Are two speed transmissions worth it?
 

After numerous discussions with team members and doing a bit of research I'm still wondering are two speed transmissions worth the money, weight, time, etc... I am speaking more along the lines of the AM gen 2 shifters not a custom one off application. It seems that in most cases it depends on stratagies but in a overall statement are they worth it?

A few people on my team believe that there is no point to having them. I always say to them that we've always had robots in the mid speed range ~7-8 fps and I'd love to have two speeds somewhere around 5 fps in low and 10 fps in high. It seems that we always try to tell our alliance partners yeah we are offensive primarily but we can play defense but it always seems to be that we never have the required power to push other robots out of the way. Not saying that we need super pushing power or light speed but I would love know that I have a little extra power and a little extra speed.

Also are my speeds a bit off? Would the speeds that come out of the transmission be higher or lower with normal gearing (KOP gears)? And what experiences have you had with your teams transmissions? My GMP (Grand Master Plan) is some kind of six wheel or eight wheel drive (like 1270) with IFI high traction wheels. Any advice on 6 or 8 wheel two speed drive trains would be greatly appriciated

-Dustin

Re: Are two speed transmissions worth it?
 

Two great examples of efficient use of a 2-speed shifter this year are 968/254 (custom) and 330 (AM).

Both had a low speed around 5-6 fps and a high of 15-16 fps.

It may seem unnecessary, but I have a great perspective on these drive trains as I have played defense on 330 in about 5-6 matches (including 3 in finals) and in their shop on their practice bot. I also played defense on 968/254 in at least 4 matches.

Their low speed gave didn't allow me to out push them, and their high meant that they could easily break away. All of these teams used this advantage very well.

For reference, we had a single speed at 10 fps with a small CIM, big CIM and FP that was traction limited.



I would recommend the AndyMark.biz shifters for getting started. They take all the work out of it, and even 254/968 are planning on using the guts of them next year. My team is currently doing a prototype of the previously mentioned base with them integrated.

Overall, shifters can be very useful if you have the weight. You will never get a group to agree on this though, as it is a hot issue.

Re: Are two speed transmissions worth it?
 

The value of shifters varies directly depending on your driver. If your drive uses them a lot to their advantage (take 254 for example), then yes, they are worth it. If your drive almost never uses it, then no, it's not worth it at all. However, if you plan to train your drive to take advantage of, or otherwise build your drive around the robot, then yeah, I think they're totally worth it.

Re: Are two speed transmissions worth it?
 

Teams should analyze the game each year before they make a decision on the transmission or other parts of the robot. There are years in which two speeds are optimum and other years single speed is best. The same can be said for treads, crab drive, multi-wheel or omni-wheels, large diameter or small diameter, aritculated arms, etc. In a defensive game, low speed pushers may be best. In a game where a robot must travel a distance often than high speed might be best. In a year where you might climb a ramp, a high speed only box may not work. There is no hard and fast rule on this decision. Analyze, brain storm and play the game with miniatures or team members playing the robot parts. Use your technology wisely.

Re: Are two speed transmissions worth it?
 

If they work, then yes. We had 3 speed this year, and The bottom one, (2.6 fps) was the only way we could score with heavy defense (Yeah, you 48 :))

But before we perfected them, That thing on our control board wasn't a shifter at all... It was a "Get stuck between gears and Lose the match" lever.

Re: Are two speed transmissions worth it?
 

Something I'm curious to investigate is some sort of current-based shifting "algorithm." Have the drive default to a reasonable high gear (9-10 fps), then shift to low whenever the current draw grows beyond a certain value for a certain period of time. Then shift back to high when the current draw falls below a certain value for a certain length of time. Then have a manual override of some sort. Pretty much, the system only shifts to low to push.

Re: Are two speed transmissions worth it?
 

I thought they were very useful this year. I shifted about 6 times in a match and especially when defense was getting played on us, I thought it came in handy.

Re: Are two speed transmissions worth it?
 

You could do this with encoders.

If the measured speed of the robot is significantly less than what it should be, it must be hitting something and then it shifts down. If the robot is in low and going 95-100% speed, then it isn't hitting anything and will shift back up.

I made a vex robot with that exact functionality.

Re: Are two speed transmissions worth it?
 

