08-05-2013 11:21 PM

Re: pic: 3CIM Ball Shifter

I love the 3-CIM shifter, but the ratio is terrible. 17 ft/s is a great high gear for 3 CIMs, and 5 ft/s is a great low gear for 3 CIMs, but speeds of 9-12 fps low or high gear don't benefit much from the extra CIM. In order to see a noticeable increase in power/acceleration with the extra CIM, your high gear needs to be pretty high (I'd say 17 ft/s is a good starting point), and your low gear needs to be pretty low (4-5 ft/s is what I'd personally do with 3 CIMs).

tl;dr - the extra CIM isn't going to help unless your high gear is really high, and your low gear is really low.

08-05-2013 11:35 PM

KrazyCarl92

Re: pic: 3CIM Ball Shifter

You could go after a traction limited at 40 Amps per motor Low Gear in the range of 7-9 fps with 3 CIMs, whereas this range is around 4.5-6.5 fps with 2 CIMs per gearbox. However, then you're running the risk of popping the Main Breaker with a 240 Amp traction limit with just your drive train. I would tend to go with a 160 Amp traction limit in low gear on my drive train even with 6 CIMs, just to be sure I won't pop my main breaker in any reasonable sustained pushing match. At least until I would get more experience working with 6 CIMs in drive gearboxes. Because of this preference, the advantage of 6 CIMs in a shifting drive train would be better acceleration at higher speeds, not a faster low gear (even though reasonable arguments could be made for a faster low gear).

I do agree though, I already much dislike the gearing differential between low gear and high gear of the VP ball shifter for 2 CIM gearboxes, and it seems even less attractive for 3 CIM gearboxes.

08-05-2013 11:54 PM

apalrd

Re: pic: 3CIM Ball Shifter

I couldn't disagree more. I think 5 ft/s is a terrible low gear speed.

Think about what your functional objectives are for the drivetrain in general. Set some hard numerical goals. Make sure you include all reasonable aspects, including weight, power input (motor selection or options), and dynamic performance goals. Top speed is actually a terrible metric of drivetrain performance. Acceleration and dynamic performance are huge, especially when driving fast, but actual top speed should not be a functional objective. Most objectives in FRC are time to x, where x is game dependent. We like to use sprint distances, the time it takes to travel x feet from a standstill, where x is dependent on the game. Sometimes there are several x's, depending on the game. 15'-20' long distance analysis is usually good for mostly open field games, while 10' is usually good for short distance pick and place maneuvers, and you can prioritize based on your game strategy.

THEN, start turning those functional objectives into machine attributes, with numbers and analysis to back them up. Do some math, using one of the many spreadsheets available on chief delphi if needed, to see what the minimum hardware possible to achieve your functional objectives is. Can you meet all of your dynamic goals with a single speed gearbox for your motor input? Good. The fun stops here then. You should then use hard test data, usually by building it and testing it fully weighted, to see if your correct.

As you get better at this, and design, build, and test more drivetrains, you will get much better at setting the functional objectives correctly to start. I also suggest you benchmark other robots and teams, to see what kind of performance they can get with what power input they have, to set your functional objectives.

IF you decide you can't meet your functional objectives with a single speed gearbox, then you can evaluate a multispeed gearbox. Since it's easiest to start with COTS, you can evaluate what ratio spreads you can get from the commercial suppliers. AM sells 4:1 and 2.56:1 spread, while Vex sells 2.2:1 spread, but it's possible to make something different by changing the mating gears. With the dog shifter, you also have to be careful your gears don't crash into the dog.

The ratio spread is the most important attribute about a shifting gearbox. Modifying the final drive ratio (final chain or gear reduction) is super easy given the vast assortment of COTS 20dp spur gears, but the shifted gears are much harder to change. Initially, do your analysis with a COTS shift spread and modify the final drive ratios to get your desired performance in either or both gears (depending on what your desired performance is).

You will find that some of your performance metrics are easier to meet in low gear, and some are easier to meet in high gear, and some aren't that great in either gear. This is where, if possible, you would ideally like to optimize the shift ratio spread to put your two gears where they best meet your targets. This is also where you learn the importance of setting your functional objectives properly, and simulating properly. All of this comes with experience, which I don't expect you to have yet, but you can start from the vast knowledge of the Chief Delphi community.


