Drive Base Help
 

A bit of background: We had a very very rough season this year with a bot that fell apart multiple times and could barely drive, let alone play the game. In our rookie year two years ago we did very well, but everyone that was on the team that year has since graduated, taking any technical/mechanical experience with them. We have no stable mentorship (working on that, though) and team culture virtually does not exist. Basically, we're a rookie team with no rookie benefits, little commitment, and minimal guidance. So, three of us have decided that we want to get our stuff together and are leading a summer journey to start from scratch and design/build a new bot for offseason, learning tons of stuff along the way. Except, we're very inexperienced (explain like we're five). Plz halp!

Wheel-wise, we want pneumatic wheels for sure. We have 8-inch wheels from our original bot, but because we want to upgrade from a 6WD to an 8WD (moat), we want to switch to 6-inch wheels for frame perimeter reasons. Our major concern is being able to get over drive obstacles-have any teams run into issues with 6-inch wheels on obstacles?

Drive base-wise, here are our ideas:
1. We want the wheels to stick out the front so that drive base height doesn't matter
2. 8-wheel drive
3. two center wheels dropped (also need advice on how much to drop wheels proportional to wheel size)

We have entirely ruled out a custom base and are now choosing between the KoP AM14U3 and VEX's VersaChassis. The VersaChassis looks like it will allow us to fulfill requirements 1 and 2, but we're not positive on whether we can drop the center wheels a significant enough distance to matter on the field. Which chassis would be a better fit for the bot we're trying to make?

Also, got any other miscellaneous tips?

Any and all input is appreciated!:D

Re: Drive Base Help
 

If you have the drive, all power to you to make your team better! :D
Keep in mind that bumper rules are a thing, so sticking your wheels out the front will only work if you have a bumper support ahead of that (maybe higher than the wheels?).

Versachassis stuff can only drop you 1/8", which is not enough for pneumatics most likely. Many teams had luck with colsons this year or a combinations of colsons and pneumatics; maybe 6" colsons in the center, dropped, and 6" pneumatics on the outside? That could solve your problem.

Versachassis is expensive once you total up bearing blocks, gearboxes, etc. KOP chassis with 6 8" pneumatic wheels is my suggestion purely from a cost standpoint. Custom will run you a bit more, and versachassis the most, mainly because of the gearbox setup. Unless you want to mill your own mounting holes for the gearbox you are practically forced to use the $300 3-cim ballshifter, so although the build quality will be really good you will be spending some money.
That being said, while working with versachassis I may have missed something major on gearbox integration. The advertisements say "any gearbox" so there might be a method of mounting that I've missed.

If you CAD everything, you can solve some of your beaching issues and stuff there. Just draw your drivetrain and the moat, and set it up in different positions. Just a simple 2D sketch side view is enough.

Re: Drive Base Help
 

An 8WD w/ 8" wheels shouldn't cause a frame perimeter issue:254 971 1425

Re: Drive Base Help
 

For pneumatic wheels I would reccomend a drop of 1/4" and for any other wheels I would reccomend a 1/16" drop (of course if you really want 8wd but can't do a center drop you could have omnis as your outer wheels)

Re: Drive Base Help
 

Good COTS parts like those offered by Andymark, VEXpro and West Coast Products do cost money, but they are also high-quality and reusable. It is important to consider COTS parts as investments, investments that when used well will not only assist you in gaining success but also something that you can reuse many times, in different seasons if you take care of them. You listed the two options you are currently considering, the Andymark KOP chassis and the Versa-chassis. You said that you have ruled out a custom chassis, the great thing about the Versa-chassis is that it is custom. By using bearings blocks, sprockets and chain and the versa-frame tubing you can build a high quality custom chassis easily and quickly. The Versa-chassis is a West Coast Drive (WCD) arrangement, and is undoubtedly one of the best FRC drivetrain designs. Building a WCD chassis with the parts available from VEXpro and West Coast Products will put you in a great position for future seasons, as you will learn a great deal and you can use the Versa-chassis design every season (254 has used a Versa-chassis style arrangement (WCD) with great success every season, its principles can be applied to any game).

