Some Versa Chassis Questions

[ksafin]

I had some questions about the Versa Chassis and I hope some of the drivetrain-gods in this forum could enlighten me.

I'm using this image for my examples (http://www.vexrobotics.com/media/cat...rsachassis.png)

1) Wherever you place versablocks for wheels, you will have to cut a circular hole through the tube stock in order to get your axles on, correct? That is, the tube stock comes completely undrilled and that part comes down on you

2) Where does the actual power transmission come in? Although putting it in the tube stock would be a great space-saving measure, it seems to me that the picture shows sprockets on the inside of the chassis.

3) The gearbox in the picture has me confused. Where is the output shaft? It doesn't look like there's anything on the inside of the chassis that can be chained to the sprockets?

4) I'm assuming rivets are pretty much mandatory for use with VersaChassis, since none of us are going to be holding bolts somewhere in the middle of a 4 foot tube stock.

I guess if anybody can give me a quick laymans run-down I'd appreciate that too.

Thanks

[DampRobot]

Originally Posted by ksafin

1) Wherever you place versablocks for wheels, you will have to cut a circular hole through the tube stock in order to get your axles on, correct? That is, the tube stock comes completely undrilled and that part comes down on you

2) Where does the actual power transmission come in? Although putting it in the tube stock would be a great space-saving measure, it seems to me that the picture shows sprockets on the inside of the chassis.

3) The gearbox in the picture has me confused. Where is the output shaft? It doesn't look like there's anything on the inside of the chassis that can be chained to the sprockets?

4) I'm assuming rivets are pretty much mandatory for use with VersaChassis, since none of us are going to be holding bolts somewhere in the middle of a 4 foot tube stock.

I guess if anybody can give me a quick laymans run-down I'd appreciate that too.

Thanks

As RC and JVN have said before, the idea of the VersaChassis is to be able to build a great drivetrain with only a hand drill and a hack saw. Everything is pretty much non-critical toleranced (ie, clearance) or match drilled.

1) Yes, that is correct. I believe a 1" hole would work well, as you want clearance for your hex, plus some for tensioning. They sell you extrusion with no wheel holes drilled, you have to do that yourself (you can also just buy regular 2x1 tubing).

2) One wheel (usually the center) is direct driven out of the gearbox. The outer wheels are either chained or belted to the output shaft of the motor, where the sprockets or pulleys usually live inside the gearbox (but outside of the tubing).

3) The output shaft goes through the bottom of the gearbox, through the frame tubing, and into the center wheel. This way, if a chain/belt run breaks/skips, your drivetrain can still drive.

4)Rivets are really better than bolts here (lighter, quicker to install, etc), but you can use bolts too. They'd need to go all the way through the tubing though. As you said, putting a nut inside the tubing would be unrealistic.

Here's what you do to put together a VersaChassis: Figure out your ratios, wheels, and frame dimensions. Order parts. Then, take a hack saw (or band saw) and cut your frame 2x1 to length, trying to keep the cuts relatively square and accurate piece to piece (+/- 1/16 would probably be fine, +/- 1/4 likely would be pushing it). Figure out where you want your wheels to go in the tubing, and drill 1" clearance holes there. Press bearings into your versablocks, and clamp them on the tubing in the approximately right locations. Make sure that the versablocks are assembled such that they're with the slot up on the outside and the slot down for the inside wheels.

Then, figure out about how long you want your wheel shafts to be, and cut them to length (with a hack saw is fine). You'll use shaft collars to retain stuff on the shafts. Slip them into place in the versablocks, and add on the necessary wheels, sprockets and hardware. Either test fit your belts or measure and cut your chain to the right length at this point. Then, assemble your drive gearboxes, and mount them to your side frame tubing by bolting them onto a half versablock located on the outside of the tubing, with their output shaft going through a bearing in the versablock. You might have to do some match drilling at this stage. Once you've verified that your wheels are about where you want them, drill a #7 hole around the midline of the tubing close to the outside versablocks to mount your cams. These mount with a 10-32 button head, with the head on the outside and the cam on the inside. To tension each wheel in turn, rotate the cam with a wrench until the chain is tensioned, then tighten down the versablocks and the cam screw. Test your drive sides before assembling the frame to make sure everything is running right.