My ideal vehicle speeds (useful for comparison, not terribly useful for analysis) of a 6-CIM 2 speed drivetrain are around 8.5 and 15 fps for low and high respectively (90% eff speeds), based on several years of simulation, test data, model improvement, and more simulation. But I don't have enough data for 6-CIM drivetrains, I need to build, instrument, and test one to see how I like it, and improve the model accordingly to design the next one.

Is your functional objective to be traction-limited at 40a/motor (240a for the entire gearbox, note) in low gear? Are you actually going to push a solid wall and hope the main breaker (120a) doesn't trip?

@krazycarl92, IMHO the simulation and data I have suggests a lower ratio spread is better, and that the VP ball shifter has too much spread. It's all about what you really want, and really need, and how you want to use your gears.

08-06-2013 12:24 AM

Re: pic: 3CIM Ball Shifter

The point wasn't that for any regular old shifter you need a super high gear and a super low gear. It was that by adding another CIM motor to each side, you don't see any major benefit until upwards towards 16-17+ ft/s, and any speed below 5-6 ft/s. I got this information from JVN's acceleration calculator. You can see by testing multiple ratios that between the speeds of 8 ft/s and 12 ft/s there is almost no noticeable difference in acceleration at all between 4 and 6 CIM drives (even between 13-15 ft/s the change isn't large enough to be too noticeable, though it is mathematically larger than the change found in the 8-12 ft/s range). This "magic window" holds some of the most favored speeds in FRC unfortunately, which is why I suggested a really low gear and a really high gear to fully take advantage of the extra CIMs. If the shifter was a 4-CIM, then 10 ft/s is a wonderful low speed since you're getting everything you can out of your motors.

08-06-2013 12:45 AM

apalrd

Re: pic: 3CIM Ball Shifter

Why do you want a really low low gear? What objectives does it achieve?

Why do you want a really high high gear? What objectives does it achieve?

I don't really care if you optimize the benefit of adding the extra motors, the goal should be to optimize the system as a whole.

There are a lot of variables that you aren't likely seeing. Not limited to electrical system resistance, battery current capacity, motor heating/thermal performance, and the acceleration/current profiles which are all important differences between 4 and 6 motor drives. I can't say for certain how important they are, since I don't have data proving most of it one way or another, but I have lots of subjective and theoretical suggestions.

I am well aware that 6 motors is a marginal performance gain theoretically. The limiting factor moves from the motors to other things somewhere between 4 and 6 CIMs, which is why you don't see much improvement.

08-06-2013 02:20 AM

donkehote

Re: pic: 3CIM Ball Shifter

I think the 6 cim drive systems should incorporate amp clamp style amp meters feeding info back to the crio. Used to trim the victor output to keep the amp draw on the main breaker below a threshold (dont know what would be safe but you get the idea) therefore allowing non traction limited drive. when in a push fight, you may get close to the amp limit, and doing this kind of monitoring of the overall amp draw could save you popping the main breaker, and going inop for the match.

I know those amp clamps are quite cheap, like less than $60, however, using induced voltage on a small gauge wire rapped around the battery lead might provide a similar kind of overload sensor.

08-06-2013 03:29 AM

bardd

Re: pic: 3CIM Ball Shifter

Did you make sure the plates will hold up? It looks like the top CIM's mount will bend back the first time the robot get hit from the side. I think you should run a stress analysis before continuing your work. Other than that I really like your design! Looks very streamline. Do you intend to build it or are you designing just for fun?

08-06-2013 09:50 AM

KrazyCarl92

Re: pic: 3CIM Ball Shifter

I fully agree that whatever drive train and gearing is chosen, it should be chosen as a solution to a set of functional objectives. Ideally these objectives are based on proper strategy, physical analysis, and experience. (This sounds an awful lot like engineering)

The two main functional objectives I would aim to achieve with most games and a 6 CIM gearbox are (over simplification):
-Traction Limited at 160 Amps Total for the drive train (best met in Low Gear)
-Time to travel a particular distance, based on strategy (best met in High Gear)

Usually the time to travel reasonable distances in FRC is optimized by gearing which corresponds to a top speed somewhere between 13-18 fps, accounting for voltage drop and inefficiency. This doesn't change terribly much between 4 and 6 CIMs. Our functional objectives and corresponding gearing seems to agree here.