The off-season is the perfect opportunity to experiment with the Versa-chassis and the skills you learn will be of great benefit.

Re: Drive Base Help
 

Have you looked at the WCP SS gearboxes? They are about $120 for a 3CIM gearbox,that is high quality, lightweight and natively Versa-chassis compatible:

http://www.vexrobotics.com/vexpro/mo...es/wcp-ss.html

I disagree with you about cost, the VERSA-chassis will be about $780 with everything minus wheels for 8 wheels. If you are wanting to use the Andymark chassis with 8 wheels, you will need to purchase the upgrade kit which costs $300 and allows you to use 8 6inch higrip wheels. This means the total cost for the Andymark chassis is $899( Keep in mind the $599 KOP bit)

In comparison, you can make a Versa-chassis with 8 6 inch traction wheels for about $860, so roughly the same cost. But the Versa-chassis is way more versatile and you can use the same parts next year, and the year after, which you can't do at all with the KOP chassis.

If you learn how to make a WCD chassis in the off-season you can opt-out of the KOP, receive a $450 PDV from Andymark, which you can buy anything from Andymark with and be able to build a really good chassis next year, which will give you so many more options when designing your robot next.

Re: Drive Base Help
 

Omni-wheels sort of destroy the point of having pneumatic wheels, the main reason for having pneumatic wheels is for the impact absorption, especially on the front and rear wheels. If you were going to have to use omnis it'd be better to just make a conventional chassis with non-pneumatic wheels, like hi-grips, versa-wheels or colson wheels

Re: Drive Base Help
 

Quote: Our major concern is being able to get over drive obstacles-have any teams run into issues with 6-inch wheels on obstacles?

We first considered 6" wheels on the current KoP frame and found the wheel center was too low to get over the rock wall. Thus we went for 8" pneumatic wheels. Even then, our frame hit the rock wall. To help us get over, we cut the side rails to hit the rock wall with an inclined face of the frame.

Another option we considered was a custom lower axle location. Due to our lack of machining tools and expected build time, we opted out of this option.

Last summer we built some robots out of 3/4" plywood. We used wood blocks in the corners to add strength. It worked great and was very cheap.

I like the idea of using 8 wheels with a diameter of 8". A number of top teams used this approach. If you have a drill press, you can clamp all the frame rails together and drill one axle at a time, so the axle holes line up. If you use chain the axle hole positions won't be as critical as if you were using belts.

Let us know how it goes.

Dave

Re: Drive Base Help
 

If your concerns are that you don't yet have the experience for a lot of design work (but you do have some money to spend) then PURCHASE A DRIVETRAIN, instead of designing one. VersaChassis is great but you still have to machine it together, make sure all your distances are correct, source the correct length belt/chain. Using the AndyMark pneumatic wheel upgrade kit as a guide for what to buy is a great way to go (or just buying it if it comes back in stock). We were very successful crossing defenses using that kit by simply slapping an angled plate on the front of the robot. The 1/8" drop center distance was perfectly adequate after we under-inflated our outside tires.

If cost is really an issue you could try to reuse an old LOP drivetrain (or even this year's if you have it!).

As you learned this past season, the drivetrain is the most important part of the robot, without it you can't do all that much. Focus on putting great things on top of the robot rather than mucking around with the most important part. Next year you will likely be able to use the KOP again, and once you have stronger design skills, you can start building your own drivetrain.

Re: Drive Base Help
 

My biggest piece of advice:

While asking for guidance and rules of thumb are a good way to start, learning how to test and tune a chassis quickly is where you will get a lot of benefit.

Center "drop" is there so that there is more normal force on the inner wheels than the outer. This reduce scrub (lateral friction which counteracts steering and turning). Too much drop will actually have the wheels off of the ground, and can cause tipping during starting and stopping depending on Center of gravity height and relative position.

