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

Madison

02-01-2012, 16:51

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

http://i40.tinypic.com/23kf76h.jpg

http://i40.tinypic.com/j9n0oo.jpg

http://i40.tinypic.com/1ya29.jpg

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

02-01-2012, 17:16

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

02-01-2012, 17:52

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

02-01-2012, 18:01

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

02-01-2012, 18:12

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

Madison

02-01-2012, 18:19

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

02-01-2012, 18:26

Thanks Madison!

Quote from @FRCDesigns (http://www.twitter.com/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

Andrew Lawrence

02-01-2012, 18:36

Madison

02-01-2012, 18:49

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 :)

Andrew Lawrence

02-01-2012, 18:53

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

02-01-2012, 19:18

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.

Andrew Lawrence

02-01-2012, 19:21

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

02-01-2012, 19:23

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.

Andrew Lawrence

02-01-2012, 19:25

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? :confused:

Madison

02-01-2012, 19:25

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.

Mk.32

02-01-2012, 19:27

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

It doesn't work like that.
You need a CAD program as Madison said.
Try this thread: http://www.chiefdelphi.com/forums/showthread.php?t=98442&highlight=CAD+MAC

msimon785

02-01-2012, 20:03

Try ida-step (http://www.ida-step.net/). Its not fantastic, but it does let you view universal .stp CAD data on a mac.

Mk.32

02-01-2012, 20:28

This may be of some interest.
http://www.andymark.com/product-p/am-0273.htm

BrendanB

02-01-2012, 20:58

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.

1114's KoS is essentially 6wd, 6in plactions, with toughboxes or Supershifters from AM. We used it in 2011 and loved the power it had over other robots. I feel like yours takes it to another level of steroids. It reminds me a lot of 2056's 2008 drivebase which I have been looking at a lot this off-season. http://www.2056.ca/photos.php?id=197790310237440&offset=25

Are there any major differences in the supershifters over regular shifters?
Is there a reason for the double tensioners on the front chain run?
Any closer pics of the tensioner assembly?
Do you have an estimated speed?

Looks very clean simple! I love the simple mounting for the transmissions as that is my one peeve with COTS transmissions is getting them secured and still remain easy to work on!

Andrew Lawrence

02-01-2012, 21:33

apalrd

02-01-2012, 21:55

I may have done calculations wrong, but this thing looks like it's gonna go REALLY fast, like 22 fps. Is it supposed to be like that, or did I do my calcs wrong? (Most likely got those wrong, but I did it twice and got the same answer)

What are you calculating the ratio with (What reductions in each stage, and what motor free speed, and speed loss constant?)

I get 3.86 and 9.86 ft/sec with no speed loss and 5310 CIM free speed, for reference.

The stages of reduction are:
12:40 CIM->cluster shaft
15:48 OR 28:35 cluster shaft->shift shaft
16:36 chain

It seems like a lot of chain reduction with 4" wheels. The ratio chosen seems to be perfect for 6" wheels (5.79 and 14.83 ft/sec with no speed loss, 4.69 and 12.01 with speed loss, 46 amp wall-push in low gear)

Andrew Lawrence

02-01-2012, 21:58

What are you calculating the ratio with (What reductions in each stage, and what motor free speed, and speed loss constant?)

I get 3.86 and 9.86 ft/sec with no speed loss and 5310 CIM free speed, for reference.

The stages of reduction are:
12:40 CIM->cluster shaft
15:48 OR 28:35 cluster shaft->shift shaft
16:36 chain

It seems like a lot of chain reduction with 4" wheels. The ratio chosen seems to be perfect for 6" wheels (5.79 and 14.83 ft/sec with no speed loss, 4.69 and 12.01 with speed loss, 46 amp wall-push in low gear)

Well that seems kinda low. My 22 fps is definitely wrong, and I've unfortunately lost the paper I used to calculate it (off to clean my room now!).

Madison, is Apalrd right? This looks like one of the best kitbots I've seen, but 10 fps and 3 fps are not my cup of tea. :|

Akash Rastogi

02-01-2012, 22:00

Madison, is Apalrd right? This looks like one of the best kitbots I've seen, but 10 fps and 3 fps are not my cup of tea. :|

Madison won't cater to what speed each person prefers. The speed is up to you with your reductions.