Now looking at our other objective, we have to do some math to figure out what gearing we want. I arrive at the 160 Amp total current draw at the traction limit because 40 amps per motor has been used as a low gear standard by many teams for many years on 4 CIM drive trains largely without issue. Then last year, we hear about many 6 CIM drives tripping the main breaker. To be sure that our robot won't trip the main breaker, it would be nice to design it such that it won't, which we can achieve with proper gearing. These claims are also supported by the main breaker spec sheet. A properly functioning breaker will be at risk for tripping after 10 seconds at 240 Amps, whereas it will go for over half of the match at 160 Amps. This is also neglecting any other sources of current draw on the robot.
To do that math, we will need some assumptions:
-145 pounds for battery + bumpers + robot
-6 CIMs in drive train
-4 inch wheels
-CoF=1.2
-Efficiency = 80%

Our gearbox will need to be designed to overcome a tractive force of 174 pounds. If I want this traction limit to occur at 160 amps of total current draw, that will require that the drive train achieve this traction limit at 26.7 amps per motor. Based on motor curves, this corresponds to 63.2 oz. in. of torque output from each motor. This is equal to 3.95 in. lbs. Which means that the drive train as a whole will input 23.7 in. lbs. before taking efficiency into account.

Our desired output torque is 348 in. lbs. This leads to a gearing of 16.5:1, using the square root of 0.8 to account for efficiency (making the best guess assumption that efficiency losses apply evenly to speed and torque).

This gearing corresponds to a top speed of 4.8 fps using a speed derating of 85%. (5.6 fps theoretical)

This shows that a low gear speed of 5 fps for a 6 CIM drive train is perfectly reasonable given this particular design objective.

The gearing spreads for a gearbox to complete both functional objectives I mention would be between 2.6:1 at the lower speed end and 3.6:1 at the higher speed end.

Commenting on another person's experience because they speak of drive train specs in terms of top speed is undue. By that logic, teams like Simbotics and The Cheesy Poofs who have published on their website their robots' top speeds in each gear would really be in need of experience. This actually shows a wealth of experience because it takes tremendous experience to be able to look at a design, hear a number in fps, and then immediately know what this means for the performance of the drive system. Based on a number in fps or gear ratios, I can look at a teams robot design and understand what the implications are for their drive performance. If something seems off or unreasonable about gearing decisions, I will ask a team about their thought process. At this point, I usually learn something new or realize the team doesn't know what they're doing. It is the industry standard to speak in terms of top speed; we wouldn't answer the question "What's the top speed of your robot?" with "We travel 10 feet from a dead stop in 0.95 seconds."

08-06-2013 10:07 AM

apalrd

Re: pic: 3CIM Ball Shifter

I agree that top speed is useful for comparison and benchmarking. OP also said it was his first gearbox design, so my experience comments are justified. We don't design around top speed, but we talk about it a lot when we compare gear ratios quickly. But for analysis, we switch back to our accel times, accel curves, and stuff.


The question really is if one of your functional objectives is traction limited push current.

We no longer use that as our metric for low gear. We design low gear to meet a lot of the short game dynamics objectives, and we're getting better at quantifying current. We spend a lot of time in high gear high current scenarios, so any way we can reduce those (high gear launches and zero-point turns especially) by improving low gear performance (and actually using it for short game driving) is a huge improvement to us in overall electrical draw.

08-06-2013 10:59 AM

Chris is me

Re: pic: 3CIM Ball Shifter

While this discussion has quickly gone on a tangent, I do have a question: Other than lowering current draw for pushing situations, what's the point of a low gear? Unless you're traveling quite fast, your acceleration won't be notably better. For short distances it seems a low gear would be helpful, but because the distances traveled are so short, you're not saving that much time anyway.

I guess what I'm wondering is when someone would want to use a 7-9 FPS low gear with a 14-16 FPS high gear. It seems like to me the only situation where low gear would be more useful than high gear for those speeds would be when you have to push or make really fine adjustments, and both of those are accomplished well with a ~5.5 FPS, 40A traction limited low gear.

I don't have any experience here; I've only ever worked with single speeds, so I'd like to learn.

08-06-2013 11:14 AM

AdamHeard

Re: pic: 3CIM Ball Shifter

We use our low gear in more of a West Coast Style. It seems like 254/968 (when I was growing up) rarely used their low gear, even for short distances. It was moreso for the few times you were forced to push through defense.

We use it in the same way, and then also use it for thins like balancing on the bridge last year.

For how our drivers operate, I view low gear as insurance that lets you gear as fast as you desire for other objectives, but still have a drive mode where you won't get destroyed by defense (tripping breakers, etc...)