Reduction in scrub can make a world of difference in smoothness and power draw when turning. Too little scrub can make a chassis feel "squirrely" or unstable. A good testing program will have you adjust things until you no longer like the performance (a different negative attribute shows up like pitching or difficulty driving straight), and then backing off that parameter to find a happy medium.

Make sure you run your tests at weight and on similar carpet. Testing on smooth concrete and only 50 lbs will lead to very different results than testing at 120-150 lbs on carpet. This is especially true for pneumatic tires. With hard wheels, the primarily "spring" element is the pile depth of the carpet, thus teams tend to run lower drops (1/16" to 3/16"). With pneumatic tires, the tires will also spring down a bit which varies a lot depending on tire pressure.

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Lastly, with regards to 6" wheels, you are at a disadvantage to impacting a 4" beam with the 6 inch wheels. In order to go over it, you will need some sort of "leading edge" or guide. Even with COTS chassis, this is important to consider. That is not to say a 6" tire will not go over, You just have to be a bit more clever. I saw a team this year using 4" wheels and it would go over the Rock wall just fine, but they were very clever with other chassis elements to help them maneuver (494/70).

Do some searching, and you will find good testing programs other teams have conducted. I know 234 has some nice white papers out, and there are several other threads discussion chassis and mobility.

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Lastly,
Buy extra sprockets to play around with gear ratios a bit. Use the JVN calculator, but then compare your results with the calculator, and try other ratios (say plus and minus 20%) to see what you think. Several years I have seen teams "go faster" by gearing slower... For many FRC games, robots are doing short sprints of about 12 to 16 feet. Sometimes sacrificing top speed will help improve time to distance.

Re: Drive Base Help
 

I should've worded that better :yikes: I was talking about using omnis with conventional wheels (like 1986 in 2013)

Re: Drive Base Help
 

One option you could do to get effective drop would be to run 8" colsons with a press-in hub for the inner wheels and 8" pneumatic wheels on the outer, using VersaBlocks. The 1/8" drop of the VersaBlocks will be exaggerated by the diameter difference in the wheels - the 8" pneumatics are actually 7.65" diameter - and the Colsons won't sink into the ground as much as other wheels would. The inner and outer wheels are generally the ones that have to take impacts anyway.

Re: Drive Base Help
 

A couple questions:

1) What is your current robot running? Without a team number, we can't exactly pull up pictures. (And there is no shame in sharing your team number. We had this beast and still didn't make the show at either of our regionals.)
2) Are you going to be running this at an off-season tournament somewhere? (This shifts the priorities of "good experience" vs. "can compete with it".)
3) You mention your in-season drivetrain fell apart--what failed? Depending on what you have and the failure modes, it may just be something was installed improperly or a matter of beefing up a part. :)

Re: Drive Base Help
 

I've driven a basic robot with six 6" pnuematic wheels over wooden defenses. It was built on an AndyMark frame from 2012. For motors and gearboxes, it had two CIMs and a ToughBox Mini on each side. There were no bumpers, but it had no problem crossing defenses, even the rock wall. However, I don't think that frame would fit eight 8" wheels; there wasn't a lot of free space between the 6", so I think six 8" would be a very tight fit, if they fit at all. I haven't seen the AM chassis this year though, so it might be different.

Re: Drive Base Help
 

It seems like using this with pneumatic wheels would be very easy:

http://www.team221.com/viewproduct.php?id=130

Re: Drive Base Help
 

It was an AM2014 chassis that you drove at the Zone but you bring up a good point. The old AM2012/2013 C-Channel chassis is very easily adapted for 8wd as we did do in 2012. (we later converted it to 6wd because of balancing issues)

This one is the AM2013 version which I believe had the new and improved corner brackets that made the chassis really rigid:
http://www.andymark.com/product-p/am-2494.htm

The newer sheet metal chassis can be modified for 8wd but you need to be really careful of where you put the support structure in between the sheet metal plates to prevent it from falling apart. Our 2014 robot had issues because the supports were not easily placed or modified on the AM2014 for what wanted in our chassis but we made it work.

