FRC3880 - The Tiki Techs - 2015 Drivetrain and Transmission Prototype.
Current setup: 4x2 Colson in the center set and 4x1.5 Colson on the outer set of wheels. This hex frame with the motors over the tires and chain in tube allows potentially a free center area of over 16.5"_x_28" to work with. Depending on battery orientation and electronics there is ample space potentially available for just about any tool ideas.
The custom transmission plates will allow use of any of the WCP dog gear and pinion sets allowing drive speed customization to suit the new game dynamics. A well as allowing motor and encoder orientation on either side. (separate post)
More to come! Looking forward to an exciting season!
The only way I could see using 4 separate gearboxes (assuming you want all those motors) is if they were fully COTS. If you are making your own plates you might as well optimize it.
Also, if that frame outside the wheels is not supporting the axles you could replace it with standoffs between the wheels (to comply with bumper rules) and move the drive rails out almost an inch on each side.
I’m with you on this. With a smaller footprint the last 2 years, you could acquire more space to work with inside the drive rails area. Because our drive base is modulated using standoffs and plates, we were able to run our chain inside to add even more space AND have the access to the chain, sprockets, etc.
I like the hexagon shape. I’m assuming its to “help” get out of T-bone situations, if necessary?
Not so sure what I think about the 8-motor, 4-gearbox setup. Looks really heavy - what benefits are there, specifically, over a two-gearbox 6-CIM setup? Keep in mind that you’ll also need more air and more tubing and more failure modes to shift with this gearbox arrangement.
But we still didn’t like the bumpers. We used 2 “C” shaped bumpers and was strong but was not to our liking. The idea is to have a one piece bumper drop over and lock on.
Yes this hex frame was done with “Tbone” in mind. Though last year with the 6 cim 2 speed low gear layout we had not many issues with that. Though it should help with getting pinched against a wall…
This is an off season project to try out some odd ideas thought up. The transmissions were done separately so that they can be used in other areas beside just drive.
We like the idea of putting the motor weight over the main drive wheels with the battery centered. Even though this looks like less space it has more internal space than last years robot. The outer frame is 2x1 while the drive tubes are 1.5x3". Gives a great exterior edge for LED ground effects… FRC Swag!
We were so underweight last year… Was strange to have to add weight, so we were not concerned with that on this prototype.
The idea is to have the electronics tray nested with the pneumatic shifters and run a plate above all of that level with the top of the frame for a clean deck almost the entire size of the robot. We will have the battery and electronics orientated flat at that time. The vertical battery was added to check the COG. which at the moment is centered on the robot at 4" off the ground.
Not knowing the game this platform leaves a lot to play with.
Of course as soon as the game is released all will change.
If desired I can put up some other views of the drive. There are some newer revisions done and can put up some of those pictures if desired.
My hex drivetrain is about 28 lbs. How much does this weigh? It looks overkill heavy, and a lot of your custom solutions seem to be poorly thought out. Could you detail your thought process behind the major details of the design?
The idea is to have two driven axels… and a bit more power with added traction of 8 wheels
We are currently working on a single transmission plate that has two driven axels. We are waiting on our CNC to arrive that will allow us to make the larger more complicated plates. These current plates are done by hand on our small lathe / mill. That is the biggest reason they were separated. That and there was thinking of being able to run front and rear at different speeds. No clue personally why, maybe climbing? Sometime we build off ideas just to do so.
Current weight without the battery is 25lbs including electronics shown.
This is our first attempt at a hex frame. Most of this design was based on what materials we have or can get locally. Being in Hawaii, shipping stock material to prototype with is very expensive, so we have to be creative with what is on hand and available. There is nothing here but Lowes and Home Depot. No real machine shops or metal vendors or the like here.
Being a 4th year team we always enjoy learning different ideas, constructively…
The drivetrain is set up as a WCD with the outer wheels offset (1/8" above the center).
We never had any scrubbing issues with our 6 wheel WCD. The center wheels are 7" apart and should not see much scrubbing. We do have some Omni wheels for the front/rear if tests proves it to be an issue.
Just working on crazy ideas, never know what it could accomplish…
I use the term “poorly thought out” very loosely. It’s just part of the vocabulary. What I mean to say is I can’t tell your train of thought in this design, and there are many design choices I question because I do not understand the reasoning behind them (hence why I asked about your thought process behind it).
