Rookie team questions on chassis and drive train
 

Well we obviously had no idea what we have gotten ourselves into but are excited to be apart of the program. We received our KoP and categorized each item and placed it into a closet with drawers and cataloged where we put each item. Then the team just sat there for a while and stared at each other with a blank look on each of our faces because none of us know really what any of the parts are used for or do. After much reading we have a better idea at what we want to do.


I'll try to limit my questions to a manageable amount but i'm sure i'll ask too much.

Regarding our chassis would it be better to just use the KoP provided one for simplicities sake or CAD our own and weld it in our school mechanical shop? We were thinking of using 3/8ths inch aluminum cut to 1" width and basing the shape off of what we have seen very commonly done in the photos section.

We plan to use the KoP wheels for now in a 6 wheel drive format. Would it be better to buy omnidirectional wheels for the outer 4 or to drop the middle wheel? The KoP doesn't seem to have come with enough sprockets for a 6 wheel drive so i'm guessing we will need to buy more.

The KoP comes with two CIM motors but most designs i've seen have had 4 so i believe we will be purchasing an additional 2 but we are not sure if we need additional gearboxes for each CIM motor.


Hopefully we will have all of this in CAD tomorrow so that we can move on to our manipulator design but we are just so unsure on how to proceed so any addition tips or advice to a rookie team will be much appreciated.

Re: Rookie team questions on chassis and drive train
 

The KOP CIMple gearboxes should have spaces for your additional CIMs.

Dropping the center wheel or using omnis on the outside is a bit of a tradeoff. Using omnis will keep your robot more stable and make it rock less, but aren't as good for pushing power. Dropping the center wheel will introduce some rocking, which could be detrimental trying to reach the high goals. However, you will gain more pushing power.

I would recommend sticking with the KOP chassis, but that's just my opinion. Alternate drivetrains can be lighter, but usually take more time to make and are more complicated.

Re: Rookie team questions on chassis and drive train
 

No such thing as asking too much. There is such a thing as asking too fast, but not too much.

CIM motors: Each gearbox takes 2 (or one, if that's your design).

KOP drivebase vs. custom: As you're rookies, KOP is the way to go. You can bolt, rivet, or (shocker) weld it. Tip: Make sure that you're 1" undersize in all directions. It's no fun getting to your first event to find that you don't fit in the sizing box.

6WD drop-center works well and resists turning a bit better than omnis on the corners. I believe the KOP chassis has a dropped hole somewhere on the side rails--that's about right. Yes, you will need to buy more sprockets/wheels.

As it's your rookie year, you'll want a solid drivetrain. KOP plus an extra set of wheels, chained with #35, is very tough unless you throw a chain--and there are ways to mitigate the damage even then.

You're doing some things right already: You're asking for advice, and you're organizing, and you're CADding. And working on the drivetrain first.

Re: Rookie team questions on chassis and drive train
 

for the drive train it greatly depends on the type of robot you are making (fast, slow, manurvable, good grip)

as for the chassis I would recomend using the KOP chassis your first year to save you build build time, we used it last year and it worked out well letting us focus on other problems

Re: Rookie team questions on chassis and drive train
 

I would HIGHLY recommend using smaller (6") wheels with the kit transmission this year. The provided gear ratio is VERY fast, faster than you might be able to control with 8" wheels.

Re: Rookie team questions on chassis and drive train
 

Rather than switch out for smaller wheels could we just buy larger sprockets to put on our current wheels? That would make the wheels turn slower but overdoing it might make them turn too slow.

My team was pretty set on building a custom frame but i don't think everyone was quite sure how much work that is actually going to take.

Re: Rookie team questions on chassis and drive train
 

That would also work, to a point.

At this point, I'd go with the KOP frame, and then study the custom frames posted in CD-Media to get a better idea. It's not exactly easy, but it's not exactly hard. Might be a little much right now, but maybe next year it'll be easier.

Re: Rookie team questions on chassis and drive train
 

well first is a learning experience if your build team wants to custom make a chassis then let them learn it

just be sure to leave yourself enough time to do so

Re: Rookie team questions on chassis and drive train
 

Ok so i'm going to assume that we choose to do a custom frame would the 3/8" aluminum be best or is there a lighter or stronger option? Maybe i'll do a fast sketch of what we lined out.