Re: Drive Base Help
 

Wow, so much help! You guys are great! :)

Re: Drive Base Help
 

I did look at those, and they only supply two mounting points to the versablock. I did not have enough experience to know whether 2 mounting points would be enough for it, but if somebody who's done it before can comment that would be nice.

I'm not sure about that versachassis price. What components did you plan on buying?

Re: Drive Base Help
 

Ok, to answer some questions:

We are planning on taking the new bot to an offseason event, probably Calgames. Our old bot ran a KoP 6WD with 8-inch pneumatics. We had major issues with our gearboxes, which happened to be the exact same 3-CIM ones suggested before. Since the only thing we could do was defense, our gearboxes took a lot of stress and it was enough to fracture and completely shred our aluminum gears. We were advised to just use 2-CIM systems in the future and also decent steel gears.
Also, we didn't secure our gearboxes very well, and that combined with the hole we had in the frame for intake resulted in the bot bowing inwards and twisting the wheels/axles out of alignment. The wheels were actually hitting the metal of the base. This was probably exacerbated by turning scrub, since all wheels were on the same level. So, we took the bot apart multiple times at competition, which was a pain with the KoP base.
We aren't trying to rebuild the same bot though-we're entirely redesigning.

Also, with 6 8-inch wheels, it was a really really tight fit. We had to trim down the bars perpendicular to the wheels so that they wouldn't hit the metal. Also, does the KoP base have pre-drilled holes that would let us drop wheels a good distance?

The AM2494 and 221's chassis seem simple and stable, but would we be able to drop wheels with them?

After reading through, we're leaning towards the VersaChassis. Also, using four Colsons and four pneumatics sounds good. When teams go over obstacles like the cheval and moat, they tend to fly over and then land. Is stress upon landing an issue with the Colsons?

Thanks so much for the help, everyone! :D

Re: Drive Base Help
 

The 221 system does not have a center drop, but you can easily remedy that by using smaller wheels for the outside wheels ;)

Re: Drive Base Help
 

From working the AndyMark booth at Championship, I can say you were far from alone with aluminum gear issues this year. (I'm betting you busted the smaller ones first.) Aluminum gears are a nice way to get the edge with a flat field and west coast drive, but they do run up against limitations when subjected to the abuses of this game (both the field defenses and the bigger wheels increasing the loads). If you've got the ToughBox Mini from the kit, give it a look; its steel gears will be plenty for the off-season. You can then use those lessons learned to assess how exotic next year's drivetrain needs to be. (I should point out, 4 of the 5 regional wins I've been around for were with the kit frame; 3 of the 4 had the that-year's-kit gearbox and the other ran the AndyMark 3CIM4U upgrade.)

The Team Cockamamie Robot in 3 Days build also ran an open front and saw the same frame bending you describe on a smaller scale before we parked it--it also had a way-too-small bellypan in hindsight and suffered for that. You aren't going crazy there either. Strongly consider a sturdy plywood bellypan on your offseason robot; it will lower your CG a bit and give you some great resistance against twisting and bending.

If you're using the AM14U3 with 8" pneumatic wheels, there are different hole placements and belts you're supposed to use. They sold them as a kit, which would place the axles at the correct place to avoid notching the end bumpers. It would also space the outer plates out further to cut down further on rubbing.

We didn't drive the Team Cockamamie robot on carpet or at high weight (we were waaaaaaay under), but the drop was enough for that. You can also play with air pressures there; a little less pressure in the corner wheels will increase the effective drop.

4901 used a variation on the 221 chassis for its drivetrain this year, except we knew we wanted drop (especially since our corner wheels were pushed inboard). We ended up using 1x3 tubing for the drive rails, which was overkill but suited the purpose of putting our axle holes exactly where we wanted.