Yep. I knew about this option, but measuring current draw appeals to me more. It seems as though it would be "simpler" to get a definitive answer as to which gear the robot should be in. 1126 and 33 have succesfully done auto-shifting on a 4 speed transmission using the encoder approach.

Re: Are two speed transmissions worth it?
 

I am the only one to have voted "no" so far...

We used our 2 speed AM shifters 1 out of every 2 matches this year. They helped us dart across the field, but we never used them for an extended period of time.

I'll admit they weren't useless... but they weren't worth the weight of the pneumatics.

If you're going to use pneumatics anyways I would say "go ahead." But otherwise save the weight and put it where it counts - in the scoring device.

Re: Are two speed transmissions worth it?
 

Like has been said above it really depends on the game. Also it depends on how well your team can make them. If you cannot shift and get stuck between gears you will only hurt yourselves so if you are thinking about doing it, make some prototypes in the offseason see if you can pull it off.

For shifting maybe I'm old fashioned but I would prefer a manual selection of gears to give the driver exactly what they need/want.

Re: Are two speed transmissions worth it?
 

Yeah but there are shifting device that does not require pneumatics thought. Forgot what they are called but they run on electricity and weights like nothing.

Re: Are two speed transmissions worth it?
 

servos.

I love transmissions and like the 4 speed auto's better then anything else. They give you the speed and pushing power you need and a mix in the middle to not lose power.

Re: Are two speed transmissions worth it?
 

Are you thinking of solenoids? Also I have seen teams use servos to power the shift mechanisms.

curses other Alex beat me to it

Re: Are two speed transmissions worth it?
 

Yeah, that's it.

Re: Are two speed transmissions worth it?
 

The pneumatics are not a problem we always use them.

Re: Are two speed transmissions worth it?
 

We got two speed working pretty well in 2005 and 2006 with no technical problems, but the drivers got so caught up in the match that they would forget to switch gears and got pushed around. I guess it's fine when your drivers have had enough practice though ;)

But yea, besides the question of whether your drivers will use it, a nice 5-15 two speed is really worth the extra work.

Re: Are two speed transmissions worth it?
 

Yes. According to everything these people have said i would pretty much say they are worth. And apparently if i dont say that they are i cant work on the robot next year. And that makes me sad =(

Re: Are two speed transmissions worth it?
 

We bought AndyMark.biz dogs, and the smaller dog gear from them. We would have never been able to manufacture a dog like it ourselves. We had few to no problems this year shifting. We manufactured our own second dog gear, but not having to manufacture both was a life saver.

Re: Are two speed transmissions worth it?
 

I tried to do that this year. More to enhance our pushing power (ie prevent spinning out) than to shift gears but that was the next step. Never had time to collect data and get it working, though.

Re: Are two speed transmissions worth it?
 

This year we used a 6WD with 8" Roughtop AM Performance Wheels and the AM servo shifter (2 speed) with a pair of the little CIMS into each. We also had a 10:24 out to the wheels which gave us theoretical hi/low speeds of 15.6 fps and 6.10 fps resepectively and more realistic continuous 30 amp speeds of 12.3 fps and 4.8 fps. Calcs were largely done in this spreadsheet by JVN. http://www.chiefdelphi.com/media/papers/1676

Re: Are two speed transmissions worth it?
 

We tried this but found that usually, if we were in 2nd gear and all of the sudden had a current spike, the motors were already close to stalling, or they were pulling so much current they would reset the RC. Well, in either of these cases the DeWalts we used weren't able to shift.
Basically, I'm sure it can be done, but keep in mind that the motors might not be turning when the robot is told to shift, so design your shifter accordingly.

As a driver, I think I liked the control over the system. 1st gear (5 ft/s) is painfully slow in a 2 min match, and getting pushed around is so frustrating you have to downshift.

Re: Are two speed transmissions worth it?
 

We experimented with the allegro current sensors in the off season of '05 and had it working exactly how you said. We integrated it into our '06 bot with AM pnuematic shifters, but it annoyed our driver and so he always used the override mode and manually shifted. Perhaps with more practice a driver could get used to this autoshifting behavior. I say current based autoshifting is a cool thing to look into - make sure to set it's thresholds high enough so that it's not shifting when turning if you use high friction wheels and skid steer.

Re: Are two speed transmissions worth it?
 

