pic: One Tough Train

[Kevin Sevcik]

How stiff is that chassis, anyways? It definitely looks good, but we tried a bent sheet chassis one year and we definitely had problems with it flexing. and especially with it twisting since it didn't have any stiffness at the corners.

[Rod]

Originally Posted by Kevin Sevcik

How stiff is that chassis, anyways? It definitely looks good, but we tried a bent sheet chassis one year and we definitely had problems with it flexing. and especially with it twisting since it didn't have any stiffness at the corners.

The bottom plate is 1/4" thick Alum. I hope it will not flex too much

[Tristan Lall]

Originally Posted by Rod

The gears used are a 55 tooth 3/8 face 20 DP for output and a 5 tooth stem pinion on the end of the Cim motor.

I just realized; you've got an 11:1 reduction there, meaning that your quoted speed numbers are sort of conservative (I'd say you estimated 3000 rpm from the CIMs). With any luck, under normal loading (no pushing), your motors will tend to spin closer to their free speeds (5342 rpm) than their max. power speeds (2671 rpm).

Actually (using free speed), your top speed would be closer to 11.6 ft/s. I've found that free speeds of motors provide a better approximation of robot top speeds than anything else--with the extra voltage from a full battery roughly accounting for the load on the motors from normal driving, and allowing an estimate of free speed = operating speed. (This varies, depending on the drivetrain, and is clearly not the product of rigourous calculation! If anything, it overestimates the speed.) The 6.5 ft/s @ 3000 rpm figure seems more consistent with assuming that the robot will run most of the time at full power. That's not a realistic number to work with, because you'll never know what your power output actually is, when pushing something around--you certainly can't hope to be at max. power in any given pushing match. If anything, when pushing another robot, you'll be on the slow side of max. power (that is, the high-torque side).

And one more note: I was using the max power figure earlier in the chain calculations, while quoting free speeds. In reality, since max. power occurs at 50% free speed, you should (if you want to be rigourous about it) divide the speed I gave above by 2, and use the corresponding power figure on the chart. With some rough interpolation, and the #25 14-tooth instead of the 13-tooth sprocket, you're at about 0.12 HP rated. But I think that these compounding safety factors are getting a little absurd. I wouldn't bother with this last step, if only because this is a mere robot, and we don't need to overbuild it to last forever without failing. As long as it lasts the season intact....

[Bill Gold]

Lookin' good, Rod.

Why not put the gearboxes on the center wheels and use two output sprockets (one to the front and one to the back)? This will eliminate the possibility of this drivetrain becoming a 4wd (3wd on one side, and 1wd on the other) with the loss of just one chain, or a 2wd with the loss of two.

Sorry if this was brought up earlier in the thread… it’s almost 3am, and I’ve been doing something that a lot of 21+ year olds tend to do

-Bill

[Ryan Dognaux]

Looks good, similar to the 254 - 60 drive. I was going to mention what Bill just said, it might be better to drive your bot from the center wheels. That way, if you throw a chain, you'll still have at least 4 wheels that are powered by the CIMs. This is how we had our drive set up at first this year, but then decided to switch out our front and back wheels with the AndyMark Omniwheels.

[Matt Reiland]

Originally Posted by sanddrag

Ah, okay. So you really don't have 3 (close fitting) bearings on the shaft. Also, now I can see the need for couplings. Looks very small/compact!

I'm not sure if this would be a good idea but it seems like those couplings are taking up a lot of space in your otherwise compact design. If you got a gear just big enough to bore out and key to fit over the CIM shaft to keep the tooth count small (for 20P I believe this would be a 12T) then you could increase the 55 tooth gear just a little bit (maybe to 60) or maybe even keep it that size for a faster robot then you could move the CIMs in closer and mount them by the face to that first red plate.

Not sure if anyone else has seen this but it is THE coolest, easiest, and cheapest way to put the CIM motor into a custom gearbox. I already ordered a bunch for next year

http://www.andymark.biz/am-shifter-cim-gear.htm

I will definately be adjusting my design to use these, it just doesn't get and easier. The right bore, keyway, everything.

[Rod]

Originally Posted by Bill Gold

Lookin' good, Rod.

