6 Wheel Drive, Wheel/Drive Assembly

[tiger1dd]

I'm the newbie, and since I'm the only non-college person on the team that can use inventor, I've been assigned to create a six wheel drive. I was wondering where I could maybe get the different parts to the wheel assemblies+dimensions, as well as some different wheel designs, dimensions, and if you could even post any ipt files for me to analyze, that would be great. Sorry I'm asking so much, I just got a big load put on my back.

Thanks in advance!

[CraigHickman]

Take some time to browse the images in CDmedia. Especially search for 6 wheel drives, and check out the West Coast drives for the most minimalist approaches to this. Once you're familiar with what is out there, model every part yourself. Taking shortcuts will get you through a build season, but doing it right can get you a job.

[tiger1dd]

Alright, I found the Cdmedia, where can I find West Coast Drives, inside CDMedia?

Thanks!

[Adam.garcia]

Hello,

Check these websites out! They have a lot of parts already designed in inventor, which you can use.

http://www.firstcadlibrary.com/
http://www.3dcontentcentral.com/parts/browse/Robotic-Accessories/User-Library/140/185/185/Models.aspx?title=FIRST+Robotics&isredirect=true&level=10

These will help you get started with designing an actual robot.

If you have any questions, just pm me and I'll be glad to help!

Thanks,
Adam

[tiger1dd]

WOW! Those two links were exactly what I needed. I'll post what I make shortly. Thank both of you guys so much!

[Edoc'sil]

The simplest 6 wheel drive to build is two traction wheels in the middle and omnis on the corners. No issues turning at all, but it can be pushed in a circle if its hit just right. we loved the maneuverability that this drive offered us this year.


Love to see what you come up with.

[dtengineering]

And before you start assuming that you have to make it out of metal...

also search the CD media photos for "wood" and "plywood".

Or fibreglass (particularly what 842 does with it.)

Jason

[CraigHickman]

And before you start assuming that you have to make it out of metal...

also search the CD media photos for "wood" and "plywood".

Or fibreglass (particularly what 842 does with it.)

Jason

This! Very this! I've been trying to convince a few team members to try a bamboo robot for a few years now...

[Edoc'sil]

How well does the fiberglass hold up? I have used it for other applications and it doesn't see to be robust enough for FIRST, but then again neither does balsa, and I have seen those bots.

[JamesCH95]

McMaster has CAD files of almost everything they sell, so if you find a bearing, bolt, sprocket, or widget that you like in their catalog, go ahead and download it!

[sdcantrell56]

How well does the fiberglass hold up? I have used it for other applications and it doesn't see to be robust enough for FIRST, but then again neither does balsa, and I have seen those bots.

Fiberglass holds up extremely well in a FIRST setting. Im not sure of any team who has used plain balsa for there robot. We use baltic birch plywood and it is incredibly strong and easy to work with

[Chris is me]

How well does the fiberglass hold up? I have used it for other applications and it doesn't see to be robust enough for FIRST, but then again neither does balsa, and I have seen those bots.

Pulturded fiberglass is beastly for FIRST. Main problem is it weighs a lot, but you can be shockingly liberal with lightening and it will still hold strong. 2791 used it this year to make a bumper frame for roughly 7 pounds. It's great because you can machine them in any school wood shop, and pultruded fiberglass already has some convenient flanges for structure. 1726 has used it for a cantilevered dead axle 6wd before and it seemed to work for them; their bases are a little heavy but they don't tip! I might make some pultruded fiberglass CAD now...

In many applications you may prefer bent aluminium though. We replaced a lot of square fiberglass tubing with kitbot c-channel and saved a lot of weight.

[Andrew Schreiber]

Pulturded fiberglass is beastly for FIRST. Main problem is it weighs a lot, but you can be shockingly liberal with lightening and it will still hold strong. 2791 used it this year to make a bumper frame for roughly 7 pounds. It's great because you can machine them in any school wood shop, and pultruded fiberglass already has some convenient flanges for structure. 1726 has used it for a cantilevered dead axle 6wd before and it seemed to work for them; their bases are a little heavy but they don't tip! I might make some pultruded fiberglass CAD now...

In many applications you may prefer bent aluminium though. We replaced a lot of square fiberglass tubing with kitbot c-channel and saved a lot of weight.

This post raised a very good point. The trend seems to be to make your base as lightweight as possible. The upsides to this are obvious but the major downside is that it may mean your CG is higher in the air. This doesn't mean you want a 90lb drive train but is just meant as a warning to check where your CG will be. A good drive train is only useful when it has wheels on the ground.


Where does 1771 source its baltic birch? Is it a local supplier or is it online? Ive been wanting to price it out to see if some projects would be cheaper using wood. (Plus, they would look nice imho)

[sdcantrell56]

Where does 1771 source its baltic birch? Is it a local supplier or is it online? Ive been wanting to price it out to see if some projects would be cheaper using wood. (Plus, they would look nice imho)

It is definitely cheaper than aluminum. We buy it from a local lumber yard and I believe its about $30 for a 5'x5' sheet of 12mm ply. Be sure to get true baltic birch as there is some birch ply that uses softwood for the filler layers.

