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Unread 03-14-2012, 05:41 PM
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[FTC]: Sensor Ideas

I was wondering what the FTC community thought of this.

I am working on a project that uses pretty much maxes out the idea of an FTC bot. Sensors motors and everything. But in the idea of having it possibly a competition enabled robot I want to get fancy with some sensors and motors.

So my question is, Would it be possible to use a multiplexer with 4 light sensors to count rotations of something? Giving feedback to a Continuous rotation servo allowing for this system to be accurately programmed? Kinda like an encoder?

Am I just crazy or would something like this work?

- Andrew

- P.S. I might post some render later when I get the entire system done.
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Unread 03-14-2012, 09:51 PM
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Re: [FTC]: Sensor Ideas

Sounds interesting and very possible -- but wouldn't it be easier just to use an angle sensor to keep track of rotation?
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Unread 03-15-2012, 08:14 AM
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Re: [FTC]: Sensor Ideas

By the way does anyone know the true RPM of the Continuous Rotation Servo? I am wondering if I have to make a gearbox (more than likely) Right now the ratio is 5.5:1 Which I'm pretty sure is pretty slow for rotation

Just wondering.

Also if anyone has any ideas for making makeshift encoders I'd like to know since this system would simply max out the amount of encoders you can possibly use (to my knowledge) on an FTC bot and I want to find a way around that.

Maybe make a few encoders plug into the protoboard? If anyone has any ideas I'm open for them.

- Andrew
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Unread 03-21-2012, 12:10 PM
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Re: [FTC]: Sensor Ideas

So I have finished (for the most part) the design for this thing.

Welcome to the FTC Imbedded Wheel Swerve Drive (IWS Drive) Google+ Album here:

https://plus.google.com/u/0/photos/1...84077534644098

As some of you might have seen

http://www.chiefdelphi.com/media/photos/37673

This module, it inspired me to try to do the same, but at a different scale.

It uses alot of resources, so I dont think a competition worthy version will actually be built. However If it does get built I want to see it and make sure you email me pictures and video!

What sets this apart from most FTC systems is that it uses absolutely no Tetrix structural metal. Why you might ask? Simply because I think it would be awesome to see a team attempt to build an entire robot using as little Tetrix material as possible. It would teach alot to students and has potential for some really awesome mechanisms

As for the construction of this thing.

The Frame.

The frame is 1" x 1/2" x 17.8" C Channel Riveted to a 17.8" x 17.8" x 1/16" water-jetted piece of AL. (doesn't have to be, I just have those resources available)

Bearings, Turntables, and Custom Gears.

They are made from laser-jet sheets of 1/8" and 1/16" thick Delrin, reason for this is because of the offset of the 1/16 inch sheet metal belly pan. All gears are compatible with the Tetrix gears as well this allows one to use them elsewhere if need be.

Motor mounts.

They are modified as well. Since I find the Motor mounts in FTC kind of large and bulky in this application I have made them thinner. However one chooses to do that is ok However I would use a mill personally. The motor mount also has gearbox mounting holes in it which is made from laser cut Lexan or Delrin (It doesn't really matter)

Motor Sleeve.

The motor sleeve is a piece of schedule 80 PVC It is machined out in the center to a couple thousandths smaller than the OD of the motor. It is then pressed onto the motor ensuring a very tight connection. On the outside before it is pressed on two grooves are machined into the sleeve at predetermined distances that act as "tracks" for the bearings. Which brings me to the next topic.

Imbedded Motor Inside Wheel.

How this was accomplished was by drilling out the center of the wheel with a considerable bore which is larger than the motor. From there there are through bolt holes drilled. Which attaches the bearings. (Yes Bearings If you remember the Pivot bearings) This drive uses 16 per wheel However can be reduced to 8 per wheel if need be. The Drive gear also needs to be heavily modified and drilled with the same bolt pattern at the wheel and threaded to a 4-40 threaded bolt that is 1.5 inches long (I think)

Now that I think I'm done with the mechanical portion, its onto the sensor/electrical/programming portion.

Drive Wheels.

Each drive wheel has enough space allotted so that you can attach the FTC encoder to the drive motor as usual to give you a feedback on how far you have gone. The wires would be suspended above the center of the wheel to prevent extreme tangling and give you 360 degree rotation (with limits of course)

Pod Rotation.

This is done through the continuous rotation servo, since lets be honest. None of us want to dedicate 8 motors to the drive train. Even I say 6 is max, even this year. But nonetheless, If the specs I found on the Cont. servo are accurate the 5.5:1 would have rotated it something like 1 per minute or something ridiculously slow. So what I did (not shown in renders) is made a small custom gearbox for the Servo. This increases the speed from the ridiculously long time it would have taken to about ~1 second rotation times. This would allow for incredibly diverse programming options and quick maneuvering of the field.

Now How do you predict where its at when its rotating you ask? Well this is where I'm stumped, but I have a few solutions. My first idea was to take a sheet of Paper or different colors lexans and crate a ring with ticks on it these ticks would be large enough for a Lego light sensor to sense, but small enough to make the system accurate. That would be done through a sensor Multiplexor to the NXT.

My second idea was using the Protoboard. Now I'm not sure how expansive the Protoboard can be feel free to enlighten me if this is possible. How it would work is you would use the encoders provided in the FTC kit through a custom gear system to basically sense how far the pod has rotated over time, this would be applied one per pod thus giving you 4 encoders for the pods total. Encoder count now currently at 8 for the drive train.