Re: Rookie team questions on chassis and drive train
 

I don't recommend a custom chassis as rookies. I was on a team that was not experienced and we made heavily customized drivetrain components that failed completely during competition. There is nothing more demoralizing than not being able to drive. Focus on reliability and simplicity. If your machine performs consistently and accomplishes at least some scoring aspect of the game you will do very well as rookies. Consistency is a very hard thing to achieve in this competition. I can't tell you how many times veteran teams pick up solid rookies as the 3rd or even 2nd team in an elimination alliance because they are reliable and can put up some points, or run some interference in a pinch. Sometimes the rookies are even up in the top 8 picking, even with a kitbot chassis and reliable manipulator.

Additionally I second the thought about the gear ratio being extremely fast this year for the kit chassis. Consider going a bit slower, especially if you are planning on have an arm to reach the tall posts, as the speed may be just what causes your robot to tip over. Going with smaller wheels can allow you to lower your machine's center of gravity and add to your stability as well. As far as omni's, there is an important consideration to make here. Are you planning on playing defense? Are you expected to be heavily defended against? Since the scoring zone is protected, you shouldn't expect defense while scoring so having the added maneuverability of 2 or 4 of the 6 wheels being omnis could help your ability to turn and get situated to score the tubes. If you are worried about getting pushed around in the middle, consider only two omni's or all traction type wheels. If you use a dropped center wheel, and have a tall arm placing tubes, the effect of the slight tilt of the robot from one set of 4 wheels to the other set of 4 can be magnified and cause problems. Good luck!

Re: Rookie team questions on chassis and drive train
 

3/8" is either too big or too small.

The most common wall thickness is 1/8" on a 1x1 or larger tube. For a drivetrain, you probably want at least a 2"x1"x1/8" wall tube. Unless, of course, you have sheet metal thickness.

A 3/8" outside dimension tube will be too small for a drivetrain.

Re: Rookie team questions on chassis and drive train
 

I would suggest you use the Kit Bot. It's pretty strong and not that heavy - there's no shame in using it! It's a very good option this year.

Re: Rookie team questions on chassis and drive train
 

My rookie year we made our own fraim from 80/20 it worked very well for us and we made it to worlds so my suggestion would be to buld a simple effective desin THAT IS VERY EASY TO FIX!!!!!!! and if you are planning to make your chassy i would go for a 4 weel driveshain we went with 6 weel drive and it proved a challange to get the middle weel just right

Re: Rookie team questions on chassis and drive train
 

80/20= HEAVY, and the kitbot frame is much simpler

Re: Rookie team questions on chassis and drive train
 

In your rookie year, I strongly advise you to use the kitbot. It provides a robust chassis and is just sitting there for you to assemble. Put it together and let your drivers get some practice ASAP.

If there is someone on the team who insists on building a custom chassis, let them do it, but continue development on the kitbot chassis. You simply do NOT have the time to figure out custom stuff. 1/12 of your time is already gone - think about that.

3/8" aluminum is a bit heavy, it really depends on what exactly you do, but I've rarely seen such heavy material on a robot in 7 years. Our drivetrain side plates are 1/8" thick if that helps.

Re: Rookie team questions on chassis and drive train
 

My study suggests that you need to be about 1/16 or 0.064" sheet Aluminum. 1/8" is too much. 3/8" is a tank for a chassis with no ability to to add anything.

Do a weight study. At most you should have 40 pounds allocated to chassis, gearboxes, motors, chain, and wheels.

Depending on your approach above 8" above the floor, you need a lot of stuff, motors, actuators, hinges, etc. to make an arm or whatever work for you.

Any comments on designing for weight are welcome.

Re: Rookie team questions on chassis and drive train
 

For the drivetrain, unless you're actually using sheet, 1/8" wall tube can take everything thrown at it. I don't quite trust 1/16" in drive chassis applications. Even with the bumpers, the drivetrain takes a massive beating. From before bumpers were even allowed outside of the box, 1/8" has yet to fail on any robot I've known about. Welds have failed, but the structure has at best bent. And this is with full-speed, metal-on-metal, defense all over defense. Heck, falling from the 10' high bar in 2004 hurt my team's robot less than running our lift down when it was all the way down already!