[JamesCH95]

Pulturded fiberglass is beastly for FIRST [...] It's great because you can machine them in any school wood shop

I hope you're machining that wet...the dust is terrible for people and machine equipment.

[Chris is me]

I hope you're machining that wet...the dust is terrible for people and machine equipment.

We avoid breathing the stuff and end up replacing the blades and hole saws frequently. "Fiberglass burn" is a common ailment on the team :(

[tiger1dd]

Here's what I've come up with, a 6 wheel drive, the two middle wheels are powered, the wheel on each corner is an omni wheel, even though this is just 1 side, you can see where I'm going with it.

You've all helped me so much already, so any comments/criticism/corrections/suggestions are welcomed!

http://i919.photobucket.com/albums/ad35/tiger1dd/Robot/sideview.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot/mainupclose.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot/omniupclose.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot/hiddeniso.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot/iso.jpg

[Edoc'sil]

Nice job, looks like your getting the idea. Your wheels may not actually the same size (6 in?) so you may need to offset the traction wheel by a bit.

How are your shafts powered? the omnies will be chained to the traction, right? Also how is the middle axle powered, keyway? I would suggest hex shafts like this one http://www.andymark.biz/am-0520.html No idea if it fits your gearbox, but I am certain you could find one on andymark.biz if those are toughboxes on the drivetrain.

[sdcantrell56]

This is definitely a good start. In addition to whats already been said, I have a couple more suggestions:

1) you should really try to push the omni wheels as far out as possible without compromising strength. This will improve stability front to back.

2) flip the plates or add fillets on the bottom as well. In my opinion its always better to have the bottom of the plate filleted to help it not catch on something.

3) If using material that thin definitely add flanges to the top and bottom to make it stiff enough.

[Akash Rastogi]

We avoid breathing the stuff and end up replacing the blades and hole saws frequently. "Fiberglass burn" is a common ailment on the team :(

Avoiding this is not good enough. PLEASE use a face mask and obviously goggles while cutting through fiberglass. Glass dust is not Good Eats.

[hektormagee]

I really suggest looking into "Team 221". (Robotics Company, not a team) the universal six wheel drive chassis was designed by some mentors on our team and we have used this system for the last 5-6 years with absolutely no problems with integrity, function, or modularity. Its very simple and maybe would provide you with a couple of ideas. The premiere function on the design is the built in Chain Tension system. All it takes is a couple of turns with an allen wrench to make sure the chains are tensioned correctly. You just set it, and forget it!

http://www.team221.com/viewproduct.php?id=35

[tiger1dd]

A big thanks to all who've helped me out here, I've made the following changes:
Changed plate thickness from 1/16" -> 1/8"
Filleted The bottom edges
Moved omni's forward another 3 inches,
and added a top and two separate bottom flanges, extruded 1/2"

I was also going to cut out a few triangular patches to reduce weight, but I was worried about compromising the integrity of the plates. Instead of spamming up the thread, I'll just post a link to the album on photobucket:

http://s919.photobucket.com/albums/ad35/tiger1dd/Robot%20V%201%20Rev%20A/


Once again, let me know what you think! Questions/Comments/Suggestions/Criticism, all is welcomed!

Thanks!

[JamesCH95]

We avoid breathing the stuff and end up replacing the blades and hole saws frequently. "Fiberglass burn" is a common ailment on the team :(

Get a wet tile saw with a diamond abrasive blade. One can be had for a little over $100 from many places. I got one for cutting carbon fiber tubes, there's very little spray and zero dust.

Avoiding this is not good enough. PLEASE use a face mask and obviously goggles while cutting through fiberglass. Glass dust is not Good Eats.

If you insist on cutting things dry still, or don't have a choice, get a full face mask, preferably of hazmat quality with the appropriate breathing cartridges, and tyvek suits. They will make a huge difference and don't cost too much.

[Chris is me]

If you insist on cutting things dry still, or don't have a choice, get a full face mask, preferably of hazmat quality with the appropriate breathing cartridges, and tyvek suits. They will make a huge difference and don't cost too much.

We'll look into making our pultruded work safer, but at competitions and for quick jobs, is running a vacuum next to the hole saw insufficient?

[tiger1dd]

Well, I think I've got it!
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot%20V1%20Rev%20B/inside.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot%20V1%20Rev%20B/outside.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot%20V1%20Rev%20B/iso.jpg

[ttldomination]

The CADs above look legit. I would also recommend added some support bars closer to the omnis. This'll help keeping the drive modules straight when you move.

I'm sure you would've gotten to that sooner or later when you worked on it, but I just wanted to make sure that I put that out there.

Also, just add a couple of cuts on each module. That'll not only help with weight, but also with design.

- Sunny

[tiger1dd]

Hmm... Could you go into a little further detail? I'm not quite sure what you mean by support bars...

[JamesCH95]

We'll look into making our pultruded work safer, but at competitions and for quick jobs, is running a vacuum next to the hole saw insufficient?

