Author Topic: Hacked servo speed  (Read 3006 times)

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Offline izuaTopic starter

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Hacked servo speed
« on: February 13, 2008, 10:38:09 PM »
I'm thinking of using hacked servos for my first robot. The advantages really outweight the flexibility if you build your own gearbox, wheel mounts, power and control stages, and so on. Plus, servos are widely available and cheap.

But what would the final speed be? I played with a friend's servo at 180 degrees (yes, from .5 to 2.5 ms pulse width :P), and it took it about half a second for a half rotation. So, if I get a second for a full rotation, and at 60 mm diameter wheel, I'll get like, 6 cm / second speed. I don't think that's really fast, but then again, it might be even low, if they won't put out the required torque.

So, I'm asking you out there, who hacked servos, how fast are the hacked servos spinning compared to the original, angular, speed?
I'm also thinking, I could just use the gearing, overvoltage the motor and make a small power level inside the enclosure. I heard the hacked servos don't offer a speed ramp, either, so it's either full speed or stop.
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Offline airman00

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Re: Hacked servo speed
« Reply #1 on: February 13, 2008, 10:46:43 PM »
when you hack a servo you lose position control , but you gain speed control.
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Offline izuaTopic starter

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Re: Hacked servo speed
« Reply #2 on: February 13, 2008, 11:43:13 PM »
I know that. How fast would the hacked servo turn compared to the unhacked servo?
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Offline airman00

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Re: Hacked servo speed
« Reply #3 on: February 14, 2008, 05:44:40 AM »
I know that. How fast would the hacked servo turn compared to the unhacked servo?

it would turn at the same speed as before
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Offline izuaTopic starter

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Re: Hacked servo speed
« Reply #4 on: February 14, 2008, 06:29:23 AM »
So i guess i'll need quick servos for a good speed. Or is the average low-cost servo, with bigger wheels just fine?
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Offline Rebelgium

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Re: Hacked servo speed
« Reply #5 on: February 16, 2008, 05:11:23 PM »
So i guess i'll need quick servos for a good speed. Or is the average low-cost servo, with bigger wheels just fine?

All depends on what you want your robot to drive over. For normal floors, normal servo's will be ok.

I know that.
According to the last sentece in your first post, you didn't.
« Last Edit: February 16, 2008, 05:13:44 PM by Rebelgium »
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Offline Admin

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Re: Hacked servo speed
« Reply #6 on: February 18, 2008, 09:13:41 AM »
A hacked servo (in theory because I never measured it) would be faster because there is no final angle for it to slow down at.

Servo speed is also affected by torque, such as a heavy robot to pull or arm to lift.

Doubling wheel diameter will double the robot speed (assuming torque isn't limited).

Offline izuaTopic starter

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Re: Hacked servo speed
« Reply #7 on: February 18, 2008, 10:14:19 AM »
So is the opposite true? Using a lower wheel diameter (lever) will grant me more torque, so I can go on steep hils or haul pb-acid batteries  ;D
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Offline Rebelgium

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Re: Hacked servo speed
« Reply #8 on: February 18, 2008, 11:19:09 AM »
yes
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Offline paulstreats

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Re: Hacked servo speed
« Reply #9 on: February 20, 2008, 06:33:17 PM »
And so back to your original post.

How did you work out that a full rotation of a second on a 60mm diameter wheel would travel at 6cm per second?
this is more like 28.26 cm per second which will be fine. (if were working to the usual pi R2)

 


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