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Motor Choice 
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Post Motor Choice
Hi guys!

I have a project on my mind but before I start I need to plan a few things, one of those is the motor choice

I actually have 3 standard NXT motors
4 XL PF motors
2 Medium PF motors

My project needs many motors and I need to be able to tell 'em the angle, so let's put the PF motors away...

I was looking for mindsensors motors but I have a bit of trouble trying to plan the starting purchase, please help me understand how they work and their limitations :)

I understood that:

Port Splitter for NXT
Could allow me to plug the 3 standard NXT motors to one single port and still have all their features

8 Channel Servo Controller for NXT (NXTServo-v2)
This is my friend, right?
Allows me to plug 8 motors, I can choose from all Mindsensors motors

Motors
I have a choice in swing degree limit or get continuous loop ones, but basically they are the same thing
I can see from their site that they have medium or light motors, are there any large ones? And how do they compare to, let's say, PF motors?
I also noticed "RC" on some motors, while it doesn't talk about them being radio controlled I can see no other meaning to this RC, what is it?
A mounting kit is REQUIRED to mount each motor onto a Lego technic building

Battery
I can plug only ONE 4AA Battery Holder with NXT Mount to the 8 Channel Servo Controller
This will allow me to control one motor at a time and it's not possible to control all of 'em at once
... or maybe I can plug a battery holder to each motor to gain this ability?

That's all I think I understood, I'll be glad if anybody prove me wrong on something before I start ordering all the pieces :D

Thank you in advance


Fri Jan 29, 2010 6:00 am
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Post Re: Motor Choice
Hiya Jampoz,

I moved your topic to a better place.

Quote:
I understood that:

Port Splitter for NXT
Could allow me to plug the 3 standard NXT motors to one single port and still have all their features

No, this is not the case. Look carefully on that page, it has a note at the bottom:
Quote:
Upto three motors can be attached to SPLIT-Nx. Turning motor port ON through the NXT program will turn all the attached motors ON at once.

This is useful if you need to run all motors at once, however independent control of each attached motor is not possible and encoder values of the motors can not be used. i.e. rotation control feature of motor blocks can not be used.


Quote:
8 Channel Servo Controller for NXT (NXTServo-v2)
This is my friend, right?
Allows me to plug 8 motors, I can choose from all Mindsensors motors

Yes, you can use any of the servos that Mindsensors sells. I am not sure if it's your friend, but they work quite nicely :)

Quote:
I have a choice in swing degree limit or get continuous loop ones, but basically they are the same thing
I can see from their site that they have medium or light motors, are there any large ones? And how do they compare to, let's say, PF motors?

They are completely different from PF motors. These are servos, you give them a specific pulse and they move to a specific position or in the case of a Continuous Rotation servo, rotate at a specific speed.

Quote:
I also noticed "RC" on some motors, while it doesn't talk about them being radio controlled I can see no other meaning to this RC, what is it?

They are standard Remote Control servos, ie servos used in RC cars or boats or planes. You don't need a remote control to use them, you just need a controller, which is the NXTServo2 in this case.

Quote:
A mounting kit is REQUIRED to mount each motor onto a Lego technic building

Yeah, it will make your life a lot easier. You could make it work without them but it requires a lot of fiddling and may not be as reliable.

Quote:
I can plug only ONE 4AA Battery Holder with NXT Mount to the 8 Channel Servo Controller
This will allow me to control one motor at a time and it's not possible to control all of 'em at once
... or maybe I can plug a battery holder to each motor to gain this ability?

All the servos will be powered by the one battery holder and you *can* control them all at once using the controller. TYou don't need a battery holder for each servo. The battery holder connects to the controller which in turn powers the servos.

If you have more questions, be sure to ask!

Regads,
Xander

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Fri Jan 29, 2010 7:42 am
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Post Re: Motor Choice
Thank you, that's some nice info!

So what's the difference between a servo and a motor, the first one has the ability to move at certain degrees, is that all?
Can I achieve the same speed (PF motors) when looping continuously?