Because of this, we love a real slow low gear.

08-06-2013 12:02 PM

Aren_Hill

Re: pic: 3CIM Ball Shifter

Quick bit of advice, it is probably good form (on both the ball shifter and dog gear setups), to put your third reduction after the shifting shaft.

This method can be seen on the Ball Shifter with optional 3rd stage, and the AndyMark Sonic/Super Shifters.

This lowers the overall torque being transferred by the shifting components, which results in less chance of failure and lower required shifting forces.
See this thread for once instance of failure: http://www.chiefdelphi.com/forums/sh...ght=20+carnage

Doing this would also allow you to make your gearbox overall shorter as you can offset the last output shaft in whichever direction you like.

08-06-2013 12:13 PM

apalrd

Re: pic: 3CIM Ball Shifter

Our driving theory around low (this was not always the case, but several of us on 33 have converged on this point independently) is that accelerating from a standstil is better in low gear, usually to around 60-80% of the low gear speed, than in high gear. So any time where we never reach peak speed in low, it's faster to drive in low. These are marginal gains in time. BUT, since high gear is in the 'bad side' of the motor power curve for the entire time (with 2:1 or more spread), the current draw from high gear will be WAY higher than in low. For the same or worse dynamic performance. This becomes MUCH worse on a dieing battery, which can frequently be seen near the end of a match.

We've sometimes run auto-upshift software to automate this, it begins the shift around 60% of low gear speed, but the shift takes time to execute under load (not sure exactly what speed it's at by the time the dog disengages).

We also run auton in low gear usually, for precision/control reasons, so a slightly high low gear is good for this. But we could run in high, we just don't, so it's not a huge objective.


I guess this differs from the 'west coast' opinion that 'high gear is where we operate, and low gear is just in case we need to push'. We operate in both gears.

08-06-2013 12:15 PM

AdamHeard

Re: pic: 3CIM Ball Shifter

I don't disagree with your points at all, I like the level of automation you've built in.

I don't know that anyone has run a decent autoshift out here.

I can certainly appreciate the lesser current draw, a dirty secret of some teams out here is we buy a new set of batteries every year, and if we didn't we'd like show worse performance on the field.

Part of this is we practice A LOT, so we use the last 1-2 seasons of batteries for practice to keep the new seasons worth nice.

08-06-2013 12:19 PM

Lil' Lavery

Re: pic: 3CIM Ball Shifter

I have another question. Why bother with a 6-CIM, 2-speed drivetrain at all? It seems like a lot of resources to invest in only marginal gains over either a 4-CIM, 2-speed or 6-CIM single speed.

08-06-2013 01:13 PM

Andrew Schreiber

Re: pic: 3CIM Ball Shifter

33 Ran an autoshift in '04 with their 4 speed. The the whitepaper is http://www.chiefdelphi.com/media/papers/1580 but it doesn't go into much detail on the shift algorithm. I'm sure Jim has/would describe it somewhere.

08-06-2013 01:21 PM

Karthik

Re: pic: 3CIM Ball Shifter

Something very important that also needs to be considered is what is the opportunity cost of those two extra CIMs. The concept of opportunity cost is invaluable in making effective strategic designs decisions, especially when it comes to resource allocation.

Here's a Kahn Academy lesson that does a great job of explaining opportunity cost. A bit more detailed than is needed for these purposes, especially in terms of the PPF, but hey at worst you're going to learn some extra stuff.

https://www.khanacademy.org/science/...?v=pkEiHZAtoro

08-06-2013 02:20 PM

AdamHeard

Re: pic: 3CIM Ball Shifter

They're not out here

08-06-2013 02:30 PM

Cory

Re: pic: 3CIM Ball Shifter

For us it came down to the fact that we wanted to utilize our drive motors to hang (we set our initial goal at less than 10s) and we also wanted to maintain the responsiveness and acceleration of our 2011 robot, except 30 lbs heavier. To do that we needed the extra CIMs.

08-06-2013 02:35 PM

Gregor

Re: pic: 3CIM Ball Shifter

PTO's are an entire different ballgame, and negate some (most?) of the issues Karthik was trying to bring to light with looking at the opportunity cost.

08-06-2013 03:12 PM

Ian Curtis

Re: pic: 3CIM Ball Shifter

These are design philosophy issues. Sometimes your design philosophy leaves every day performance on the table. Airplanes could be a lot lighter (and more efficient) if they weren't good for a very very very very bad day.

