Mounting of drive system
 

On our bot the wheels has always been keyed to the axel shaft and this year we want to try to have the wheel spin on the axel we have the correct wheels set up i just want to know what is the best/most commen way to attach the wheel to the frame.

any tips pictures would be great =D

Re: Mounting of drive system
 

Ah, going from a live-axle (axle turns the wheel) to a dead-axle (wheel turns on the axle)? Common methods include just using a bolt that only has thread on the end, or a steel shaft that is pinned in at both ends.

Re: Mounting of drive system
 

In 2006 we had our wheels spin freely on axles. The funny thing is that the axles were able to spin freely too. It worked!

Just make sure the bolts connecting the sprocket to the wheel are strong enough.

Sam

Re: Mounting of drive system
 

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

Re: Mounting of drive system
 

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.

Re: Mounting of drive system
 

Really simple method is to just drill a hole in each side of the frame, and put a tube spacer on each side of the wheel bearing, and a long bolt thru the middle.

Better is to also add a tube between the bolt and the spacers and bearings, so the bolt can be tightened up all the way and not spin, as shown in the drawing.

Re: Mounting of drive system
 

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)

Re: Mounting of drive system
 

last year we had a shaft collar on the out side of the axle and a pipe acting as a spacer between the wheel and the frame. but we did have a very hard time lining the chain up.

Re: Mounting of drive system
 

I think that a dead axle is the only way to go. The reason being is that the torque is moved out from a tiny key to a bolt pattern on the side of the wheel which causes less wear and problems and allows you to remove a lot of weight.

The method of using a "pillow block" with no bearings is a good method and the industry name for these are shaft hangers. On our 2005 robot we used a 5/8" aluminum tube axle with shaft hangers that had a socket head cap screw holding the axle in the shaft hanger and keeping it from spinning. If you want to use a aluminum axle I would recommend using a Rulon or PEEK Flanged plain nearing pressed into your wheels. Rulon and PEEK are PTFE(teflon) composite berings that are specifically designed for soft shaft materials. Many other beraings are designed for hard or very hard shaft materials such as hardened steel axles and those are heavy.

A nother way to do mount a dead axle if you are using palt side panels on your drive train is to tap the end of you axle and machine a flat in to the end of the axle and and then machine a corresponding shape into the face of the side plate and then drill a hole for the screw through the side plate. But this requires a lot of machining

If you do it right there is virtually no torque on the axle and if you make sure to have little to no unsupported length in the axle then it will have no chance to deform or bend. We even used a 1/2" aluminum tube axle on the front caster wheels that we had on our 2006 robot.

Re: Mounting of drive system
 

I guess some folks just like using their frame as pillow blocks, and others just use the blocks.

Come to think of it, I can only think of one year in my five on the team that 330 has used blocks--we had an odd frame designed for the 6" step in 2004, and used blocks to lower the rear wheels.

Re: Mounting of drive system
 

Here's a picture of last year's prototype drive train.

Each axel is a 3/8" bolt riding on two pillow blocks. The pillow blocks have a slot milled in the bottom to keep them in-line with the 80/20, preventing them from twisting. The pillow blocks can slide in the 80/20 to tension the chains.

We used slightly larger aluminum tubes as spacers to position the wheels on the axels. We used this system last year and it worked really well. However, we'll be using canelivered wheels in 2008 and will therefore need to use live-axels.

Re: Mounting of drive system
 

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

Re: Mounting of drive system
 

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.)

Re: Mounting of drive system
 

I'd tend to agree, but I think it would be really handy to put a couple of current sensors on the drive motors and get quantitative numbers on how much difference it makes. Plus, adjustable pseudo-pillow blocks really aren't that much harder than what we'd be doing anyway. Assuming the kit frame doesn't change much, we'll probably be using the it next year, and to get less rock rock on it, we'd have to go to a pillow block style mount anyway, might as well adjust it.

Re: Mounting of drive system
 

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

Re: Mounting of drive system
 

A hex shaft is another option for a live axle. No "tiny" key required.

Re: Mounting of drive system
 

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

Re: Mounting of drive system
 

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

Re: Mounting of drive system
 

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

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

Re: Mounting of drive system
 

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.

Re: Mounting of drive system
 

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.

Re: Mounting of drive system
 

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

Re: Mounting of drive system
 

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.

Re: Mounting of drive system
 

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.

Re: Mounting of drive system
 

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

Live and dead axle drivetrain
 

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.