Team 1658 flying inverse differential swerve Video+CAD files

[SndMndBdy]

I'm curious about that worm gear that you've got. It looks 3D printed - is that right? Can you give us some specs and tell us how you made it? Does it seem like it will be sturdy enough to hold up well?

[sanelss]

Originally Posted by GeeTwo

If the top motors are going "full speed" (which I read as free speed, or nearly so), they are generating no torque and thus producing no mechanical power. The bottom motors are going "nearly full speed", they are generating low torque, and are operating well down on the power curve. Where does this "high power" originate?

In that situation there wouldn't be much as you mentioned. If we drive the system like that and we try to move, as we increase the load on the system the speeds of both motors will be loaded down and slowed down until it hits a point where it has sufficient torque to move. Or we can try to keep it in the higher power band but that would arbitrarily limit our top speed when that amount of torque isn't required. With a desired output speed, the faster we run the motors the faster total speed differential we can get making the top speed of the robot higher. But indeed there isn't much power available there but as in a regular control system when you apply a load the speed will be reduced to the point where torque is high enough for the task. In our case both motors will be slowed down so our torque will vary while our total speed output remains the same.

Or at least that's what we think, could be wrong. The whole point of building the prototype was/is to find out if we're just kind of wrong or completely wrong XD

[sanelss]

Originally Posted by SndMndBdy

I'm curious about that worm gear that you've got. It looks 3D printed - is that right? Can you give us some specs and tell us how you made it? Does it seem like it will be sturdy enough to hold up well?

they are NOT 3d printer. They are plastic though(nylon?)they are actually very common garage door opener gear sets you can buy at sears. Though they are twice as cheap online. In fact, andymark uses the exact same set(but they hex broach theirs) on one of their 90 degree transmissions. We used two sets last year to drive our elevator mechanism and they held up just fine.

As far as specs/how it was made take a look at the CAD files.

[sanelss]

Originally Posted by Electronica1

I just want to double check, the transmission you are using is similar to this, correct?

Maybe? From what he said it indeed sounds like he just made an overly complicated inverse differential but he seems to hide the fact that he has another motor somewhere counter driving one of the gears and doesn't mention that both motors need to be able to provide the torque you want out of the system. This seems like one of those try to scam investors out of money schemes but since he seems to be hiding information can't really say.

[Jared]

I really like the idea behind this - I think it may have applications beyond just drive trains.

Something you may want to look into is gearing the upper and lower motors at different speeds, with a non-backdrivable reduction for the high speed motor. This would let you get a wider range of gear ratios without having to run motors at really high speeds.

This paper, if it is ever released, describes the exact same idea in a planetary differential with some equations/control ideas that might be useful.

https://ras.papercept.net/conference...=103&Number=70

[Ty Tremblay]

Originally Posted by Ari423

BTW anyway we can get the CAD either in STEP format or on GrabCAD so Solidworks users can take a look?

Second. Would love to take a look.

[sanelss]

Originally Posted by Ty Tremblay

Second. Would love to take a look.

isn't solidworks able to import inventor files? inventor can import solidwork files it would be odd if the opposite isn't also true. As mentioned in the other reply I don't have inventor at home nor will have access to the cad pc until after the season starts so I can't do much on this end but i'm sure you can find converters online at worst case but i'm fairly certain solidworks should allow you to be able to import inventor formats.

[asid61]

Originally Posted by sanelss

isn't solidworks able to import inventor files? inventor can import solidwork files it would be odd if the opposite isn't also true. As mentioned in the other reply I don't have inventor at home nor will have access to the cad pc until after the season starts so I can't do much on this end but i'm sure you can find converters online at worst case but i'm fairly certain solidworks should allow you to be able to import inventor formats.

It depends on the version from my experience. Where is the Inventor CAD? I want to try importing it, so I'll post back in a second.

