Need help in creating program to use servo's to shift drive

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Posted by Travis Covington at 2/12/2001 2:18 AM EST


Student on team #115, MV ROBOTICS, from Monta Vista High School and Hitachi Data Systems - 3com - NASA Ames.


In Reply to: rotating robots syndrome
Posted by Joe Johnson on 2/11/2001 9:53 PM EST:



so no serious damage could be done? just that it might not fully engage and your bot would be dead or spinning in its tracks?

thanks again

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Posted by Ken Patton at 2/12/2001 12:20 PM EST


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.


In Reply to: Re: rotating robots syndrome
Posted by Travis Covington on 2/12/2001 2:18 AM EST:



Serious damage could be done. Once you "miss a shift," the likelihood that the gear selector will slip out of gear the next time is increased. Its dependent on how long you grind away during that missed shift.

So, if it does happen, don't let it grind away. And have some spare gearboxes if you are at risk to this happening.

I'll bet that Technokats went through a few gearboxes during the development of their system to its current reliable state.

Ken

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Posted by Andy Baker at 2/12/2001 1:40 PM EST


Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.


In Reply to: it gets worse
Posted by Ken Patton on 2/12/2001 12:20 PM EST:



Yes, we went through a few gearboxes, but not too many. I cannot remember more than two. I credit Jeff Burch for a conservatively-written piece of software that did not take any risks.

On the other hand, during the initial stages of this design, many people on our team were passionately emotional about whether or not we should do this. It was a big risk, we argued about it for a long time. The '99 Motorola Regional was tough for us. We blew a gearbox and some of us were ready to pitch the gear switching mechanism.

We stuck to it and finally got it to work consistently. This design is paying off for us and many other teams. I have not kept count of the number of teams who have contacted me about this design, but I expect to see more than 15 different teams using our gear shifting design from '00.

Sure, we are "giving away" this design. Seeing teams succeed with it will be a definite reward for us, sure, but also for FIRST in general. Upping the level of competition is good for us all. I think that we all enjoy seeing what each other come up with and there is a lot of informal "sharing" of ideas.

I think that this should happen more. It would be nice for teams who have minimal resources to be able to use other teams' past year's designs.

As for this year, we've got some trade secrets... but don't we all?

Andy B.

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Posted by Jay Lundy at 2/11/2001 6:44 PM EST


Student on team #254, The Cheesy Poofs, from Bellarmine College Preparatory.


In Reply to: Yep, something like that
Posted by Andy Baker on 2/10/2001 11:24 PM EST:



: : Something like: Stop. partial forward, partial backard,
: : shift, partial forward, partial backward. Continue.

: : Basically, you have to take the stress out of the
: : mechanism to get it to shift out of gear and then you
: : have to wiggle it to get it to fully engage in gear.

: Yes, I believe that's how we do it.

: BUT, I do not know the code. Our software guys don't let me near the keyboard.

: We've refined it down to the point where it takes under two seconds.

: Andy B.

I don't quite understand the partial foreward, partial backwards and all that stuff. We have a simple gear shifting system that works everytime, takes about half a second to shift, and works with the press of a button. I wont go into much detail, but the code is only about 10 lines long and easy to read. It is really helpful because we can use high gear for speed, but when going up the ramp we lose traction so we go into low gear and keep going.

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Posted by Jay Lundy at 2/11/2001 2:37 AM EST


Student on team #254, The Cheesy Poofs, from Bellarmine College Preparatory.


In Reply to: Need help in creating program to use servo's to shift drive
Posted by Barry Horwitz on 2/9/2001 10:55 PM EST:



Stephen's program is correct, it's just that it is better if you give it some leeway. I forget exactly what range I let the joysticks be, but because the calibration on the joystick could be off by 1,2, or even 3 and the speed controllers still stay inactive, I used a slightly different IF statement:

if p1_y > 131 or p1_y 131 or p2_y

noShift:

I found that this works better. I think the range in my program is actually a little bigger than 123-131 and it still never stalls, but do whatever you want. I also suggest (if you haven't already done this) to use the LEDs on the operator interface to tell you what gear you are in. Also, assuming you are using servos to shift gears, make sure you wait about a second after shifting gears to move again or you risk stalling. Better safe than sorry.