Quite astounding, great work. I particularly like the chain route. Any reason why 3 of the chain idlers are sprockets and 2 are just rollers? Why not make all 5 rollers (making the general assumption that the rollers are lighter)? What thickness are the walls? What thickness are the walls of the channel on the cross-supports?
Also is there any way to reverse the direction of the CIM mounts to move the wires to the inside of the robot?
Outstanding work though. Looks like a well-designed drive base.
Well, originally it was one idler (on the tensioner) because It was easier to cantilever the tensioner and that worked better with an idler. Now that I think, We could’ve put a roller on the shoulder bolt just as easy. The idler below the transmission was just added because I forgot to check to see if the chain clears the shifters (doh). So, it was easier just to use an idler on hand.
Wall thickness on the 3/8" plate is 1/16". Same as what 687 and us ran last year. The tubing is 1/8" wall.
We could of reversed the CIMs (and still can, you can see the mounting holes for them [well, actually its for a AM planetary, but a CIM fits too] on the rear transmission), but we didn’t want to cantilever them with the plastic plates. We also like the space it saves on the inside of the robot. The wires will be routed, tied down nicely, and covered to prevent any robot from entangling with them. You may not be able to tell from the picture, but they are about 2" from the edge of the robot.
Thanks for the feedback, it’s all ways appreciated.
it looks really good, the machining is obviously top notch. I am wondering if you have put any thought into the amount of chain wrap on a sprocket? best rule of thumb is that you need at least 120 degrees wrap on each sprocket, I have a feeling that the center wheel is just about at 120 degrees. If you have the option have you considered moving the idler on the bottom left towards the center wheel which will increase the wrap on the center while keeping your left wheel with plenty.
looks really nice, those plates must have taken forever to machine out like that, do you have a total weight for the drive train, and just the plates? i’m also wondering how well the transmissions hold up out of that material
I want to echo Greg’s chain wrap comment, that center sprocket makes me nervous.
Also your front and rear standoffs (plates) dowl pinned together? I never would have thought of doing it that way. I probably would have just used counter sunk #8’s. Just curious as to why you did it that way.
This looks good, I like the 1 chain loop idea you’ll know if running it that way works pretty quickly to. The gearboxes look great as well I am going to recommend you keep a close eye on them though with the plastic plates even though I know it’s a proven design. Has there been any problems with the chasis plates trying to shift back and fourth? Also I’d like to hear the answer for the question Sean asked about the rollers. I think it is excellent man good luck with this design with some testing and tweaking it should do well.
Yes, I am a little concerned about the chain wrap. It is pretty close to 120 degrees, and it is a prototype (294 cover your ears; I also didn’t want to fix everything that might be a issue because I wanted the new kids to work with the more experienced ones to fix it and learn. But also, a lot of the mistakes were me legitimately messing up ) so I left it to see how it turns out.
Kind of funny story about the pins. One of the mentors that was advising told me to add a bunch of pins rather than bolts… So, once the design had a 5" tall plate one each side, I decided, why not just put a bunch of pins? It’s not going to hurt, and If the base is run without bumpers those corners will be taking lot of shear on impacts.
EDIT: techtiger; what do you mean about chassis plate shifting back and forth? Do you mean the left and right modules, or the inner and outer plate of each module. On the 2007 base which had very similar framing, neither was an issue. The entire frame was very, very stiff.
EDIT2: spazdemon548, sorry I missed you. I’m not sure what you mean by clockwork spacers; but, for the gearbox standoffs, and all the other spacers standoffs we bought a whole bunch of spacers from mcmaster for cheap. We bought two different outer diameters, and the inner undersized (so we can just chuck it in a lathe and open it to what we want real fast) and in a whole bunch of lengths from 1/32" to 1". In the past I had them make some really funky spacers; now they can get almost any spacing with off the shelf parts. FYI, borisdamole can testify to the painful amount of spacers I had cut .
Also, the wheel drop is either 3/16" or .2. I don’t remember which but they’re pretty close. That’s about what we ran all year with our adjustable height.
M Krass; Allways look forward to your input. I don’t have the CAD with me, so I can’t pull a weight from that. I know some of the components off the top of my head though; each panel ~ 3, each wheel ~ .4. We’re weighing the finished assembly this weekend for some real world data.
It is pretty easy to adjust the tension on the chain, just turn the thumb screws. So, it should be done every match. Hopefully it can’t loosen enough in one match to cause the failure.
Hmmmm. the 3/8" plate is just what we’ve been using since the original design (this is the 3rd iteration). The machining time isn’t that bad because it can be run while they’re simultaneously cutting on the manual machines. I guess 1/4" would save a lot of time, but would it be worth the strength loss? Weight isn’t a big issue, each panel is only 3 lbs right now. But now you’ve got me curious, I’ll look into 1/4" and see how it will compare in weight, strength and the amount of material removed.