What I see when looking at this frame immediately is the large quantity of gearboxes, and the large quantity of CIM motors. I understand earlier you said you made the decision of the 8 motors for the sake of “more power”, but doing the math on my end shows marginal improvements in usefulness that do not seem worth the extra weight nor the risk of blowing the breaker. So I’m wondering what was the in-depth reasoning behind your choices for 8 motors, as well as the initial reasoning for 4 different gearboxes (I know you said you’re planning on a new gearbox, but I’m curious about why you thought 4 different ones was the best solution initially).
Also, your frame layout with the 2x1 making the hex on the sides makes me question if you will be able to take your wheels off. For a true WCD the ability to easily remove your wheels is invaluable at times, and it appears like you’re sacrificing this ability to shape your frame in this method. Out of all the ways to make a hex shape, why did you choose this one?
Speaking of framing, your 2x1 appears to be 1/8" thick - the more common style for a WCD - so with all of your tubing non-lightened, 8 motors, 4 gearboxes, and colson wheels, I really have a hard time believing that this drive system even without the electronics is 25 lbs. You have almost 20 lbs solely in drive motors, let alone solid 2x1x1/8 aluminum tubing and 4 large gearboxes, and then the added electronics makes it impossible for me to believe this is 25 lbs.
Your constructive iteration is the key to success - I just try to restrain from constructive criticism until I understand the thought process behind the design, so that I can better focus my advice towards the design and the designers.
Oh, I didn’t realize there was a drop. I faintly remember team 118 having to use different sized wheels because they could not enough space in the tube to have a big enough drop with the sprockets and chain. Did you have a solution to that problem or did everything seem to fit inside the tube just fine?
If you could consolidate your gearboxes into two 3 cim gearboxes, you could save a ton of weight and motors. I don’t see the point in adding the power above 6 cims, unless you’re planning on hitting 20 fps+ with 0.01s less time(not really math, just an order of magnitude calculation).
As others have pointed out, there isn’t much reason to go with 8 motors over 6, or even 4.
But even if you insist on 8, or at least having the option to mount more motors, you can still save a considerable amount of weight and improve performance by combining 4 on a side into a single transmission, with two output shafts. You can still do so with the WCP DS components.
Duplicating the shifting mechanism on both sides adds quite a bit of weight and cost and means that shifting may not be synchronized. Separating powertrains between front and back means that you could lose half your power if you’re wedged or tipped up on your back four wheels. And there’s more friction and inertia with all those stages.
Also, mounting the encoder on the input cluster like you’ve shown will introduce quite a bit more backlash between the encoder and your wheels, and will require knowledge of the precise shift state to schedule gains properly. Combining everything into one gearbox should give you some options to keep the encoder on the gearbox if you need to, while putting it much closer to the wheel, preferably downstream from the shift mechanism.
Apparently, hex/octagonal, chain-in-tube, CIM-over-center-wheel WCD is the new fad in DT Design.
Don’t miss the forest for the trees here people.
This is coming from a team that rocked an octo-WCD in 2014.
Consider performing a honest and thorough weighted design table to determine if some of the innovations you are proposing actually outweigh the costs.
I would encourage all teams to practice this evaluation method in the pre-season. Just like there is no better time to learn CAD and DT Design, there’s no better time to learn how to objectively evaluate designs based off a set list of requirements/criteria (trust me, this is no easy task. It is arguably harder than actually designing the mechanism!)
Beyond big-picture, love the effort being put forward. Winners are made in the off-season!
I detect a serious lack of power and weight in this drivetrain. Far too little power, you’ll get pushed all over the place, and not nearly enough material, your robot will float away in a light breeze. I would also certainly increase your gear count, you can never have enough reductions, efficiency can be dangerous. Additional gears certainly help your weight situation too, 4 individual gearboxes certainly capitalizes on this.
He says in the previous image that EACH gearbox weighs 15lb. Something is very wrong somewhere with weights in this CAD model as the WCP 3 CIM shifter this looks similar to would weigh 8.5lb with 1 CIM and 1 MiniCIM. I suppose the 15lb could be referring to each SIDE of the drive, ie. 2 of these put together, that gives a much more reasonable number. Still thats 30lb in just gearboxes, so, going under the stretch assumption that 25lb is this drive WITHOUT gearboxes thats a 55lb drive, which sounds much more reasonable.
All of that is a moot point though because OP has stated that the only reasons that there are 2 gearboxes per side is because they don’t currently have the ability to make large enough plates to combine them, and that they want to be able to use the gearboxes elsewhere when the project is done.
A side note to that, MOE has had some success making plates that are larger than the travel distance of our mill by splitting the drawing into 2 parts with 1 shared hole. The shared hole is used to align the second drawing to the plate. You will also need 2 flat reference sides. This may not be possible in your situation and it may not be accurate enough for gear spacing but it worked well for chain.