Okay I was thinking about using a four wheel omni drive next year and was wondering what kind of transmissions other people have used, I know that we get two tough-boxes in the kit and was going to use these and the ones from this year
I have seen other teams with dewalts and banebot transmissions but i wanted something easier and more reliable(which is always better)
i could always do something else but i like the manueverability of omni drives verses having the power of a conventional drive since we had trouble turning this year and we were really slow also our am-two speeds broke and we were stuck in low gear
First I’m pretty sure you don’t KNOW whats in the kit, they may go back to giving you a bunch of gears and saying make it yourself.
Banebots is about as simple as it gets, however the reliability is debatable.
There are other simple single speed transmissions that will be right about as easy, you have to define all of the points that you want a gearbox to have, then identify the gearing needed and how well each system that you find will work for that. kit gearboxes will also be very simple to utilize.
Well there’s a few point to consider. You want a four-wheel omni drive. What kind of four wheel omni drive?
Are you referring to a true omnidirectional drive (strafing ability) or simply a tank-drive with omniwheels?
If you’re looking at a tank-drive with omniwheels, I advise against it. You’ll get shoved sideways very easily and a well thought-out tank drive with regular wheels can turn just as well. In short, the advantages just aren’t there.
If you’re looking at a true omni drive, please elaborate. Crab? Omni wheels? Mecanums?
As for the kit, only time will tell. However, you can plan based on the Andymark boxes, and if they aren’t in the kit, either adapt or buy some.
Last year, my team (1293, D5robotics) used the 8" mecanum wheels from AM along with 4 BB transmissions, one for each CIM. Mechanically the bot worked fine last year, but we had some very very strange coding issues with the accellerometer that caused the robot to be highly uncontrollable at Palmetto.
We had no issues with the single CIM banebot planetary transmissions, we found them to be delightful (moreso than the dual CIM BB gearboxes, which shattered on us at Palmetto in 07, but that could be attributed to the fact that they were in the front of the bot, unprotected, and took a direct hit as we plowed into another bot at full speed)
The “white” chassis is made from UHMW, a nice and flexible plastic but very strong. We took a 1 1/4" (I think) sheet of it and water jetted the chassis from it. It offered a kind of makeshift suspension system that is vital with mecanum drives. It kept all the wheels on the ground since it was able to flex and absorb the vibrations caused by the wheels. The chassis UHMW costs 200 dollars for a slab that large.
i thinking 4 omni wheels at 45 degrees and i was assuming the toughboxes will come in the kit again seeing as how they worked great
well mecanums are 330 dollars so that kinda limits them there
and for some reason we have always had a problem with weight and being slow i dont know why? but UHMV wouldent that be likley to kinda bend and twist ad stuff and not be signifigently better than the kitbot chassis
last year 1714 used an omni drive. We used the Andymark tough boxes without a problem. I would also recomend using the molded plastic omni wheel. We tried to use the coolie dualie wheels at first, but they would bend.
If you’re looking to build that sort of omni drive, I see no reason your plan (4 tough boxes, 4 CIMs) won’t work. Be careful to:
a) Do the math on the speed/torque this combination will yield (searching CD will get you lots of help with this, and many in this thread can assist).
b) Take into account that some of your speed/torque will be lost to wheel scrub (the wheels will be driving against each other as well as forward/backward). I’m sure someone here knows more about this than I do.
I’d say your first step is to define your goals. Speed? Pushing power? Terrain ability? (this type of DT works best only on flat ground)
From there, work back to your desired gear ratio. See if the toughboxes are within your needs. If they aren’t, you can modify them pretty easily by swapping out a stage or two, or adding a stage after the gearbox. You could also design and manufacture your own boxes, but I gather you don’t have the resources for this.
If you are not directly driving the wheels with the gearbox output shaft, 1-2 stackerboxes and a chain reduction seems to be a very light and compact option. You could probably direct drive from a stackerbox, but I would modify them to replace the output shaft with a 1/2".
the stacker boxes look great but but those are more for arms and stuff right?
we do have the tools and machine to make our own but we would have to purchase gears and deal with shipping and its just a pain and would probobly not as reliable
i would have gone with the plastic molded omnis anyways because they are the cheapest
and i was planning on making my final decision after the kickoff to see what terrain is involved something tells me it will be flat and require lots of movement again
A gearbox is a gearbox; A toughbox is just two sets of the gears in the stackerbox (different bores/shafts… same ratios) in a larger package with the ability to mount two motors. If you don’t need to mount two, as is the case, I’d say the stackerbox is a much better option as it is much lighter and more compact.
so its got a 3-57-1 ratio and with two that would be very fast and the toughboxes are 12-75-1 so it would be faster(tourqe is not a concern since its omni wheels)
and they are cheaper than the toughboxes and the two from this year have been dismantled and pieces lost!
