Simple 2-Speed 6WD for teams with few manufacturing resources

[Madison]

In the Fall each year, I often give presentations to Washington state teams about drive design and considerations. In my most recent presentation, I recommended that teams investigate the popular new "Kitbot on Steroids" concept put forward by 1114, but did so with no real experience with the kitbot or modifications of it of my own. I trust 1114 enough to know that the advice is good advice, but I wanted to see what it would take to build an enhanced Kitbot and to do so with as few manufacturing steps as possible.

The design requires the following power tools:

• Band saw
• Drill Press
• Scroll Saw
• Belt Sander
• Grinding Wheel

The design was built around the following requirements:

• High traction 6WD wheel arrangement
• Shifting 2-speed transmissions
• 4 CIM motors for drive
• Active chain tensioning
• Electrically isolated control systems area
• No precise machining required
• As many COTS parts as reasonable

I will continue adding to this thread with more detailed information. I hope to include a complete bill of materials, more detailed views of wheel and tensioner assemblies, and maybe even drawings.

There's a STEP model attached. It isn't perfect; I took some shortcuts and so, if you look closely, you'll find that some of my bolts aren't located quite properly. By and large, though, I think it's accurate enough to work from.

[Madison]

I'll start with the bill of materials.

All prices are per item/package

Frame
(1) - C-Base Chassis Kit (AM-0952) - $155.00
(2) - AM Shifter w 2.56:1 Spread (AM-0001) - $350.00
(4) - 16 tooth, 1/2" keyed bore #25 chain sprockets (AM-0277) - $11.00
(1) - 3/8 Screw Size x 2.5" Long Nylon Spacer (94639A621) - $8.62
(1) - 3/8 Screw Size x 1.25" Long Nylon Spacer (94639A863) - $6.80
(1) - 32" x 48" x 1/8" Thk Perforated PVC Sheet (92985T25) - $51.11
(1) - 12" x 24" x 1/4" Thk ABS Sheet (8586K372) - $23.95

Wheels
(6) - 4" x 2" VEX Pro Wheels (IFI-WHEEL-420-38) - $39.95
(6) - 4" x 2" Roughtop Tread (ROUGHTOP-420) - $4.95
(4) - Sprocket Hardware Pack (IFI-SPROCKET-HDWR-X8) - $3.99
(2) - Dual Sprocket Mounting Hardware (IFI-SPROCKET-HDWR-DUAL) - $4.99
(8) - 36 tooth, #25 chain flat sprocket (AM-0099) - $11.00

Tensioner
(1) - 9/16" ID x 1/32" Wall Thkness Nylon Tube (8628K57) - $4.90
(1) - 1/4" Schedule 40 PVC pipe x 48"
(16) - 1/2" Wide Flat Washer
(16) - 1/4" ID Compression Spring

[Mk.32]

Wouldn't 35 chain be better, as it is more tolerant to misalignment
Also http://www.andymark.com/product-p/am-0836.htm might be a better choice for a belly pan since it is already drilled out.

But it sure does look nice; we are debating whatever to do custom or kit frame this year and this definitely is a nice reason to do kit.

[Madison]

Originally Posted by Mk.32

Wouldn't 35 chain be better, as it is more tolerant to misalignment

But it sure does look nice; we are debating whatever to do custom or kit frame this year and this definitely is a nice reason to do kit.

#35 chain will be more forgiving of misalignment, though saying that it is better is probably a stretch in my mind.

The stack up of parts for each wheel fits pretty closely into the width available within the C-Base, so located everything should be pretty straightforward. The mounting plate that supports the transmission is the part that can lead to the most trouble and is, honestly, probably the weakest part of the design. I hope to provide an alternative gearbox setup using Super Shifters and eliminating that plate. I went down that route first because I started designing with my team in mind and making that part is trivial for us. Similarly, we have a lot of parts on hand for #25 chain and none for #35 chain.

That being said, the design works just as well with #35 chain. The AM shifters come with #35 sprockets anyhow. Replace the 36 tooth #25 sprockets with 26 tooth #35 sprockets (AM-0142) and the ratio remains pretty much unchanged. The IFI sprocket mounting hardware is all designed to accommodate #35 chain, so spacing everywhere should be fine.

Edit to add:
The AndyMark perforated sheet works just as well. The McMaster-Carr part number I included is what we've used in the past. It's also pre-drilled. It's PVC rather than polycarbonate as well, for what that's worth.

[Mk.32]

What are the differences between the PVC and the polycarbonate for this kind of application?

[Madison]

Originally Posted by Mk.32

What are the differences between the PVC and the polycarbonate for this kind of application?

There's probably little appreciable difference, really. The PVC is a bit lighter, I think, but the polycarbonate is probably a bit more rigid. Six of one and half a dozen of another.

[Starke]

Thanks Madison!

Quote from @FRCDesigns

The Simple 2-Speed 6WD from FRC488 has been added to FRC Designs! Check it out! http://www.frc-designs.com/html/drives.html

Looks great! Love it!

