05-06-2011 19:13

Joe G.

Re: pic: 6WD Practice

Looks nice! To answer your questions...

1/8" tubing sounds good, maybe a bit thick for some parts like the outer rails. Many good drivetrains have been built this way, and with sheet metal. Designing with sheet metal is really a different animal entirely. The primary advantage of sheet metal is the time in which complicated parts can be made and assembled, and the use of rivets or bolts, which allows changes to be made more easily than with a welded frame. Which route you should go really depends on what resources your team has. If you have a sheet metal sponsor, go for sheet metal. If you have welding capability, go with a welded frame. Fantastic robots have been made with both.

At the very least, I'd CAD up plans for mounting the bumpers to the frame. With a non-cantilevered system like this, it shouldn't be that hard.

I don't see any problem with mounting the components like this, particularly since you've placed all your speed controllers on top for ventilation. As described, I don't think wiring would be a problem. One thing to consider would be mounting the top board on a hinge, so that it it acts almost like a hood to the lower board. Wires could then be run so that they flex along this pivoting joint.

I'd leave them out for now, and just try to keep open space on the main body of the chassis in order to leave your options open. You never really know what you'll be mounting, and a generic structure will tend to be heavier than one that was built specifically for the task at hand.

The general consensus among top teams seems to be that small wheels have more going for them. I'd design for 4" wheels.

As for the outer wheels, that depends. Is the center wheel dropped? Most 6 wheel systems will lower the center wheel by about 1/8th inch, which only allows 4 wheels to contact the ground at once. This makes the effective wheelbase of the robot much shorter, allowing it to turn with ease. With a dropped center, adding omnis to the corners would make the robot nearly uncontrollable. However, if the center wheel is not dropped, omnis on the corners would probably be a good idea to help it turn. Generally, however, drop-center is the preferred system, since it allows you to keep high-traction tread on all your wheels.

I'd put sprockets in, so you know that they fit, and know what to order when you go to make the drivetrain. The actual chain is generally more trouble than its worth to model, you can if you want the model to look fantastic, but there's no real reason to.

If you are using dead axles, all you need is to insert bearings into each side of the wheel for the proper shaft diameter. Generally, 3/8" or 1/2" shafts are used.

If you are using live axles, bearings become more complicated. For a system like this, you would want a bearing in each chassis rail. I think you'll have a hard time finding bearings small enough to be mounted in a 1" rail, with a large enough bore to support a drive shaft. One option to consider would be pillow blocks, mounted above or below the frame. Or, you could simply use larger box material.


Other comments:
-It looks like your center wheels are direct driven off the gearbox. If this is the case, you have no choice but to use a live axle here. Since this is the case, I would suggest altering your frame in one of the ways described above, to make it more supportive (no pun intended) of live axles. Alternatively, you could simply leave this axle cantilevered, if your gearboxes are up to supporting this kind of load, and use dead axles for the remaining wheels.

-Any particular reason why the wheelbase is so short? Generally, one of the main reasons smaller wheels are used is to allow you to place them at the very ends of the chassis, creating more stability.

-Have you modeled the Analog/Solenoid breakouts, and DB37 cable? Space on top of the cRIO is looking a little tight.

-I'd consider creating room for more jaguars, or switching over to victors. Five speed controllers only leaves you one motor for your manipulator.

05-06-2011 19:21

Aidan S.

Re: pic: 6WD Practice

I have a couple of suggestions for your electronics.

First, instead of having a two-tiered electrical board, place a single sheet of lexan across the entire length of the frame, so you don't have to hang wires across an open space. Two tiered electrical can be a pain to wire and troubleshoot.

Second, mount the power distribition panel, main breaker, and battery close together so that you can cut down on wire lengths.

Its important to have your cRio and digital sidecar accesable for troubleshooting. You may want to consider using CAN cables instead of PWMs for your jaguars.

You should also leave space for a compressor and air cylinders in case you want pneumatics.