Superstructure, yeah, I can see (and have used) 1/16" wall. But we aren't talking superstructure yet.

40 lb for a chassis is kind of light. A 50-60 lb chassis (with some of the superstructure power) is more like it, though I'd shoot for 50 when driveable. Heavy chassis=low CG. Low CG=less chance of tipping. As we all know, tipping == bad.

Designing for weight is not about making everything as light as possible. It's about tracking weight--where is it going, how much is going there, stuff like that. If you don't have one already, get a scale--you'll want both a platform type and a fish (or hook) type. Before a part goes onto the robot, weigh it and note the weight in the sheet. Try to get an estimate of how much the robot will weigh--most CAD programs have a way to do that. Then you know where you can remove a lot of weight quickly.

Re: Rookie team questions on chassis and drive train
 

I have a question, and it fits this thread well. Me and one of the 3 other freshmen on the team see a problem, and no one believes us since we're "freshies":mad:

Our team wants to use a two-wheel drive system:confused: , and the other person and I are the only people against it...
I really need some help on this one unless we're gonna have a robot snails call slow :/

Re: Rookie team questions on chassis and drive train
 

The number of wheels does not affect your speed, the only thing it will affect is handling/maneuverability.. a 2 wheel drive system has been used by several teams in the past effectively. However, the recent standard has been to use a 6 or 8wd. The only disadvantage to a 2 wheel drive this year is not having enough power to push your way through, since I am assuming you will have casters or omni wheels on one end.

I would recommend one thing for you, the kit comes with a great basic 6 wheel drive base, if your team is not using the Kit of parts system, the three of you should spend 2 or 3 days building this and putting it together to show your point.

dont let your shorter FRC experience slow you.

Re: Rookie team questions on chassis and drive train
 

For what it is worth, rookies should take the kitbot chassis, assemble it without cutting for today and get it driving. You will find what works best and give yourselves some experience putting the parts together. But start driving. As you make decisions on what you want the robot to do, then start making parts. Please watch the Grant Imahara video on design. Unless you have a good veteran team helping you and have a lot of experienced mentors who might be able to bypass some of these design steps, you are letting time slip through your fingers.
If you have a welding shop capable of welding aluminum and if you have someone experienced enough to weld tubing, then 1" square tubing is a material that many teams use for the robot frame. It does require other specialties for robot building like knowing that square tubing will deform when bolts are passed through and hogged down tight.
Oh, one last item, the sizing box you need to fit into is unforgiving. You either fit inside or you go borrow a saws all and starting cutting. Plan your chassis 1/4"-1/2" under max dimension in every direction. (i.e. 27"x37"x59")

Re: Rookie team questions on chassis and drive train
 

This is a question regarding the rookie kit of parts. This Year the two teams we are mentoring only received two CIM motors in the KOP. I thought that the rookie teams use to get four CIM motors in the KOP. If not, this is an unfair advantage for the veteran teams because we already have ours.

Re: Rookie team questions on chassis and drive train
 

Joe,
Only two have been provided in the past. The optional two additional CIMs were purchased by teams.

Re: Rookie team questions on chassis and drive train
 

Even as a veteran team (our 5th year in competition now), we're using the kitbot chassis. It's strong, light weight, easy to work with, and comes with mounting holes pre-drilled! We made a custom chassis in 2009... while we got everything working just fine, we ended up spending a lot of time on the chassis that we could have really used elsewhere. There is no underestimating the affect of any time saving activities.

I want to second what Al said about the sizing box, and to add to that weight. Both are unforgiving. Pay attention to them both throughout the build season, and actively design your plans with them in mind. Don't aim for a 120lb robot - you'll end up over. Don't aim for a robot that's 28" wide - you'll have bolt heads that stick out. One of the hardest things for a team to do is show up at competition and have to start drastic modifications to get within the height/weight restrictions. I've seen teams spend an entire day (or more!) drilling holes in their robot to try and lighten it enough to pass inspection. I've even seen teams that had to remove their entire manipulator in order to pass inspection.

We always build ours 27"x37" to ensure we fit in the sizing box. We always aim to be at least 10 lbs under weight - then bolt a steel plate onto the bottom of the robot at competition to bring us up to 119.5lbs, once we have the official measurement and know how much we need to add. Probably the worst feeling in the world was weighing in at our second competition last year and being almost 5lbs over... all the students started freaking out a bit. Then the inspector removed his foot from the scale, and we were fine.