So, if they aren't controlled remotedly, why use RC on the name?


And sorry for posting in the wrong section, I thought it didn't have anything about programming so choosing this one seemed wrong at first

Thank you again for your help!


Fri Jan 29, 2010 10:11 am
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Post Re: Motor Choice
Hiya Jampoz,
Jampoz wrote:
So what's the difference between a servo and a motor, the first one has the ability to move at certain degrees, is that all?

No, a motor driver by sending current to the coils directly to control the speed and direction. A servo is a motor with a small control circuit that drivers the motor depending on the length of a pulse that is sent to it every 20ms.

Quote:
Can I achieve the same speed (PF motors) when looping continuously?

That depends entirely on the servo in question.

Quote:
So, if they aren't controlled remotedly, why use RC on the name?

They are servos that are generally used for remotely controlled vehicles.

Regards,
Xander

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Fri Jan 29, 2010 10:40 am
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Post Re: Motor Choice
Nice, thank you!

Now, why having a limited swing servo when one can have a continuous loop for only +2$?

After all these info I guess I'll grab a controller with at least 2 servos to test out some things :D


Fri Jan 29, 2010 11:02 am
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Post Re: Motor Choice
Oh, another thing... I'm reading the specs of each servo, it seems like they need almost a second for a complete turn, I guess they are good for moving stuff/rotating joints and not for speed purposes...

What do you think after your experience?


Fri Jan 29, 2010 11:07 am
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Post Re: Motor Choice
Jampoz,

Quote:
Now, why having a limited swing servo when one can have a continuous loop for only +2$?

The limited swing servo will set itself to a specific angle depending on the pulse length and stay there. This is very useful for joints. The continuous rotation (CR) ones are great if you have something that needs to turn at a specific speed.

Quote:
Oh, another thing... I'm reading the specs of each servo, it seems like they need almost a second for a complete turn, I guess they are good for moving stuff/rotating joints and not for speed purposes...

Some of them are slower than others. However, having said that, I don't think you'll be building anything with them that will race down the hall at great speed. At least not with the ones that Mindsensors sells. That is not what they're designed to do. On a CR servo With fresh batteries you'll get about 400 degrees per second and with flatter ones you'll be sitting at about 315 degrees. Mind you those are probably unloaded speeds, so as soon as you add some load to that, they will slow down some.

Regards,
Xander

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Fri Jan 29, 2010 12:25 pm
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Post Re: Motor Choice
Oh, does it mean I can't set a specific angle on CR servos?


Fri Jan 29, 2010 12:31 pm
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Post Re: Motor Choice
Jampoz wrote:
Oh, does it mean I can't set a specific angle on CR servos?

That's right. Unless you know exactly when to switch it off, which will be well neigh impossible.

Xander

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Fri Jan 29, 2010 12:46 pm
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Post Re: Motor Choice
Oh man that's the thing I took totally wrong, thank you!
Now they both have a purpose to me :bigthumb:


Fri Jan 29, 2010 12:52 pm
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Post Re: Motor Choice
So, apart from the Mindsensors ones, what choice do I have when buying servos or motors?


Mon Feb 01, 2010 4:25 am
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Post Re: Motor Choice
The servo controller will work with most standard RC servos. The only problem might be connecting them with Lego. The Mindsensors mounting pieces may not fit on them.

You can also use PF motors using two adapter cables available from Lego. Just Google for something like "connecting PF motor to NXT". With the PF motors you will be limited to the 3 motor ports on your NXT.

Xander

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Mon Feb 01, 2010 4:31 am
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Post Re: Motor Choice
Alright Xander!

So lemme get this straight, the RobotC drivers are needed to interface with the controller, it doesn't matter what kind of servos you plug onto it as long as they are supported by the controller itself, right?


Mon Feb 01, 2010 12:45 pm
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Post Re: Motor Choice
You assume correctly, sir!

Xander

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Mon Feb 01, 2010 1:37 pm
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