Why not put the gearboxes on the center wheels and use two output sprockets (one to the front and one to the back)? This will eliminate the possibility of this drivetrain becoming a 4wd (3wd on one side, and 1wd on the other) with the loss of just one chain, or a 2wd with the loss of two.

Sorry if this was brought up earlier in the thread… it’s almost 3am, and I’ve been doing something that a lot of 21+ year olds tend to do

-Bill

Thanks Bill,
This year we have almost the same gearboxes in the center with 2 sprockets, it works very well. It has been so long since we have lost a chain that I don't see it as a problem, yes it could happen. The trade off is that we always need weight in the back to counter the arm and the open space will allow us more freedom in our arm design. This is all a guess, who knows what the 2006 game will bring.
See Ya in Atlanta

[gburlison]

Originally Posted by Rod

Thanks
A few answers
The gears used are a 55 tooth 3/8 face 20 DP for output and a 5 tooth stem pinion on the end of the Cim motor. The stem pinion has a 3/8" Dia. so it can not be mounted on the Cim shaft. That is why the Cims use a coupling and are not face mounted. I have put 3 bearings on a shaft many times and never had a problem. Our robot this year uses the same gearboxes and works perfect. The sprockets are 14 tooth #35 with 5/8" Bore. This year we had to add weight to our robot (17 Lbs.) We have a 55 Lb. drive train this year, that does not count the arm. So next year if we have a 68 Lb. drive train it should be about right. I read these boards every day, just don't post too much. Our designs have been built, they are posted here both the CAD drawings and this year's Robot. CAD drawings are titled Light weight drive train, we built a slightly modified version of it.
See Ya

Rod,

Did you check the weight of this design in inventor?

[Rod]

Originally Posted by gburlison

Rod,

Did you check the weight of this design in inventor?

Yes It is 68 Lbs.

[mtaman02]

Not a bad design, I love it when plans come together early in the 2006 season, many of the issues get resolved fairly early.

Couple of issues though
1) do you have an alternative design to compensate for objects on the field which may include going up or down or over.

2) do you have an idea of how you gonna be able to balance the weight out along the base of the robot since the majority of the weight is from the parts and the parts is mainly in the rear / front of the robot.

[Rod]

Originally Posted by mtaman02

Not a bad design, I love it when plans come together early in the 2006 season, many of the issues get resolved fairly early.

Couple of issues though
1) do you have an alternative design to compensate for objects on the field which may include going up or down or over.

2) do you have an idea of how you gonna be able to balance the weight out along the base of the robot since the majority of the weight is from the parts and the parts is mainly in the rear / front of the robot.

1) Larger wheels and gears. The center set of wheels can be removed with no major changes.

2) The battery can be moved to the front.

[sanddrag]

How much does the base pan and all those little bars weigh? While the plate is nice for mounting stuff too, I'm betting you could make a lighter stronger frame with box tubing. (although you did mention that you designed this to be heavy).

[team222badbrad]

I am not sure if this is mentioned in any previous posts, but upon first look I noticed something you may not have thought about in the design of your robot frame.

Those three rods of tubing in the front and back may potentially bend upon impact of other objects causing them to come in contact with the wheels, which could be potentially bad.

Just figured I would let you know!

Nice Inventor work by the way!

[Rod]

Originally Posted by team222badbrad

I am not sure if this is mentioned in any previous posts, but upon first look I noticed something you may not have thought about in the design of your robot frame.

Those three rods of tubing in the front and back may potentially bend upon impact of other objects causing them to come in contact with the wheels, which could be potentially bad.

Just figured I would let you know!

Nice Inventor work by the way!

The bars are 3/8" solid stainless steel. My thought is that are more likely to spring than to bend.

[Matt Reiland]

Originally Posted by Rod

The bars are 3/8" solid stainless steel. My thought is that are more likely to spring than to bend.

Wow, that is an incredible amount of weight to be putting into the base!! 3 rows of solid steel bar plus what looks to be large blocks of aluminum to hold them? Add in the weight of about 12ft of chain and you should be at about 75 lbs.
Have you considered aluminum tube maybe 1/8" wall 1" dia?

All the 1/4" in the base is a little heavy for a first robot, you could build the whole thing out of 80/20 and still be a bunch lighter. Just my 2 cents but I have yet to see a robot that has that much weight to burn unless you plan on having no manipulator.?

It does look nice and clean in inventor, great job on that.