Angelbots Offseason 8W WCD
 

The Angelbots are proud to present our recent offseason drive base, Lovingly referred to as the Taco Bot.

https://www.youtube.com/watch?v=5Zf_TNny2TM

The Taco bot is a 8 wheel WCD, powered through a WCP 3 CIM Gearbox with a 2.92 spread with 14 tooth CIM pinion gears, giving us a calculated speed of 6.5 ft/s in Low, and a speed of 19 ft/s in high. We used the Versablock system, with the two center blocks dropped, and decided to use #25 Chain as our power transmission from wheel to wheel with 16t sprockets, as opposed to 9mm HTD belts for reliability and serviceability Reasons.

This is a test platform for a Hexagonal chassis design, using different length bumper supports to achieve the shape, while staying within the bumper rules from last year. We wanted to try as many new things as possible, and as such we are testing two different types of wheels. A 2 in wide colson wheel with cut tread, and a 3D printed wheel with blue nitrile tread, both of which are 4 inches in diameter, and Hex driven. We put 2 in wide versions of the 3D printed wheels in the middle of the robot, and 1 in wide versions on the outer wheels, as it could have some interesting effects on traction and turing dynamics, and have a positive effect on spatial constraints with a hexagonal chassis.

We are in the process of making bumpers currently, and are using sailcloth on the sides, and cordura on the front and back, to have the ability to escape pins and pin other bots.

We have yet to add extra weight to simulate actual driving dynamics, and we are limited in terms of a carpeted area that we could use, but we are very happy with the way that the Taco bot has been performing.

More pictures to come later.

Let me know what you guys think, any and all feedback is welcome.

And yes, Waldo, We do need better battery maintenance.

Re: Angelbots Offseason 8W WCD
 

Absolutely beautiful! It's nice to see somebody actually running high speeds on a 6 cim drive for a change.
It looks like you've thought of pretty much everything in your design too.

Re: Angelbots Offseason 8W WCD
 

Thank you, a lot of research went into this drive base. After reading through some of the threads about 2 vs 3 CIM drivetrains, we decided to go all out and gear aggressively. After all, it's better to fail before the season starts, and Offseason projects are for trying new things. It has been a great opportunity to teach ourselves some valuable skills, and we have been able to get team members up to speed on operating our CNC Router, including aluminum routing, a first for us.

Here is a gallery of some progress pics and closer shots.
http://imgur.com/a/OKjst

I would love to get some feedback on the wiring, or any other aspect of the bot that could be improved.

Re: Angelbots Offseason 8W WCD
 

Nice work!
We will be test driving our WCP gearboxes for the first time tomorrow, seeing your video makes me even more excited :D

Questions: Did you guys shorten the output shaft on the gearboxes?

What is the durometer of the Colson wheels you attached? Are they different from the grey kind?

Re: Angelbots Offseason 8W WCD
 

I have been following your WCD efforts, your version looks fantastic, I really like your 1/16 in polycarbonate solution to covering the gearboxes, we may have to borrow that idea, as our covering is just tape currently. If I may make a recommendation, I would invest in snap rings to retain your wheels as opposed to lock collars, which are a good short term solution, but will come loose and fall off in the long run. Plus snap rings are cheap.

We did shorten our output shafts to fit a VexPro live axle colson hub exactly. The drive base went through a thorough CAD process, and we used those measurements to determine the amount to remove. We used a metal specific chop saw, and a bit of sanding to size ours, which worked beautifully. It was done while the gearbox was disassembled, so you may have some issues doing it now, however, your spacer fix should work just fine for testing.

The wheels used are actually the same durometer as a classic grey Colson, at 65A, + or - 5A. We went with them for a few reasons.

1. Initial thoughts on the matter were that a wider wheel would increase traction, by increasing the surface area of the contact patch. After more research, and the recent CD thread about Traction vs Friction and this very topic, It is no longer so cut and dry, and rather depends on your interpretation of the classical physics models of friction and how they transfer to the real world. It looks like it will end up increasing Traction, due to the increased amount of things to grab into the carpet and push against it, most applicable in a Nitrile type of wheel, and less so in a colson. We do intend to capitalize on the effect by cutting a tread pattern into the wheels, as we have had great success in the past with that technique.

2. We wanted to try as many new things as possible, and 2 inch wide wheels were an easy addition to that list.

3. Honestly, Black looked pretty cool

Re: Angelbots Offseason 8W WCD
 

are you using 35 chain for this set up, cause if you are would recommend you use 25 chain instead cuts down on the weight of the drive base and works just as well for this application

Also whats with he beefy gussets, if your trying to support the upper frame of the drive base why not do something like this, it saves you more space as well as supports from all the post instead of just your 2 points.

