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grassHopper Hybrid Drive System by: gotgreen
A simplified hybrid “H” drive provides convertible pushing power. This solution offers a very lightweight option to teams in the FIRST Community with limited machining capability.
Thanks to Team 33 and 148 for providing the inspiration for this simplified drive system. We have competed in our first regional successfully using this drive and would like to give back to the FIRST community similar to these generous teams. This platform can be used by teams with limited machining capability to dramatically increase the level of competitiveness.
I am having issues wrapping my head around the hybrid shifter mechanism and the elastic tension, do you have a video of the mechanism shifting by any chance?
Apologies that it was not clear. The shifting bearing block is loose on the frame and has to be tensioned. Theraband is connected to the top of the shift plate where the pneumatic cylinder is attached and tensioned to the frame vertically. This seats the bearing block lower lip into the frame when the wheels are up. Also, when pivoting the blocks the chain is loose when up and tight when lowered. Ideally the pivot point should be moved out to reduce this issue. A small piece of theraband can be connected to the bottom of the block and tensioned to the frame. We are not using this. We just attached a small tensioner and it is working fine. The drivetrain complete w/o electronics is right around 30 pounds. I will double check the wieght when back at the build site.
I must admit a certain level of annoyance with this publication… we are working on a drivetrain almost identical to this one in function and theory that we thought was novel. We being Team 95, The Grasshoppers.
Your drawings show one lift plate and bearing block on each of the articulated axles but the photos show two. Did you find that the forces on the axle cause the two lift plates to “twist” relative to each other?
Yes! That was the inspiration. It was an experiment our drivetrain mentor had in mind in the pre-season of 2014, but we just didn’t have the time to try it out. He was confident that it would be successful, so we went ahead and tried it out during the build season as the drivetrain for our robot, and the results were amazing, we had all the benefits of a standard butterfly/nonadrive without any of the complexity - this was made with all COTS parts including VersaChassis and without any CAD, CNC, or anything like that - pretty much just a band saw and drill press. Our offseason changes made it much more efficient as well, and many people noticed a significant increase in agility going into competitions in the summer.
Game permitting, we’re definitely looking into using it again!
No, we didn’t experience any noticeable torque on the plates. The system we used in the offseason held up through three full-size competitions (TRI, IRI, TRR, soon to be four with Remix) all with significant amounts of defense. We always had the ability to push others around when we wanted to and were able to break free from other teams attempting to pin us.
If by pitchy, you mean likelihood of falling over face first during sudden acceleration/braking - we came very close to tipping ourselves over, but it never actually happened (before someone brings it up, the one time we were tipped over was due to another robot intruding our perimeter and pushing us over from the side). I attribute this to our somewhat top heavy design (relative to other robots, our catapult’s pivot point was much higher than others’) and the short wheelbase of our 8-wheel square drivetrain. Nothing that wouldn’t happen with a standard 8-wheel drive.
