Alternate encoders?
 

Question for the CD community... We want to put encoders on our shooter wheels, however we have a small problem - we're using 1/2 inch shafts, and none of the encoders from US Digital support shafts that big!

We're direct-driving the shafts, so there's no real chance for us to stick the encoder elsewhere, short of adding belting over to an idler sprocket just for the encoder (which we don't really want to do).

So, any suggestions out there for a reasonably priced encoder that works on a 1/2 inch shaft that would mount similar to the US Digital ones?

Re: Alternate encoders?
 

Does the shaft stick out the end? If so, can you find someone with a lathe to turn the end of the shaft down to the correct size?

We have a few latching Hall Effect sensors on order, for our shooter encoder. Then we need to figure out how to put a magnet on the shaft, or the wheel, or something.

Re: Alternate encoders?
 

We are searching for something similar. Would you care to share the source/part number of the Latching Hall Effect sensors you propose to use?

Re: Alternate encoders?
 

Sure, see this thread

http://www.chiefdelphi.com/forums/sh...d.php?t=100422

Re: Alternate encoders?
 

Unfortunately, no. The design we're going with will have 2 550's powering each wheel, and they'll be mounted directly onto both ends of the shaft (through an appropriate gearbox). As you can imagine, this design does present some interesting challenges... like how to get an encoder on there!

Re: Alternate encoders?
 

These encoders support up to a 1" bore:

http://www.usdigital.com/products/en.../rotary/kit/e6
http://www.usdigital.com/products/en.../rotary/kit/e3

Re: Alternate encoders?
 

Is your shooter setup something like this:



If so, you can use a set of gears (as shown above), small polycord pulleys, timing belt, etc. to power an auxiliary encoder shaft.

Re: Alternate encoders?
 

Something to think about from our experience in Aim High is static electricity. In 2006 our ball shooter was a terrific generator of high voltage charges. Sparks could jump half an inch! That same year we used those larger US digital encoders and went through about half a dozen of them...destroyed by static.

If you have an all metal shooter it may not be an issue because the charge will have somewhere to go. Otherwise think about where the electrons will go to roost.

Re: Alternate encoders?
 

Interesting you should mention that...we were playing with the VanDeGraff generator in our teacher sponsor's room...and I completely missed the fact that we're building our own on the robot!

Re: Alternate encoders?
 

We're trying to keep things simple and avoid having an idler like that just to power the encoder (although we have done similar idlers before).



bear24rw, thanks for pointing those out... I swear, I looked all over but must have missed those somehow. It sucks that they come out to be about $70 each though!

Re: Alternate encoders?
 

We had a similar issue in finding a decent encoder. I found and gutted an old Ball Mouse, using the optical components to sense a slotted wheel.

A ball mouse has four IR LEDs (clear case) that shine onto four Photodiodes (red case). Starting with a 7805 voltage regulator (to convert robot's 12V), I fed a pair of LEDs (wired in series) the 5V through a 100 Ohm resistor.

Each photodiode has a surface-mount 10k resistor associated with it. +5 goes to one side of the photodiode, I pick off the signal from the other side of the photodiode (which also goes to the resistor), and the other side of the resistor is ground.

The Photodiode output is fed through a 74LS14 inverting Schmitt Trigger ('cause that's what I had) but I suppose any TTL device would buffer it OK. (A Schmitt Trigger is used exactly for this kind op application, 'debouncing' any inputs)

I think the cRio can handle the data rate, if I measure the time between pulses to check speed. If not, we might use an Arduino board to handle the counting via Interrupts and also do the PID calculations, feeding only motor speed control data back to the cRio.

Testing it tomorrow.

(Are you old enough to know what a Ball Mouse is?)

Re: Alternate encoders?
 

But do you know what a steel ball green eyed mouse is?

http://www.youtube.com/watch?v=cGUVJCaJti4

Re: Alternate encoders?
 

I think an optical IR emitter/transmitter pair would work fine in this case.

In fact, now that I think of it, I suppose that you could possibly use the motor fan as your interrupter if you position them judiciously.

If you are less adventuresome, you can use spokes in your wheel or even white/black stripes painted on the shaft can do the trick.

Joe J.

Re: Alternate encoders?
 

If your using one motor and have a shaft end to work with, can go the analog route. Hint: when is a motor not a motor?

Re: Alternate encoders?
 

That's interesting. I've never taken apart a ball mouse before, but now I want to. The only question is where to find one. I suppose I could go ask at the local ancient history museum...


(and yes, I'm old enough... I started programming about 18 years ago :p)

Re: Alternate encoders?
 

That is a pretty good description of my house, I have somewhere around 80 old computers....

Try the thrift stores or ebay

Re: Alternate encoders?
 

