To Gecko, or not to Gecko...that is the question!

[samualt]

I have bought some really cool servo motors. But, they have the following encoder:

"The encoders are 1024 pulses/revolution which means with the Gecko drives you get 4096 steps/rev. You will need a very fast step generator to use the Gecko 320 with these motors. Or you could use the pulse multiplier(G901) with the Gecko 320, and any pulse generator will work. The encoders run on 5V and have differential outputs. " - Chris B.

I assume from all from this (I really haven't a clue, LOL) that my encoders are not Gecko friendly and thus will need allot of other stuff to make them work. For around $60 each ($180 total...yikes!) I could just buy some Gecko friendly encoders at USDigital . Or, I could use some servo drivers that accept differential encoders (Like Rutex which are a little more expensive but very fancy. Anyone like those?)
Or, I could spend an inordinate amount of time fiddling with very fast step generators, multipliers, and other domahickies.

What's a boy to do? What is the cheap, easy, simple way?

[HuFlungDung]

Is there no way to use a reduction factor in the software? Just because the encoder puts out 4096 steps/ rev for feedback, does not mean that the step generator needs to put out that many pulses for movement. At least, it shouldn't have to, IMO. But then, I don't know the system at all.

[samualt]

Part of the problem is that the Gecko's can't use "differential encoders". They only understand TTL type encoders. If I understand Chris B. you can make it work through some fenagling but it sure isn't plug-n-play.

[HuFlungDung]

I thought differential encoders was a system of using two encoders per axis, or an encoder and a scale per axis, for feedback. One keeps track of the motor rotation, and the other keeps track of the actual screw or scale position.

I must be mistaken. So what is it?

[samualt]

HuFlungDung:
I have no idea.

I just know the gecko manual says:
"The encoder must be a digital quadrature TTL output type that operates on a single +5VDC power supply."

and the Rutex pages says:
"encoder feedback - TTL or differential"

[balsaman]

The gecko 320 takes the pulses from the encoder and multiplies it times 4. Actually it counts each edge of the pulses from the two channels as one pulse (200 pulses is 400 edges times two channels is 800 edges). Each pulse from the pulse generator (computer usually for us) will move the motor one encoder pulse. This works great as long as you have encoders in the 200 to 400 CPR range. When you get 1000 cpr encoders the computer will have to put out 4000 pulses to rotate the motor once. On 5 tpi screws thats 20,000 pulses per inch. At 100 inches a minute thats 2,000,000 pulses a minute. That's a lot to expect from a PC out the parallel port.

The easiest is to buy some new 200 cpr quadrature encoders.

Eric

[HuFlungDung]

Eric, can he just use one channel of the encoder?

[balsaman]

The gecko needs the second channel to know which way the motor is turning. The channels lead/lag each other. If channel a is lagging b, it may be clockwise, and if b is lagging a, counterclockwise, for example (this varies from setup to setup, and sometimes you need to switch the a and b channel inputs on the geckodrive to make it work).

Eric

[Mariss Freimanis]

You can use a differential encoder with the G320. You simply don't use the complementary channels (A-not, B-not). The problem with differential encoders is they usually consume more than 50mA of power supply current, the G320's limit. You have to power the encoder from a seperate +5VDC supply.

Mariss

[balsaman]

My encoders don't say on them how much power they consume. I am using the gecko's 5 volt supply. I am thinking mine may be diferential, because they have wires for A/ and B/. Is that the same as A not and B not? Is the 50 ma supply protected against overcurrent? Should I be worried?

Eric

[Mariss Freimanis]

Get your multimeter, set it to DC Amps and measure the supply current using your PC +5VDC supply. If it's less than 50mA then you're OK.

The +5VDC regulator in the G320 is a 78L05 and it is internally current limited to 100mA. This regulator is driven by a TL783C regulator set to +12VDC. It gets its supply from the 18 to 80VDC input to the drive. It is this regulator that will overheat if more than 50mA is drawn from the +5V (ENC+) output.

Mariss

[balsaman]

Since my encoders draw 100 ma (I checked), I have switched to the PC's +5 volts (the common pin to the step/dir pins). I put a 500 ohm resistor from the enc+ to the enc- on the drive.

Man, I am glad I saw this thread.

Eric