Cheap encoders
 

Yes, I'm cheap and therefore always looking for cheap robot parts. Look at these 128 CPR encoders at BG Micro.
http://www.bgmicro.com/index.asp?Pag...D&ProdID=12916 Now, if the kitbot trans has an out put shaft for these, one part of the robot would be cheap and easy this year.

Re: Cheap encoders
 

That price looks great, but I'm unable to find the specifications for them anywhere. Have you had any luck finding them? Operating voltage, max RPM, etc?

Re: Cheap encoders
 

Tom, I found this site (http://www.electro-nc.com/products/encoders.shtml) Might be of some use but I don't have the time to really dig any more on this.

That being said, the lack of full documentation on the linked site worries me. Most reputable sites provide a little more information on their products. Also, quadrature encoders are usually MUCH more expensive which sets off another flag for me. I would be careful ordering from this site, if you do make sure you monitor your credit card well after that.

Re: Cheap encoders
 

That encoder is for a control panel for a human to turn like a dial.
It wouldn't hold up to the rigors or rpm's of a drive train.

Re: Cheap encoders
 

These are our favorite cheap encoders: http://www.chiefdelphi.com/media/papers/1743

Re: Cheap encoders
 

Most likely very true. But that should not prevent a team from grabbing a few of these. At $4 a piece when you purchase four or more, they are a serious bargain!!

So, what can they be used for??

Learning how to use encoders.
Prototyping designs.
Manipulators that don't beat the tar out of an encoder.
Small personal projects.
Verifying that your code behaves as you intended before you put it on the Big Bot.
etc. etc. etc.

No doubt these are not as durable as what you might get from a company like US Digital, but if care is used, they should be quite useful in many implementations, as long as you understand what you are working with and how to use it.

Besides, at this price, you can afford to make a few mistakes and not ruin a really nice encoder.:p

Re: Cheap encoders
 

These are not mechanical encoders. They are optical encoders. The specs, look at this link.
http://docs.bgmicro.com/pdf/oak-grigsby%20encoders.pdf
It's hard to tell from the doc if they have sleeve or ball bearings. Any way they should work for attaching to the output of a trans.

Re: Cheap encoders
 

If they turn out to use ball bearings then I'd like them :)
I'm not one for sleeve bearings except in low rpm uses.

Re: Cheap encoders
 

I'm with you 100% on that.

I'll let you know exactly what they are when mine arrive. I ordered 5 this morning.:)

I have plenty of projects that can benefit from these if they are even barely decent.

Re: Cheap encoders
 

Here's a link to a catalog page. Specs are at the bottom of the page. 91 series looks to have sealed sleeve bearings rated at 300 RPM. Still a great deal for lower speed applications.

http://www.electro-nc.com/oak/p0104.pdf

Re: Cheap encoders
 

My conscience would like to make a statement: Rotary encoders, pretty much the most necessary sensor in a high performance motion control system, are probably not a place you want to cut cash in your robot.

I might be wrong in this case... but if I were building a machine of some kind, I'd probably try to save money elsewhere on a less critical part... maybe buying cheaper limit switches or something else that doesn't need to be as precise... or maybe buying looser tolerance bearings if you don't need super precise shaft positioning...

That's my 0.55 Rubles.

-q

Re: Cheap encoders
 

It is a good thing these will mostly be used in my own Vex robots, or maybe a motorized recliner operated by my lil' Arduino.:cool:

I will also use them to help my programmers get familiar with encoders and their usefulness, as you mentioned. But, you are correct, when it comes to the competition robot, reliability is paramount. (Oooo, there's that word again;) )

Re: Cheap encoders
 

I have bought stuff from BG before. They are a surplus reseller. Someone has 10,000 widgets they don't need, they sell them to BG cheap, and BG resells them. They send out a catalog every quarter that is actually quite enjoyable to read. I get the idea that it is a one man show. Some of the item descriptions have been great. like "I don't what this thing is, but if you hook it up to 12 volts it makes a really loud, hideous noise, and for $1.50, how could you go wrong?"

So, they may not know a lot about what they are selling, but for the price, you can do some research yourself.;)

Re: Cheap encoders
 

Ok, if it is a small surplus supplier that alleviates my concern somewhat, I still say be careful ordering things, too often people will try to separate you from your money.

Re: Cheap encoders
 

I have had positive experiences with BG micro. I have also had positive experiences as a FIRST student getting free encoders from encoder manufacturers. (don't everybody swamp them at once)

Re: Cheap encoders
 

Here is some more detail on these encoders.

Metal housing, bushing not bearings, .25 in dia. shaft, some resistance to rotation but not much.
I processed this picture to bring out details that would otherwise be difficult to see.

Re: Cheap encoders
 

Mark McLeod was right. They're intended for use in a control panel with a knob attached for people to turn. They'll "work" as a drive shaft encoder, but they probably won't be very robust.

Re: Cheap encoders
 

Most definitely decent quality, by that I mean not garbage, but not the type I would used for a drive train either. I plan to connect a pair to a couple globe motors we have attached to our '09 control system tomorrow. This will allow our programmers to figure out exactly how to code for them. It will also allow them to see if they can come up with an autonomous routine mock up. Heck, at $4/ea., I could care less if they fail in just a few days use, as long as the students learn how to use encoders for various applications.

Re: Cheap encoders
 

I recieved mine last week. Yes, they are sleve bearings, but I had no problem hooking them up and getting counts up to about 300 rpm. I would not want to use them at high rpm like controlling the velocity of a ball shoot like in aim high. My thought is that they would be fine at the rpm that they would see if the AM tough box is in the KOP and they ship with the encoder 1/4" shaft extension. The key point is the mounting and coupling. Stress on the shaft would eventual cause failure. The other thing is if they maintain a crisp square wave at higher RPM. I would at this time not write them off.

Re: Cheap encoders
 

I too purchased a few of these. I really don't understand the quality concerns people are expressing. While this exact model number isn't available, other comparable models of the same brand are available from Mouser Electronics for about $51.67. Not a cheap part at all. Mechanically, they seem more robust than the plastic housed US Digital encoders I have. The published specs seem to be comparable to the popular US Digital part as well. (I'm not knocking US digital, I like their parts and will almost certainly be using some this year.)

It's true, they have sleeves and not ball bearings. This doesn't reflect quality as much as intended purpose however. Sleeve bushings work just fine in the right application.

So, what application? With a life of 10,000,000 rotations at 300 rpm, I get something like 550 hours of operation, or about 16000 FRC matches. Our robot won't see that many. 300 RPM is a little slow for a drivetrain but they should be fine for just about any other lower speed application. I'm pretty sure I'll be using these somewhere this year too.

So, at $4 each, I couldn't resist taking one apart to see what is inside. I slipped the snap ring off the shaft and gently pried the back cover off. It came right apart with snap. The disk is what appears to be etched stainless and the circuit board is a simple affair without any screws to come loose. The drag on the shaft is due to the grease used and the good fit of the sleeve and shaft. So this leads me to another thought.

At the most, I think our robot could only see about 100 matches. More likely, fewer than half that. So now, I can think about de-rating. If I put these on my drivetrain, they might rotate up to 500 RPM or so. Not even twice the rated speed. I'm willing to bet that this won't reduce the life by a factor of 160, so I should be good to go.

The only issue I see is if as mentioned by Gdeaver, the wave form goes soft at higher speed. I'll bet not, but I'll put a scope on one to make sure.

Would I use these on the drivetrain of a bomb disposal robot at similar speed? No way! Lives could be at stake. To save a few bucks my team can use elsewhere? You bet. It's a good exercise in value engineering. YMMV