pic: drivetrain idea (comments please)
 

Re: pic: drivetrain idea (comments please)
 

looks very similar to what 1712 did last year ...
http://www.chiefdelphi.com/media/photos/29579
1/8" was the center wheel drop we settled on and we were very happy about the performance of our drive train. Some say 1/16" may not be enough drop, but I've never actually seen it to verify.

Re: pic: drivetrain idea (comments please)
 

I'm assuming you mean 1x2 aluminum extrusion. 1/16" or 1/8" wall thickness? Is it all rectangular extrusion, or is some of that C channel (I can't tell from the picture). How is it fastened together?

As for the driveline, what do the chain runs look like, how are they tensioned?

Re: pic: drivetrain idea (comments please)
 

What's your final gear reduction off the tranny?

Re: pic: drivetrain idea (comments please)
 

It's 1/8 in wall thickness, all rectangular extrusion, and it's welded together. (is C channel stong enough to replace some of it with.) My idea for the chain run was to have one chain around the rear and middle wheels and the gearbox sprocket on the inside of the wheels. With another chain going up to the front from the middle wheel on the outside. Not sure how its tensioned jet.

Re: pic: drivetrain idea (comments please)
 

For us 1/8in drop has worked very well though 1/16in was never attempted.

Questions: will you be supporting your toughbox further or is that it. second why use such a big sprocket when you can use a much smaller one

Re: pic: drivetrain idea (comments please)
 

side note: this will only be the second time that we have used wheels (we have used tracks) and are still new to wheels.

It will use the same mount that came in last years kit, a diagonal support. the sprockets are mostly for looks and the gear ratio will depend on our strategy in the next game.

Re: pic: drivetrain idea (comments please)
 

We used c-channel last year and it was plenty strong. we also only used angle stock on the ends and plywood as a base to provide lateral strength.

We had no problems except a pent angle stock in the front from the collisions but it was no big deal with the plywood behind it.

Re: pic: drivetrain idea (comments please)
 

If you have the machining capabilities and if you are going to use 1/8 inch tubes, look at loosing weight by drilling holes or pocketing by cncing. Weight matters and the drivetrain looks pretty nice. I'll get back to you on the tensioners, I have some in the making right now.

Re: pic: drivetrain idea (comments please)
 

What!? No more treads!? Blasphemy! :ahh:

I'll admit the ol' 753 design didn't seem to help teams 997 or 668 this year, but they've won lots of regionals over the years...

As for the drop, I've found that 0" with two omnis works best... But that's just me ;)

Re: pic: drivetrain idea (comments please)
 

Yeah, the tracks didn't help 997, we bearly lost at Davis. The two omni's in the front works really well and the 1024, the Kilabytes, had a lot of success this season with it. The only thing is with omni's is that you lose a tad bit of pushing power. If you want to do the drop with 6 traction wheels, every drivetrain is different. So different drops are needed. But the general idea is that only 4 wheels touch the ground at one point in time. If you want the drop to be adjustable, try this:

It worked really well on our offseason robot. The top is CNC'ed into the frame and the second part bolts on.

Re: pic: drivetrain idea (comments please)
 

If you use center traction wheels. Definitly make sure that your outer wheels will slide. Like omni...

Re: pic: drivetrain idea (comments please)
 

As long as your frame is stiff, you will be perfectly fine with 1/8" drop. You can use 6 traction wheels with this and you will be able to turn well and have great pushing power. If you want to use omni wheels then you do not want any drop at all. I am a fan of all traction wheels for more power and so that all of the wheels are the same for replacing them if something goes wrong. Either way you go just remember it is either a drop of the center wheel with all traction wheels or omnis with no drop, never both.

Re: pic: drivetrain idea (comments please)
 

1/8" is a pretty standard drop, and should drive just fine. I also echo the recommendation to us C channel where you can to save weight. The front and the back rails are especially good candidates for that, and you could also use them on the inner driveline rails if you do it right.

