pic: Team 3572 Chassis Project

[Deke]

I like the layout, it is very creative.

It looks like the cim plates are 1/8" thick, if they are, I would suggest at least 1/4" thick with the Cims cantilevered off them. 1/8" works if both sides are supported, but a big bounce or hit will put a large load on that thin plate.

The middle drive pulley to the cims looks cantilevered from the frame tube, I'm not sure if would would be an issue or not, but it would help if you can support it with a bearing on both sides. Some testing of the current layout will let you know, just something to watch out for.

I would suggest the dead axles with blocks for the outside wheels like you suggested, we ran cantilevered dead axles last year and loved the performance over live axles. With your belt layout, it makes it easier to run dead axles versus live axles as well.

[JesseK]

Originally Posted by Infinity2718

It looks like the cim plates are 1/8" thick, if they are, I would suggest at least 1/4" thick with the Cims cantilevered off them. 1/8" works if both sides are supported, but a big bounce or hit will put a large load on that thin plate.

This was my next comment since the CIM mount plates seem a bit tall. If the two mount plates were combined into a single mount plate, the design may be able to add strength without adding weight. It could also incorporate more belt wrap around the pulleys.

[Andrew Schreiber]

Originally Posted by 75vs1885

looks like the cims would interfere with the bumpers, and they could get damaged if hit to hart from another robot. Is there an advantage to having them pointing outside opposed to inside?
Other than that it seems really solid.
btw, would the electronics board be mounted underneath?

We (125) ran all last season with them dangling outside the frame like that. Had 0 issues with them. (1x Preseason, 4x Districts, DCMP, CMP, numerous off seasons)

Just remember that the wires exist and have minimum bend radii.

[Deke]

Originally Posted by JesseK

This was my next comment since the CIM mount plates seem a bit tall. If the two mount plates were combined into a single mount plate, the design may be able to add strength without adding weight. It could also incorporate more belt wrap around the pulleys.

Running a support beam across between the plates would help too, just something like a hex shaft could be used, but it would be annoying having that hang over the middle of the bot. Even a 1/4" plate would make nervous without a gusset or additional support.

[MrBasse]

The motor plates are 1/8", but they are also steel. This would allow us an easier time adding supports to them. A bar across might not be a problem depending on where the electronics end up. I would like to avoid it if possible though.

The majority of our components were made of 1/2" conduit last year as it weighs much less than the aluminum of equivalent strength. Plus, I hate TIG welding. Once I figure out what I'm doing, I'm usually done with the project. If we need support we will most likely go back to 1/2" conduit. $2.50 a stick can't be beat with proper welding ventilation. Plus when you are done you can paint it aluminum color and nobody ever knows.

I'll keep an eye on the pulley for flex. If needed we can just extend the shaft and add another hole into the inner bearing plate. That was actually in the original design, but the shaft was cut short for prototyping and it seemed okay. Only building both sides and beating the snot out of it will tell if it will hold up though.

[asid61]

Looks pretty nice, but clean up the front/back axles in the cad. Either cantilevered live axle or dead axle will work, but decide on one pre-season.
Personally I recommend live axle, as it's easier to swap out wheels or gearboxes if something breaks.

Also, 12fps is too slow. Gear for around 15fps at least. We ran around 16.5fps at CalGames on 4 cims with no problems; we were running 12fps during the first half of the season, and the extra speed was very exciting.

[protoserge]

How do you adjust your belt tension and alignment?

Did you account for mechanical drivetrain loss when calculating your 12-13 fps?

I'd be curious as to the drive belt engagement given your configuration.

[MrBasse]

Originally Posted by stinglikeabee

How do you adjust your belt tension and alignment?

Did you account for mechanical drivetrain loss when calculating your 12-13 fps?

I'd be curious as to the drive belt engagement given your configuration.

We can use the motor mounts to apply more tension if needed, just have to drill more holes.

Speed is based on JVN's calculator set to 81%. and double checked by my awful math and an 80% efficiency.

Belt runs can be seen here. After teaching drafting for ten years I realized I had never used the design accelerator in my life, so I had to play with it for a while to see what it could do. Ignore the fact that there is a 9mm belt on the wheel pulleys. That would be an 18mm belt there.

[MrBasse]

Originally Posted by asid61

Looks pretty nice, but clean up the front/back axles in the cad. Either cantilevered live axle or dead axle will work, but decide on one pre-season.
Personally I recommend live axle, as it's easier to swap out wheels or gearboxes if something breaks.

Also, 12fps is too slow. Gear for around 15fps at least. We ran around 16.5fps at CalGames on 4 cims with no problems; we were running 12fps during the first half of the season, and the extra speed was very exciting.

With two speed gearboxes last season we had our high gear running us around 18 FPS and it just didn't get used that much. It very much should have, but it didn't. Our drivers have always just seemed more comfortable with a more controllable machine at a lower speed.

[Scott Kozutsky]

Originally Posted by MrBasse

With two speed gearboxes last season we had our high gear running us around 18 FPS and it just didn't get used that much. It very much should have, but it didn't. Our drivers have always just seemed more comfortable with a more controllable machine at a lower speed.

They need more practice. There were teams geared to 22 fps this year and they weren't doing too badly once the drivers learned how to use it. Maybe try adding an easily adjustable 3rd stage like the versachassis WCD has so you can get your drivers up to the maximum speed they feel comfortable with. Our driver this year was geared to 16fps and wanted to go faster.

[asid61]

Originally Posted by Scott Kozutsky

They need more practice. There were teams geared to 22 fps this year and they weren't doing too badly once the drivers learned how to use it. Maybe try adding an easily adjustable 3rd stage like the versachassis WCD has so you can get your drivers up to the maximum speed they feel comfortable with. Our driver this year was geared to 16fps and wanted to go faster.

+1. It's better to have the ability to go fast is all I'm saying; that way you have a choice.

[hrench]

Looks interesting. I'd consider moving the motors lower and flipping them inside to lower the CG. Also, they look vulnerable where they are.

[MrBasse]

Originally Posted by hrench

Looks interesting. I'd consider moving the motors lower and flipping them inside to lower the CG. Also, they look vulnerable where they are.

The height they are at is set by the pulley positions and the belts available. Putting them inside eliminates the added floor space gained by putting them outside. I'm also not too worried about them hanging outside the frame as the bumpers will almost completely cover them. We have been putting our air storage there for the last three years and have never had an issue, so I am fairly confident in the location of the motors. This is something we will keep an eye on to be sure though.

Originally Posted by Scott Kozutsky

They need more practice. There were teams geared to 22 fps this year and they weren't doing too badly once the drivers learned how to use it. Maybe try adding an easily adjustable 3rd stage like the versachassis WCD has so you can get your drivers up to the maximum speed they feel comfortable with. Our driver this year was geared to 16fps and wanted to go faster.

We will wait and see what the game is before we make gearing choices. If we gear up all we have to do is move two holes and spread the middle wheels a bit. We can get all the way up to ~18 fps by changing one gear. Or up to ~16 fps by changing a few pulleys in our primary reduction.

I agree on practice, but without the funds for a practice robot and typically finishing up with hours to go, it is hard to come by. Also, a location big enough with carpet that would allow real practice has long been a dream of mine.