Chief Delphi - pic: 3216 Swerve

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Re: pic: 3216 Swerve

Quote:

Originally Posted by ekapalka (Post 1395149)

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?

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.

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.

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.

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...

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!

That's a good encoder. To align the wheels, you can use a hall effect sensor and magnet aligned such that the wheel are all pointing the same way when the hall effect sensor is activated. Alternatively, putting a hole directly above each wheel axle and stretching surgical tubing between the wheel axles will make a pair wheels face the same direction. Then you just set constants in the program to get them aligned properly.

Belts are fine. They offer greater efficiency at the cost of width/ space. I just think that you could use a large reduction to the wheel axle instead of using so many gears. Then you could just use a belt or just a pair of gears to go to the coaxial axle from the cim.

0.25in is pretty hefty. Keep in mind the WCP gearboxes are heavily pocketed. When you pocket your swerve modules, which you should, make sure to get the pocket design checked out by a mentor/ engineer to maximize strength and minimize bending. Get the wheel very close to the edge to stop bending issues.

Vex bevel gears are fine. The low pitch gives them resistance to bending issues. What do you mean by a set screw? Avoid set screws on shafts whenever possible. A machine shop, or even a basic benchtop mill will be able to cut a 3/8" hex on the end of a 1/2" hex shaft without problems.

10lbs? I'm a huge weight freak when it comes to drivebases. Especially when it comes to swerve drives, the main setback that I see with them is size and weight. Size you are good on. 10lbs is very heavy though. Even if this will not be used in competition, I strongly advise you remove unnessesary weight. Like I mentioned with removing gears, there are ways to reduce weight.

Quote:

Originally Posted by Tyler2517 (Post 1395223)

What is the use of all the extra material below the wheels axial?

The module looks supper tall. This will give you a higher center of gravity decreasing performance.

The co-axil looks complex.

I don't see the need for the gears. Most teams that i have seen that don't use shifting go directly from the cim to the co-axie with a timing belt and the majority of reduction in the yoke. Removing the gears will give you a higher mechanical efficiency and less moving parts in the high speed parts of the transmission.

The top of the modules bearing can definitely be using a bushing saving weight and cost. I personal like the thrust bearings riding on the bearing like 1640.

The plates look complex with a lot of milling operations on places that are not holding weight. Mainly where the bearings are why is this? It would be lighter and cheaper not to have to get plates that thick and mill them down even if the beaing plate are not smooth.
Over all a great start

I have noticed that designing a tall module with a cim facing up actually produces a similar COG when compared to a very short module with the cim facing down. Unless you can get the cim facing sideways, which requires more bevel gears and such, it's easier to keep a tall module.

Re: pic: 3216 Swerve

I don't have time to list all the little problems with this module but I see many. I would suggest you search out the cad files that are available from several teams that have done swerve coaxial. See how they have solved many of the module design problems.

Re: pic: 3216 Swerve

Quote:

Originally Posted by Tyler2517 (Post 1395223)

What is the use of all the extra material below the wheels axial?

Looks, I guess. It weighs a fraction of the modules weight, but I'll remove it if need-be to save on weight later.

Quote:

The module looks supper tall.

Yep. It's 7.125in from the bottom plate to the ground. The centre of gravity, however, depends on your frame and how you mount it. Most modules I've seen are pretty tall, so I didn't pay it much attention. The thing I've most commonly seen is to lower the internal components within the frame so that is only has about 1" of clearance. Like this. I'm thinking of using gears instead of belts or chain to reduce the size, but the CIM is about three inches from dragging on the ground

Quote:

The co-axil looks complex.

...Yes. Quite. This is the only part we don't have the means to make ourselves.

Quote:

I don't see the need for the gears. Most teams that i have seen that don't use shifting go directly from the cim to the co-axie with a timing belt and the majority of reduction in the yoke. Removing the gears will give you a higher mechanical efficiency and less moving parts in the high speed parts of the transmission.

If I were using gears in the rotating module, I would have a lot more options as far as ratios go, but VexPro pulleys only come in a few sizes, and I'm using the lowest reduction available. I'm still considering my options, though.

Quote:

The top of the modules bearing can definitely be using a bushing saving weight and cost. I personal like the thrust bearings riding on the bearing like 1640.