If you have the capability, direct drive to one of the wheel pairs (typically the center pair) is a great option. I don't know if you can do that with the KOP gearboxes, but one less chain means less weight, and also ensures that you can still drive, even if you throw all your chains.

Re: pic: drivetrain idea (comments please)
 

Are you planning on running the chain between the middle and rear wheel then up and over the tranny? If so, I would be concerned about the chain wrap on the transmission gear and how much tension you'll need to keep it from skipping. That looks like maybe 60 degrees of wrap.

Re: pic: drivetrain idea (comments please)
 

I would also agree that directly driving the center wheel if at all possible is the best solution. As has been said even in some extreme case that you throw every chain, you will still be mobile and able to play the game. Also with this extra safety, you can run#25 chain or even timing belt without worrying that if one breaks you will be immobile. As far as using the kitbox in direct drive it can be as simple as having a new output shaft fabricated and making a hub for the center wheel or you could fab up completely new plates and only retain the gears form the kit transmission. Either way it is relatively easy to do and I would be willing to show you some designs I have done using kit stuff. Also I'm sure you could find a machine shop to fab up a new output shaft to keep cost down.

Re: pic: drivetrain idea (comments please)
 

IMO if you're expecting to break #25 chain you are doing something wrong :ahh:

Aside from the fact that even with 3 chains at least one wheel will always be powered if one chain breaks (I can attest to this having happened ;)).

Most of the off-the-shelf gearboxes (with the exception of the AM SS) require a second reduction after the gearbox, especially with 6" wheels. A second reduction will also allow you to "tune" your speed.

Just my 100 sense.

Re: pic: drivetrain idea (comments please)
 

I would recommend running your chain like so:

Like so:

http://andyburchardt.com/robotics_re...0Drive%201.jpg

Re: pic: drivetrain idea (comments please)
 

I never expect to break a #25 chain in the drivetrain and in fact we ran the entire season without ever having to replace the drive chains. However, for some people who seem to still be shy about using #25 chain and reaping the great weight savings, using it in a drivetrain where the center wheels are directly driven gives an even greater incentive to use the lighter chain.

Re: pic: drivetrain idea (comments please)
 

#25 chain is more sensitive to proper tensioning. #35 allows teams to be really sloppy and still quite effective.

As to the original question: I like the idea, very similar to our 2007 robot. We used a kitbot frame with a second level of frame at the height of the top of the wheels, primarily to get a flat platform.

Your implementation seems somewhat heavier than necessary. The inner rail doesn't add much strength, it can be 1/16" wall, while the outer rail will take a beating, count on bumpers to stiffen it and lend impact resistance.

You also need to consider cross-rails from outer to inner rail, and again from one inner rail to the other - that way, an impact's force is transmitted to all four elements, not just the one impacted.

If you can mount the gearboxes lower - gotta think about the sprocket wrap - you can end up with a flat (or nearly so) platform over which your manipulator can be built.

Don

Re: pic: drivetrain idea (comments please)
 

why did you put the gear box in between the back set of wheels?
Our team did a direct drive of the center wheel and then chain drive to connect the two outside wheels for power this worked great and we did not have to drop the center wheel.:)

Re: pic: drivetrain idea (comments please)
 

As mentioned earlier, there are many different types of drivetrains and each one is unique. 4 wheel omni's, offset 4 wheel omni's, crab, rocker 6 wheel drive, direct drive 6 wheel drive, 2 wheel drive with casters, and the list goes on. It all depends on your team. We do the exact same thing this team does but we have a two stage frame:

We are able to make braces for the gearbox and we mount them lower so it IS NOT a 60 degree wrap, it is less than a 30 degree wrap. A direct drive does have its advantages and disadvantages.

Re: pic: drivetrain idea (comments please)
 

I would add a cross-brace (1x1 square tubing, 1/16" wall) to keep the frame strong and square...maybe two. They would also serve as additional mounting points for electronic boards and other devices.

