Author Topic: servo for $50 robot  (Read 751 times)

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Offline beachboy612Topic starter

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servo for $50 robot
« on: June 20, 2012, 12:45:15 AM »
I hooked up my servo to my microcontroller and sent the hex file in order to make the gears turn.  I cut the pot off and gear tab and followed all the directions.  Just for kicks I did not zero the pot and put it all back together just to see it rotating 360.  It did rotate completely, but was so slow compared to the unmodified servo I started with.  Could I have possibly contaminated the gears?  and if so, would it be best to wash them all and regrease them to make sure they are not contaminated?  this is coming from a complete noob so please let me know.  dont want to do any uneccesary damage.  Please let me know what you think the reason is for the slow gears.

Offline Webbot

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Re: servo for $50 robot
« Reply #1 on: June 20, 2012, 11:48:51 AM »
The velocity/acceleration  of a servo tends to relate to the difference between its current position and where you want it to go. ie tell it to swing through a large angle and it will move fast, but for a small change it will move slowly (otherwise it will overshoot).

The trick with modifying a servo, by centering it and gluing the pot, is that it thinks that it never gets to where it wants to - so it just keeps on turning trying to get there (to no avail). By gluing the pot to '0' then the larger position you give it then the quicker it will move to (try) and get there. Hence you can get different speeds. However: this does depend on servo model to servo model - never expect some kinda linear speed increase (don't forget that servos are being used as 'cheap' motors).

So if you haven't glued the pot to '0' then that can give you problems as its 'current position' is no longer fixed and hence effects the speed at which it tries to move.

Re-grease etc? Well wouldn't hurt - especially if you've shed lots of grease playing with it. Main thing is - now you know the code works - is to get it to center to the best of your ability before gluing it.



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Offline beachboy612Topic starter

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Re: servo for $50 robot
« Reply #2 on: June 20, 2012, 12:32:16 PM »
Thanks for the info Webbot.  I think I should regrease because I did drop the gears a few times in the kitchen where it may have collected small dust particles.  Can i just wash them all without incurring any damage?  I am using a HS-311 servo by the way, same as in the tutorial.  I am pretty sure there is something wrong because a robot moving that slow is just not cool.  i have another servo to modify so hopefully it goes better.  I used this stuff called gorilla glue and it wasnt very great with the gluing of the pot as it did not completely enter the pot crevices.  probably need to use a different super glue.

Offline beachboy612Topic starter

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Re: servo for $50 robot
« Reply #3 on: June 20, 2012, 12:34:20 PM »
would it be more accurate to saw the pot at the lowest level using a knife, then use pliers to zero it? 

Offline Gertlex

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Re: servo for $50 robot
« Reply #4 on: June 20, 2012, 01:57:46 PM »
The fact that its moving slowly is not a mechanical problem (aka not grease/gears).

If you remove the gears of the servo, and just look at the output pinion of the motor as you move the potentiometer, you will see its speed varying.  This is perhaps also the best way to center the servo/potentiometer.  When the motor sans gears is not spinning, its definitely centered.  (Because there's friction in the gears, you can have a slightly non-centered servo where the torque being supplied to the motor is not enough to overcome the gears' friction.)

Quote
would it be more accurate to saw the pot at the lowest level using a knife, then use pliers to zero it? 
More accurate than what? It should be sufficiently accurate, though.  Tweezers will also work well for pot adjustments.

Gorilla glue will work, but keep in mind that it expands a lot.  You want to make sure that the expanded glue isn't getting in the way of anything.

(I've not modified a hobby servo in a few years, so I forget how much of a potential problem the glue expanding is...)
I

 


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