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-   -   pic: Drivetrain Concept (http://www.chiefdelphi.com/forums/showthread.php?t=129914)

echin 29-06-2014 20:06

Re: pic: Drivetrain Concept
 
The center wheel uses a rod running vertically through the side cross pieces of the frame and the 1/4" aluminum plates. Four springs would attach to a tabs on the top gusset of the cross piece at each corner and the bottom attachment plate on the center wheel module. The plates should flex a little and allow the wheel to maintain constant contact with the ground, and because of the springs, there would be little force pushing up on the cross pieces to bend them, but it would probably be better to change at least one set of the cross piece gussets to 1/4".

For the outside U channel pieces, I was planning on using a structural bumper mounting system consisting of long pieces of box tubing bolted to the frame along its entire length, which would be attached to the plywood of the bumper. This would essentially turn the outer frame pieces into pieces of box tubing without adding the extra weight. For the inner frame pieces, I will switch them to the .1" Vex tubing or 1/16" tubing. How much would increasing the length of each leg of the T shaped gussets on the frame increase the rigidity? It seems like that would improve the rigidity by a fair amount, but I have not made a frame using gussets before, so I have no experience with that.

I was planning on adding some kind of spacer between the two side frame pieces, but I want to be able to easily remove the outside piece to more easily take off CIMs and wheel modules, so I haven't come up with a good way of doing that yet that wouldn't require sheet metal or welding, which we can't do.

To make the wheel module shafts easier to line up, I was planning on latheing down the ends of the shaft to slightly under 1/2" and rounding the edges, then using round bearings. That would cost less and be easier to line up.

To change the maximum speed of the drive, I would just change the ratio using a different reduction in the sprockets. Since we will hopefully try building this drive before the start of next season, I wanted to make it easy to adjust so that we could try different confiurations and possibly adjust during the build/ competition season if we needed to. I set the speed at 20 fps because it seems like it would never be reasonable to gear faster than that.

The CIMs do not touch any of the bearings (that's one of the reasons the gears are the size they are), but if I were to use smaller gears, I would lathe down the end of the gearbox shaft to 1/4" or 3/16" so that the bearings could be smaller (that's what I did on the center wheel).

Hopefully, we will actually make this drive, so a lot of the design is based on our machining capabilities. We have access to CNC/ manual milling machines at our sponsor's shop, but in house, the only metal working stuff we have is a drill press, a small lathe, and a horizontal band saw.

jimbo493 30-06-2014 09:45

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by Tyler2517 (Post 1391423)
It has a lot of motor weight 6cim/2miny cims..... its a lot of weight in motors.
Even more then a swerve would be.

Not in my team's current design, we have a Cim and a MiniCim powering the wheel, and a bag powering the steering. the whole thing is 4cims 4 minicims, and 4 bags...

XaulZan11 30-06-2014 11:55

Re: pic: Drivetrain Concept
 
I would reach out to teams who have built an a drive with perpendicular wheel(s) to hear their perspective. At least from watching robots with them in the past, they didn't seem to use the sideways drive much to make it worthwhile.

Chris is me 30-06-2014 13:51

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by jimbo493 (Post 1391590)
Not in my team's current design, we have a Cim and a MiniCim powering the wheel, and a bag powering the steering. the whole thing is 4cims 4 minicims, and 4 bags...

Just be aware that this configuration would be illegal under the 2013 and 2014 rules. You're allowed to use up to 4 total of either mini-CIMs, BAGs, or a combination of the two. You weren't allowed 4 of each.

echin 30-06-2014 14:29

Re: pic: Drivetrain Concept
 
How many teams actually use a H drive? I know that 624 and 148 do, but how many others are there? From watching match videos of these teams, it looks like they primarily use their center wheels for getting out of defense, but do not use them continuously.

Also, has anyone ever tried using a CIM as part of a spacer? If it was possible to mount something to the outside frame piece that touched the back of the CIMs, it would act as several large spacers and make it much more difficult to bend the frame in.

Bryce Paputa 30-06-2014 14:38

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by echin (Post 1391629)
How many teams actually use a H drive? I know that 624 and 148 do, but how many others are there? From watching match videos of these teams, it looks like they primarily use their center wheels for getting out of defense, but do not use them continuously.

Also, has anyone ever tried using a CIM as part of a spacer? If it was possible to mount something to the outside frame piece that touched the back of the CIMs, it would act as several large spacers and make it much more difficult to bend the frame in.

1625 made a gearbox a while ago (offseason of 2010 or 2011) that did this, unfortunately I don't remember what it was called to search for it.

XaulZan11 30-06-2014 14:43

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by Bryce Paputa (Post 1391631)
1625 made a gearbox a while ago (offseason of 2010 or 2011) that did this, unfortunately I don't remember what it was called to search for it.

