pic: 3216 Swerve

[ekapalka]

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[ekapalka]

Another angle

[coalhot]

I'd double check some of the VP kits, I distinctly remember there being an extended output shaft add on/kit.

[glennword]

Have you thought about utilizing the tapped hole in the end of the VP output shafts? you could either use a 1/4-20 screw and somehow clamp on the sensor shaft that way, or you could drill it out, and put a tapped setscrew hole in the side of the shaft to lock onto the sensor shaft.

[Adrian Clark]

Originally Posted by glennword

Have you thought about utilizing the tapped hole in the end of the VP output shafts? you could either use a 1/4-20 screw and somehow clamp on the sensor shaft that way, or you could drill it out, and put a tapped setscrew hole in the side of the shaft to lock onto the sensor shaft.

Using the tapped hole on the end of the shaft is a good idea, it's worked for us in the past but not exactly as you describe it. In 2013 our shooter wheels were on two vp gearboxes and we needed to attach encoders to each for control. Our solution was to thread in a bolt with the head removed and couple this to the encoder via a short piece of surgical tubing held on by zip ties.

-Adrian

[anthonyttu]

A tension system for the belts. It could be very difficult to assemble without something. Also you might want to look into sliverthin bearings http://www.silverthin.com/ They are a few X more expensive then the ones you used but can be worth it with the weight and size.

[ekapalka]

Originally Posted by glennword

Have you thought about utilizing the tapped hole in the end of the VP output shafts? you could either use a 1/4-20 screw and somehow clamp on the sensor shaft that way, or you could drill it out, and put a tapped setscrew hole in the side of the shaft to lock onto the sensor shaft.

The problem I'm facing is that the absolute encoder/potentiometer needs to rotate with the module 1:1. The only solution I have been able to come up with is to have a separate series of gears originating from the VersaPlanetary at the same ratio as the belts, but I've run into found a few issues with that (stemming from the short VersaPlanetary output and/or vex and andymark gear thickness). I'm trying to keep as much as possible contained within the plates that make up the body of the module (and I'm trying to go no higher than 1.25" from one to the other). I'm sure there are a lot of ways around this I haven't thought of... [EDIT] I could use a motor other than the BAG motor with a lower RPM and have 1:1 pulleys turning the module. Then mount the sensor right on top of the VersaPlanetary

Originally Posted by anthonyttu

A tension system for the belts. It could be very difficult to assemble without something. Also you might want to look into sliverthin bearings http://www.silverthin.com/ They are a few X more expensive then the ones you used but can be worth it with the weight and size.

Hmm... I was told that properly spaced pulleys wouldn't require a tension system :/ I guess I'll get looking into how that's done. As for the bearings, do you have a ballpark estimate for the prices they offer? I like the weight and look of them, but the bearings I've found are only $19.

Even if my team actually decides to go through with this and build it (which I'm almost certain they won't), we're probably not going to use it in competition because of the technical problems that undoubtedly go along with swerve.

I was wondering if anyone had any thoughts about holding the pivot yoke to the rotating module using screws (8xM5). Its not something I've seen done, so there's probably a reason...

[edited]

[ekapalka]

Originally Posted by Andrew Lawrence

If you know the ratio between the output shaft of the VersaPlanetary and the rotation of the module you can compensate for a non 1:1 ratio in the code.

Yeah but that means that the modules have to be perfectly aligned every time its turned on or the wheels have to be in the same orientation when the robot is turned on as when it was turned off (and the last angle value would have to be persistently saved so it remains between reboots). I'm also the programmer, so I'm trying to avoid having to do that

[asid61]

Okay, so I have a few questions and suggestions for you:
1. Why do you need the encoder to have a 1:1 ratio? You can still tell if the wheels are out of alignment, and realistically it would be better to just have some way of keeping them in line for calibration mechanically, with something such as surgical tubing between the axis of the wheels. I think 1640 had something on keeping modules in line on their Swerve Central site.

2. Is this a shifting design? If not, you are almost certainly using way too many gears and pulleys. You can probably cull almost every gear by using a sprocket reduction to the wheel. For example, using a 10t #25 sprocket on the shaft with the bevel gear and a 42t #25 sprocket on the 4" wheel (I assume it's 4 inches) will net you around 18fps adjusted, and you can lower that via a single pulley reduction going from CIM to turning module. Less gears means cheaper and less complex.

3. Mount the encoder to the end of the versaplanetary and save yourself some time. I think Western Digital sells 10mm shaft absolute encoders, so you can drill out the 1/4"-20 tap on the end of the shaft and add a set screw.

4. Is the center of the turning module, looking down from the top, equidistant from both of the sides that mount the swerve module? That way you don't need to worry about module orientation when putting it on a chassis, and programming becomes a bit easier.

5. How thick are the top and bottom plates, and why? Just curious.

6. You don't need to use roller bearings for turning the module. Bushings can support tons of weight at low rpms, which you are running at anyway. Even a thick plastic bushing on the top plate can provide a strong interface. Ball bearings will work fine, but I think a flanged bushing would work better so you don't need to depend on a press fit or put a lot of axial load on ball bearings.