It's certainly better than not having a vac, but the safety guys shouldn't . If you don't have the right tools try to keep everything wet, I used a hack-saw over a sink to cut some pultruded carbon fiber tubes and it didn't kick up any dust. You can get wet tile saws that are very small and portable, some can even be disconnected from their mounting base and used like a cutoff tool. Even a tub of water with a little aquarium pump and hose to squirt water over the cutting area is very useful, and a good Lenoxx blade/hole cutter, even hand powered will make short work of fiber composites. I've used all of these "wet cutting" methods indoors with no detectable air born dust.

A buddy of mine used to do a lot of fiberglass work, even with a face mask (not a hazmat one though) and after a year or two he couldn't exercise much at all, he'd start coughing up blood. Fiberglass and carbon fiber are really nasty if the right precautions aren't taken.

Feel free to send a PM if you have any other questions, I don't want to derail this thread anymore ;) I was responsible for setting up a couple fabrication areas at my college, with a very knowledgeable (read "strict but very correct") safety officer.

/thread jacking

[ttldomination]

Hmm... Could you go into a little further detail? I'm not quite sure what you mean by support bars...

Of course. Right now, you have two 80-20 bars spanning across the middle of the chassis and they hold the two drive modules together.

If you can also add bars in front of and behind those bars, that'll provide more support, because when you turn, the modules are going to be torqued about the current middle bars, and the modules are more susceptible to bending.

- Sunny

[Edoc'sil]

Of course. Right now, you have two 80-20 bars spanning across the middle of the chassis and they hold the two drive modules together.

If you can also add bars in front of and behind those bars, that'll provide more support, because when you turn, the modules are going to be torqued about the current middle bars, and the modules are more susceptible to bending.

- Sunny

^^ What he said.

Also it doesn't look like there is anything keeping the plates in their proper positions, you need to ad some bolts to keep them in place.

[tiger1dd]

So I'm thinking about adding maybe 4 pieces of 8020 between the inside/outside plates just to hold them together better, any other suggestions? I'm not sure if I said that the omni's won't be powered, I think someone might have been thinking that earlier, but, any other suggestions would be much appreciated.

[ttldomination]

Any particular reason you choose to go with the omnis as compared to 6 traction wheels?

And I think that you'll really want to consider driving those omnis. You're wasting a lot friction that you can be using to help you push other robots as compared to just the friction that's present on that one center wheel.

Other than that, it looks good. You might wanna consider cutting out parts out of the chassis for weight and a nice look.

[tiger1dd]

Well, I think it would be just a little more difficult, this being my first design to go with a full 6 wheel powered design. I think this would be very fast, and would turn on a dime, which is what I was hoping for. But, many better designs will probably be thought up this summer.

So, he's what I'm doing now:
Adding 4 8020 supports between the inside/outside plates
Adding 2 more 8020 support beams across the front and back,
and
cutting out some sections reduce some weight.

Pictures will be posted shortly. Thanks for the advice!

[sdcantrell56]

Well, I think it would be just a little more difficult, this being my first design to go with a full 6 wheel powered design. I think this would be very fast, and would turn on a dime, which is what I was hoping for. But, many better designs will probably be thought up this summer.

So, he's what I'm doing now:
Adding 4 8020 supports between the inside/outside plates
Adding 2 more 8020 support beams across the front and back,
and
cutting out some sections reduce some weight.

Pictures will be posted shortly. Thanks for the advice!

Adding power to the outer wheels is no more difficult that attaching sprockets to the wheels and chaining them. Any unpowered wheels are a total waste for power. For simple chain tensioning just slot the mounting hole so you can slide the wheel out to take up slack in the chain

[ttldomination]

You don't have to add the chain in CAD. All you have to do is add sprockets that line up and keep a consistent chaining scheme.

[tiger1dd]

I will probably add the sprockets in there later, I just want to get the chassis and sub assembly perfected right now.

What I did was, I added more 8020 to the front and back,
and cut our teams symbol (yin-yang) for this year, into the bot to hopefully lighten it up a bit.

Here are some pictures, and as always, suggestions are hoped for.

http://i919.photobucket.com/albums/ad35/tiger1dd/Robot%20V1%20Rev%20C/yinyang.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot%20V1%20Rev%20C/inside.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot%20V1%20Rev%20C/top.jpg
http://i919.photobucket.com/albums/ad35/tiger1dd/Robot%20V1%20Rev%20C/iso.jpg

[CraigHickman]

Looking good! You're learning fast, keep it up!

My main suggestion is a method of thinking about the rigidity of your chassis. Think of a box made of cardboard being pushed from a corner: The box will flex, as squares are not very rigid. Now think of a triangle being pushed from a corner: Little to no flex.

As much as you can, remove open rectangles from your design, and try to keep a solid shape. If it helps, try some balsa wood or cardboard experiments to get yourself familiar with the different polygons and their rigidity.

You're on the right track though!

[JamesCH95]

Mounting a plate or sheet across the 8020 beams will do a great job of stiffening up your chassis. A thicker (1/2") piece of plywood spanning all of the beams will tie everything together very well and give a nice clean surface to mount electronics and mechanisms.