Okay. Let me just start her. I’m a coach for a newer team 5547. the last 2 years we have used the rhino tracks with much success. Stronghold they worked awesome. steamworks they worked great for pushing bot out of the way trying to play defense on us. the down fall to the tracks is they are slow. Last year we ran 2 Cim single speed gear boxes and our bot ran at about 8 fps. Our team members want to use tracks again as kind of a tradition, but they want more speed from the bot. they have discussed using 2 or 3 stage shifting gear boxes. I have done some research and if we were to attempt this feat we would most likely go with the vex pro 2 cim ball shifter. 1. they are not super expensive. 2. they have good reviews. 3. if needed we can add a 3rd stage if staling is an issue. the other coach and i have agreed to give it a shot but we are both really new to this idea. I’ve tried using the vex calculator with little success, well because they don’t have a track selection for the wheel size. this may only be a preseason experiment, but we are going to try it out. So basically i’m looking for any tips or insight. Suggestions to what gearing may be suitable. Thank you
Basics about or bot is:
rhino trax tank treads
2 cim gear boxes
bot weight is 80 lbs.
I don’t think I’m ever going to use aluminum gears in a drivetrain ever again. I’d rather drill out steel gears to save some weight and not have my teeth get chewed up by the end of a single competition.
To use the Vex calculator, JVN spreadsheet, or any other similar tool with a treaded drive, use the size of your driven pulley as the wheel size. Treads themselves are not inherently slower than wheeled drives. The math behind gear reductions and travel speed is the same for both. The only significant differences you may experience is the amount of “scrub” you have to overcome to turn, which may lead to higher current draws when turning (which, in turn, may suggest using more reduction than you would need in some variants of a wheeled drive).
Also of note, you can still match the top speeds of other robots without turning to a 2-speed shifter, just by adjusting the gear ratio you used in your single-speed gearbox.
Not really sure what that has to do with the OP’s questions. While the OP is considering using a VexPro gearbox that uses aluminum gears, the jump here is rather large. And your gripes about aluminum gears seem ill-founded, given the positive experience with them that hundreds of teams around FRC have. 1712 has been using aluminum gears in our drivetrain since 2013 (with 40+ matches each year), and the only issue we’ve experienced was in Stronghold when we had too much reduction for the 14t gears we were using (sheared teeth, not tooth wear).
What are you using to lubricate your gears? Are you re-applying that lubricant at any point? What are you doing to shield your gearboxes from carpet debris?
The implication is, “were I looking to do what you’re looking to do, I’d look at replacing the aluminum gears with lightened steel gears.” I think that’s pretty obvious. He is not required to take (and you are not required to agree with) that advice.
I’ve spoken to quite a few teams who had similar issues to ours; they might not be as vocal about it, but they’re definitely out there.
A. The recommended grease.
B. Yes.
C. Solid covers.
We’ve always built rock-solid, robust, excellent drivetrains. Excepting last year’s attempt at swerve (which I advised against), the only issues we’ve ever had–ever–are with aluminum gears. Swapping aluminum for steel (using withholding allowance between events) solved those problems completely.
If the OP ignores my advice and is happy with the choice and it works well for them, awesome. If he takes my advice and is happy with the choice and it works well for them, awesome. If he ignores OR takes my advice and is unhappy and it doesn’t work well for them, call it a learning experience.
You have great test data stored on you driver station. The DS stores current voltage trends for every match. You can look at those logs to see if you have any headroom to increase the speed. (If you are already close to browning out, higher gearing will not be helpful.) It might be worth re gearing your single speed gear box to see how the higher speed works.
Your tracked robot will never be as fast as the wheeled robots. One of the trade offs of high traction tracks is more friction losses and more torque require to turn the robot…
There is definitely something missing here. Quite a few teams run aluminum gears without any issue at all.
Are you running custom gearboxes? or a COTS one?
My first guess assuming custom is you’re machining tolerances put your gear C-C in an unhappy range. If you’re using COTS, there is some error in one of the three answers above.