As already suggested, using 1/16" wall tubing for the inner frame members is a good idea, but it may not be readily available in the 1x2 size you've chosen (not saying that it's not out there). In the case where you cannot find the 1/16" wall stuff, 1/8" wall U-channel would be a good option to save weight.

Re: pic: drivetrain idea (comments please)
 

for cross bracing are team used a heet of 1/2" plywood to create reidgity from side to side. It has the second benefit of giving you a flat surface.

Re: pic: drivetrain idea (comments please)
 

You'll really want to attach the frame members at more than just the ends. I would attach the two outer rails to each other between each wheel at a minimum, and since you're welding, it'll be real simple to do.

You can use just about any material, but if fastened in enough places, it creates a sheer-web that greatly increases the rigidity of the frame. Depending on the material, you may also need a centered crossbrace to keep it from sagging.

I have found 1/16" wall 2x1 to be very available.

Re: pic: drivetrain idea (comments please)
 

definitly the cross brace or extra bracing is going to be needed. Otherwise it will bow over time. Can some one explain the degrees of rap to me. I'm still a little new to the drive train systems.

Re: pic: drivetrain idea (comments please)
 

You want 120 degrees MINIMUM of chain wrap on each driven/driving sprocket.

Re: pic: drivetrain idea (comments please)
 

there will be other braces going across but their placement will depend on our design for other stuff. the reason i put gearboxes on top of the frame member is because is easier then direct drive

Re: pic: drivetrain idea (comments please)
 

why not do direct drive with the super shifter? That is set up out of the box for that and gives you 2 speeds. If you wanted to you could also machine symmetrical plates for the super shifters so that each side of your frame could be identical.

Re: pic: drivetrain idea (comments please)
 

I question that it is easier because then you have to worry about the chain loosing contact with either the middle or the back wheel. on the direct drive you only need to make sure the output shaft is the right length and this makes it really easy to make duplicate sides and parts cause they will all be the same size and postion. All you have to do is switch the positive and negative into your h-bridge or what ever you are using to control the motors.

Re: pic: drivetrain idea (comments please)
 

If you use 2x1 and at a 1/16" for the frame, make sure if the shaft is live put bearings in the frame. But if the wheel rotates on the shaft, put bushings in those spots where the shaft rests. If you leave the shaft by itself in the frame, over time it will eat away at the frame. I prefer to stay away from direct drive because you either have to hex or key your wheels.

Re: pic: drivetrain idea (comments please)
 

I feel like broaching your wheels and sprockets for hex shaft and using live axles is actually potentially more reliable. At least you dont have to worry about the bolts holding the sprockets to the wheels from loosening. Another thing they could do is have simple bearing blocks machined out of 1/4" thick aluminum to give something a bit more substantial for the bearings to sit in. Although I would agree that if they are using the kit wheels it makes more since to go with dead axle since you would then have to use a keyed hub of some sort.

Re: pic: drivetrain idea (comments please)
 

Direct Drive is awesome, but a the drive he has set up will be fine and will work just as good. As long has he has aligned the sprockets up and the chain, he will be fine. Nice drivetrain and keep cadding.

Re: pic: drivetrain idea (comments please)
 

I saw someone mention tracks in this thread a ways back, and they didn't provide much of a competitive advantage in this years game as it has in some, although were fine tuning and improving upon what we had.

Re: pic: drivetrain idea (comments please)
 

the one advantage to this idea i can see and have found out from discussing this with other is that you can add a second gear ratio to the spin. But i see no problem in your design other then i would think about not dropping the center wheel at all. keep up these ideas because they cause great discussions. I know I learned alot.

Re: pic: drivetrain idea (comments please)
 

Unless you want to not be able to turn well at all and potentially trip the breakers whenever you attempt to turn you have to lower the center wheel. We lowered it 1/8" last year with 6 kit wheels and it was perfect. No noticeable rocking but it could still turn perfectly. The only way to not lower the center wheel is to use omni wheels in the corner to allow slip while turning.

