pic: Team 980 Breakaway robot

[David Brinza]

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[Chris Fultz]

Nice. I like the belt drive. Were you able to take advantage of the Gates offer?

[David Brinza]

Originally Posted by Chris Fultz

Nice. I like the belt drive. Were you able to take advantage of the Gates offer?

Unfortunately, the Gates offer didn't include belt sprockets quite large enough (D = 5.5"). Our custom sprockets were fabricated by our new team member, Schroeder Torsion Bars in Burbank.

[drtysteve384]

nice looking robot, how do you move the ball and it looks like you have a ball holder... no chain either?

[David Brinza]

Originally Posted by drtysteve384

nice looking robot, how do you move the ball and it looks like you have a ball holder... no chain either?

No chain in our robot this year.

The foam roller provides ball control and is driven via a CIM/AM planetary gear combination using belt drive. The kicker is driven by enclosed compression springs with a pivot point that puts the kicker "over center" in the cocked position. A winch using two window motors reels up the kicker. We use a large cam on another window motor to push the kicker down through center to fire the shot. The kicking mechanism requires just three limit switches for operation: one on the kicker, one on the winch, and one on the cam.

[Lil' Lavery]

Originally Posted by David Brinza

Unfortunately, the Gates offer didn't include belt sprockets quite large enough (D = 5.5"). Our custom sprockets were fabricated by our new team member, Schroeder Torsion Bars in Burbank.

Why such large sprockes? Are you using your belts to double as a tread drive while you go over the bump?

[RogerR]

It appears that you have a suspension on the front wheels, with the pivot 3"-4" ahead of the center wheel axle. If this is the case, it seems as though the center to center distance will change between the front and middle wheels, which would lead to the belt tensioning and loosening based on were the front suspension is in its travel.

If the above is true, how do you handle this?

[Chris is me]

Early in the season there was talk on 1714 of using a 6 wheel drive with pulleys between the wheels like this one to double as power transmission and bump climbing aid. Is this why you guys decided to go for timing belt, or did you guys have other reasons? I'm interested in alternatives to roller chain for drivetrains, so any info is appreciated.

[David Brinza]

Originally Posted by Lil' Lavery

Why such large sprockets? Are you using your belts to double as a tread drive while you go over the bump?

Exactly. The treads are off the floor except when we traverse the bump.

Originally Posted by RogerR

It appears that you have a suspension on the front wheels, with the pivot 3"-4" ahead of the center wheel axle. If this is the case, it seems as though the center to center distance will change between the front and middle wheels, which would lead to the belt tensioning and loosening based on were the front suspension is in its travel.

If the above is true, how do you handle this?

The center-to-center distance radius is large, but the compression of the shock is quite limited, so the amount of tension change isn't large. We are considering a very simple idler (just a roller on a spring), if we find belt slippage to be a problem.

Originally Posted by Chris is me

Early in the season there was talk on 1714 of using a 6 wheel drive with pulleys between the wheels like this one to double as power transmission and bump climbing aid. Is this why you guys decided to go for timing belt, or did you guys have other reasons? I'm interested in alternatives to roller chain for drivetrains, so any info is appreciated.

Yes, "dual use" mentality was at work here. This is the first time we've deviated from chain in our drive system. We'll know in two weeks whether we made the right call.

[Ryan_Epperson]

Originally Posted by David Brinza

Exactly. The treads are off the floor except when we traverse the bump.

Food for thought...

http://forums.usfirst.org/showthread...ighlight=chain


I know the teams that I mentor saw it as no issue they were designing their robots as well... Looks like we are going to be ordering smaller gears and installing them on thursday!

Good luck!

[Chris is me]

Originally Posted by Ryan_Epperson

Food for thought...

http://forums.usfirst.org/showthread...ighlight=chain


I know the teams that I mentor saw it as no issue they were designing their robots as well... Looks like we are going to be ordering smaller gears and installing them on thursday!

Good luck!

Belt drive isn't metal so it doesn't break the rule cited above.

[Ryan_Epperson]

good to know...

I would think that Belts are going to have more traction than metal, but that's just me.

[Chris is me]

Originally Posted by Ryan_Epperson

good to know...

I would think that Belts are going to have more traction than metal, but that's just me.

They probably do (though less than roughtop). The rule doesn't limit traction, just metal as a traction aid (mainly due to carpet damage, etc).

[Ryan_Epperson]

Originally Posted by Chris is me

They probably do (though less than roughtop). The rule doesn't limit traction, just metal as a traction aid (mainly due to carpet damage, etc).

That's what it seemed like to me. The chain on the Robot only brushes the carpet and in the 20+ times that they floored it over the bump the wheels were the only thing that ended up being damaged, the carpet was perfectly fine. So this would leave me to want to think that they are on then... but we need to check it out on thursday on the practice field to be sure

[David Brinza]

Originally Posted by Ryan_Epperson

That's what it seemed like to me. The chain on the Robot only brushes the carpet and in the 20+ times that they floored it over the bump the wheels were the only thing that ended up being damaged, the carpet was perfectly fine. So this would leave me to want to think that they are on then... but we need to check it out on thursday on the practice field to be sure

The way <R08> reads,

ROBOT wheels, tracks, and other parts intended to provide traction on the carpet may be purchased or fabricated (“traction devices” include all parts of the ROBOT that are designed to transmit any propulsive and/or braking forces between the ROBOT and the FIELD). In no case will traction devices that damage the carpet or other playing surfaces be permitted. Traction devices shall not have surface features such as metal, sandpaper, hard plastic studs, cleats, or other attachments. <snip>

I doubt inspectors will allow a chain that contacts the field. Chains close enough to the circumference of the wheel as to contact the field on a bump will provide (however small) propulsive and/or braking forces to the robot. Chains are made of metal, hence they are prohibited as traction devices. I would also worry about lubricant in the chain transferring to the carpet, thus violating <R36>.