Shifting Device
 

Has anybody out there come up with a good idea on how to shift the drill motors from high speed to low speed?

how about a leadscrew mechanism and some kind of collar around the shifter.

Or howabout a servo?
Check the whitepapers.

shifter
 

We are using servos to shift the drill motors. We used a similar system in 2001. We have found that this works quite well and reliably

Last year we used a servo, and we are looking to using the same thing. (we have a 2 speed transmission) the only problem was the servos are not the most reliable thing....so we are trying to work the bugs out of it!

Want..to post..but..team kill... if I do....


Sucks being an animator..

use a very short pnumatic cylinder.

Last year we used servo's to shift. It worked pretty well. We got sick of having to stop when we shifted, so we have redone our transmission :) Can you say 'Variable Speed Drive'?

Programing
 

come on guys, there's a much easier way. program a max speed allowance then just add a trigger command that will allow you to switch to a higher speed. it's doable in not a lot of coding and with multi-bank programming it's like nothing to add in.

Re: Programing
 

Are you serious????

If you are... you might want to confer with the more mechanically inclined members of your team so they can edumacate you better.

2001 we used a servo to shift. We got it working well so it never failed to shift.

2002 we built a custom transmission so we could shift on the fly, but this year we decided to try the new drill motor transmission that comes with the kit. We got the shifting to work with just a servo, and it has worked 100% so far (though we've only had a running base for a day or so).

Re: Programing
 

::Must not flame..must not flame..must not flame::

Uhh....the theory you describe there won't really help you torque-wise..which is the point of having a tranny, so you can shift from High-speed to High-torque....

Last year we used servo's to shift. It worked great except you had to stop. The only other problem we had was that it would pop out of gear every once and a while. To solve that proble we used a coulple of springs.

Re: Re: Programing
 

The whole point of shifting gear ratio in a drive train is to trade off between speed and torque. You have constant power from the motor, and since Power = speed times force, or angular velocity times torque, you get a combinations of speed and force from the motors depending your wheel size and your gear ratio.

By switching to a different ratio, you slow down your robot but you get more pushing force, or you speed up your robot but you have weaker pushing force. Controlling it in software only limit how much power you have from the motor, and thus making the motor weaker when you slow it down, instead of trading off speed for torque.

Few ways I've seen for shifting gear ratio: Drill motor's transmission using a servo or pneumatic cylinder, that's the most simple way for a team to shift gear ratio.

Have two sets of wheels with different ratio, and lower one set at a time depending what ratio you want. You can shift on the fly that way.

Custom gear box like team 45 and 60 last year, or the 67 bot at 2001, where you use pneumatics to move gears outside the drill transmission to from one ratio to another ratio. This is much more complicated, and if your team doesn't already know how to do this, I wouldn't start right with only a few weeks left in the 6 weeks.

Or, you can add more motors to your drive system, and get more mechanical power out of it that way. You have more overall power, and thus more torque and speed at the same time.

team 69 did the same in 2001 and 2002
We used pneumatics to shift on the fly for 2002 using the big atwoods i believe if you need a diagram i can find one just email me xdohhhx@aol.com

also to reply to the programming reducing it would work but not give you the same aspect as shifting.

This year we are going to have an awesome drive train again! Watch out NH and TX!

The numbers on the side adjust the speed. It's not that big of a change but it does get faster and slower. One thing you could do though is create a gearbox to shift gears from low speed to high speed.

Re: Re: Re: Programing
 

Very nice post!

Which numbers on the side? If you're referring to the 1-15 on the black part, that's actually a clutch that will change how much torque the drills will put out before slipping. If you find a real drill with numbers like these (most good ones have them), try setting it to something like 1 and holding the end while you turn it on. It should start clicking and not really provide much force against your hand.

If you're referring to some other numbers, I'm sorry. Could you please explain as I would be quite interested.


--Rob

$@#$@#$@#$@# Straight! i will be one of the first ones to hurt u jim(jk); LOL
well first lets wait and see if we actually get it to work this eyar before we actually say anything. Once we get its on our robot and working we can brag then!

Cipher X

Hehe, good point..and if we dont get it to go through, we'll post it online to "Help the other teams in the name of gracious professionalism" and see if anyone else can see what we did wrong.