Something else I think is important for many teams to consider is that there is a driver in the loop. Even if your slow gear is Killer Bees fast, if you're driver isn't up to snuff you will spend lots of time monkeying around when you could have been scoring. I still think one of the best things FIRST could do to improve game play is make the default speed of the kitbot slower. You see lots of operators that really just don't have the practice to be efficient at top speed.

08-06-2013 04:14 PM

apalrd

Re: pic: 3CIM Ball Shifter

Our 11 code has the full implementation of it (for a 2-speed), but the code is a bit messy and I would implement it differently now. It's drivetrain/autotrans.vi. Upshift was enabled (and the driver feedback was all good), both downshifts were disabled due to driver feedback (Specifically he would rely on coasting into the peg with a tube, and the coast down would throw off his maneuvering as he was slowing down). Better calibration could have likely improved this.

The logic is fairly simple. We do three types of shifts:
Upshifts
Coast down shifts
Kick down shifts

Acceleration should be multiplied by the sign of velocity (or the abs of velocity should be used to calculate acceleration) to normalize for changes in direction.

Upshifts are based on thresholds for speed (greater than), abs of avg of throttles (for skid steer - this is pre-halo and culver drives) (greater than), vehicle acceleration (greater than), abs of diff of throttles (less than) (not turning)

Coast down shifts are based on absolute low speed (~2fps).

Kick downs are based on speed (we used 8 fps, which is higher than redline in low) (less than), abs of avg of throttles (greater than), not turning, vehicle acceleration negative and less than calibration (large negative number).

Upshift handles normal upshift driving.
Coast down shifts back when the vehicle speed is close to zero so it can upshift again at he next launch.
Kick down shifts down when you hit something and need to push.

This algorithm worked well enough for FRC. The corner cases (when turning) are simply ignored by the autoshifter, which was 'good enough'. We also impose a minimum time between shifts to prevent gear hunting, most automatic shift implementations see this and our solution is a 500ms inhibit timer.

08-06-2013 04:25 PM

magnets

Re: pic: 3CIM Ball Shifter

How did you stop kick down shifting from happening when you ran into stuff? I tried a similar thing, but it would wear the shifting dogs out pretty quickly when we would hit something that couldn't be pushed.

08-06-2013 05:00 PM

Tom Ore

Re: pic: 3CIM Ball Shifter

To generalize what Aren is saying, always try to put your mechanical advantage as close to where you need it as possible. (That is, pass the big forces or big torques through as few components as possible.)

08-06-2013 09:08 PM

MichaelBick

Re: pic: 3CIM Ball Shifter

I agree that 6 CIMs are overkill if you aren't using a PTO. 4 CIMs + 2 550s seems like a good compromise and additionally makes it harder to blow the main breaker(our 6 motor drive was geared for 19.2 FPS @ 100% efficiency and never blew the main breaker). I agree with karthik though: if you can't find an easy way to add the extra motors, it isn't really worth the effort of completely repackaging the gearbox.

08-06-2013 10:16 PM

DampRobot

Re: pic: 3CIM Ball Shifter

Agreed. Maybe this is just a west coast perspective, but in my mind a slow gear gives you the ability to have a super fast top speed (15+ fps as some west coast teams like to have). A low gear is only used when you're in a pushing match, or positioning accurately such as in autonomous, which isn't all that often. I personally don't see much point at having a low gear being lower than traction limited, which is about 6fps for a 4 CIM drive.

Part of this may (and I'm speaking with a complete lack of emperical evidence here) be because of a slight efficiency advantage of WCDs over "east coast drives." Most non-WCDs I've seen have more places where power can be lost (gears, more chain reductions, 35 chain vs 25 chain, etc). West coast drives have as little as two reductions down to a wheel, and typically have either 25 chain or belts to transmit power to outside wheels. Non-WCDs on the other hand are usually based off AM shifters, which require at least three reductions for the power to release the wheels to reach the wheels. Perhaps this small added efficiency lets west coast accelerate slightly more quickly in high gear.

I know I just threw out a bunch of stuff which I really can't prove and don't 100% believe is true, stuff that I would usually not post. But, given the apparent difference between east coast and west coast perspectives here, I wanted to propose a theory that might explain some of the differences.

In terms of 6 CIM vs 4 CIM drives, I'd say 6 CIMs is nice but not really necessary. You'll accelerate better, be faster and more powerful, but there are real drawbacks. One is current draw, which detracts from other mechanisms and can trip the main breaker. The other, as Karthik pointed out, is that it takes away from your ability to have CIMs power other mechanisms.

