHitePapers

#14

Whoops here is the picture

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#15

Please answer these two questions:

What’s the most important advice you can give to teams about drive train? If you are only allowed to give 10 advices about drive train, what would they be? (please don’t limit your reponds to 10 if you have more advices )

  1. Use the simplest system that meets your basic needs and is consistent with your team resources (money, design, manufacturing). I’m reiterating everyone else’s advice because this is soooo important and many teams forget this.

  2. Expect to put in more time on your drive system than you originally estimate. If you cannot move around, you cannot use those wiz-bangy fancy devices that you have mounted on top of the drive system.

  3. Stay focussed on the drive system until it actually works. This includes breaking, redesigning, and fixing.

  4. Don’t forget that you have to wire it and program it and put together an operator interface too. If you have a complicated drive system, you will need to invest some more time and resources in programming (and variables).

  5. The more complicated the drive system, the more training time will be required to drive it effectively. If you get 10% performance out of a spectacular system, you may not be as effective as someone getting 100% performance out of a simpler system.

  6. Sometimes differential back wheels and front-casters work. But they have lots of hidden disadvantages, especially if there is a hill in your future.

  7. Consider forced air cooling of your drive motors using the fans in the kit.

  8. You have limited resources. The more resources you devote to your drive system, the fewer resources are available for other devices.

  9. Make it robust. If you plan to attend more than one event, your drive system is going to take a beating.

  10. Buy extra drive motors (if possible). The drill motors only go for about $25 each. You don’t want to have your entire competition go down the tubes for the lack of a $20 part. Buy extra 30 amp breakers.

  11. Make your drive system easy to get to and easy to replace/repair. If you have to disassemble your robot to tighten that one loose screw, you might miss matches.

How do you come up with a drive train most sutiable to the game? In another word, how do you pick through the many many designs you have from your experience/learned from others and choose the perfect one that you think is best for the game/your robot?

  1. List all possible types of drive systems (rear differential-caster front, rear differential-Ackerman front, tank drive (treads or chain driven tandem wheels), swerve drive, etc.

  2. Qualitatively determine what the attributes of each system are (speed, maneuverability, power, complexity, etc.) and assign a value.

  3. Look at the game and determine what strategies are available.

  4. Assign attributes to the strategies (maneuverability, speed, etc).

  5. Pick strategy and assign weights to the drive system attributes based on that particular strategy.

  6. Add up the value*weight for each drive system. Make a decision based on which one floats to the top.

Andrew, Team 356

#16

I’m surprised no one mentioned this.

BUILD SPARE PARTS!

Anyone with machine shop experience will know that setting up the machine often takes longer than actual “cutting metal” time. So, while you’re set-up for an operation, build a couple of spares.

-=- Terence

#17

Matt-

what I mean is don’t just drop a sprocket onto a motor arbor shaft and expect it to carry the entire weight of the machine. I can’t tell you how many teams we see which have a drill arbor with a sprocket “bit” directly driving a wheel sprocket. The immense drain on the motor either causes a fuse to blow or a wobble in the sprocket destroys the drill gearboxes.

Better would be to have the drill motor axle supported on both sides of a sprocket. This drives a series of two or more sprockets which are equally well supported and that builds up the advantage for the wheels.

Personally we prefer sprockets to gears at team 25 since, in the event of a seizure, the chain is the weakest part of the system and it jumps before teeth get ground off.
You can also easily replace a chain without tearing out a whole gear box by using a snugging device somewhere in the system.

We have not have one fail us in three years. And our results speak for themselves.

WC:cool:

#18

The main thing I try to stress to rookie teams is to design the drive train so that you can fairly easily modify your speed (whether it be through a chain drive where you can change the sprockets or wheels where you can change the diameter). I ran a workshop a few weeks ago on Mobility; you can download it from the Resources page on the web site for the Canadian Regional (go the first table on ‘Workshops and Seminars’ and the Mobility workshop is available in PowerPoint and Acrobat format). The robot I used as a case study, though, isn’t really great; I built it in three days (you’ll notice the shaft from the motor should be better supported).

#19

Guys, Guys, Guys…

You all are forgetting something… Just make shure it runs first! THAN get all the bugs out…:smiley:

#20

Short and simple: adding more motors for power is pointless if your wheels slip. Only gear it down to a low enough velocity such that your wheels just barely never slip (i.e. they are providing maximum force without slipping at stall torque). Or… go to tank tread as many teams do, where you rarely (if ever) have to worry about slipping. On the other hand your options for mobility is decreased with a tank tread.