Anyway I think thats everything I can think of for now.

Comments, Questions, Concerns?

Enjoy

- Andrew Remmers
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Unread 03-21-2012, 07:04 PM
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Re: [FTC]: Sensor Ideas

Cool!

What if you just used a servo, or a geared up servo, to rotate the pod?

Also there is something like this on YouTube if you search for "ftc vector drive" (I'm on my phone right now). This is a much better version than that, though.
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Unread 03-22-2012, 08:34 AM
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Re: [FTC]: Sensor Ideas

Quote:
Originally Posted by h3x View Post
Cool!

What if you just used a servo, or a geared up servo, to rotate the pod?

Also there is something like this on YouTube if you search for "ftc vector drive" (I'm on my phone right now). This is a much better version than that, though.
It does use a servo geared WAY up if you look at the CADs (when you get the chance) I have to gear at least 1:8 to get it to rotate as quickly as I want it to.

- Andrew
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Unread 03-22-2012, 11:34 AM
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Re: [FTC]: Sensor Ideas

Looks awesome!

From maneuverability perspective this is great (totally dig the motor inside wheel assembly btw) but the Tetrix wheels have a tendency to be quite slippery (well not slippery but it's not good for traction).

Have you thought about using LEGO motors to do the servo's job? I know there are much more complications but the advantage is they have built in encoders. (oh and btw there's no limit on how many encoders you can use... just ports. Even then you can still have a SMUX that hooks up to four protoboards... on EACH LEGO SENSOR PORT!!!) Theoretically that's 12 (assuming you want to save one for the motor controller, even though that can be hooked up to the SMUX also but I personally never tried it) SMUX ports (or 15 if you decide to connect the Motor Controller to one of the SMUX).

Anyway, I don't recall how many Digital ports are on each SMUX (I think it's 6?) so yeah. If you run out of space for encoders to plug in in motor controllers, just wire it up to the SMUX. A bit more programming required but it definitely works.

Lastly, our team actually built a robot with only 3 TETRIX metal structural pieces! I'll post some picture if I get around to it (preparing for VEX Worlds). We won't be attending CMP because we want to dedicate our resources to VEX (even though the FRC robots look so legit and tempting to go watch).

Oh btw, THE RENDERS LOOK AWESOME!!!

Oh just actually read through your post again and saw the note about the protoboard. The old protoboard has 6 (don't quote me on it) digital and 5 (analog) ports. And the digital ones can be programmed to be I / O (not when it's on the SMUX but oh well). You just wire it up like how encoders are wired up (2 ports in Digital ports). The new protoboard has much more ports and much more functions for analog ports but I have never experimented with one so I can't speak for it.
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Unread 03-22-2012, 12:57 PM
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Re: [FTC]: Sensor Ideas

Quote:
Originally Posted by TRWSHSHLX View Post
Looks awesome!



Lastly, our team actually built a robot with only 3 TETRIX metal structural pieces!

Oh btw, THE RENDERS LOOK AWESOME!!!
Firstly, I commend you! I have been waiting for this day ever since I saw the new materials introduced. I would really enjoy seeing pictures and renders if you wouldn't mind sending me a PM when you get the pictures Ill give you my email address. I certainly would like to add it to my library of cool robots!

Second Thanks. Making these renders was kind of a new experiance, since I rendered them at work on my computer which runs Solidworks. I have never worked with the solidworks renderer before so it was intresting playing with it. Lucky for me its hard to screw up. But its also hard to get exactly what I wanted (which I never did get)

My next project is similar. However it allows for unlimited rotations to the pods and I will attempt to use no Tetrix metal again as well besides motor mounts (somecases not even needed),gears and whatnot.

- Andrew
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Unread 03-22-2012, 02:56 PM
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Re: [FTC]: Sensor Ideas

https://picasaweb.google.com/1100253.../FTC3237201112

Here's the album for the pictures I scrapped from my engineering notebook.

We took out our linear lift and completely changed the robot after one of our qualifiers (even though we won it) because we had qualified for VEX worlds the weekend after it. From that point on was all improvs and they weren't record in the engineering notebook so I don't have the final CAD that accurately represent the robot. But however you see from the pictures you have to look REALLY close to find the TETRIX metal we used.

Oh and somehow we managed to win another qualifier with the brand new robot and did what we wanted to do in state. The joke on our team was we won't go if we are alliance captain (which was impossible because 3531 the Short Circuits were there and they are an amazing team & also because our robot doesn't do well in qualifying rounds), but we will go to CMP if we won the Inspire. Of course we didn't but it was still a fun season and we can focus more on VEX.

Anyway, questions comments concerns are welcome! If anyone want me to upload a copy of the engineering notebook (it wasn't really thorough because I didn't record EVERY detail our amazing mechanic does and took it for granted, but nonetheless, it still records the development for our robot up to the first qualifier) I will do that but for now I'll hold it off.

BTW, Oregon is sending four teams to worlds! Look out for 3531. Go check their robot out if you have a chance!
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Unread 03-22-2012, 03:55 PM
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Re: [FTC]: Sensor Ideas

Ok I think I have a new team to add to my list of favorites!

This is awesome. Seriously. Congrats for doing something I have been wanting to do for soooooo long.

- Andrew
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