Two would yield a ratio of 12.75:1, just like the toughboxes (both are made up of 14:50 reductions).
Torque/speed is still very much a concern. If you gear it too high, accelerating will take forever and low speed movements will be hard to control.
I have never built an omni-wheeled drivetrain, but I imagine directly driving off of two stackerboxes two 6" omni wheels would yield a decently fast drive, probably around 9 fps (assuming that at free speed, it’d be just shy of 11 fps).
oh i must have missed that day in math class:confused:
so your saying that two stackers is just like one toughbox in that case it should be around 12fps depending on how much wheel slip there is
and i was under the impression that if you have it geared high it would have less torque(therefore less wheel slipping) but a higher final speed or am i backwards? or is it like this because there omni wheels?
Higher torque=faster acceleration, more power at low speeds, easier turning(this last point is less of a concern with omnis)
Higher speed=higher top speed
Since most FIRST bots don’t have much room to move or much time to accelerate, a top speed over about 11ft/sec is usually excessive.
Wheel slipping has to do with how “sticky” your wheels are. If you have more torque than your wheels’ “stickiness” can transfer to the floor, and then your wheels will slip. Though lower torque reduces the risk of slipping, it also reduces maneuverability, pushing power, etc. I don’t know much about the AM omni wheels, but an omni wheel should be designed to be very “sticky”. (Regular wheels must slide sideways to turn, omnis don’t.) Perhaps someone could enlighten us as to the sliding characteristics of the AM omni wheels.
I’m sorry, I misquoted the price, the actual price of a slab of that size is 200. Here is the mcmaster-carr product number for the sheet we got.
8752K518
Sorry for the confusion.
Also back on topic, we originally went with the 45° omni design in cad, but decided to go with the mecanums. Here is the inventor render of the omniwheel bot. Also, if you have access to a waterjet (or even if you don’t) you can try and setup a way to get those mecanums cheaper. We contacted AM and just got the sideplates for 180 dollars, and we fabricated our own rollers from brass tubing bought off of mcmaster and sheets of rubber which we then jetted out the rollers from. It ended up saving us about 100 dollars for the set overall.
I think the debate on the BB transmissions has been settled… in favour of Banebots.
Comments on the BB transmission reliability comes from the initial batch of gearboxes that were shipped in the KOP two years ago. Through an effort between teams, FIRST and Banebots the reliability issue was identified as an insufficiently hardened final stage carrier plate. Banebots took responsbility for the problem and issued every FRC team replacement, properly hardened, carrier plates, and then took additional steps to toughen their gearboxes.
As far as I know, teams using the new carrier plates and/or new transmissions have had no issues with the BB transmissions.
The BB transmissions are ideal for omni-drive drivetrains as they are extremely easy to use in direct drive (as opposed to chain drive) applications. You just put the wheel on the output shaft, saving all the weight of the chain and sprockets, as well as the potential failure of having the chain come off. In my experience, the upgraded Banebots make for the most reliable drive system out there… and we’ve got a mecanum drive with four of the 12:1 gearboxes on board with two regionals and several demonstrations behind them to back it up with.
Bane bots are keyed. we used them on our mecanum bot this last seasons with the 8" andy mark mecanum wheels. Honestly engineering the actual drive train was a piece of cake. We made a cad file of where we needed to drill holes in a sheet of 1/4" aluminum and then printed it out and drilled it in our smithy(drill press mode). The real troublesome part mecanum or holonomic drive is the programming. you need a way to keep your bot going straight. If you look on TBA our bot didnt fair well at the NASA VCU regional but we eventually got the kinks worked out in our programming and got the thing to drive reasonably straight. Dont worry so much about the calculations, those are easy, worry about programming, that is very hard and takes a long time to test. On average, teams that i have talked to take about a year to develop a good mecanum/holonomic code, so plan for this to be a rocky season
well we have plenty of help this year with programming including our new mentors Chas(former student now at college programming king) and Lexi(from g&t conveyors)