Re: Angelbots Offseason 8W WCD
 

Nice job, I am curious to see how you are going to attach the bumpers.

Re: Angelbots Offseason 8W WCD
 

Your point about #25 chain is a very valid one, #35 is overkill in most FRC drivetrain applications, and #25 is more than adequate in a well designed, aligned, and thought through power transmission system. That is why we are, in fact, using #25 chain.

The side rails and gussets were designed around our strengths. The picture you posted is one of 254's drivetrains, and while they have a fantastic design, we do not have access to the same resources that they do. They design around a welded aluminum frame, where as we depend largely upon gusset and Versaframe construction, due to a lack of machining resources.

This is a large part of those beefy gussets. Another part of the reason behind them, especially the strength, is that they will be the main support for the bumpers on the side of the bot. All the force from a hit on the side will go right to those.

We plan on the bumpers attaching with a latch of some sort at the point of the hex, and a section of C channel at the front and the back. The plan thus far is to have two piece bumpers, U shaped on each side of the robot.

Does anybody have any interesting, unconventional solutions to bumper mounting, or thoughts about our bumper situation?

Re: Angelbots Offseason 8W WCD
 

I noticed some voltage drop "twitch" in the video do you think you might need to reduce the gear ratios to optimize the current flow better for a complete robot with more motors?

Re: Angelbots Offseason 8W WCD
 

That was the dead battery.

Re: Angelbots Offseason 8W WCD
 

This makes sense, otherwise that is one nice drive!

Re: Angelbots Offseason 8W WCD
 

You wouldn't even have to weld it you could use the versa hole pattern and bolt your upper frame to the bumper supports instead

Re: Angelbots Offseason 8W WCD
 

There was indeed Chatter as the voltage dropped a significant amount. This was after a decent amount of drive practice and testing, so the battery was reasonably depleted. We have found that we are burning through batteries, as a high speed 6 cim drivetrain draws a large amount of power, far more than a lower speed robot, such as our Bot last year. We did anticipate this, though it is more than we thought, resulting in lower drive times than expected. We will be investing in better, and more, batteries. I think I remember seeing a thread about that here a while ago.

Going with a high speed 6 Cim drivetrain has both advantages and disadvantages. We do not have the pushing power that a lower speed drivetrain would, especially since this drive is not traction limited. This means that we would have to work to avoid any and all pushing matches in high gear, and depend more on our speed and maneuverability to get around opponents. If we need enough power to push through an obstacle, we would then have to change to low.

Are there any members out there who have experience with a non traction limited drivetrain? Thoughts, Experience, Anecdotes? I am curious as to how it could affect gameplay and strategy, as well as other design decisions on the Robot.

I am having trouble visualizing utilizing the method that you mention with a design similar to ours. Could you be more specific in your description?
Why bolts as opposed to rivets? Where would the bolts go? How would you achieve the Hex shape with minimal machining resources, and simple construction techniques similar to this one?

The Versaframe is remarkably, well, Versatile, but it can be difficult to create angled designs and structures in certain applications without access to a sheet metal sponsor or an in house metal brake, or some other way of creating bent sheet parts. Any tips, tricks, or thoughts about how to achieve this type of structure, and strangely angled parts in general with VersaFrame and rectangular tubing construction? Or is there an equally simple, better way of doing this?

Re: Angelbots Offseason 8W WCD
 

I thought you guys might be interested in seeing this.
Some GoPro footage from our latest drive practice/testing session.

http://youtu.be/zNTg9TYfCkQ

I think there are some potential applications for problem diagnostics using a GoPro, as it is now easy to see that the left gearbox is looser than the right, and may be the cause of some of the drift on the robot.

After some more driving and fun, we are still thoroughly pleased with this drivetrains performance.

Do any teams use a support between the gearboxes on a WCD?

It could be anything from an Andymark Churro, to a piece of versaframe, But I am wondering if any other teams have had issues or designs in the past that they would be willing to share.

From what I have seen, It is not common practice. Are there any specific reasons behind it?

Re: Angelbots Offseason 8W WCD
 

We defiantly do! First year we used the extruded aluminum (churros). Lately we make a bracket that mounts over the top of the gearbox and connects to the upper frame that is usually part of the bumper sub frame.
Even if you get them tightened I have seen deflection of the tube itself. You need to consider there is usually another 80+ lbs on the frame at competition. Lots of vibrations too.. That is asking a lot from those few mounting bolts..

Looking good, keep it up.
Aloha!

Re: Angelbots Offseason 8W WCD
 

Now with bumpers.

http://youtu.be/V0e3UXbAFAk