Re: pic: drivetrain idea (comments please)
 

Careful about blanket statements like that. Team 25 doesn't exactly drop their wheels (to my knowledge) and they still turn easily. I'm not sure exactly how they do it. It sure doesn't affect the rest of the robot, though. There may be one or two teams who use similar setups.

Re: pic: drivetrain idea (comments please)
 

oursystem did not need a drop but we used omni for comp. as long as you reverse the direction of one side to turn you should be fine. only you gent more friction thus lower speeds

Re: pic: drivetrain idea (comments please)
 

I don't know of teams not named 25 who have been able to skid steer with a 6wd with no dropped center and no omnis. I'd say it's a pretty safe blanket statement.

Re: pic: drivetrain idea (comments please)
 

They've been telling other teams how they do it. Then again, not many have copied the design.

I'd also guess that many who try it for the first time (without asking advice here first, that is) quickly find out about the scrub and the "fun" associated with it, and change to an omni/drop configuration.

Re: pic: drivetrain idea (comments please)
 

I would say it is a very safe blanket statement. I was waiting for someone to chime in with team 25 as an example. Yes they do not drop the center wheel and they do have 6 traction wheels but as far as I know, they and maybe 103 who share a similar drivetrain are the only teams that don't drop the center wheel and have had success. I would say unless you are team 25, which no one is and very few are at there level, then I would recommend dropping the center wheel. You are not sacrificing any performance and in fact are improving your ability to turn and not trip the breakers.

Re: pic: drivetrain idea (comments please)
 

World Finalist 348 also used a team 25esque drivetrain. Having experienced their defense, I can attest to the speed and pushing power of this design. However, it did have a tendency to buck back and forth violently.

Re: pic: drivetrain idea (comments please)
 

I was just watching a video of Team 25's match on the blue alliance and man they are spectacular.

Re: pic: drivetrain idea (comments please)
 

As the conversation has drifted more towards true skid-steering drivetrains, I thought I'd point out my favorite: 1662 in 2006. Their drivetrain was very similar to the one posted at the beginning of this thread, but instead of six kit wheels, they had a four-wheeled drivetrain with 2"x8" IFI wheels. Talk about a robot that's hard to turn!

For those of us that aren't able to pull of such feats, six wheel drive with a dropped center works great. I would just recomend (as several others already have) that you add some bracing between the side rails of the chassis. I would prefer stickier wheels, too, but as it sits it looks like a solid base for your bot.

Re: pic: drivetrain idea (comments please)
 

A sprocket is basically a circlular object (360 degrees). You want the chain to wrap around at least 1/3 of the sprocket (120 degrees). I personally suggest at least 150 degrees wrap with no more than 180 degrees.

The more wrap you have the more forgiving your drivetrain will be, but you trade off that forgiveness with added drag and friction. Going less than 120 degrees of wrap invites the chain to jump off of the sprocket.

Re: pic: drivetrain idea (comments please)
 

25, et al, are able to run 6WD skid steer without a dropped center wheel because they have an understanding of CoF and CoM. You need enough torque to overcome the friction of your wheels, and that means understanding where your CoM is, what your CoF is, and how much weight is on each wheel. Needless to say, you need to do a fair bit of math ;)

And as far as not sacrificing anything with a lowered drivetrain ... everything is a tradeoff. Lowering the center wheel shortens your wheelbase and gives your oppenent a lever arm in which he can rotate your robot. The trick, for your opponent, is knowing when, and which side, that lever is on.

Re: pic: drivetrain idea (comments please)
 

Another thing about 25 is that there wheels have a much lower Cof than wheels treaded with conveyor belting and they have custom patterns cut into them which most likely aids in the turning. I would say it is a safe bet to lower the center wheel unless you have a backup plan for when your robot doesn't turn. Additionally even if it does manage to turn the bucking mentioned is enough of a deterent to want to drop the center wheel. Imagine precisely aiming while the robot is bucking...not something I would want to deal with.

