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Author Topic: Modified Servo Lifespan  (Read 2355 times)

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Offline pete2009Topic starter

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Modified Servo Lifespan
« on: June 24, 2009, 03:57:02 PM »
I spent some time today speaking to a hobby store owner. I asked him what he would recommend as a method of propulsion for a robot.
The choice was between a DC motor or a modified servo.

He said that even if we ignore the fact that DC motors give more power the servos servos aren't really meant to be on continuous rotation by design, therefore they do take more strain (ie lesser lifespan) then a DC motor. In his shop servos cost more then the DC motors so he wasn't telling me that just to make some money off me.

Can anybody comment on this if DC motors are in fact better? This is ignoring the fact that servos are a lot more plug and play then dc motors.

Also can someone PLEASE clear up for me, what exactly I need to drive 9V motor from an ARDUINO board. Please post a link to a product if possible for the part. Shop is immaterial I just want to see what the sucker is and what it looks like.

Thanks



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Re: Modified Servo Lifespan
« Reply #1 on: June 26, 2009, 12:46:47 PM »
Servos are not the same as motors. Its like saying the only difference between a bike and a car is price :P

95% of all my servo failures are due to gears breaking, and its always the plastic gears. Get a more expensive servo with higher grade gears, or buy a bunch of replacement gears to fix it when they break.

Most of the gear failures are due to high shock forces, not wear.

Offline pete2009Topic starter

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Re: Modified Servo Lifespan
« Reply #2 on: June 26, 2009, 02:26:50 PM »
I realise that servos are not the same as motors, but my question is which would last longer under similar conditions.

Offline Trumpkin

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Re: Modified Servo Lifespan
« Reply #3 on: June 26, 2009, 07:35:31 PM »
Quote
I realise that servos are not the same as motors, but my question is which would last longer under similar conditions.
Hard to say, the dc motor would probably last longer. If you get a high quality metal gear servo it will last for quite a while (long enough that you won't have to worry about it).
Quote
Also can someone PLEASE clear up for me, what exactly I need to drive 9V motor from an ARDUINO board. Please post a link to a product if possible for the part. Shop is immaterial I just want to see what the sucker is and what it looks like.
You would need an H-Bridge, the type of H-Bridge is completely dependant on how much current your motor draws, so nobody can really show you a specific part.
Robots are awesome!

Offline Ro-Bot-X

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Re: Modified Servo Lifespan
« Reply #4 on: June 26, 2009, 08:00:01 PM »
Pete,

I have a Roboduino on my robot and cheap (plastic gears) standard servo modified for continuous rotation. I used this cheap servo just to see how well is working and I have to say it's ok-ish for that money (about $7 each). I used to have a pair of Parallax continuous rotation servos (Futaba) and they are less noisyer.

The problem I have with the servos is they are slow and noisy. Better quality, metal gears servos are less noisy, but still slow. So, I am looking into geared DC motors that are as quiet as possible (high quality motors) and have integrated encoders (I can build the encoders, but I prefer not to). I also need the cheapest solution, so I have ordered surplus Faulhaber motors (with encoders) for a bit over $10 each, that I will receive sometime next week.

To interface these motors with Roboduino, I am working on an I2C motor controller module. This module will have it's own microcontroller on board and a motor driver (H-bridge). You can connect the H-bridge directly to the Roboduino for simple motor control. But I  need to count the encoder pulses, use smooth ramp up and ramp down speed, keep track of traveled distance, that's why I use a second microcontroller just for this module.

So, to answer you question(s), to have a reliable motor, use eighter servos or DC motors with metal gears. If you need faster, use DC motors. To interface with Arduino, use an H-bridge, that you will need to choose after you get the motors, because it depends on max current the motors will draw. If you need advanced DC motor control, use a second microcontroller (plus H-bridge) to deal with the motors.

Choose the motors, find out the max current, and I'll recomend an H-bridge chip.
Check out the uBotino robot controller!

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Re: Modified Servo Lifespan
« Reply #5 on: June 26, 2009, 08:26:46 PM »
I realise that servos are not the same as motors, but my question is which would last longer under similar conditions.
Depends on the motor and the servo :P

A $2 el-cheapo motor will fail way before a $300 servo ;D

You'd do better looking up a specific servo for people complaining that it failed, and statistically figuring out how long it'll last. It also depends on the application, and how well you treat it. For example, an el-cheapo motor will last much longer if you put a cap between its leads, etc.

Offline TrickyNekro

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Re: Modified Servo Lifespan
« Reply #6 on: June 27, 2009, 09:37:50 AM »
Then.... Durability is kinda how you use the servo...
A plastic gear servos are prone to shock... But.... I had build a tank robot... that truly had much trouble in this poor life
but it's running one some 2 years old servos.... That had worked many many hours....
When a servo runs adjusted for continues rotation mounded on a robot... it's kinda hard to find an object so hard to
to immediately stop the servo... and shock will be adsorbed some way....
What kills servo is an extreme command.... Which means, having the servo go all the way fast forward, and immediately order it to
break and reverse with full speed.... I did that test on a sub - micro servo with almost no load, only to find that it broke down
after some hours testing.... which was quite disappointing...

So what really feels like being the magical word is..... RAMP UP speed... Don't accelerate or brake on full throttle or brake.....
Take an example of real cars...... the do miles and miles on normal runs.... But when pushed to limits... the only do some circuits
before they need a service.....


Regards, Lefteris
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline Admin

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Re: Modified Servo Lifespan
« Reply #7 on: June 27, 2009, 09:56:40 AM »
When a servo runs adjusted for continues rotation mounded on a robot... it's kinda hard to find an object so hard to
to immediately stop the servo... and shock will be adsorbed some way....
What kills servo is an extreme command.... Which means, having the servo go all the way fast forward, and immediately order it to
break and reverse with full speed.... I did that test on a sub - micro servo with almost no load, only to find that it broke down
after some hours testing.... which was quite disappointing...

So what really feels like being the magical word is..... RAMP UP speed... Don't accelerate or brake on full throttle or brake.....
Agreed. I used to have my ERP do ninja moves with its arms, but the stop/start motions kept breaking gears. Now the arms ramp up speed, like doing Tai Chi or something. Servos last much longer now :)

Offline TrickyNekro

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Re: Modified Servo Lifespan
« Reply #8 on: June 27, 2009, 06:04:29 PM »
Good thing you can still use their ESCs, when broken eeehhh?
« Last Edit: July 03, 2009, 04:01:25 AM by TrickyNekro »
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline RoboChan

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Re: Modified Servo Lifespan
« Reply #9 on: July 02, 2009, 11:26:13 PM »
To interface these motors with Roboduino, I am working on an I2C motor controller module. This module will have it's own microcontroller on board and a motor driver (H-bridge). You can connect the H-bridge directly to the Roboduino for simple motor control. But I  need to count the encoder pulses, use smooth ramp up and ramp down speed, keep track of traveled distance, that's why I use a second microcontroller just for this module.

Can you make a tutorail for this i want to do something like this.

 


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