Drive Base Help

[redfancy]

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!

[asid61]

If you have the drive, all power to you to make your team better!
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.

[roboruler]

Originally Posted by asid61

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.

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.

[asid61]

Originally Posted by roboruler

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.

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?

[roboruler]

Originally Posted by asid61

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?

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

[Chris is me]

Originally Posted by roboruler

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 chain 10foot $10 each (need 2) $20 total
#25 16tooth 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

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.

[roboruler]

Originally Posted by Chris is me

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.

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.

[Billfred]

Originally Posted by Chris is me

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.

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.)

[asid61]

Originally Posted by Chris is me

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.

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.

[GCarnes]

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.

[SoftwareBug2.0]

Originally Posted by redfancy

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.

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

[carpedav000]

Originally Posted by redfancy

.
3. two center wheels dropped (also need advice on how much to drop wheels proportional to wheel size)
D

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)

[roboruler]

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.

[roboruler]

Originally Posted by carpedav000

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 monism as your outer wheels)

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

[DaveL]

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