One final note about number of motors in the drive train... 2 versus 4 is always an interesting argument, and it relies completely on what capability you want your robot to have. If you feel the need for extra pushing power, use 4. Otherwise, 2 will give you the same max speed and work great - just without that extra oomph of pushing power. If you want to use a CIM motor to power a manipulator of some sort, you'll have to only use 2 on the drive train - the rules only allow 4 maximum on the robot.

Re: Rookie team questions on chassis and drive train
 

Another vote for kitbot here.

Our first year, we built the kit bot, bolted it together,and got it running. About week 3, we tried to weld it together. Removing all the bolts saved about 6 pounds. However, it left us with a warped and unusable frame. And we had to "copy" the kit bot out of the 1.5" square al tubing we had. It turned out fine for us, but it was a close call.

As per the welding, it can be done without warping, by an experienced welder, and with some braces. If you want to weld it, you can cut some 1" thick pieces of wood that fit inside the channels in the tubing and span across the "channel" that the drivetrain is ussualy located in. Clamp it all together, and you should have a solid base to weld together.

Good luck this year!

Re: Rookie team questions on chassis and drive train
 

Well after i showed how easy it was to put together the KoP chassis and drive train we kinda went with it and have it halfway done. Currently we have the frame together with the wheels and are working on the gearboxes.

Most of the members however want to only use a 2 wheel drive powering just the middle of the 6 wheels. I had thought that the extra traction of using all 6 wheels would be best so the wheels don't slip on the carpet. Also we may switch the 4 corner wheels to omnis or some other type of wheel.

Also i kinda feel like the team lost direction and organization. We don't have a clear leadership chain of command or any way to come to a consensus other than having everyone vote voting. Unfortunately most member havn't looked into the manual or chief delphi much and i feel that as a team were making some very bad decisions. I don't want to make the mistake of trying to take command myself though but a leader is better than no leader.

Re: Rookie team questions on chassis and drive train
 

Power all 6. If you decide to try other configurations, remove a chain. If it doesn't perform the way you want it to, put the chain back on.

If you do omnis, remove any drop. 6WD drop+omnis on the corners = spin city, because you effectively have a 2WD the entire match with the resistance of ball casters or less. Having omnis on one end, or having 4 omnis on the floor, provides slightly better traction.

Regarding the leadership vacuum:

If the team has no direction, somebody needs to step up and provide direction. That could be a mentor, could be a student. That person needs to have the final say on a design, but should see what the team thinks and why before making that design. If that person is you, step up and do it. If someone else is doing it, let them step up and offer to help them. Even if it's keeping the team focused on, "We need to do X, Y, and Z", someone needs to step up to leadership.

For next year: Team Handbook. Seriously, it'll save this type of situation happening.

Re: Rookie team questions on chassis and drive train
 

I would highly encourage you to use the kitbot. You have an unprecedented opportunity to use a well-designed six wheel drive system. In the past teams have been only been given a 4 wheel drive system... which could be altered and made into a six but did require additional work..
You HAVE a solid six wheel drive system in your hands....you only have to order the sprockets to make it a six wheel system (and purchase more chain and links...)

You can customize it to get the speed you want by purchasing whatever cogs you want to use on your wheels if you think these are not the speed you want.

Try it out now... see if you can handle the speed.

By all means ... try to power all wheels on the floor... you will receive maximum traction this way, which leads to better acceleration.

When I started doing this we had no kitbot... we had no transmissions in the kit... our first bots weren't bad but could have been much better in this critical robot component.

By all means make your own if you want... but this is an opportunity you should not pass up.

Remember your resources are limited... time being the most critical...
spend your time and effort on programming, a way to move and place tubes, the minibot and its deployment... the use of sensors and automation.

In the off season, study other robots and what they do do for drive trains... or design your own from scratch... work out the kinks...

I don't think you will find many veterans that will tell you that this drive train couldn't be on Einstein in April.... indeed historically, something over 80% of all Einstein robots have been six wheel drives.
This % goes up if you don't count the first few years by the way... recently six wheel drives dominate.

They may not be the "sexy" drive train but they sure work!!

Good luck... We hope to see you in St. Louis!!