EDIT: Nope, turns out we need "Inventor 11" to open inventor assemblies. https://gyazo.com/085d9a7b724d8e8d3cae02e00aaa5ca8

[sanelss]

Originally Posted by asid61

It depends on the version from my experience. Where is the Inventor CAD? I want to try importing it, so I'll post back in a second.

EDIT: Nope, turns out we need "Inventor 11" to open inventor assemblies. https://gyazo.com/085d9a7b724d8e8d3cae02e00aaa5ca8

what about the .ipt files or the drawings? ye not sure how assemblies would be handled even if they were exported, i guess the entire assembly would just become 1 part? only thing i can suggest is maybe look for an online converter there's nothing I can do until season starts.

[Ty Tremblay]

Originally Posted by sanelss

what about the .ipt files or the drawings? ye not sure how assemblies would be handled even if they were exported, i guess the entire assembly would just become 1 part? only thing i can suggest is maybe look for an online converter there's nothing I can do until season starts.

Do you have access to Inventor? If so, you can open it and just use Save As to save the assembly as a STEP file.

[Ari423]

Originally Posted by sanelss

what about the .ipt files or the drawings? ye not sure how assemblies would be handled even if they were exported, i guess the entire assembly would just become 1 part? only thing i can suggest is maybe look for an online converter there's nothing I can do until season starts.

You can just upload the files to GrabCAD and we will be able to look at them online without any software at all.

[lucas.alvarez96]

So this is gonna be a bit noobish, but reading through the thread and watching some videos, I still can't grasp the idea behind the inverse differential. I understand that 2 motors run independently and control the output velocity, but how do they manage to do that? And did you make or buy those parts?

[GeeTwo]

Originally Posted by lucas.alvarez96

So this is gonna be a bit noobish, but reading through the thread and watching some videos, I still can't grasp the idea behind the inverse differential. I understand that 2 motors run independently and control the output velocity, but how do they manage to do that? And did you make or buy those parts?

A differential gear system is standard equipment on automobiles, easiest to understand on old rear-wheel drives. A drum is turned in the direction that the wheels should turn as an average (using bevel and crown gears in most cases), and another bevel gear is mounted to the inside of the drum to turn the wheel axles. If the wheels both move at the same speed as the drum, this later bevel gear does not rotate about its axis. If one of the wheels has to move a bit faster (e.g. in a turn), the bevel gear will rotate to let one move a bit faster than the other. The extreme case is when you're stuck in the mud and one wheel spins freely while the other does not turn at all. The net result is that average speed of the wheels must equal the speed of the drum. Inverse differential is if you run the differential backwards - put motors where the wheels normally are and use the common shaft as an output.

I'm not sure what flying means in this context.

[MrBasse]

I have rebuilt more differentials than I want to think about and taught automotive for a handful of years. I had a tough time following the last description, so I'll point you to an old but good video.

https://youtu.be/K4JhruinbWc

Start around 3:20 for how the differential works, then just replace wheels with motors and the concept should be pretty clear.

[sanelss]

Originally Posted by GeeTwo

A differential gear system is standard equipment on automobiles, easiest to understand on old rear-wheel drives. A drum is turned in the direction that the wheels should turn as an average (using bevel and crown gears in most cases), and another bevel gear is mounted to the inside of the drum to turn the wheel axles. If the wheels both move at the same speed as the drum, this later bevel gear does not rotate about its axis. If one of the wheels has to move a bit faster (e.g. in a turn), the bevel gear will rotate to let one move a bit faster than the other. The extreme case is when you're stuck in the mud and one wheel spins freely while the other does not turn at all. The net result is that average speed of the wheels must equal the speed of the drum. Inverse differential is if you run the differential backwards - put motors where the wheels normally are and use the common shaft as an output.

I'm not sure what flying means in this context.

flying in the sense that at top speed they are moving REALLY fast... it's rather scary especially when we had it mounted to a bench spinning at top speed unloaded....