After you've gotten your two halves of the drive assembled and you can see that they're working correctly, it's time to assemble the frame. Take the two sides of your drive, and your front and back tubing, and arrange them in the shape of your frame (sort of a fat H on it's side, like in the picture you linked to). Then, take the Vex Pro T shape gussets, and clamp them onto your frame, so your frame is essentially assembled how you want it, just with clamps holding it together and without any rivets. Then, match drill each hole in the gussets with a #10 drill bit and install 3/16" diameter by 1/4" grip rivets (or any other size rivet or screw you like) in each hole. Once the drive is assembled, test driving it around (with an old electronics board or such) to make sure it's preforming as expected. Try making it turn on carpet, as this can be a huge problem for robot drives. Finally, when you're satisfied that it's strong and working as expected, cut a wood bellypan to size, and rivet or screw it onto the bottom of the frame. You'll likely want clearance holes in it for your gearboxes.

[R.C.]

Everyone above has done a great job answering the questions posed by the OP, thanks a bunch! I'd like to add a few side notes:

The VersaChassis was designed to a flexible but high quality/reliable drive system that requires zero CNC. It is also based off the WestCoast Drive Systems that FRC teams: 254/968/973/1323/1538 etc... have used over the past few years.

Some of the design thoughts that went into this:

-Any Size: We know that every team would like the option of choosing what size chassis they build. So the Versachassis allows teams to do that. Teams can build to whatever size they want. Some examples: 28"x28" - 32x24" - 24"x32" and so on. All you have to do is hacksaw or bandsaw the tubing to length.

-Any Wheel: Everyone has their own taste/preference of which wheel to use. The versachassis has an extra long shaft so you can use ANY wheel that is on the VEXpro/WCP site including traction/colson/versawheel/mecanum etc...There is a tapped hole at the end of the shaft for a 1/4" bolt plus washer. Teams can also snap ring or shaft collar their wheels on.

-Any Gearbox: Teams can use any gearbox that has holes designed for the VersaBlock. Which includes the WCP SS/DS/3 CIM w/ PTO. Along with the new 3 CIM Ball Shifter! The cool thing is teams can upgrade form a Single Speed to a Dual Speed without rebuilding their current VersaChassis.

-VersaBlock: Designed so teams do not need to perfectly machine into the rail, the VersaBlock holds all the tight tolerances and controls the drop. It is offset 1/16 from center line, so to control drop you can just flip the block! It also have a VersaPattern machined into it so you can use this for arms and other manipulators.

-Driveline: Teams can use sprockets or belts with the current system. The VEXpro belts are toleranced so teams can FIT 2 9mm belts on a 15mm pulley (actual 18mm inside width).

-Tensioning: The cam feature is really nifty, it allows teams to perfectly tension chain or belt. PIC 1 and PIC 2. Basically as you turn the cam it tensions the chain.

I attached here another example drive line that shows how to use sprockets. The sprockets currently hang off of one side of the VersaBlock. Your ALSO able to put the sprockets completely inside the tube if you'd like.

Hopefully this sheds some light on some of the components and our goals. Please feel free to ask any questions or email VEXpro/WCP. We (VEXpro/WCP) are working very hard on getting the manual and more product info out in the next couple of weeks.

Thanks!

[DampRobot]

Originally Posted by R.C.

-Driveline: Teams can use sprockets or belts with the current system. The VEXpro belts are toleranced so teams can FIT 2 9mm belts on a 15mm pulley (actual 18mm inside width).

RC, do the 15mm pulleys (for 2 9mm belts) fit where 2 sprockets usually would in the drivetrain? What if we want to use 15mm belts?

[R.C.]

Originally Posted by DampRobot

RC, do the 15mm pulleys (for 2 9mm belts) fit where 2 sprockets usually would in the drivetrain? What if we want to use 15mm belts?