And as for the being easily spun with a lowered center wheel, as long as the drop is not substantial, you will not be easily turned by another robot and you will still be able to turn when you want to and push other robots.

Re: pic: drivetrain idea (comments please)
 

with our teams direct drive we simply did not need to drop the wheel down. but if you do drop it, i feel, that it allows for the rocking motion of your robot to be a deteriater of how well your robot will trurn when you need it. Also with a droped wheel you must make sure your whieght is truly centered or you completly loose advatage of that extra two wheels up front.

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Not necessarily. Look at 254, 968, 330, 60, 294 and a host of other teams that use 6WD "drop" style. They don't rock much, do they? If anything, the rock helps them.

Yes, you can put your weight dead center. But if you do, you lose most of 4 wheels, not 2. If you are balanced, only the center two are touching (if your drop is too large and you have perfect balance). When you move forward or backward, you get two more wheels. But as soon as you go the other way, you lose those two and get the other two. You keep doing this all match.

On the other hand, let's say you put your CG aft (or forward) of the center. You have four wheels in contact with the carpet and providing most of the power. You have two more that are not giving as much, but they are still contirbuting. When you rock the other way, you immediately rock back. This helps keep the robot upright (between the teams I named, I don't think more than one or two have stayed on flat the ground for more than a few seconds in years, and that was on going over sideways), as well as providing a baseline for the drivers on performance.


Oh yeah, and the rocking motion deteriorating the turn? Not hardly. The shorter wheelbase helps the turn, and with the CG at one end, you won't notice. With the CG in the middle, then you get some "fun" as first one end is on, then the other--faster turn in the middle, followed by a sudden slowdown as the end hits, repeat as necessary. Not good for fatigue in the parts.

Re: pic: drivetrain idea (comments please)
 

LOL. I never said easily turned, just that you'll have a shorter wheelbase and give your opponent an lever arm in which to turn you.

Again, everything is a tradeoff, and the key is to match the drivesystem to the game requirements.

Re: pic: drivetrain idea (comments please)
 

i meant that you have to make sure the wieght is balance because otherwise you could end up only have the four wheels touching the ground. i gess but that just makes the robot seem jerky to me because the front wheel will loose and gain tration on weather you have the robot acelerating or deacelrating.

Re: pic: drivetrain idea (comments please)
 

And there's a problem with only four wheels on the ground?

Actually, the front (or back, depending) will likely be in contact with the ground the whole time (with a small enough drop). It won't contribute as much as the rest, but it will still contribute.

Jerky? See that team list I put up in my last post? Go to the Blue Alliance and pull up some video of those teams, especially 60 and 254, who popularized the dropped-center designs.

My point was that by centering the weight precisely in the middle (which is hard to do in the first place), you lose much of the point of dropping the wheel, as the weight shifts become random and can easily throw off your drivers. By placing it strategically, you eliminate that and get a better robot.

Re: pic: drivetrain idea (comments please)
 

The entire point of dropping the center wheel is that you only have 4 wheels touching the ground at any point in time--this cuts your wheelbase length in half. When you rock, you still have 4 powered wheels in contact with the ground at any point in time. This is a good thing.

Re: pic: drivetrain idea (comments please)
 

Except team 25, of course :rolleyes:

While several teams (25 and 103 are local examples) have excellent drivetrains with no drop, any team contemplating a six-wheel drivetrain had either better be prepared for a lot of hard development work OR have 1/8" or so of center wheel drop. Failure to do either may result in a robot that does not turn well.

The rocking effect is minimal, depending on your tread material (soft is less rock, hard is more), and we have not found it to be a serious issue, even using a stock KitBot frame.

Don

Re: pic: drivetrain idea (comments please)
 

Use blue nitrile tread from mcmaster, it doesn't rock as much and lasts about 2 full seasons.

Re: pic: drivetrain idea (comments please)
 

OR put omnis at one end.

Omnis and drop together could be really interesting... I wouldn't do it. You'd get effectively a 2WD at time.