1625 called it a Lobster drive in 2011.

51 did an H drive in 2011. 217/148 did a similar drive in 2010. I'm sure there are others that I'm forgetting.

Abhishek R 30-06-2014 14:50

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by echin (Post 1391629)
How many teams actually use a H drive? I know that 624 and 148 do, but how many others are there? From watching match videos of these teams, it looks like they primarily use their center wheels for getting out of defense, but do not use them continuously.

Also, has anyone ever tried using a CIM as part of a spacer? If it was possible to mount something to the outside frame piece that touched the back of the CIMs, it would act as several large spacers and make it much more difficult to bend the frame in.

Yeah, the main thing we've used the center wheel for is getting out of defense. After we made some changes to the actuation of the traction and center wheels, we saw a large increase in mobility which proved really useful when we tried out the changes for the first time at the Texas Robotics Invitational. We'll be judging our opinions on the usefulness of the wheel after the rest of our offseason events, but so far it's been pretty good. We were almost impossible to t-bone at TRI because of the ability to spin out.

Bryce Paputa 30-06-2014 14:53

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by XaulZan11 (Post 1391633)
1625 called it a Lobster drive in 2011.

51 did an H drive in 2011. 217/148 did a similar drive in 2010. I'm sure there are others that I'm forgetting.

I was talking about the CIMs as spacers idea, but I was able to find it, http://www.chiefdelphi.com/forums/sh...ad.php?t=86668

echin 01-07-2014 19:40

Re: pic: Drivetrain Concept
 
I'm almost done with the next revision and I'll post a picture when I'm done (I'll be gone for the rest of the week so it might be a while). I changed the center wheel to a pivoting piston actuated system instead of linear spring loaded, which saves some weight. I also removed the back wheel module and changed the drive to something more like 624's grasshopper drive. This requires the drive to tip at an extreme angle to use the traction wheels and only saves a little more than 1 lb, so I may change it back to more like what I had before.

An H drive would be able to drive like a swerve with some fairly simple programing, so why does it seem like most teams using H drives don't drive them like swerves?

randantor 01-07-2014 20:06

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by echin (Post 1391807)
An H drive would be able to drive like a swerve with some fairly simple programing, so why does it seem like most teams using H drives don't drive them like swerves?

We experimented during build with field-centric drive controls for our H drive. The difference in power between the X and Y drive directions meant that it wasn't particularly useful because the robot still needs to be pointing forwards to go at any decent speed for travel. Also, our team specifically isn't able to get access to a decent-sized area for driver practice very often, so the additional time needed for our driver to get used to it didn't seem worth it.

Tyler2517 01-07-2014 20:08

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by echin (Post 1391807)
I'm almost done with the next revision and I'll post a picture when I'm done (I'll be gone for the rest of the week so it might be a while). I changed the center wheel to a pivoting piston actuated system instead of linear spring loaded, which saves some weight. I also removed the back wheel module and changed the drive to something more like 624's grasshopper drive. This requires the drive to tip at an extreme angle to use the traction wheels and only saves a little more than 1 lb, so I may change it back to more like what I had before.

An H drive would be able to drive like a swerve with some fairly simple programing, so why does it seem like most teams using H drives don't drive them like swerves?

A swerve drive has 100% thrust vectoring. An h drive will almost always be weaker moving in one of its directions. It may be faster accelerating in one direction then a swerve but a swerve can accelerate the same rate on all directions making holonomic motion easier.

RyanCahoon 02-07-2014 00:50

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by randantor (Post 1391808)
We experimented during build with field-centric drive controls for our H drive. The difference in power between the X and Y drive directions meant that it wasn't particularly useful because the robot still needs to be pointing forwards to go at any decent speed for travel. Also, our team specifically isn't able to get access to a decent-sized area for driver practice very often, so the additional time needed for our driver to get used to it didn't seem worth it.

What are your thoughts on using something like Ether's Halo Auto-Rotate controls with an H drive?

dragon_pilot 12-10-2014 14:47

Re: pic: Drivetrain Concept
 
So basically nonadrive but without gearboxes?

randantor 12-10-2014 15:21

Re: pic: Drivetrain Concept
 
Quote:

Originally Posted by RyanCahoon (Post 1391843)
What are your thoughts on using something like Ether's Halo Auto-Rotate controls with an H drive?

After offseason modifications, our center wheel is now pneumatically actuated, so it isn't in contact with the floor when we aren't trying to strafe. There is a noticable difference in acceleration when the wheel is down because we lose weight from the other wheels. The center wheel output follows a half-second ramp from 0 to full power, and the time that it would take for it to add any useful speed is much longer than it takes for the robot to just turn without it.


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