Has anyone tried using last years Rockwell Automation light sensor for the kit of parts? They spec it as having a 1Ms response time. Unknown to me is how focused it is and how close it can be to the axle.

Re: Alternate encoders?
 

A one Mega-second response time?

I guess if you have a truly massive shooter wheel that spins one revolution per fortnight it'll work. :)

Re: Alternate encoders?
 

I pick them up at garage sales all the time, have a box full. Just to take them apart and use for things like this. Just have to keep your eyes open. The local thrift stores probably have some, too.

Started programming at 4? I'm impressed! :p

Re: Alternate encoders?
 

I guess erring that way is better (for my ego, at least) than what some of my students have guessed!

Re: Alternate encoders?
 

Start in the basement...


Jim, I had never seen a steel green-eyed mouse before, nice link. But I owned a 5150. I still have my Heathkit 5150 clone downstairs - all hand-soldered (including the card cage) and socketed. Runs Norton Commander.

Re: Alternate encoders?
 

Team 159 prototyped with the S6 encoder this year and we have found them to be incredible. The Index channel allows for virtually any speed to be used, and they seem to be bulletproof. Having their own casing, shaft, and other hardware rather than relying on the mounting makes them easier to work with as well.

Re: Alternate encoders?
 

Yes. USDigital does make encoder kits which support a 1/2" shaft, they are just in a slightly different line than the one that comes in the kit.

In the past, we have had good success with part # E6-200-500-N-S-H-D-B. (See http://www.usdigital.com/products/en.../rotary/kit/e6 for more info.) This year, we'll probably order some similar encoders with fewer counts/rotation (the above part #is for 200 counts per rotation) since the shooter wheel speeds will be quite high. The above part is also available with a 64CPR disk.

We used a USDigital through-hole kit encoder in 2009 to control shooter-wheel speed and in 2010 to control the power delivered to our kicker. We didn't have any problems with these encoders during the entire competition season.

Note that when ordering parts from USDigital, there is a discount available for FIRST teams (at least there has been in past years; we haven't yet placed an order this year) that gives teams "one up" discount pricing. The USDigital pages all mention quantity discounts -- essentially, FIRST teams get the next-level quantity discount. (i.e. order 1 encoder and get it at the unit price for 10 encoders; order 10 encoders and get them at the unit price for 50 encoders...)

Re: Alternate encoders?
 

So people aren't the only things that go to Arizona to retire. Got a KIM?

Re: Alternate encoders?
 

Managed to find an "old" ball mouse at home last night. I think I got it for "free" with a computer back in the day, and never used it, so it still looks like new. Didn't stop me from taking it apart, though!

Re: Alternate encoders?
 

Nope...but I think I programmed one in the early 80s in "EE for dummies" class.

I do have a little S-100 stuff, but none of it is put together enough to work.

I sure hope we get our latching hall effect encoder thingy working soon! It makes the meter change, but the cRio doesn't see it.

Re: Alternate encoders?
 

When you do get it working, you should let us all know what the setup is :) Last night we tried putting together our own "DIY" encoder, and it seems to be working great on the scope... I think tonight we need to see how it works with the cRio. Assuming all goes well, I'll be back here with a circuit diagram and a digikey parts list for anyone who wants to make their own. It's certainly cheaper than buying one(enough parts to make ~10 of them for $20)!

Re: Alternate encoders?
 

Jim, any chance of you bringing in your o'scope tomorrow? I'm kinda old school in that I like to see what the signal really looks like. Seems like every time we hook something new up to the control system it takes some sort of divine intervention before it shows up on the dashboard. At least scopes are pretty trustworthy in the right hands.
Dave

Re: Alternate encoders?
 

Squirrel - I have PCBs arriving today that I put together for the US1881 Hall Effect sensor. If all goes well I will know by tomorrow if my design translated from breadboard to PCB layout without issue. Are you having trouble with using the US1881? I can share my schematic later when I get home. It is pretty much the 3 wire design in the data sheet, but I also threw in an FET and LED on the output so an LED will turn on/off each rev for easy visual confirmation that the sensor is getting power and working.

Re: Alternate encoders?
 

We did get the sensor to appear on the cRio, it was something that the programmer didn't have running that he needed to have running, he figured it out eventually. So we probably don't need the scope, unless you want to look at other stuff to...I can bring it in, no problem.

Re: Alternate encoders?
 

I almost hate to post this, but I had been watching these for over a year on ebay. I picked some up last week, got them on Friday and happy with the design and they worked just fine with the cRio. It's a 3/8" shaft.

My intro to engineering teacher told me the definition of an engineer, is one who can do with a nickle, what any fool can do with a dollar.

I probably have a half a dozen ball mouses downstairs... so I am playing the part of the non-engineer fool...

http://www.ebay.com/itm/260297277041...ht_2001wt_1035

Scott.