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messer5740 07-02-2017 21:30

H-Drive Strafing issues
 
Hey CD
So we are experiencing traction trouble with our H-Drive chassis. When we attempt to strafe, sometimes the wheel just turns and doesn't catch on the ground. We were doing it on polished cement, so that may be an issue, but what to do you all think, what should we do?

Hitchhiker 42 07-02-2017 21:35

Re: H-Drive Strafing issues
 
When we did this in 2015, we found that on carpet, the robot sinks significantly into the carpet for the wheel to catch. You should probably try this out on carpet and see if this is the case. If it is, great! If it still doesn't catch, you may need to lower your center wheel.

Southpaw 07-02-2017 21:38

Re: H-Drive Strafing issues
 
Carpet will most certainly help, what wheel is your strafing drive?

Cothron Theiss 07-02-2017 21:40

Re: H-Drive Strafing issues
 
Is the strafing wheel at a set position? Is there any way you can increase the amount of normal force on that middle wheel? Carpet will almost certainly help. But it probably won't fix the problem.

messer5740 07-02-2017 22:58

Re: H-Drive Strafing issues
 
The center wheel has no applied force on it, but we do have the majority of our heavy weight items (battery, etc.) toward the center wheel. It is just an Omni wheel with rollers. We should be taking it up to the practice field soon

Joseph Smith 08-02-2017 06:31

Re: H-Drive Strafing issues
 
1 Attachment(s)
In 2015 our strafe wheel was in a spring powered suspension setup to keep it in contact with the ground. I don't know what your setup looks like, but it's very difficult to keep weight on a fixed center wheel without lifting up other wheels. One of the best methods I've seen is what 148 did in 2014 with their "rocker" module. Perhaps someone from their team can elaborate on it further.

GeeTwo 08-02-2017 08:15

Re: H-Drive Strafing issues
 
We tried strafe with H-drive in 2015, using a hard chassis mount. No matter how high or low we put it, it never worked right. Off season, we used a pneumatic cylinder to apply a steady force to it, and it worked first try. Springs can also work, I understand. The force on that wheel should be roughly between 20% and 35% of the weight of your robot, depending on how much strafe force you want and how much forward drive force you're willing to give up while you strafe.

messer5740 08-02-2017 09:59

Re: H-Drive Strafing issues
 
Quote:

Originally Posted by GeeTwo (Post 1641936)
We tried strafe with H-drive in 2015, using a hard chassis mount. No matter how high or low we put it, it never worked right. Off season, we used a pneumatic cylinder to apply a steady force to it, and it worked first try. Springs can also work, I understand. The force on that wheel should be roughly between 20% and 35% of the weight of your robot, depending on how much strafe force you want and how much forward drive force you're willing to give up while you strafe.

Think it would work if we just ran it on the carpet? We are using a Vex versaframe H drive chassis

Chris is me 08-02-2017 10:04

Re: H-Drive Strafing issues
 
Is the center wheel rigidly mounted to the frame, or is it articulated? An articulated strafe wheel will do a much better job contacting the ground. One COTS way to do this with VersaFrame would be to use a drop drive module with only one wheel in it (I've never tried this, it just seems like it would work).

If your frame uses VersaBlocks, be sure you don't accidentally have the drop center in the wrong direction.

A picture would really help here.

pmattin5459 08-02-2017 10:44

Re: H-Drive Strafing issues
 
Quote:

Originally Posted by messer5740 (Post 1641970)
Think it would work if we just ran it on the carpet? We are using a Vex versaframe H drive chassis

He said that with a hard mount, no. You need some sort of actuation. I would suggest the RoboWrangler way from the comment above if you don't want to use pneumatics.

GeeTwo 08-02-2017 11:13

Re: H-Drive Strafing issues
 
Quote:

Originally Posted by messer5740 (Post 1641970)
Think it would work if we just ran it on the carpet? We are using a Vex versaframe H drive chassis

Quote:

Originally Posted by pmattin5459 (Post 1641993)
He said that with a hard mount, no. You need some sort of actuation. I would suggest the RoboWrangler way from the comment above if you don't want to use pneumatics.

Correct. It didn't matter whether we ran on bare floor or carpeting; we never got a useful strafe with fixed mounting, even when we tried a slot and use cable tension to hold the gearbox/wheel down.

messer5740 08-02-2017 11:20

Re: H-Drive Strafing issues
 
Quote:

Originally Posted by GeeTwo (Post 1642007)
Correct. It didn't matter whether we ran on bare floor or carpeting; we never got a useful strafe with fixed mounting, even when we tried a slot and use cable tension to hold the gearbox/wheel down.

So you suggest Vex Versadrop?

Chris Hibner 08-02-2017 11:50

Re: H-Drive Strafing issues
 
When we did our H-drive in 2011 (which worked very well), our center wheel was on a simple suspension system. We put the center wheel on a swing arm and used a gas strut from McMaster Carr to provide the spring and damping. The trick was to size the gas strut to provide 1/5 of the robot's weight to the center wheel.

GeeTwo 08-02-2017 11:58

Re: H-Drive Strafing issues
 
Quote:

Originally Posted by messer5740 (Post 1642008)
So you suggest Vex Versadrop?

That would be one way, and the only COTS design that comes to mind. Our off season version was home brew, and not at all optimized, more a proof of concept. In some way, you need to have the wheel able to move up and down, and apply a relatively steady force to hold it down as it moves. Pneumatics gives you the option of lifting the strafe wheel up (or at least not pushing it down) to maximize traction on your primary drive wheels.

EricLeifermann 08-02-2017 11:59

Re: H-Drive Strafing issues
 
Quote:

Originally Posted by Chris Hibner (Post 1642017)
When we did our H-drive in 2011 (which worked very well), our center wheel was on a simple suspension system. We put the center wheel on a swing arm and used a gas strut from McMaster Carr to provide the spring and damping. The trick was to size the gas strut to provide 1/5 of the robot's weight to the center wheel.

If you don't have space for a gas shock constant force springs work well too.


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