Where to get shaft encoders

[D.Viddy]

I have been trying to make some, and frankly. I would rather puchase shaft encoders from a supplier. I have looked on digi-key and future. But is there anywhere else I can get it?

[rbayer]

If digikey and future don't carry them, they're not going to be legal to use on your robot.

[bigqueue]

Originally posted by D.Viddy
I have been trying to make some, and frankly. I would rather puchase shaft encoders from a supplier. I have looked on digi-key and future. But is there anywhere else I can get it?

The answer of course is to make them...and since you probably have access to all the internals of your transmission and drive-train....you can place the sensor anywhere in there and measure as accurately as you want! (might I suggest hall effect...it is very simple and straight forward)

Good luck,
-Quentin

[ttedrow]

Page 830 in digikey catalog http://dkc3.digikey.com/PDF/T031/SectG.pdf

[D.Viddy]

That's exactly what I needed. Big help!

[D. Gregory]

Does a shaft encoder measure rpm? If it doesn't, what does.

[bigqueue]

Originally posted by D. Gregory
Does a shaft encoder measure rpm? If it doesn't, what does.

A shaft encoder generally measures the amount of rotation of a shaft.....but if you look at the amount of rotation with respect to time, you essily have RPM.

[D. Gregory]

So, is that what I would use if I wanted to prgram a dead reckoner using rpm. I.e. all motors turn 3000 revs foward, stop, left side 1000 rev foward-right side 1000 rev backwards, stop, all motors turn 10000 rpm foward.

[D.Viddy]

The way shaft encoders really work is with ticks. They send ons and offs to the control system, and every tick (or on) that is sent to the RC would be a certain angle. So if an encoder could send 36 ticks per revolution then you would no that every tick recieved is 10 degrees. So if you could how many ticks have gone by you could easily know when one revolution has occured.

[Jnadke]

Digikey does sell some Rotary Optical Encoders. These are single-piece enocders for motor-monitoring applications. Up to 3,000 RPM. You won't be able to use them on the robot controller though, as it is far too slow. You'll need to feed the data to a separate microprocessor and use that to count shaft rotations, then feed the data to the robot controller.

Be careful when devising a way to mount them. This Bournes Data Sheet says it doesn't tolerate much axial stress. You might snap it off.

You could contact Bournes and see if they'll send you a sample. You'll still have to include the $50 price tage in your $200 total (that eats up $100 there -- one for each side), but it'll possibly save you some money.


Basically, what I'm trying to say is... this is an option, but it's not for the inexperienced.

[D. Gregory]

I can't really afford that, I'm on a tight budget. Is there any easier and cheaper way to do dead reckoning? Time perhaps?

[Adam Y.]

It looks alot easier to make one than to buy it. Btw how are you trying to make it.

[seanwitte]

Digi-key has some mechanical shaft encoders that are only a few bucks each. Has anyone used one of these?

They're in the bottom right-hand section of the catalog page. There is one that has a 4 bit gray code output. Does it function like 4 switch inputs to the controller? I'm assuming its a passive device.

If thats how it works, then you should be able to grab the nibble on each loop and use it to figure out how far it went during the cycle. As long as your wheel doesn't turn more than 16 times between samplings it would be fine.

They don't have the hex output version, only the 4-bit gray code. Its defined in the data sheets so you can convert the gray to hex in code.