Common misconception. Yes, there are more losses. But there have been some FAST tracked bots around. (Well, back then they were fast. Nowadays I’m not so sure.)
You may need to adjust the efficiency numbers in the JVN spreadsheet down from the 80-85% range towards 75%, but you can get a tracked robot up to the speed of a wheeled robot. Just bear in mind that that will likely come at a cost elsewhere.
Single-speed isn’t bad, per se. But making sure you can run at the speed the game requires is a whole 'nother animal. And the speed the game requires varies: Stronghold was slow-ish (not a lot of room to get up to speed before catching air), Steamworks was on the faster side. There are “fast” games (typically open-field type) and “slow” games (field is crowded and/or has chokepoints). If you adjust your desired speed to the game you’re playing, you’ll do much better than if you say “I’m going to mix a gearbox and wheels like this” and do it the same every year.
We built our own tracks for most of the off-season, we made the mistake of trying to use 6 cims and push(big mistake). When we dropped down from 6 cims to 4 cims all of our problems were gone, in fact we won our first ever event as the captains of our alliance. We had it geared to go 4.5fps in low and 17fps in high with a lot of traction. Our drive wheel was the VEXpro 6" traction wheel and from the gear box to the wheel we ran a 12t to a 24t with no 3rd stage. This was our 2016 off season bot, the only real difference was what we used for sprockets.
1086’s 2016 robot used treads and vex shifters and it worked pretty well. We didn’t notice the treads being any slower than the 6wd we did in the past. The Linatex treads from brecoflex we used had a ton of grip so the drive was very responsive. The only down side was it took a fair amount of maintenance reattaching the backing, but the extra grip was worth it.
COTS 3-CIM dog shifter from Vexpro with polycarbonate side-shields to prevent debris from getting inside; extended output shaft supported on both sides (so it’s not cantilevered) positioned in laser-cut sheet metal to minimize any lateral loads on the output axle.
The aluminum gears shredded over the course of quals (on one side) and started to wear on the other through the tournament at TVR–finally gave up the ghost in the semi-finals; we replaced the gears with steel and had no problems through FLR + all summer demos + an off-season competition.
Can you provide pictures of the set-up and “shredded” gears? What ratios? Which gears within the gearbox were the culprits?
It doesn’t surprise me that 4140 steel gears would survive a scenario that 7075 aluminum gears wouldn’t, but what does still concern me is the rapid wear on your aluminum gears.
I assume by “COTS 3-CIM dog shifter from Vexpro” you actually mean the West Coast Products dual-speed gearbox. If so, did you ensure your pinion gears were in the right half of the “snowman” hole for your CIM motors when mounting them? If a 13 of 14 tooth pinion was being used on the “inboard” half of the snowman hole (or shifted there during competition), it wouldn’t surprise me to see increased wear on the 42t spur gear.
I hear you. We have a stack of 6 of these bald 50t aluminum gears from the first stage of our vex 3cim ball shifters (Not the same wear as yours, but still). It’s happened on each of our robots from 2016 and 2017, the latter of which were carefully assembled and lubricated. We won’t be using aluminum gears again in 2018 if I can help it.
By the way, why don’t you look at the EVO shifter from AndyMark? The Rhino tracks already have a mounting pattern that fits the EVO. It’s almost certainly your best option here.
It’s interesting that the idler gear is the one that got eaten, rather than a gear in the output stage that sees more torque.
We had one failure that looked similar to this on our drivetrain from last year, where the idler gear wore out in a similar way. The cause was one of the motors being knocked out of alignment. Apparently we hit a CIM on something and actually bent the front mounting plate of the motor, putting the rotor out of alignment with the gearbox. Whatever the impact was cracked a chunk out of the plastic gearbox as well. We never noticed until the idler gear started to wear and we noticed it was driving funny.
All of our other aluminum drive gears have all survived, but we only use two CIMs per gearbox. We’ll likely use similar drivetrain setups in the future.