7. What bevel// miter gears are you running? I've never found a good place to get them cheaply at other then Vex, and the Vex bevel gears are pretty large.

8. How much does this weigh? If it weighs more than 8-9lbs, you need to rethink weight distribution. It's definitely possible to get it lower than that.

Overall, it looks very slick. I like the bearing mount on the top of the module. I hope your team can build a swerve!

[ekapalka]

Originally Posted by asid61

1. Why do you need the encoder to have a 1:1 ratio? You can still tell if the wheels are out of alignment, and realistically it would be better to just have some way of keeping them in line for calibration mechanically, with something such as surgical tubing between the axis of the wheels. I think 1640 had something on keeping modules in line on their Swerve Central site.

The encoder I'm intending to use is a USDigital MA3 absolute magnetic shaft encoder (not the incremental encoder used to measure speed). Preferably, the robot should be ready to go as soon as its turned on with little or no calibration (which I guess might be unrealistic, but I'd still like to make the code relatively straightforward). I'm not sure what you mean by a mechanical solution... something to align the wheels with human assistance, or something else?

2. Is this a shifting design? If not, you are almost certainly using way too many gears and pulleys. You can probably cull almost every gear by using a sprocket reduction to the wheel. For example, using a 10t #25 sprocket on the shaft with the bevel gear and a 42t #25 sprocket on the 4" wheel (I assume it's 4 inches) will net you around 18fps adjusted, and you can lower that via a single pulley reduction going from CIM to turning module. Less gears means cheaper and less complex.

Its not a shifting design. The max free speed is supposedly around 16.5fps. Aside from the weight difference, I'm not sure why I chose to go with belts. I chose the particular gears I'm using to take up the least space. I tried with various other ratios, but the one I chose allowed me to make the plates that hold the module together significantly smaller by having the gears be positioned close around the bearing. Like this.

4. Is the center of the turning module, looking down from the top, equidistant from both of the sides that mount the swerve module? That way you don't need to worry about module orientation when putting it on a chassis, and programming becomes a bit easier.

I'm currently re-designing the body, but the version shown in the pictures is equidistant. Unintentionally, though - I'll make sure to do it this way in the final design as well.

5. How thick are the top and bottom plates, and why?

0.25in, because its the thickness of the WCP SS and DS gearboxes. Additionally, its the thickness of most Vex/AndyMark bearings (minus the flange), to there's a lot of nice flush edges.

7. What bevel// miter gears are you running? I've never found a good place to get them cheaply at other then Vex, and the Vex bevel gears are pretty large.

Vex 15t Bevel gear. I haven't found a problem with them other than the fact that they're 3/8in hex and most everything else is .5in hex, so the shaft going to it has to be milled from one to the other and it needs to have a set screw put in it...

8. How much does this weigh? If it weighs more than 8-9lbs, you need to rethink weight distribution. It's definitely possible to get it lower than that.

With quite a bit of hardware missing, it weighs 10.25lbs, but once I add the missing hardware, cut out relief pockets, and (maybe) trade out one of the heavy bearings for a bushing, it should be around 9-10lbs. Its not for competition, so I'll be satisfied with anything under 11lbs.

Thank you for your input!

[Jared]

Originally Posted by ekapalka

Hmm... I was told that properly spaced pulleys wouldn't require a tension system :/ I guess I'll get looking into how that's done. As for the bearings, do you have a ballpark estimate for the prices they offer? I like the weight and look of them, but the bearings I've found are only $19.

If you can get the center to center distance correctly, like if you're doing it on a mill/CNC, you won't need tensioning.

Silverthin bearings are nice, but really pricey. If you've got the room for thicker ones, you could save some money. I know 1640 uses a large ball bearing, a large thrust bearing, and a bushing on top.

[kk052]

Originally Posted by ekapalka

The problem I'm facing is that the absolute encoder/potentiometer needs to rotate with the module 1:1. The only solution I have been able to come up with is to have a separate series of gears originating from the VersaPlanetary at the same ratio as the belts, but I've run into found a few issues with that (stemming from the short VersaPlanetary output and/or vex and andymark gear thickness). I'm trying to keep as much as possible contained within the plates that make up the body of the module (and I'm trying to go no higher than 1.25" from one to the other). I'm sure there are a lot of ways around this I haven't thought of... [EDIT] I could use a motor other than the BAG motor with a lower RPM and have 1:1 pulleys turning the module. Then mount the sensor right on top of the VersaPlanetary


Hmm... I was told that properly spaced pulleys wouldn't require a tension system :/ I guess I'll get looking into how that's done. As for the bearings, do you have a ballpark estimate for the prices they offer? I like the weight and look of them, but the bearings I've found are only $19.

Even if my team actually decides to go through with this and build it (which I'm almost certain they won't), we're probably not going to use it in competition because of the technical problems that undoubtedly go along with swerve.

I was wondering if anyone had any thoughts about holding the pivot yoke to the rotating module using screws (8xM5). Its not something I've seen done, so there's probably a reason...

screws can be inacuate, also how are you planning on putting a pully on if you cant change the center distance in any way?

[Andrew Schreiber]

You could always use an incremental encoder and an index (limit switch of some sort) as a zero.