H Drive

[Mr.Twister]

I Was wondering if anyone could explain to me what an H-Drive is. Also, it would be great if you could add a couple pictures or videos. Thanks

[asid61]

4 omni wheels in a regular 4-wheel drive configuration, and 1 omni wheel in the center of the robot perpendicular to the other wheels in a simple form.

See:

[Mr.Twister]

Thanks! So all the wheels are directly driven I was thinking using chains on the sides and directly drive the middle, is that a good idea or should I stick with directly driving all of the wheels?

[Pault]

Originally Posted by Mr.Twister

Thanks! So all the wheels are directly driven I was thinking using chains on the sides and directly drive the middle, is that a good idea or should I stick with directly driving all of the wheels?

No problems with that. In fact, I would say that it is better, because if the front 2 wheels lift off the ground, you will still be driving your back wheels with 2 CIMS of power. Same goes for if the back 2 wheels leave the ground.

[Mr.Twister]

Originally Posted by Pault

No problems with that. In fact, I would say that it is better, because if the front 2 wheels lift off the ground, you will still be driving your back wheels with 2 CIMS of power. Same goes for if the back 2 wheels leave the ground.

Thank you paul i will try and post a picture once I create it in Autodesk to see what you think

[GeeTwo]

Chaining or belting each pair of wheels with the same center lines automatically distributes the necessary extra torque to the wheel which you're accelerating away from. If you have a CIM for each wheel, it also appropriately redistributes the torque and power of the two CIMS to the two wheels.

Getting the weight load on a strafe wheel correct can also be tricky. This year, we modified a KoP drive train into an H, and ended up pulling the strafe module to minimize weight. Try to make the strafe wheel so that it will carry a defined load, either through a spring or pneumatic cylinder. Using a cylinder also allows you to retract the strafe wheel, which better supports climbing ramps and so forth.

[Ether]

Originally Posted by GeeTwo

Chaining or belting each pair of wheels with the same center lines automatically distributes the necessary extra torque to the wheel which you're accelerating away from.

It automatically distributes the extra torque to the wheel with greater traction, once the one with lesser traction reaches its traction limit. Which wheel has greater traction depends on magnitude and direction of acceleration, location of center of mass, and wheel tread material (if wheels are not indentical).

[trumpthero786]

Here is a video of us testing our 8+1 wheel H-Drive. We later scrapped it for a different set of wheels altogether, but this was our first time strafing with it. Yup. Nine wheels.

https://www.youtube.com/watch?v=2rAjU9ncg8w

[Karthik]

Originally Posted by asid61

4 omni wheels in a regular 4-wheel drive configuration, and 1 omni wheel in the center of the robot perpendicular to the other wheels in a simple form.

See:

You can find full CAD files and a Bill of Materials for an entirely COTS H-Drive here:

http://www.vexrobotics.com/vexpro/examples-guides

[cbale2000]

It's probably worth noting that to make an effective H-Drive you really need to have the center wheel on some kind of suspension otherwise its very hard to get traction.
We found that out the hard way this year (our first time building an H-Drive), even after dropping the center wheel 1/16" we still only had enough traction to strafe about 75% of the time.

[logank013]

Originally Posted by cbale2000

It's probably worth noting that to make an effective H-Drive you really need to have the center wheel on some kind of suspension otherwise its very hard to get traction.
We found that out the hard way this year (our first time building an H-Drive), even after dropping the center wheel 1/16" we still only had enough traction to strafe about 75% of the time.

I don't know much about this drive train but, I'm assuming it isn't a good drive to have in games like Ariel Assist because in that game, drives needed a good amount of traction? Thanks. Just wondering.

[BenGuy]

Hello, I'm from 3641, we did a different kind of H-Drive. Our system was called a deca drive, this consists of 2 CIMs driving a center gear in the middle of a seesaw type system with two small omni wheels on the ends, connected by gears to the center gear being driven by the CIMs. When power is applied either way, the system throws that side down into the ground (just from the motor's torque) and spins the omni wheel at the same time. If we switch the direction of the motors, the seesaw simply tilts to the other side. When the system is not being used, the seesaw balances even with the bottom of our robot, allowing us to easily go over the scoring platforms. This deca drive worked very well for us in Recycle Rush, and thanks to our four main drive wheels being omnis as well, we were very maneuverable.

Pictures of ours are attached, and a video of robowranglers with a similar system is right here: https://youtu.be/oRwvQ2D_B-c?t=34s

[BenGuy]

Originally Posted by cbale2000

It's probably worth noting that to make an effective H-Drive you really need to have the center wheel on some kind of suspension otherwise its very hard to get traction.
We found that out the hard way this year (our first time building an H-Drive), even after dropping the center wheel 1/16" we still only had enough traction to strafe about 75% of the time.

Our system, which I explain in my last post, was able to move up and down as far as it needed to get enough pressure to move the robot, whether we were on carpet or foam or solid concrete.

[GeeTwo]

Originally Posted by BenGuy

Hello, I'm from 3641, we did a different kind of H-Drive. Our system was called a deca drive, this consists of 2 CIMs driving a center gear in the middle of a seesaw type system with two small omni wheels on the ends, connected by gears to the center gear being driven by the CIMs. When power is applied either way, the system throws that side down into the ground (just from the motor's torque) and spins the omni wheel at the same time. If we switch the direction of the motors, the seesaw simply tilts to the other side. When the system is not being used, the seesaw balances even with the bottom of our robot, allowing us to easily go over the scoring platforms. This deca drive worked very well for us in Recycle Rush, and thanks to our four main drive wheels being omnis as well, we were very maneuverable.

Pictures of ours are attached, and a video of robowranglers with a similar system is right here: https://youtu.be/oRwvQ2D_B-c?t=34s

Thanks for the renderings! I like that the swing is clutched to the cluster axle, which causes the wheel on the side that you're accelerating away from to touch the carpet, which should improve traction. I do have a few questions about some of the details:

• Did you have trouble overshooting your strafes? There does not seem to be any way to properly brake in the strafe direction.
• The gearing looks rather fast for strafing in Recycle Rush; counting of gear diameters, I get about 8:1 or 9:1. Did you actually use strafing as a means of travel, or just to line up for pickups and scoring? Unless you needed the top speed, you could have made the output cluster gear smaller, pulled the wheels pulled in to match, and probably done as well with one CIM.
• How do you control the coupling between the seesaw and the cluster shaft, to get the proper wheel loading? Is there a friction clutch between the output cluster gear and the seesaw, or is it just in the bearings, or what?
• Is there a spring, or does the seesaw return to the horizontal when not driven just based on gravity? Given the amount of friction needed in that bearing, the short offset of the CoG from that shaft, and the large moment of inertia of the seesaw, gravity doesn't appear to be enough.

[Zebra_Fact_Man]

Originally Posted by logank013

I don't know much about this drive train but, I'm assuming it isn't a good drive to have in games like Ariel Assist because in that game, drives needed a good amount of traction? Thanks. Just wondering.

Not necessarily; it just depends on how you want to play the game. As you may be able to tell from the pic below, 33 played 2014 with just 4 omnis and did just fine. Didn't even need powered strafe.

They went with the "run from your enemies and be too fast for them to catch you" route.