Yep,

Thats where they would go, you just have to manipulate the washers around, which will be discussed in the user manual guides. We designed for a single pulley to save teams money and make it a easier drop in solution. It won't stock fit two pulleys @ 15mm wide. But you can extend the spacers and it'll fit in there.

[Kevin Kolodziej]

Maybe I'm missing something, but it seems as though the WCP DS 2 CIM gearbox does not have room inside for sprockets/pulleys inside the gearbox. Using the WCP DS - Dual Speed Base Kit step file from the Vex website, there is no room on the output shaft inside the gearbox for pulleys or sprockets. A couple ways off the top of my head to solve this:

1. Modify the 3/8 hex shaft (I assume this is the "Standard Input Shaft" listed in the included items?) to be longer and use longer standoffs to gain the necessary room.

2. Do not modify anything but use additional standoffs and/or structure to space the outer plate of the gearbox away from your chassis rail.

Your solutions may vary.

Will there be layout drawings posted for the new gearboxes at any point?

One other thing I was surprised to find once I finally got a chance to tinker with the files is that there is less than 1/32" ground clearance for the 2 CIM gearbox (3 CIM is likely similar) when using the 3.25" Versawheel:

[DampRobot]

Originally Posted by Kevin Kolodziej

Maybe I'm missing something, but it seems as though the WCP DS 2 CIM gearbox does not have room inside for sprockets/pulleys inside the gearbox. Using the WCP DS - Dual Speed Base Kit step file from the Vex website, there is no room on the output shaft inside the gearbox for pulleys or sprockets. A couple ways off the top of my head to solve this:

1. Modify the 3/8 hex shaft (I assume this is the "Standard Input Shaft" listed in the included items?) to be longer and use longer standoffs to gain the necessary room.

2. Do not modify anything but use additional standoffs and/or structure to space the outer plate of the gearbox away from your chassis rail.

Your solutions may vary.

Will there be layout drawings posted for the new gearboxes at any point?

One other thing I was surprised to find once I finally got a chance to tinker with the files is that there is less than 1/32" ground clearance for the 2 CIM gearbox (3 CIM is likely similar) when using the 3.25" Versawheel:

Attachment 15670

I'd betcha that that's the standard version of the DS gearbox. There's a "WCD" version with room inside for your sprockets or pulleys or whatever. It also includes a wheel truck.

We did a mod similar to what you described in #1 for the offseason, in order to turn a standard DS into a WCDish DS with space for only one more output sprocket. It was fairly simple to do, but requires a lathe. Of course, if what you really want is the WCD DS, then you should buy the WCD DS.

[Kevin Kolodziej]

Originally Posted by DampRobot

I'd betcha that that's the standard version of the DS gearbox. There's a "WCD" version with room inside for your sprockets or pulleys or whatever. It also includes a wheel truck.

We did a mod similar to what you described in #1 for the offseason, in order to turn a standard DS into a WCDish DS with space for only one more output sprocket. It was fairly simple to do, but requires a lathe. Of course, if what you really want is the WCD DS, then you should buy the WCD DS.

I bet you're right. I didn't look at the WCD version because we would not be using the WCD bearing blocks - only the Versablocks. I'll have to check out the WCD version CAD and see if that is in fact true. Solution #1 would be easy enough for us to do as well (we created custom gearboxes last year), just noting that it may not be a complete off the shelf solution if you don't know exactly what you're getting.

For the Vex people that may see this, you may want to make that more clear regardless of what will be in the user manuals (whenever those come out). I have a feeling I'm not the only one that would make this mistake...but I'm glad I did before I ordered anything!

[Akash Rastogi]

Originally Posted by yash101

To tell you the truth, I haven't played around with these, but it looks like there is only one drive wheel on each side, on direct-drive. That seems pointless, but is a possibility!

Please familiarize yourself with the topic in question before posting. Otherwise, there isn't much added to the discussion. There is 1 direct driven wheel, with the other three linked via chain and sprocket.

You have to drill a clearance hole for your drive shafts, but that isn't a hassle at all. The rest is taken care of by the versablock.

Check out the WCD gearboxes that are sold by WCP. WCD gearboxes usually have space before the tube for sprockets, so that the other wheels can be chained together. The gearbox direct drives 1 wheel, with the rest linked together by these sprockets.

