Mounting of drive system

[EricH]

Originally Posted by mattotters

I was personaly thinking of a pillow block with out berings, have you ever seen this?comments?

I've seen pillow blocks, but my team has gone through the frame with an axle the past three years. I can't remember if we used bearings in our pillow blocks before then or not.

Edit: We used bearings on our 2004 robot, but we had some odd-shaped pillow blocks that year, and I can't remember how we mounted our front wheels. Can't find clear enough pictures of previous robots on CD to make the call there.

[lukevanoort]

I'm actually planning on doing a bearingless pillow block style design this year (assuming the game calls for 6WD). Here's why: with a hole through the frame, you have to decide on the how much lower the centre wheel is when you make the frame; however, with a pillow-block style design, shims can be used to adjust the lowering. Since the amount of lowering is adjustable, we can then test for what gives us the best driveability. (It could also allow us to adjust the lowering before every match, but I'd rather avoid the trouble of doing that by just picking a good amount and sticking with it)

[MrForbes]

Originally Posted by lukevanoort

I'm actually planning on doing a bearingless pillow block style design this year (assuming the game calls for 6WD). Here's why: with a hole through the frame, you have to decide on the how much lower the centre wheel is when you make the frame; however, with a pillow-block style design, shims can be used to adjust the lowering. Since the amount of lowering is adjustable, we can then test for what gives us the best driveability. (It could also allow us to adjust the lowering before every match, but I'd rather avoid the trouble of doing that by just picking a good amount and sticking with it)

1/8" is what you want, no need to go to too much trouble just to make it adjustable.

[EricH]

Originally Posted by squirrel

1/8" is what you want, no need to go to too much trouble just to make it adjustable.

How much drop you put in depends how much rock you want/need. I can't remember offhand how much 330 drops their center, or any other recommendations (I'd say 3/16, but that's way too much--more likely 3/32 or 3/64.)

[Ian Curtis]

Originally Posted by EricH

How much drop you put in depends how much rock you want/need. I can't remember offhand how much 330 drops their center, or any other recommendations (I'd say 3/16, but that's way too much--more likely 3/32 or 3/64.)

We drop 3/16. It gives us great turning, but it does rock enough to be annoying.

[neoshaakti]

I'm sorry Im a nub, but does dead-axle have anything to do with using pillow blocks?
Pillow blocks are quite expensive on mcmaster-carr (about 30 bucks a piece)

is live-axle a more economical choice?

and with a live-axle, would you have to connect the sprocket to the shaft?

sorry for the nub questions

[MrForbes]

The easiest newbie way to do it is to mount the wheel on bearings on a "dead" axle that is just a bolt thru the frame. The sprocket then bolts to the wheel.

Whether or not you need blocks to mount the dead axle, depends on the design of your frame. The kit frame has flanges with holes in them designed for a bolt type dead axle. If you use that extruded stuff then you may need to make blocks or angled plates to mount the axle.

With a live axle, connecting the sprocket you can buy hubs, most teams who use a live axle make most of the parts themselves, it's not really a newbie appropriate thing to try unless you have good help.

here are some of the hubs, the keyed and hex hole type are what you might use

http://andymark.biz/hubs.html

[lukevanoort]

Originally Posted by neoshaakti

I'm sorry Im a nub, but does dead-axle have anything to do with using pillow blocks?

Nothing really. What I'm talking about is a block of aluminum with a hole drilled partway though (like halfway maybe) so it can hold an aluminum shaft as a dead axle. Then, the block is mounted to the robot with bolts and its height can be adjusted with shims. Not really a pillow block in the traditional sense, but similar.

Originally Posted by neoshaakti

Pillow blocks are quite expensive on mcmaster-carr (about 30 bucks a piece)

is live-axle a more economical choice?

Generally no. A bolt through a hole in the frame can serve as a dead axle, with live you need keyed/hex/spline/etc shafts, bearings, pillow blocks, so on.

Originally Posted by neoshaakti

and with a live-axle, would you have to connect the sprocket to the shaft?

Usually yes. If you used gears for power transmission, you'd connect those to your shaft.

Originally Posted by neoshaakti

sorry for the nub questions

Nothing to be sorry for, everyone was a newbie sometime.

[M4 Sherman]

Dead axle systems are usually lighter then the live axle, and there's less moving parts.

Also, the drop of the middle wheel on a 6wd depends on the type of wheel used.

[Alan Anderson]

Originally Posted by M4 Sherman

Dead axle systems are usually lighter then the live axle, and there's less moving parts.

I wouldn't be so quick to say "usually". If live vs. dead is the only difference, then you're probably right. The axle moves in a live system, so that's one more moving part. But the live axle system I'm most familiar with has the axle itself as the gearbox output, saving several parts (sprockets and chains at least). You can just use a live axle in the same sort of application one might use a dead axle, but you get additional design options when you choose a live axle.

[Arefin Bari]

Take a close look at the front view of the module attached to this post.

[Arefin Bari]

Also, please take a close look at the 1st picture where it shows the tensioner and how we used shaft collars instead of spacers. It was a lot less hassle when it came to take everything apart.

[ChrisH]

Originally Posted by lukevanoort

Nothing to be sorry for, everyone was a newbie sometime.

Not only that, it was a good technical question that prompted further discussion. It has been a while since we've had a good live vs dead axel discussion.

[Scott358]

Last year we used shoulder bolts as axels through the frame, which worked well.

[Steve Kaneb]

For the two years we've done 6 wheel (06, 07), Team 190 used both live and dead axles. The center wheels were driven using live axles with a keyed shaft and the end wheels were sprocket and chain driven from the center on dead axles.

Besides the gearing change between the years, the only major difference between the two drivelines was the chain path. In 06, we had a convoluted one to incorporate a system that got taken off the robot before ship, and after almost every match we were retracking a chain. In 07, we had straight chains with simple tensioners and never had any drivetrain problems (until we got to offseason demos and the bearing blocks had worked themselves loose).

The advantage to this system was that it was compact, as the center axle was just the output shaft after a gear reduction, and the outer wheels were just shafts bolted to the frame with wheels on them.