gear shifting

On our bot we use the drills as our primary motors. Unfortunately we have had problems shifting them with servos because they don’t go all the way into one position or another consistently. Has anyone run into this? Does anyone know a better way besides using pnuematics? Any ideas are appreciated!

Thanks
JSK

I think pneumatics would be awfully hard to use and not break the collar on the motor. When you shift them and they dont go all the way, as soon as you drive a bit, the gears should mesh and the collar should fully move into either the hi or low gear position, at least they do in our design.

Cory

no no no…we use the servo motors to switch as of right now…we have determined that we won’t use pnuematics that is why I said other than pnuematics.

how are your servos connected to the transmissions…one fix that I have encountered is that the servos arn’t powerful enough to shift so the fix is to extend the arm and use leverage to help… also with servos you have to come to a complete stop before shifting…if you want me to get more specific in how to use leverage please e-mail me [email protected]

We’ve used pneumatics to shift for the last 3 years without breaking a single collar…ever.

On our bot we use the drills as our primary motors. Unfortunately we have had problems shifting them with servos because they don’t go all the way into one position or another consistently. Has anyone run into this? Does anyone know a better way besides using pnuematics? Any ideas are appreciated!

How are you attaching the servo to the shifter? I would get a better idea if you tell me how.

we have the drills mounted in the plastic mounts then over top of them upside down we have the servos mounted on aluminum brackets. The servos then push the collars back and forth as needed…hopefully that clears it up a little bit. Any ideas

we have the drills mounted in the plastic mounts then over top of them upside down we have the servos mounted on aluminum brackets. The servos then push the collars back and forth as needed…hopefully that clears it up a little bit. Any ideas

And you say you are not getting enough throw with the servo’s directly mounted on the gear box? Why not try using a mechanical linkage to increase the throw? They are designed to be used with servos and are used to for linear movement. Im sorry if Im not that much help.

Try some of these. They will all fit right on the output of the servo and have multiple mounting locations for linkage. You should be able to get most of them at any quality hobby store.

http://www2.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=hitec+servo+horn&FVPROFIL=++

We use servos to switch gears too… and it was working very nicely, until our servos burninated, and we were stuck in low gear during competition. That hurt us a lot. :frowning:

hey jon did Trogdor happen to in the near vicinity to do the burninating :stuck_out_tongue:

oops I forgot to mention that we have a tiny linkage in between the servo and the collar…sry. We have a servo wheel horn with a metal linkage from that to the collar to be exact as possible.

We had a horrible time shifting with servos last year. One of the problems is that the “slider” in the trans that moves between the planetary sections pivots on 2 horizontal pins. There is quite a bit of clearance between the housing and the slider, which allows the slider to rock on the shifter pins and not mesh into high or lows squarely. You would be better off to build a custum housing and shift fork that you can space the pins 120 degrees apart. That’s what we did this year. I have a few photos posted in the Gallery. This has been a very reliable system. As far as shifting method, pneumatic or a servo would work consistantly. If you are familiar with R/C car suspensions, you can use the little ball joints and Tie-rod screws to build a sweet linkage for the servo method. :cool:

Quite frankly, I haven’t been to impressed with the servos. They have a mechanical freedom of almost 360 degrees, but our programer said he could only get 180 degrees of movement. That was a bit of a bummer, however, if anybody’s got any information to the contrary, it would be much apreciated.

S cubed

hmmm ive played with the servos before, and they looked like they had a rotation of around 270*ish.

Cory

*Originally posted by Stephen Kowski *
**Any ideas are appreciated!

Thanks
JSK **

OK - I specialize in “Any Ideas” :slight_smile:

Welcome to the club when it comes to shifting problems. The trannys on CD8 have had the engineers grinding their teeth :smiley: since day one.

In my humble ( newbe parent/research-engineer, vis-a-vis FIRST-mentor/real-engineer ) opinion, you won’t get that transmission to shift reliably without some major enhancements such as the forked slider collar that PMGRACER mentioned. Even with that, I don’t know if I’d trust it to shift me to victory in the finals at the NATs. With a 3.5:1 ratio change, the odds are of it aligning are slim. Seems to me that, rather than using brute force, some sort of synchronization is needed. But simply filing lead-ins into the plastic ring gear will not work, at least not for long - as they will surely blunt.

FWIW from a freshman’s parent, take a look here < http://www.dewalt.com/us/articles/article_cordless.asp?Site=cordless&ID=695 > Maybe the ALL METAL gear set would hook up, or maybe (if it’s kosher) a DeWalt/Bosch switch would do the trick. (How about that 3 speed tranny??) Simple and FREE pre-test would be to visit local tool store and check the DeWalt shifter?

I have some “pie-in-the-sky” ideas on how to synchronize. But it would involve considerable bandwidth and a whole bunch of hand waving; contact me directly if you’re interested.

Team 469 shifted the drills with the servo in 2001. The problem is that when you first apply power to the servo, it pulls the collar to the neuteral position. The collar will hardly ever actually shift into the desired gear on the first try. I believe our program called for two separate power bursts to the servo - the first to disengage the collar, and the second to mesh the other gear. Current must also be applied to the motors in between the two servo bursts in order to promote meshing. You may even want to do this 3 times. Our servo shifting routine actually ran independent of the main body of the program, so the loop times would be smaller and the duration of power to the servo was more consistent. It was pretty cool becuase everything else shut down while the shifting occured.

The shift was accurate 5 times out of 6 when the robot was at a dead stop, and 1 of 2 on the fly. Shifting on the fly with those drill trannys sounds VERY ugly, however.

Good luck with your drivetrain!

Jeff Alpert
Team 469

A new idea I have been toying with for shifting is totally inspired by a local Transmission builder-Liberty’s Gears- in Taylor Mi. They build custom Drag Racing Trannys that you can shift effortlessly under full throttle accelleration. Their design has a synchronized 1st gear, the rest are unsynchro’d. The way it works is very simple. The “slider” has only 12 teeth with a .500 gap in between each tooth. On the face of the gear upon which the slider grabs, there are 12 matching teeth with the same gap. The front edge of the teeth have a lead in angle cut into them to help “grab” the slider. I had this modification done to my Ford Toploader that I ran in my Camaro 10 years ago. They call it “Pro Shifting” and let me tell you, I could shift the trans under full power @ 7800 rpm!! I’m sure if I apply that same technology to our planetary, we’ll be shifting even smoother than we do now. With the amount of play that is inherent in that design, having the slider only partially engaging in low should go away. Sometimes ours will not go fully into low because there is a neutral position between the 2 planet sections abd the slider is “floating” momentarily. This has to be, since you cannot be simultaniously in high and low. Pneumatics, to me are a better way to shift. It requires less code, and is virtually trouble free. I suppose you could shift usig a Globe motor. You’d have plenty of power, but still need more code than pneumatics. Just my 2 sense…:cool:

Well thank You all for your suggestions we finally figured out how to consistently shift this year’s gearbox. took us a little over a day of work, but it will pay off at nationals :wink:

Thanks Again!

We use the drill shifted using one central servo. To fix the meshing problems we took a great idea from the Cheesy Poofs’ 2001 bot.

Our programmer rigged us up a little program so that whenever you switch gears, it stops the robot and moves back and forth really fast for a cycle or two while it switches so the teeth don’t grind.

I didn’t write the program but it works really well. The guy who wrote it goes by wakezero on CD. PM and i’m sure he would send you the program.