Hope some of these data points help!

Re: Drive Base Help
 

I suggest that if you are redesigning a robot in the offseason to complete the same challenges that Stronghold had such as the moat, I would consider using the AM14U3 from andymark with the Upgrade Kit 6WD with 8" Pneumatic Wheels. This will give you suspension and a bit of bounce when going over obstacles. Just note, this drive base CANNOT go over obstacles without in house customization. Our team noticed that at the competition our robot could not cross any defenses other than the rough terrain. We used an angle grinder to cut off about an inch off of the bottom of the front of our chassis and made an angle so that when we would hit an obstacle it would pop our bot up onto the moat, ramparts, rock wall, or rough terrain, which would allow our wheels to get on top of the defense and drive over with ease. We had only gotten stuck in the moat only one match and that was when our path was obstructed with a boulder. I also suggest adding support in the middle of any chassis to ensure the sides do not cave in (just a precaution)
Hope this helps!

Re: Drive Base Help
 

AndyMark also sells optional upgrades for the for the AM14U2/3: a wedge plate to solve this issue, and a cross plate to help with an open front/rear. One wedge plate adds close to 3" of length to the chassis length without increasing the wheelbase, but it does help get over the category B and D defenses. I can't vouch for the cross plate.

Re: Drive Base Help
 

Plus they also make it easy to run the AM churro (http://www.andymark.com/product-p/am-churro.htm) in between the gear boxes to stop the sagging from happening as much. Tap the ends of each rod and shove some 1/4-20 bolts in from the gearbox side. Most of the teams that had these gearbox sagging issues I noticed had nothing in between their gearboxes. Even the weight of 3 CIM motors can cause that sagging and that alone can shred a gearbox from alignment issues.

See the attached photo. Every team should be supporting their gearboxes in some way because it will also stiffen your frame up.

Re: Drive Base Help
 

I wouldn't worry too much about how well the robot survived this years game. This years game was brutal on robots. I'm curious as to how much drive practice or stress testing was done on the robot. During build season did you ever test it against the defenses?

Re: Drive Base Help
 

Minimal testing. Very very minimal. We never had a practice bot and our drive base wasn't ready pretty much until bag and tag.

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Also, we're still confused on if it's possible to put four eight-inch pneumatics in the KoP chassis. Does it fit nicely/work with the pre-drilled holes?

Re: Drive Base Help
 

2 mounting points normally works fine for a normal WCD. For this years game I would recommend putting bracing between the two gearboxes.

Both the Versablock and the WCP Gearbox Bearing Block work fine with the WCP gearboxes(have used both)

In regards to the Versa-chassis pricing:

Gearboxes: $130 each( need 2) $260 total
Versa-blocks: $25 each( need 6) $ 150 total
½ hex bearing $5 each( need 16) $80 total
#25/35 chain 10foot $10 each (need 2) $20 total
#25/35 ½ hex sprocket $7 each( need 16) $112 total
WCP Cam $5 each (need 6-8) $40 total
Versaframe stock 59” $25 each (need 3+) $75 total
½ hex shaft stock 3foot $12 each (need 1) $12 total

Total = $749 before wheels

Edit: This is a cost breakdown to show the Versa-chassis price, not recommended components for a particular season

Re: Drive Base Help
 

16T #25 chain sprockets are probably too small for this year's game. They're quite undersized for the torque of 8" wheels and the shock loads of hitting defenses hard. Many, many teams have thrown chains with them this year. I would do 22T if you have the clearance, or even 12T 35 chain.

Re: Drive Base Help
 

Yes, I would also recommend #35 chain, it will also be easier for you to work with. Realistically I only did the list to show the price, most 1/2 hex bore sprockets are around the same price.