Once again, thanks to everyone for all the input. Really, your opinions mean a lot.
It seems such a shame to hide such nice wheels behind a big ol’ plate, but the design seems sound. I think that if you’re diligent about checking your chain tension, since it appears the tensioning idlers aren’t spring-loaded, you won’t have to worry too much about the chain wrap on the center sprocket. If the chain gets slack, though, the excess is going to gather up at the bottom and come off that sprocket.
Almost purely for aesthetic reasons, I’d try to lower the idlers along the top and bring the chain down inside the panels.
Why are you starting with 3/8" plate and pulling so much material out of it instead of say, using 1/4" – so they’re still thick enough for bearings – and saving yourself some machining time?
I was referring to the 1/2 dia spacers separating your two 3/8" plates. I’m pretty sure there called clockwork spacers, but I might be wrong. We’ve used them at 548 for a couple years now and we love them. Here’s last years robot with them:
I agree with replacing the rollers with idler sprockets it would be much more efficient. The noise is the chain lobes bumping over the rollers. Noise like that means inefficient.
I’m guessing from the picture that it’s #35 chain?
What size wheels are you running they look about 4"?
What shifting method are you using. Two dog shifters, a ball shifter, or what?
What speeds (FPS) are you estimating from the different gear ratios?
I have to ask do you really need four gears? I mean you don’t have a huge amount of traction so having a really torquey gear ratio could mean that you don’t have enough traction to actually realize that troque and your wheels would just slip out. And how fast do you really need to go the field is only 50 something feet long so 12-15 FPS means so can get across the field pretty quick. Don’t get me wrong a four speed transmission is really cool and I respect the engineering and the maching that goes into the effort.
I would also be interested in the total weight of the system and the weight of the transmissions assembly.
I think those wheels are the same as they used last year, which would be about 6" (also, the sideplates are listed as 5" and aren’t that much smaller than the wheel).And they do have a lot of traction; they’ve lost tread playing defense with that blue material. And a four-speed of this type would be easier to design and build than a three-speed.
I’m kind of concerned about some things you are saying…
I’m not sure how we don’t have a “huge” amount of traction. The coefficient of friction of that tread was measured to be 1.1-1.2. If we wanted to max it out we could go for natural rubber that 254/968 used this year and get about 1.3. I’m not sure how this isn’t the maximum amount of traction teams have been able to get. Tank treads have been experimentally shown to only get a minimal increase (about 3% according to Andy Baker and testing he did with 45), if any (according to most. Paul Copioli will probably fight to the death on this one) at all.
Wheels are 6" btw, and yes #35 chain.
In terms of the transmission, it is an iteration of team 33’s 4 speed; which is two crash shifters in a row. This Drivetrain is designed around the AndyMark Gen 3’s (or a slightly modified 3 motor AndyMark single speed). We wanted to do something fun and different for for prototype though, and it didn’t hurt that the material for the 4-speed was significantly less than the cost of two Gen 3’s. Also, we figured the 4 speeds would give a better spread of gear ratios to show in person for prototyping next season (I think most people on the team who aren’t into drivetrains would benefit from seeing 6fps vs 9fps vs 12 vs 16 [those aren’t the actual speeds, just arbitrary numbers]).
I believe we are traction limited in the bottom two gears, and the speeds depend on the size of the output sprocket on the transmission. I think they have a 10 T on there. I have the excel at home with all the speeds (I’m going home tomorrow, and will post then). Even though the lowest gear is way past traction limited, that isn’t necessarily a bad thing; it will allow for amazingly precise alignment and will be able to hold position better while drawing less current. I’m referring to a PID loop that will hold the robot’s heading (even stationary, I think the triplets did that amazingly in 2006) very accurately.
EDIT: EricH; thanks for referencing that. The wheels are very similar to last year, just bit wider now. We were losing tread because we had two bolts side by side that almost cut the tread and have, so it was very easy to tear off. We fixed it before champs by changing it to single bolts like in the picture. Haven’t lost a tread since. Too bad you won’t be seeing it at San Diego again :(… but there is allways LA! (although, I’d much rather see 294 on the field with 330 than against… I think 294 would have a better chance of winning that match with you instead of against)
Close up shots will be posted this weekend by me (or sooner if borisdamole hears the request and goes to his livingroom).
It’s almost identical to last year’s. Pretty much it’s just a block that sits in a piece of tubing. Screws pull the black away from the chain to tension, and there is a shoulder bolt in the block that the idler sits on. It was inspired by our drive in 2005/2006 where we used pillow blocks that were tensioned that way (same way the west coast drive has been tensioned sometimes… like 968 in '06. In fact, we originally got the idea from 60).
The axles are 3/8" 7075 hex we already had laying around. Just threaded one end 3/8-16. We considered bolts, but we wanted this base to be as light as possible.