I prefer the speeds Madison has this at.

Andrew Lawrence

02-01-2012, 22:03

Madison won't cater to what speed each person prefers. The speed is up to you with your reductions.

I prefer the speeds Madison has this at.

I am clueless with calculating speed, so can anyone tell me how to calculate speeds from gearbox reductions and the motors and things? :confused:

Chris is me

02-01-2012, 22:08

Madison won't cater to what speed each person prefers. The speed is up to you with your reductions.

I prefer the speeds Madison has this at.

3 FPS is definitely too slow. It's well below traction limited.

Andrew Schreiber

02-01-2012, 22:30

I am clueless with calculating speed, so can anyone tell me how to calculate speeds from gearbox reductions and the motors and things? :confused:

http://ewcp.org/calculators/gearbox/single/ Might help you see what effect different reductions have on your output speed.

Andrew Lawrence

02-01-2012, 22:32

http://ewcp.org/calculators/gearbox/single/ Might help you see what effect different reductions have on your output speed.

Thanks!

Feroz1325

02-01-2012, 22:32

Great design! But I have 1 question.....in your bill of materials, why is there only 1 of the 2 kinds of spacers (1.25 and 2.5)? I count 8 1.25 and 4 2.5?
Thanks for posting!
EDIT: NVM silly me thought McMaster would sell 1 spacer for 8 dollars :D

Madison

02-01-2012, 22:49

This may be of some interest.
http://www.andymark.com/product-p/am-0273.htm

Thanks for pointing that out! I didn't know it existed at all.

Are there any major differences in the supershifters over regular shifters?
Is there a reason for the double tensioners on the front chain run?
Any closer pics of the tensioner assembly?
Do you have an estimated speed?

The SuperShifters have a third stage of gear reduction inside that makes them better suited for directly driving wheels. They share many common parts.

The double tensioner was mostly to get the chain away from the floor and offer ground clearance. You could probably use just one in many cases.

See below for speed.

Well that seems kinda low. My 22 fps is definitely wrong, and I've unfortunately lost the paper I used to calculate it (off to clean my room now!).

Madison, is Apalrd right? This looks like one of the best kitbots I've seen, but 10 fps and 3 fps are not my cup of tea. :|

He is right.

Alternatively, you could use the AM Shifter with a 4:1 spread between high and low. This puts it into the 11.7 ft/s and 4.6 ft/s range. That might be more in line with current sensibilities about drive speeds.

It might also be possible to use a 22 tooth sprocket on the Shifter output instead of a 16, but I'm not sure if that'd cause any interference issues. You can't go any smaller than 36 tooth on the wheels, really, because the chain will interfere with the spacers. That maybe isn't as much of a concern with the VexPro wheels as it is with the AM Plaction wheels.

Remember, the intent here is to provide a simple, robust platform for teams to use or reference. Frequently, beggars can't be choosers and so, by minimizing manufacturing complexity, you limit available choices for things like drive ratios.

Great design! But I have 1 question.....in your bill of materials, why is there only 1 of the 2 kinds of spacers (1.25 and 2.5)? I count 8 1.25 and 4 2.5?
Thanks for posting!

I believe they're sold in packages of ten.

Andrew Lawrence

02-01-2012, 23:08

Alternatively, you could use the AM Shifter with a 4:1 spread between high and low. This puts it into the 11.7 ft/s and 4.6 ft/s range. That might be more in line with current sensibilities about drive speeds.

It might also be possible to use a 22 tooth sprocket on the Shifter output instead of a 16, but I'm not sure if that'd cause any interference issues. You can't go any smaller than 36 tooth on the wheels, really, because the chain will interfere with the spacers. That maybe isn't as much of a concern with the VexPro wheels as it is with the AM Plaction wheels.

Remember, the intent here is to provide a simple, robust platform for teams to use or reference. Frequently, beggars can't be choosers and so, by minimizing manufacturing complexity, you limit available choices for things like drive ratios.

That's more my style. :) I like where this is going. By using some final staged gearing, from output shaft to wheel sprocket, do you think a speed of maybe 13 to 14 fps is achievable?

I love your simple, robust platform! It made up for not having a game hint released today. 488 never ceases to amaze me with their creations, and I can't wait to see what you come up with this season! Thanks a bunch! :D