Using the new 1/4 Scale servos with LVLM

[Philbot]

I'm excited that FTC allows the larger 1/4 Scale servos this year.

I purchased one of each servo HS-755HB and HS-785HB

The 755 works as expected (180 deg rotation) tons of torque

The 785HB is weird though. It's listed as a 3.5 Turn Sail winch motor.

So I was expecting the same control as the 755, except just expanded to more turns.

However, the wheel turns way more than 3.5 turns.

Using the LavVIEW Schematic Diagram to control the servo, if I change the servo value between 5 to 255 I get about 8 turns of motion. It's very precise and normal except for the WAY expanded range.

Setting the value to 100 will always return it to the same position.

However if I choose a servo value of less than 5 (like 0 for example) the servo turns slowly Counter Clockwise, and keeps turning forever.

So, clearly no mechanical stop, but what's worse is that once it's run like this for a while, if I set the position back to a reasonable value (like 100) it doesn't go back to the same position that used to correspond to 100.

So it's not like a normal servo with absolute positioning, and it's not like a continuous rotation servo (since it only runs continually in one direction).

I've searched all the hitec sites and they all say 3.5 turns...

Anyone have any experience with this servo..... It seems like the 0 code may be a way to "home" the servo....  But it's still generating a reasonable torque while it's moving.

Should I configure the Schematic Editor as a 180 deg, or Continuous Rotation servo?

Phil.

[ESearl]

Hey Phil,

I haven't tried these new servos yet so I can't help too much. Maybe you got a bad 785? or maybe you just have to avoid setting them to zero.

I would recommend configuring as 180 deg. The Continuous scales the input values to map from a "motor power" range of -100 to 100 to the natural 0-255 range. This will probably just add confusiion while trying to figure out new hardware.

[jerry_dcjx]

Well, I have got a hs785hb, too. I didn't purchase the servo from lego but from model shop. And I notice that this servo is actrually use for controling the sail. So the servo is actrually an CONTINUE TURNNING SERVO, and you need to control it with dc control block with coast stop methode.

[jerry_dcjx]

I have just checked http://hitecrcd.com, and it said the servo is a 3.5 turn servo. I don't know how it works, but I just consider it is a continue turning servo. http://hitecrcd.com/products/servos/boat-servos/hs-785hb-3.5-turn-winch-servo/product

[Philbot]

Hi Jerry.

I have found that what it "says" and what it "does" are two different things.

I'd be interested to hear about your actual testing.

My actual testing indicates that this servo is Neither a 3.5 Turn NOR a continuous rotation servo. 

A continuously rotating servo must rotate in both directions.  This servo only runs continuiosly in one direction.  If you go the other way it stops after several turns.

Also, when it runs in the "continuos" direction, it goes "slower" after several turns.

So, don't "assume" anything about this servo.

[jerry_dcjx]

i think it can be use as a continuous rotation servo, since a servo that can rotate more than 1 turn cannot have a rotate limit. also, there is a way to make up the rope that can rotate infinitely in the instruction. when i use it as a dc motor, it works same as a continuous rotate servo.

however, i think it still have a encoder in it, so it still can be control as a servo without lock.

[mathterizer]

Phil:

We are looking forward to trying the 3.5 rot servo. We were anticipating that it might be treated as a 180degree servo, and that the 0 - 255 would be divided across (3.5 x 360 = 1260 degress). Has that been your experience?

We were looking forward to having that positional torque that could be geared and still have decent range of motion.

Thanks.

[Philbot]

Hi

If you go back to my first post on this thread, you'll see that I "sort of" got what you want, but with some other glitches.  I'm eager to hear what others get when thry try this servo with the Servo Controller.

Phil.

[mathterizer]

Phil,

In your description offered in the OP were your identifying it as the 180 degree or the continous?

When we get ours, I'll do some detailed testing on the 'other' setting, and also see if I get anything different in LVLM 2010.

Thanks.

[Philbot]

Hi

Don't know what you mean by "OP".  However, in the Schematic Editor I tried both settings.  No real change.

In reality, Continous rotation AND 180 Deg mode both put out PWM pulses in the same range.

CR servos are meant to translate them into Speed and Direction.  180 Servos are meant to translate them into Fixed Position commands.

My "Sail" servo didn't seem to be able to decide which method it was going to use consistantly.

If it Truly is a 3.5 Turn Absolute position servo, it should go to a position and STOP.  It should NEVER rotate "continuosly" in either direction.  Mine did, in the CCW direction.

If it Truly is a Continuos Rotation servo it should be able to rotate continuously in BOTH directions.  Mine Didn't.  It eventually stopped in the CW direction.

I actually don't care which it is, I just want it to choose.

Hope you get better results than I did.

Phil.