05-06-2011 20:36

msimon785

Re: pic: 6WD Practice

This entirely depends on your team's capabilities. Both have won regionals, and even championships. Both have also failed. If your team is sponsored by a sheet-metal shop, then it is definitely the way to go. No question there. Additionally, you may consider changing the design to a double chassis. That will make the electronics more secure, and is *usually* a better way to go. Feel free to contact me at msimon785@gmail.com for any technical CAD help if you need it, however you are pretty good.
Good Luck!

05-06-2011 20:46

apalrd

Re: pic: 6WD Practice

If there's enough space, the battery might fit between the CIM motors (Vertically). That would leave a ton of room for electronics up front. I would roughly guess that there is enough room for a PD board, main breaker, and a few Jags up front, with the DSC, cRio, and more Jags in the back.

6" vs 4":
We use 6". Why? We can get AM Super Shifters which can direct drive to 6" wheels at a nice reduction, and 6" wheels are easier to find (if you want more wheel variety to choose from) than 4" wheels.

Many other teams use 4". If we could find a nice shifting gearbox pre-made, we would use 4" wheels, but the cost of machining outweighs the weight savings of 4" wheels for us. If you aren't shifting, some AM reductions play nice with 4" wheels.

Don't just pick 4 or 6 inch wheels because they are cool, or because you've heard it on Chief Delphi. Do a little bit of analysis, look at the benefits of each size, related gearbox reduction, and amount of custom machining (compared to your capabilities).

05-06-2011 22:13

BrendanB

Re: pic: 6WD Practice

I highly second this! Our team had a two tiered system that originally looked like it was going to work great until the minibot stuff went on top of it. Troubleshooting was so hard with such a small space to work with on the lower shelf and the bumpers there.

I would recommend moving the outer wheels closer to the end of the rails to have a larger foot print and better performance.

Looks really good by the way! All of these drivebases appearing on CD have me itching to get back into some CAD.

05-06-2011 22:42

lemiant

Re: pic: 6WD Practice

What is a double chassis?

05-06-2011 23:21

IanW

Re: pic: 6WD Practice

A double chassis has two levels - it would be like taking a good portion of the box frame avan currently has and adding it on top with vertical tubes in between. For example

I would recommend against a two tier electronics board. My team went with one this past season, and the electronics lead regretted giving me approval to design it that way ever since. It was just way too hard to make changes and troubleshoot, especially when time was of the essence. If you do go with a double layered one, make it easy to disconnect every wire between the two layers and to the rest of the 'bot - we did this with power wires using Anderson connectors.

06-06-2011 00:13

Jeffy

Re: pic: 6WD Practice

We didn't just have two levels of electronics this year, we had 4. They were not stacked, but positioned at different angles around the A frame. The only picture I know of can be found here: http://mmr2410.com/2011/Robot/robot

If you look, you will notice that the Crio, and Digital sidecar are on the "base" level. Then, the 4 drive victors are on the A-frame on the left side. The power distribution is on the A frame angled component along with 3 jaguars. The D-link is on the opposite side of the Angle A frame section of the Power distribution and a bit higher. We had 0 electronical failures in matches, and no problems sorting through errors. Arrange the wires in an orderly fashion and label them, and you will not have a problem.

On a side note, mounting jaguars at 90 degrees or an angle was something I saw done by many teams this year. It can free up some space and make accessing them easier.

06-06-2011 01:10

msimon785

Re: pic: 6WD Practice

I definitely second this. Team 1515 uses (and has used for the past several years) sliding electronics boards. It's actually fairly easy to accomplish. We do it by welding 1"x0.5" C channel to the frame, and mounting the modules to coroplast (corrugated plastic sheeting). To ensure quick and easy removal of the boards, we use WAGO Mass-Connecters, which allow us to have a single ribbon cable connecting each sliding-board to a centralized mass-connecter on the main bot. You can get a decent idea of what I mean from this image (sorry it's an awful pic). Personally, I find this one of the most effective ways to store E-Boards, but every team has their own style.

12-06-2011 21:19

avanboekel

Re: pic: 6WD Practice

Hey, I took a shot at a sheet metal drive train. Check it out. Let me know what you think.

http://www.chiefdelphi.com/media/photos/36931?

Thanks for all of the help!