In order for you to learn how it all works, I suggest downloading the CAD for the gearboxes and to read up/research West Coast Drives here on CD. They are a pretty simple concept, you'll probably have a "duh" moment once you check out more pictures and examples of them.

Rivets are probably your best bet with assembling with gussets and tubing. Some teams prefer small screws/bolts, but rivets can save a lot of time during assembly, and can be drilled out if dis assembly is required.

Good luck! Hope that clears some things up.

Edit: Check out the WestCoast Products facebook page for more images such as this example of 1477's drive.

www.facebook.com/wcproducts

[Gregor]

Originally Posted by ksafin

I had some questions about the Versa Chassis and I hope some of the drivetrain-gods in this forum could enlighten me.

I'm using this image for my examples (http://www.vexrobotics.com/media/cat...rsachassis.png)

1) Wherever you place versablocks for wheels, you will have to cut a circular hole through the tube stock in order to get your axles on, correct? That is, the tube stock comes completely undrilled and that part comes down on you

2) Where does the actual power transmission come in? Although putting it in the tube stock would be a great space-saving measure, it seems to me that the picture shows sprockets on the inside of the chassis.

3) The gearbox in the picture has me confused. Where is the output shaft? It doesn't look like there's anything on the inside of the chassis that can be chained to the sprockets?

4) I'm assuming rivets are pretty much mandatory for use with VersaChassis, since none of us are going to be holding bolts somewhere in the middle of a 4 foot tube stock.

I guess if anybody can give me a quick laymans run-down I'd appreciate that too.

Thanks

1) You need to cut a slot, or at least an oversized hole for the axle. The Versablocks bare the load, you just need a clearance hole for the axle. I said a slot so you can take advantage of the cam tensioning.

2) You are correct, the sprockets are on the inside of the drive rail. The axles are live axle, which means they transmit power through them, either through a key or (in this case) hex.

3) The output shaft is in line with the wheel closest to the gearbox. That wheel is directly driven from the gearbox. There are two sprockets on this inside of the gearbox, like this, which transmits power to the other wheels

4) Rivets are your friend

Originally Posted by yash101

To tell you the truth, I haven't played around with these, but it looks like there is only one drive wheel on each side, on direct-drive. That seems pointless, but is a possibility!

No.

[Ernst]

This render of the gearbox in the original post shows open spaces on the hex shafts for versahubs and sprockets like the picture Akash posted shows, just with the 3 CIM version of the gearbox. (Sorry about screwing up the page formatting!)

[ksafin]

Thanks for all the help guys, starting to get a much better understanding!

Didn't realize the gearboxes had space for sprockets.

Now, something I'm having a hard time understanding is what cam tensioning is? I see the cam tensioner part on VexPro and can't for the life of me understand its purpose.

[Akash Rastogi]

Originally Posted by ksafin

Thanks for all the help guys, starting to get a much better understanding!

Didn't realize the gearboxes had space for sprockets.

Now, something I'm having a hard time understanding is what cam tensioning is? I see the cam tensioner part on VexPro and can't for the life of me understand its purpose.

With a slotted clearance hole for your shaft, an adjustable cam can be turned in order to "slide" the Versablocks over, in small increments. Since chain stretches, the notches in the cam push against the versablock to tension it. You can check out a cam tensioning system in action on just about any chained WCD, and some belt driven ones. But yeah, just make sure the clearance slot exists.

By the way, go check out Adam Heard's user signature, he has a link to all of 973's available CAD, which include the west coast drives that I learned about all of this from. I can't recall off the top of my head if all the files include an example of cam tensioning, so you may have to check out a few of them.

I'll post back with some pictures.

Edit: This thread in general will help you out a ton - http://www.chiefdelphi.com/forums/sh...t=94288&page=2

254's media gallery isn't working for me right now, otherwise they have some of the best examples for all this.

-Akash

.

[JB987]

Cam tensions (tightens) your belt or chain by forcing blocks outward.

Beat me to it Akashi" ...learning how to type on my first IPad.