08-07-2013 09:20 AM

apalrd

Re: pic: 3CIM Ball Shifter

The whole purpose of the kick down case is to shift when you hit stuff.

The dog is a fairly robust part, have you actually worn one (of the AM stainless dogs) out?

08-07-2013 09:29 AM

magnets

Re: pic: 3CIM Ball Shifter

Yup. We managed to break one in half with our auto shifting code several years ago. We had made our own transmission with two CIMs + another motor that was based off of the AM shifting transmission. The problem was that when our driver would hit the walls in the room we were testing, it would shift into the slower gear violently. Now that I think back to it, the problem probably occurred because we were testing with a large diameter cylinder because our little ones didn't arrive yet, so we increased the pressure to 120 psi to get a faster response when we shifted.

08-15-2013 03:13 PM

evanperryg

Re: pic: 3CIM Ball Shifter

The problem with having such an insanely high gear is that the robot will be very hard to control. Another issue with such a huge difference in gearing is momentum. This year, my team used AM supershifters at 5/12fps. If we we were in high gear then switched to low at full speed, we would tip over 75-80% of the time. Imagine how bad it would be going between 17 and 5.

I'm pretty sure 111 did a 3-speed this year. Also, how could 4 speeds possibly be beneficial, even as an autoshift?

08-15-2013 03:22 PM

Andrew Schreiber

Re: pic: 3CIM Ball Shifter

Back then we had a lot less power, to get reasonable acceleration and still have a high top speed was hard.

08-15-2013 03:32 PM

Lil' Lavery

Re: pic: 3CIM Ball Shifter

Their initial design goal was 3(+) speeds, but the method they chose allowed for 4 speeds just as easy as 3. Essentially, each shifting mechanism they incorporated doubled the potential ratios. One mechanism would be two speeds, two mechanisms allows for four potential speeds. If they added a third, it would be 8 speeds. Rather than try to explain it in greater detail myself, I'll simply use the wonderful resource they posted on the gearbox (with nice pictures that explain it better than any amount of paragraphs ever could).
http://www.chiefdelphi.com/media/papers/1580

08-15-2013 03:36 PM

AlecMataloni

Re: pic: 3CIM Ball Shifter

We used the COTS two-speed ball shifters from Vex this year. Nothing too fancy.

08-15-2013 03:42 PM

apalrd

Re: pic: 3CIM Ball Shifter

We didn't want a 4 speed, we wanted a 3 speed. We wanted a fast and very fast gear, like our current design goals for high and low, but we had less power, so we needed a low low for pushing (remember this is back before bumpers) and couldn't get away with the fast-low we like now.

But, with the resources we had, it was easier to build a 4 speed than a 3 speed (since we end up with 2 2-speeds in series). The shift patterns are then low/low,low/high,high/low,high/high, with a different ratio spread of each of the 2-speeds in series. But the 2-3 shift (going from low/high to high/low) requires a double-swap shift which is just plain nasty to execute synchronously between two shifters while under power. A possible solution is to run it like a 3-speed with two options for 2nd gear, and essentially jump-shift past the 2-3 shift. This would add complexity to the shift scheduler, although more than 2 speeds already adds complexity to our shift scheduler.

A ball shifter design can do any number of speeds just by adding more gear pairs to the shafts, so it's possible to do a 3-speed instead of a 4-speed, but it's much harder to manufacture than the dual 2-speed with andymark parts or dual 2-speed mesh shifter design (or even the dual 2-speed ball shifter).

So 4 speeds was easier to build, but the 2-3 shift is bad.

08-15-2013 03:54 PM

Lil' Lavery

Re: pic: 3CIM Ball Shifter

For reference, 222 has been running a 3-speed ball shifter since 2004.

http://www.chiefdelphi.com/media/papers/1539

08-15-2013 03:56 PM

Andrew Schreiber

Re: pic: 3CIM Ball Shifter

I thought they'd gone to just running 2 speeds as of late?

08-16-2013 12:55 PM

camtunkpa

Re: pic: 3CIM Ball Shifter

This is correct. We only ran 3 speeds in 2004. We didn't find the added complexity and weight to be worth the added gear ratio.

2013 was the first season since 2004 that we haven't made our own transmissions. This season we went with the vexpro ball shifter and will likely use them again in the future FWIW.