Team 4265 The Secret City Wildbots is proud to present our off-season drive train that we are calling Dragonfly. It is a custom machined octanum drive using Vex Pro 6" mecanums, and 4"x2" Colsons, with 4 vex pro ball shifters.
Specs include:
21ft/s High gear.
10ft/s Low gear.
4 Cims + 4 Mini Cims = 6.66 Cims worth of power.
In low gear it puts out 94 foot pounds of torque.
fully loaded it weighs in at about 80lbs.
According to FIRST Regulation, we are happy, and proud to release our design include CAD and Software under the GPL for any and all to use.
As cool as it is, 80 pounds? That only leaves you with 40 pounds for all of your manipulators. I don’t see the point in any drive train being that heavy (at least you’ll have a low center of gravity). I would love to see this used in a competition but you’re going to have a tough time with that weight limit.
There’s a bunch of weight that can be dropped in terms of motors/gearboxes, if needed, that I already mentioned to Tag and his team. Plus, there are now smaller mecanum wheels available which weren’t revealed when this was being designed. That could help reduce the reductions needed as well.
In our current working version, It weighs 80lbs. in the release design, we have cut back a little bit in order to save weight. We are also looking into using alternative materials.
This is really, really well done, good job. All of these octocanums popping up is really making me rethink my dislike of mecanum wheels.
I think you’re over thinking that 80 pound weight. If you look closely, they have a total of (8) CIM Motors going through (4) Ball shifters. All of those components together (Cim motor @2.8lbs ea, Ball Shifter @2.5lbs ea) weigh just under 35lbs. I also wouldn’t be surprised if the battery is included in that 80lb figure too.
Just for reference, if this drive were only running (4) CIM Motors, each through their own Vexpro Single Speed, it’d be ~16lbs lighter, and that’s not counting all of the other components that could be removed when the motor count drops from (8) to (4). (Speed controllers, wiring, etc)
No that weight is without battery. We just reweighed, and it comes in at 78.6lbs. Also like I said we have modified the design to lighten the metal chassis frame to about 10lbs.
This is pretty cool. One thing you need to look at on saturday is if the game calls for a extra high speed/high performance drivetrain. I can only name a few games where it would be worth such a high performance drive (2008 comes to mind). If not I would try to get it to around 40-50 lbs with electronics so you have weight for your scoring system. Also does anyone have any experience with that many motors on the drive since I would think you would pop your main breaker pretty quick.
Another random question, was that a DJI Phantom in the robot video?
That weight is with the entire system save for the manipulator, including all electricals and pneumatics. As far as the number of motors, we have been running it alot, and we haven’t had any trouble with current draw.
Have you considered using a single air cylinder on each side with a linkage to move the drive mechanisms up and down? If properly designed you could potentially use a single smaller, lighter, cylinder on each side.
That’s a pretty serious drive base! I guess the offseason is the perfect time to max out a drive train for a team that has that itch.
You’ve listed just two speeds. Is the gearing from the 6" to 4" wheels setup to keep the two types of wheels at the same speed? If not, then you really have a four speed drive.
In my mind, one of the benefits of octocanum is that you don’t need shifters. It’s already providing the benefits of a two speed if you gear the Colson wheels slower than the mecanums.
That is also what 1279 found in 2011(Logo Motion) with a reduction to the traction wheels, and 4 Cims+4 775s, our drivetrain had tremendous pushing power. ‘Low gear’ was traction wheels down, high speed was on mecanums.
We also hinged on the traction wheels like you did, for strength, but put the traction wheels at the extreme front and rear for better stance when pushing. With the 8 motors and gear reduction, we had no problem turning on carpeting, even with conveyor traction belting on wheels.
Very nice Cad work and machining. Is the cylinder mount a cast part or machined?
the way that it is geared, the traction and mecanums are 1:1. but if you factor in the efficiency loss with the mecanums, the slightly larger radius makes that up, making the speeds of both modes about equal. The advantage shifters give, is that we have all the pushing power in low, but in high we can still go 21 ft/s in traction.
You might want to export it as a .step instead of providing the raw file. STEP files tend to import better into Creo/ProE and Inventor, as they aren’t a proprietary format.
Very cool modelling though. I like the combination of sheet metal (?) and tube parts.