<insert standard "it depends on your needs" text here>

1618 used Gen2 AndyMarks this year. The result was about the fastest thing on six wheels at Palmetto, while still enabling us to push as needed. (Sorry, 342.)

I was actually a little surprised to find out that our driver was using them backwards from what I imagined--apparently, the cylinders were rigged to shift to low when the joystick trigger was pressed, instead of the other way around. Acceleration in high gear was still surprisingly good.

I'm not saying anything definite, but they're certainly on the short list for next season.

Re: Are two speed transmissions worth it?
 

We used the 2 speed AM trans mostly to reduce the power consumption in a heavily defensive match. When in low (less then 5fps) we were able to push most teams (6 wheel, roughtop) and still have the available power to use the rest of hte bot. In previous years (1 spd) , a pushing match would use up everything we had. This year, the field could really be viewed as "short" so a 2 spd trans was not as useable as the prevoius year, where you had a clear 50ft run.

Also, before you look the "auto-shift" think about the situations. If you just got into a pushing match, using up 1 or 2 cycles (electric shift) to shift will kill you. High gear is great for getting you close to where you need to be quickly (.5s faster at 1/2 field for example) and low gear makes the bot have finer control (more motor turns per foot) and more power to push.

As far as electric shifting, the servo works but it's slower than pneumatics, there are not currently any solenoids allowed as they are just another form of and electric motor.

Re: Are two speed transmissions worth it?
 

We never use a 2 speed transmission. I personally dont think its worth it, because our robot has always been fast enough for us and strong enough to push many robots. People always ask if we have 2 speed transmissions and are surprised when we say no. Its up to you if you want to try it.

Re: Are two speed transmissions worth it?
 

What about the servo shifters... in all seriousness you can do either (one is not better than the other they both do the same job)

But as to the actual shifting I have a couple questions for you.

have you ever bene in a match and thought to yourself dang i wish i could go faster to get there quicker?

have you ever thought dang i wish i could go a bit slower so i could have a little more pushing power?

I can almost give you 100% certainty that every team has thought that.

The easy answer to your question is yes you should ALWAYS have the option of shifting.

We have used a shifting transmission since 2003 (except for 2006 when we made a custom single speed). After last year I realized you should never do a single speed because throughout last year i was always saying yes to both of those questions.

This year we opted for the 2 speed AM transmission because of a few reasons.

1. Reliable - It has been tested by so many teams in first with very little if any negative effects.
2. Cost - Cheaper to buy the shifter than make it, when you account for the time spent on the CNC machine making the parts and the over all cost of everything put into it. (remember less time spent on one part is more time spent on another or more time for drivers!!!)

Just my 2 cents

Re: Are two speed transmissions worth it?
 

You can only "push" with as much power as it takes to break your wheels loose, so I think proper weight distribution and wheel selection is more important than shifting.

Our team has discussed this topic until we were beating a dead horse, and we have made the decision to look into a 6 motor, single (high) speed drive train. Heck, you don't even need 6 motors.

Re: Are two speed transmissions worth it?
 

Well said, Al. We've used the AM two speed transmissions with pneumatic shifter the past two years and have been very satisfied with their performance and ours. We benefitted from the flexibility of two speeds in both games. I am quite confident that we would not have enjoyed the same success with a compromised single speed.

Re: Are two speed transmissions worth it?
 

Yes! being able to sit and push is very important and people have mention having a high speed gear to break away. Its also important for the defensive bot to have a high gear because i saw in several matches that a team that was ment as a pusher couldn't catch up to the other robot to do what it was designed to. The 2 speed transmition allows you all this flexibility. I think three speeds is a bit overkill however, but if you have the weight...why not.

Re: Are two speed transmissions worth it?
 

The discussion about automatic shifting is interesting.....do any of you know much about automotive automatic transmissions? In the old days before computers, there were two ways that they were designed. One used a vacuum modulator, which essentially measures the load on the engine. This would be analogous to the current detection algorithm. The other used a combination of throttle position and vehicle speed. This would be analgous to the encoder method.

Re: Are two speed transmissions worth it?
 

Which one saw more success? LOL.

Re: Are two speed transmissions worth it?
 