I have nothing against bushings, but I've never really used them. Are they loud? It seems to me that having no moving parts would cause some abrasion and unnecessary stress / heat. By bushing do you mean sleeve bearing? Can you make a recommendation? The bushings/sleeve bearings I have found on McMaster all have to be cut to length and are very similar in weight to the ball bearings I'm using now.

Quote:

The plates look complex with a lot of milling operations on places that are not holding weight. Mainly where the bearings are why is this? It would be lighter and cheaper not to have to get plates that thick and mill them down even if the bearing plate are not smooth.

There's a lot of material that I intend to remove once I finalize the layout. I'm not sure I'll be able to live with non-flush bearings, though. They're 19mm thick.

Quote:

Originally Posted by kk052 (Post 1395412)

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

Screws... What do you mean that they can be inaccurate? I'm hoping for strength by redundancy, which is why there's eight 5mm screws. As for the pulleys, I always figured that you could put the belt on the pulleys before you put the pulleys onto the shafts and then place it on as one piece... I guess that's not how it's done? I've never seen a swerve module using pulleys that did have a tension system.

Quote:

Originally Posted by asid61 (Post 1395534)

To align the wheels, you can use a hall effect sensor and magnet aligned such that the wheel are all pointing the same way when the hall effect sensor is activated. Alternatively, putting a hole directly above each wheel axle and stretching surgical tubing between the wheel axles will make a pair wheels face the same direction. Then you just set constants in the program to get them aligned properly.

I personally love hall effect sensors, and hope I'll be able to find a use for them in this project. Any idea if magnets will mess with the absolute magnetic encoder?

Quote:

0.25in is pretty hefty. Keep in mind the WCP gearboxes are heavily pocketed. When you pocket your swerve modules, which you should, make sure to get the pocket design checked out by a mentor/ engineer to maximize strength and minimize bending. Get the wheel very close to the edge to stop bending issues.

I'm not entirely sure how to do the pocketing, but the WCP gearboxes have no place on them where the metal is less than 0.25x0.25in (meaning that you can't have two pockets less than 0.25in from one another).

Quote:

Vex bevel gears are fine. The low pitch gives them resistance to bending issues. What do you mean by a set screw? Avoid set screws on shafts whenever possible. A machine shop, or even a basic benchtop mill will be able to cut a 3/8" hex on the end of a 1/2" hex shaft without problems.

I hate set screws, but I don't know what else to do. Aside from the other bevel gear being in the way, there's nothing to hold the bevel gear in place (unless it's force fit onto the shaft). I'm not sure if this is a viable option. I'm glad to know that it's possible to go from one size to the other, though. We don't have too many resources at our disposal, but we do have a small mill.

Quote:

10lbs? I'm a huge weight freak when it comes to drivebases. Especially when it comes to swerve drives, the main setback that I see with them is size and weight. Size you are good on. 10lbs is very heavy though. Even if this will not be used in competition, I strongly advise you remove unnessesary weight. Like I mentioned with removing gears, there are ways to reduce weight.

The bearings weigh nearly 1lb each (according to Inventor, not the manufacturer), so I'd really like to do something about them.... There's a lot of unused space in the body, so I'll be able to do a lot of pocketing to reduce weight. I'll reduce the number of gears if it comes to it, but they don't weigh very much.

Quote:

Originally Posted by Gdeaver (Post 1395539)

Thanks for your input, sort-of. I reviewed every swerve drivetrain I could find and made a huge checklist of features that they utilized. What I've tried to come up with is a collection of those things. I'm not sure if this is what you are noticing, but the first few pictures lack shafts, spacers, and sensors. I'm well aware that those are required for a working design.

Thanks everyone!

Re: pic: 3216 Swerve

That weird custom pulley thing can be made on a 4-axis CNC. However, do you really need it? Is it not possible to just modify some Vexpro pulleys to do the same thing?

To hold the bevel gear in place axially along the shaft, you have a couple options:

1. A screw clamping down on a washer on the end of the bevel gear shaft. This is pretty easy, and you only need something like a 4-40 screw, Then use a spacer on the bak of the bevel gear.

2. E-clips or circlips. Both are good. I prefer e-clips because they are easier to mount, but they also need a deeper groove. Slap one on near the end of the shaft and you're good to go.

3. Roll pins. My least favorite option, as they are a PITA to get into a hole, but if you are up to the task go for it. Theya re very strong and hold position well.

Do not use set screws. There are still a lot of axial forces acting on the bevel gear due to their operation. Set screws can and will slip.