High Torque Servo Control?????

Navic

I have a HS-5645MG high torque servo that I need for a project. I found some general documentation online about the pulses needed to control this servo, but everything I try with the BS2 doesn't work.... Well it turns, but at a pace that is barely visible.

Sites say that this servo takes 0.9mS to 2.1mS, with 1.5mS center, 4.8-6V range. I verified 5 volts and used this code:

counter VAR Byte
FOR counter = 0 TO 7
  PULSOUT 10, 450
  PAUSE 20
NEXT
END

What am I doing wrong? How can I get the BS2 to drive this servo as easily as the Parallax standard servo? Thanks in advance!

Prettybird

I am thinking of doing a similar thing in the future as my boe increases in weight. Metal gears are nice too. As touque inncreases, so does current. You will have to go with a H bridge to power your servo. I have researched some other brands and may take 1 to 2 amps compaired to the Parallax (futuba) which only takes MA. 168 oz. / in is over 3 times the power of 47 oz. / oz. Like compairing power sonsumption of a 50 watt light to a 150 watt light. Best go higher amps on the H bridge. I plan on at least 2 amps.

W9GFO

Navic said...
How can I get the BS2 to drive this servo as easily as the Parallax standard servo? Thanks in advance!

Some metal gear servos cannot be converted to continuous rotation because the output gear does not have teeth all the way around. Something to check before upgrading the BoeBot servos.

Navic, you did make a comparison to the Parallax standard servo but just to verify, the 'standard' servo is one that moves to a commanded position and then stays there. It can only move through approx 180 degrees of arc. The servos used for the wheels of a BoeBot are 'continuous rotation' servos.

In the code above I wold not expect to see any movement of the servo if the servo is already in the position that you are telling it to go to.

What happens when you run this code? (may not be exactly right - haven't programmed a Basic Stamp in a while)

Do

FOR counter = 1 to 50
  PULSOUT 10, 450
  PAUSE 20
NEXT

FOR counter = 1 to 50
  PULSOUT 10, 900
  PAUSE 20
NEXT

LOOP

Rich H

edited to correct FOR NEXT loop iterations

Post Edited (W9GFO) : 5/24/2009 4:49:33 PM GMT

W9GFO

Just looked up the gear set for that servo. Looks like it is a good candidate for continuous rotation.



Here is an example of one that would NOT work for continuous rotation. Hitec HS-81



Rich H

Post Edited (W9GFO) : 5/23/2009 4:23:20 PM GMT

Navic

I took Prettybird's advice and am using a 6V 2A power supply for the servo and it starts to respond. W9GFO - I tried your code as well as mine and notice something very strange - the servo seems to have a mind of it's own.... It moves to the positions requested then performs random motions as long as power is applied. Is there some sort of pulse that keeps it still?

W9GFO

The code I posted should have the servo moving back and forth endlessly.

Uh-oh. It is only going through each FOR.. NEXT loop 8 times which will take only 160 mS. Not enough time for even the fastest servo to reach it's destination. Increase that to 50 so that it allows 1 full second to swing each way.

To keep it still just send the same pulse over and over again, 50 times a second. This is where something like the ServoPAL comes in handy. You send it a single pulse and it continues to send that same pulse every 20 mS.

Next step, if there are still problems, is to verify that you are not experiencing brownout - and put up a picture and/or schematic of your setup.

Rich H

Post Edited (W9GFO) : 5/24/2009 4:52:33 PM GMT

Prettybird

I have found a hobby store online with a super servo and will modigy it to continous rotation for free without voiding the warrenty. Email me if interestted and state you saw in the parallax forum or it may end up as spam.

surgent

Hey mate did u have any luck with the Hs-5645's? reading this reminded me i have a pair in my stash and could prolly find a use for them if i could get them working [noparse]:)[/noparse] Thanks.


edit: ok ok, you convinced me, dug them out and they are both happy to work with my bs2px (from pulse duration 920 to 2750 if anyone cares) not quiet 180' but better than nothing.

You mentioned they can be modded to be continuous, ill see what i can find about that cause these would be a great addition to my bots [noparse]:)[/noparse] Cheers guys

Post Edited (surgent) : 6/24/2009 2:47:05 PM GMT