I agree the automatic shifting in terms of current is an interesting topic maybe someone from 33 can come and explain what they used for software and sensors on there four speed. Two speed transmissions have proven to be quite useful for 1251 as we have used them 2 years out of our 4 year existance. Both the games (06-07) had uses for a high and low gear. 06 becuase the field was open and you had to get to places fast and 07 primarly becuase you needed to get to the tubes fast but you needed a low gear to get into position to make the ringer count and hold your ground.

Drew

Re: Are two speed transmissions worth it?
 

Team 33 as well as 1126 has used encoders to determine when to shift and such. Here's a picture showing the eoncoder in red.

Re: Are two speed transmissions worth it?
 

There is no correct answer here.

The game greatly determines if you'll need to shift or not. This year we chose to go with a 6WD single speed, and NO ONE on our team regrets that decision. Our drivetrain was very maneuverable and most of all...agile. We could get from A to B in an instant (or in the case of Finals match 3 of the Boston regional, middle of the field to top of 69 in 3 seconds).

We wanted our robot to score, and concentrate on scoring. If we were going to get in a pushing match, we were going to be wasting our time. We would just go out and if someone was getting in our way, use our agile-ness to "juke" our opponents out.

To shift or not to shift...that is the question.....and i think the best time to answer it is the first saturday in January.

Re: Are two speed transmissions worth it?
 

I say [for our team] most deffinately worth it. We've used 2 speeds as long as I can remember. This year, having two speeds really gives us the option of doing offense or deffense [and we found we are better at defense by a wide margin]. Having one speed is ok, but I prefer having the two; one for more traction and one for speed [IE getting across the field fast] As long as you are good with the shifting, 2 speeds come in VERY handy

Re: Are two speed transmissions worth it?
 

While I wouldnt say more important, I would agree that it is equally important. I think each game effects the consideration for a shifting transmission. This year seemed to be a good year to shift, especially if your drivers use it. Even though we went with an AM shifter and it worked well, I do feel that if we had spent a little more time with weight distribution we wouldnt have gotten pushed around even as much as we did.

-Alex

Re: Are two speed transmissions worth it?
 

Both saw equal success in the market, the vacuum system provided a better shift "feel", the mechanical system cost less to make.

....

as to the need for two speeds....if you choose to go with two speeds, you can have a more versatile robot. 1726 built a scoring robot, but with a strong 2 speed drivetrain, and more than once we changed strategy and played only defense in a match.

Re: Are two speed transmissions worth it?
 

This year our 2 speed transmission was pretty good. In each speed there were some drawbacks, but overall we worked well, and with our chassis and nice AndyMark wheels we were pretty hard to move by defense and we sped along quickly. One thing that helps a lot is pneumatic brakes though.

Re: Are two speed transmissions worth it?
 

I think that it sometimes depends on the game too. If there's a lot of empty field to drive across like last year but still with the need for high torque, a 2 speed transmission was great. This year, there wasn't as big of a need for both a high speed or a low speed, you could go either way and win pushing matches or try to just swerve around the defense altogether. We used 2 speed transmissions for at least the past 2 seasons, and there have been benefits to it both times, especially last year.

Re: Are two speed transmissions worth it?
 

I agree with you and at the same time disagree with you. The last two years, I have witnessed that have a two speed shifter would have been very optimal. This year as well as last, offense and defense were very important parts of the game, and I think that that will remain a consistency in the future games for years to come. Therefore I believe that although you cannot make many major decisions before the game is released, a two speed shifter would be a huge benefit to start researching into because sooner or later you might realize that with two weeks left in the season that you really do need one.

Pavan.

Re: Are two speed transmissions worth it?
 

We used AM G2's and we were very pleased with the performance. We kept them in low most of the time for precise manuevering when scoring and anti-defense (resisting getting pushed while scoring). On the other hand, sometimes we had to get somewhere in a hurry (get a tube, get to a ramp), so we put it in high. Getting up ramps was much easier in low. It's nice to have options:)

If you don't like the weight you could always take the Poof's option! 1.1 lbs per side.

Re: Are two speed transmissions worth it?
 

May have been said but you dont need 6 wheel drive.
this year we used 4 wheel drive, but we had six, and offsetted the center wheel down. We noticed that on the 05 and 06 bots the front hardly ever hit the ground

Re: Are two speed transmissions worth it?
 

Sorry a correction must be made. These were IFI wheels not AndyMark. The gearboxes were AndyMark, which had good shifting. They worked great!