Not to bring this up, as i hardly post, but this caught my attention:

However, team 111 has had huge success by limiting the speed control to only 50% when you want to move slower. Only when we want 100 percent by push of the thumb button on the joy stick, we speed off. It's all about the proper gear ratio. There are ratios to maximize speed and power with each motor. You just need to know the magic number ;)

Yeah, but the guy was talking about using software control on the drill motors in high gear... major loss of torque there.

We used the programmatic shifting last year, and while you can get a bit of control from the lower speed, it doesn't do anything for your pulling power.

Because the drill motor gear boxes don't like to shift under load, we lock them in low and use a set of spur gears on a slider to shift. Not original, but it works very reliably. This year we're using both the CIM and the drill motors in low. I think we will just push the whole ramp to our goal zone.... Good Luck.

You can get a good Tourqe:Speed ratio through gears yes, but you can change it for higer torque or higher speed through shifting gears.

There are two real ways to shift, 1) Shift the planetary system in the gearbox of the drill motor. 2) Shift actual gears in your gearbox after the motor.

Having X ratio and giving it 50% power will not give you more pushing force, it will only slow your speed. The advantage to limiting power is less draw on the battery, and less chance of overheating your motor. You will NOT gain tourque by supplying less power.

If you look at the power curve for the motors, they are all in accordance to 12 volts being delivered. You can, for the most part, just shift everything down by about 1/2 to see what your speed and torque would be at 50% power. If you change gears however, you'll shift the curve to the left or right.
---
On the topic at hand..

There are 2 good ways to go about shifting.
1) Servo motor - Turn the servo and it worms the shifter over to a new position. Doesn't take much torque to slide, and the servo doesn't provide much torque.. beatiful combination, rather imple to make with a pretty wide tolerance.

2) Small Pneumatic cylinder
a) above each motor's shifter you can mount a small cylinder that is attached directly to the slider. Pneumatic extends, motor shifts. Program in to not allow motor to be moving to fast when shifting or a nice grinding sound might be heard. And grinding is never a good sound.

b) If the motor's are in line with eachother, you can have a single cylinder mounted above them both. When it extends, it pulls both pins, shifting both motors. You'll have to engineer a bit more with this one so that they both shift to the same gear. If the motors are facing oppisite directions and get the same linear force, they will shift into oppisite gears. (One low, one high). There are ways around this, such as flipping one motor around (which hurts on space) or a reverse pusher. (Reverses force on another bar to change force and shift gears in oppisite directions and same gear.)

c) Within each gearbox, after the motor, have a cylinder actuate a shaft of gears into another position. This works on the same concept as a car's transmission. When cylinder is retracted, gear "a" is being rotated by gear "b". When cylinder is extended, gear "c" is being rotated by gead "d". a and c would be on the same shaft, and gears b and d would be on the same shaft. I don't have any diagrams to show this, but if you hunt around you'll find it.

d) (I saw this in 469's gearbox last year and thought it was a very neat idea). Have the gearboxes in the same orientation as eachother, but the shifting gear (a, c above) be oriented differently. When the cylinder extends, it pushes a and c's shaft to interact c to d. mount a shaft to extend with the cylinder so they both get actuated. If you need more information I can draw up a diagram or contact team 469 about how they did this.

Can someone tell me which position is high speed and which position is low speed?

Pushing the gear shift toward the drive shaft connector puts you into low gear.

With regard to locking the gear on the drill motors: We used a ring of PVC to lock it in, but found that after a while the ring would tend to disintegrate, but the problem would not be noticed till we got a jolt and the motor shifts to nuetral (usually under full power!). So, the locking works, but its a good idea to a) make sure your lock is stable and b) make sure you can get to your motors easily. Just getting the point where wer could bring a screwdriver to bear on those motor mounts required 1/2 hour of work!

multi-seed trannys
 

Don't get too carried away with the technology. It all depends on the game rules and the course. Form follows function, and all of that...

Last year. we had a slow, but extremely reliable robot as far as the drivetrain was concerned. No spares, no adjustments, no breakers popping, no hassle. There were enough other things to worry about...