A few questions:
1) Why 4"x2" wheels? Could 4"x1" work as well?
2) (From a business point of view) Why would you say this chassis is "better" than 1114's KoS?
3) If you were to name 3 distinct features about your chassis, what would they be?

Overall, great design, great features, great everything!

[Madison]

Originally Posted by SuperNerd256

Looks great! Love it!

A few questions:
1) Why 4"x2" wheels? Could 4"x1" work as well?
2) (From a business point of view) Why would you say this chassis is "better" than 1114's KoS?
3) If you were to name 3 distinct features about your chassis, what would they be?

Overall, great design, great features, great everything!

4x1" wheels could work just as well, but I used 4x2" for two reasons:
1. There's been some talk here lately about 4x2" wheels giving a bit more pushing power than 4x1" wheels and I was curious if they could be made to fit easily into a COTS frame
2. The wider wheel actually makes it possible to use COTS spacers for the axles. A narrower wheel would require spacers that are longer than are available from McMaster-Carr. It's trivial to buy longer stock and cut it down, but I like shopping, not machining

I wouldn't say that it's better than 1114's KoS. I've seen only their brief video about the KoS assembly, so I am not even entirely sure of what their recommendation requires. This was just my stab at the idea of an enhance Kitbot.

There are few things about it that are clearly different; it uses a shifting transmission instead of those included in the kit, it uses 4" wheels rather than 6" wheels and the transmission mount and tensioner design suck

Originally Posted by Madison

4x1" wheels could work just as well, but I used 4x2" for two reasons:
1. There's been some talk here lately about 4x2" wheels giving a bit more pushing power than 4x1" wheels and I was curious if they could be made to fit easily into a COTS frame
2. The wider wheel actually makes it possible to use COTS spacers for the axles. A narrower wheel would require spacers that are longer than are available from McMaster-Carr. It's trivial to buy longer stock and cut it down, but I like shopping, not machining

I wouldn't say that it's better than 1114's KoS. I've seen only their brief video about the KoS assembly, so I am not even entirely sure of what their recommendation requires. This was just my stab at the idea of an enhance Kitbot.

There are few things about it that are clearly different; it uses a shifting transmission instead of those included in the kit, it uses 4" wheels rather than 6" wheels and the transmission mount and tensioner design suck

I THINK we may end up using this this year, that is is 1114 doesn't release their KoS soon! (Karthik, that's your cue!)

IMO, just get correctly sized chain and the tensioners won't be needed. Once again, great job! Now let's try and see how you can make this better, since improvement is always fun!

EDIT: Madison, is there any way possible to make the attached file Mac-friendly? I can't seem to open it, and now that I've downloaded it's like waiting for a game hint 4 days before kickoff!

[Madison]

Originally Posted by SuperNerd256

I THINK we may end up using this this year, that is is 1114 doesn't release their KoS soon! (Karthik, that's your cue!)

IMO, just get correctly sized chain and the tensioners won't be needed. Once again, great job! Now let's try and see how you can make this better, since improvement is always fun!

EDIT: Madison, is there any way possible to make the attached file Mac-friendly? I can't seem to open it, and now that I've downloaded it's like waiting for a game hint 4 days before kickoff!

The C-Base makes it impossible to adjust the center-center distance between wheels, so while things are an even number of pitches between wheels, the gearbox isn't an even number of pitches without shimming it upward some. This might be fine, but the tensioners also up to get the chain away from the floor; it isn't always necessary to do that, but I try to do when I can.

What software are you using to to open the STEP file? STEP should be a platform neutral format.

Originally Posted by Madison

The C-Base makes it impossible to adjust the center-center distance between wheels, so while things are an even number of pitches between wheels, the gearbox isn't an even number of pitches without shimming it upward some. This might be fine, but the tensioners also up to get the chain away from the floor; it isn't always necessary to do that, but I try to do when I can.

What software are you using to to open the STEP file? STEP should be a platform neutral format.

IDK why, but my Mac says there is no application available to run the file, and I have A LOT of applications.

[Mk.32]

OSX doesn't really have a good program to open STEP with.
You generally need solidworks, inventor, ProE/Cero and none of those are for mac.

Originally Posted by Mk.32

OSX doesn't really have a good program to open STEP with.
You generally need solidworks, inventor, ProE/Cero and none of those are for mac.

Can it be made into a PDF, or does it not work that way?

[Madison]

Originally Posted by SuperNerd256

IDK why, but my Mac says there is no application available to run the file, and I have A LOT of applications.

Well, it's a CAD model -- so you'd need some variety of 3D CAD software. Solidworks, Creo, Inventor, CATIA, etc. should all open it without trouble. AutoCAD probably can't; nor can SketchUp. I am not sure about VectorWorks, but it's not really built for the mechanical design market, so who knows.

I'll see if I can't make a 3D PDF. I haven't tried that in awhile.