Re: Drive Base Help
 

Data point: We ran 17T sprockets from 221 this year. We did throw several chains through bag-night driving and the earlier parts of Palmetto, but our analysis (imperfect as it is because you can't see inside when it happens) showed the root cause was failure at the half-link (which were of the bend-a-wire-to-pin-it-in variety, which was hitting other things inside including the other half-link). As we got more conscious of how to install the chains (and switched to better half-links), we had no problems through Orlando. And in no case did we tortuga because of the chains. (One low-bar tortuga was poor lineup, and once we lost our radio cable on a defense.)

Re: Drive Base Help
 

[quote=redfancy;1585966]Minimal testing. Very very minimal. We never had a practice bot and our drive base wasn't ready pretty much until bag and tag.

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Yeah that was a killer this season we went with a tread design ran it over some defenses and were worried about it surviving the impacts so we switched to pneumatic wheels and a suspension system. Stress testing a robot is important cause the sooner you find points of failure the more time you have to iron those points out.

Re: Drive Base Help
 

If you're using pneumatic tires, you can just inflate the center wheels slightly more than the outer wheels, or use a belt sander to take off some of the tread on the outer wheels. (or both) Not only will it create a drop center, you'll have less issues with turning scrub.

Re: Drive Base Help
 

Do you have access to a press brake? If so you could build something similar to our drive this year (pictures below). We used 8 8" wheels with 15mm belts and 4 toughbox micros at 12.57:1 (I think). We used 1/2in of drop on the centre wheels. The side plates are .090 5052 aluminium, laser cut, but could be handmade.

Re: Drive Base Help
 

We ran 16t center-to-center outside of tube this year and didn't face any problems with the sprockets until SVR, when the chain wear and bearing blocks drifting made the chains super loose (and even then we only threw them once IIRC). If one is running chain in tube or something similar with the sliding versablocks and makes solid chains with the Dark Soul chain tool, I think 16t sprockets can work.
We ran 4 CIMs on 8" AM pneumatics.

Re: Drive Base Help
 

My team used the KoP chassis with 6WD 8" Andymark Pneumatic tires. We ran the chassis in a wide bot configuration, 30" wide by 28" long. We decided these dimensions mainly by testing using the stock chassis axle holes and also through some CAD work. We also cut angles into the plates using a vertical band saw to give us a better approach angle. The main thing we learned through having a practice bot is that you need a lot of extra supports in the chassis. You can see yellow churros between the wheels that support the two side plates, as well as yellow 2" angle above the plates to support them. We ran long churros between the inner plates to support the bot width ways as well as a 1" square tube and the AM Cross Plate. We are running the KoP toughbox minis as our drivetrain gearboxes along with the KoP drive pulleys and belts. The bumpers are supported above the frame using the blue bumper brackets above the chassis. This bot held up very well all season long. Zero failures the entire season.

Attachment 20755

Re: Drive Base Help
 

They sold wedge plates?!?!?!:ahh:

Re: Drive Base Help
 

They came out later during build season.

Re: Drive Base Help
 

Inflation alone does not work, from our experience this year. Sanding down the tires may help but in the end we ran a 3/8" center drop (although 1/4" was working ok). It would be hard to get enough drop without actively doing something to add it.

Re: Drive Base Help
 

I would be careful with using the angled plate of you plan to have an opening in the middle.

Re: Drive Base Help
 

Posted on AndyMark's YouTube January 15th, after Kickoff (but in Week 1 of build season).

(scribbles notes on this for next year)

Re: Drive Base Help
 

Ah I always looked in the drive base category to look for upgrades. I didn't see the upgrades until AFTER our competitions were over.

Re: Drive Base Help
 

The 3/8 drop works well with pneumatic wheels, you are right in that inflation barely does anything at all on these specific AM wheels. I saw a team next to us really struggling at Champs to get their robot to turn without brownout issues because they neglected to include the drop. I told them to try wrapping the center wheel with layers of duct tape and that actually fixed their issues aside from the duct tape appearance.