stamp stripping out servo gears, BS2

nickm304 · 2008-12-02 22:22

Ok so I have successfully hooked up a larger JR servo and it does exactly what I would like it to do, when I swap it out with the mini servo i NEED to use (hitech HS-81) It spins furiously and strips out the gears. I am using a a 6v (4 AA in series) power supply, any ideas what is wrong? I have one set of gears left. I am running stamp BS2

servo CON 15
LOW servo

FOR i = 150 TO 1000 STEP 10
PULSOUT servo,i
PAUSE 20
NEXT

PAUSE 1000

FOR i = 1000 TO 150 STEP 10
PULSOUT servo,i
PAUSE 20
NEXT

END

Bruce Bates · 2008-12-02 22:41

nickm -

Just out of curiosity, how do you have "i" defined?

Regards,

Bruce Bates

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nickm304 · 2008-12-02 22:49

it appears i is defined as follows,

i VAR Word

perhaps it should be byte?

Its just weird because it worked on a regular sized servo, then when hooked up to a mini servo, it went crazy.

MSDTech · 2008-12-02 22:52

Many servos - the Hitech HS-81 included require a 1000 to 2000 ms pulse for positioning. Using a BS2, your code will be sending pulses from 300 to 2000 ms. You're stripping the gears by driving it too far in one direction. It won't be able to reach a position corresponding to the 300ms pulse.
Change your range for i to 500 to 1000 and see how that works.

nickm304 · 2008-12-02 22:58

MSDTech said...
Many servos - the Hitech HS-81 included require a 1000 to 2000 ms pulse for positioning. Using a BS2, your code will be sending pulses from 300 to 2000 ms. You're stripping the gears by driving it too far in one direction. It won't be able to reach a position corresponding to the 300ms pulse.
Change your range for i to 500 to 1000 and see how that works.

any idea what the range on the hs-81 is? it appears i can turn it almost 180 degrees by hand, but i saw someone online say it is only supposed to be 90? I will give 500 to 1000 a shot, thanks!

MSDTech · 2008-12-02 23:08

The only detail on the Hitech web site was that the HS-81 has a 1500ms neutral position. So whatever range of pulses it accepts, test out slowly from the neutral.
Neutral = 750 on bs2.
First check do 700 to 800 and see how it moves then keep expanding the range to get the degree of movement you require.

nickm304 · 2008-12-02 23:10

UPDATE:::
thanks MSDTech, this code appears to be working now, do you suggest any other changes?

thanks for the help guys!!

servo CON 15
i VAR Word
LOW servo

FOR i = 500 TO 1000 STEP 10
PULSOUT servo,i
PAUSE 20
NEXT

PAUSE 2000

FOR i = 1000 TO 500 STEP 10
PULSOUT servo,i
PAUSE 20
NEXT

END

Post Edited (nickm304) : 12/2/2008 11:48:19 PM GMT

Zoot · 2008-12-02 23:50

Yes, the "greater" the step value, the faster the servo will reach the final postion.

That said, I strongly encourage you to read up on the PULSOUT command in the Pbasic Manual. 500-1000 = 1ms-2ms but *only on a BS2* -- all Stamps are different. Why? Because the actual "unit" used in a PULSOUT command varies from Stamp to Stamp. On a BS2 the "unit" is 2us, which is why 500 "units" = 1000us = 1ms. But on a Stamp BS2p, the "unit" is .8us.

The "easy" way to deal with this is define a scaling constant in your program -- this constant can be changed depending on the Stamp. This lets you write your PULSOUT statements so you are always working (and thinking) in microseconds for servos, e.g.

i VAR Word
ServoLeft PIN 14
ServoRight PIN 15
SvoPulseAdj CON $080  ' convert us to pulsout "units" THIS IS FOR A BS2


FOR i = 1 TO 100
PULSOUT ServoLeft, 1500 */ SvoPulseAdj ' write it in microseconds, convert to units -- i.e., 1500us = 1.5ms (center)
PULSOUT ServoRight, 1000 */ SvoPulseAdj ' 1000us = 1ms
NEXT

FOR i = 1000 TO 2000 STEP 10
PULSOUT ServoLeft, i */ SvoPulseAdj
PULSOUT ServoRight, i */ SvoPulseAdj
PAUSE 20
NEXT

FOR i = 2000 TO 1000 STEP 2
PULSOUT ServoLeft, i */ SvoPulseAdj
PULSOUT ServoRight, i */ SvoPulseAdj
PAUSE 20
NEXT

Better yet, wrap it all in a sub so you only have to set it up once...

i VAR Byte
svoPulse VAR Word
svo VAR Bit
ServoLeft PIN 14
ServoRight PIN 15
SvoPulseAdj CON $080  ' convert us to pulsout "units" THIS IS FOR A BS2
left CON 0
right CON 1

Main:

FOR i = 1 TO 100
   svoPulse = 1500
   svo = left
   GOSUB send_svo
   svo = right
   GOSUB send_svo
NEXT

FOR svoPulse = 1000 TO 2000 STEP 10
   svo = left
   GOSUB send_svo
   svo = right
   GOSUB send_svo
NEXT

GOTO Main

send_svo:
   PULSOUT ServoLeft+svo, svoPulse */ SvoPulseAdj
   PAUSE 10
   RETURN

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Post Edited (Zoot) : 12/3/2008 12:00:25 AM GMT

stamp stripping out servo gears, BS2

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