# types of motors.. stepper.. servo..?

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#### haleemul

##### New Member
Just wondering if anyone can explain me what are stepper motors and servo motors?

what is the difference between the two? and if i were building a hexapod robot which motor would be better suited?

#### Nigel Goodwin

##### Super Moderator
haleemul said:
Just wondering if anyone can explain me what are stepper motors and servo motors?

what is the difference between the two? and if i were building a hexapod robot which motor would be better suited?

A servo motor is a normal DC electric motor, complete with gears and servo electronics - it only moves over a limited rotation in response to an input pulse between 1-2mS. They are small and very powerful for their size (due to the low gearing).

A stepper motor works in a completely different way, they provide rotation a step at a time, and move an accurate amount on each step. However, they are large, expensive, heavy and have relatively little power.

Hexapod robots commonly use servo's, steppers are unlikely to have sufficient power and are too big and heavy.

#### Rescyou

##### New Member
Servos

I would say servos are the only way to go.
Hobby servos (the ones in model planes etc.) usually don't have 360 degrees of continuous motion.

You can open them up and do some simple modification to rip out the limited rotation mechanics and even the servo electronics to make a decent mini-gear motor that will run from normal unpulsed dc. There are lots of tutorials around for modification.

Resc.

#### toowie2uk

##### New Member
I'd like to counteract a few things above, no offense intended.

Most servos need 1-2ms pulse every 18ms. You can get off shelf controllers, but not the easiest thing to control from a microprocessor, cos they are effectively analogue, but everything is possible.

A stepper motor is very useful, because with 4 transistors and 4 resistors and 4 diodes, you can control a stepper from the printer port of your computer, or using a CMOS counter (about half a dollar IC - (I'm UK - work in £s usually!) fairly easily. Stepper are very accurate.

Have a look at www.epanorama.net , or if you want some more help. reply and I will see what I can do.

#### Nigel Goodwin

##### Super Moderator
toowie2uk said:
I'd like to counteract a few things above, no offense intended.

Most servos need 1-2ms pulse every 18ms. You can get off shelf controllers, but not the easiest thing to control from a microprocessor, cos they are effectively analogue, but everything is possible.

No offense taken, but:

On the contrary, servo's are very easy to control from a micro-controller, all you have to do is provide them a pulse from 1-2mS at fairly regular intervals (the 18/20mS isn't at all critical). This is very easy to do with a micro-controller, even the BASIC STAMP finds it easy!.

You can buy pre-programmed PIC's for controlling servo's, they typically accept an RS232 input and provide outputs to feed 8 servos (and are commonly used in hexapod robots).

I wouldn't really describe a 1-2mS pulse as 'analogue', it could just as well be described as 'digital' - considering that 'digital' amplifiers work in a similar way (with varying width pulses), perhaps 'digital' would be more accurate.

#### toowie2uk

##### New Member

I own about 60 stepper motors and one servo! so you can see where my opinion lies! I see what you mean re the digital. I dont know enough about them to argue my case - I was tinkering trying to drive NE555 based PWM from a DAC on my parallel port.

Ivancho

#### Alex_rcpilot

ivancho said:
You can drive a U$10 servo with 4.8V-7.2V (smaller battery) and have a 57in/oz ... Ivancho ivancho,thaks for your post. I'm an R/C fan,and as you know,we need servos on your aicrafts.The most widely used servos here are Futaba&JR regular ones.I also found a local website selling there own servo products for robots.But since there're few people bulding their own robots here,fewer have enough experience about how to chooes robot servos.I wonder what types(or brands)of servos you often choose to build a robot in the US,and their price.Would a servo used on R/C chopper,like a futaba S9602,be suitable for a small hexapod robot? #### ivancho ##### New Member Perhaps you mean the S9206.... yes a servo is a servo, kind of thing... but I would not recommend having those only because of their price U$90 each is a little bit too much for the motors. Instead you can just go for the normal standard version like the S3003 that runs for like U$12.95. Since you are into the R/C stuff you probably know of towerhobbies. THey sell their own servos which are normally cheaper than the "brand" ones. And I believe Futaba manufactures them anyhow :wink: . Also you probably know of **broken link removed** they have a special right now for 5 servos for$51.00 (no S/H w/in US).... unless you have the S9206 readyly available I would not recommend them.... heck you may as well put them on ebay, buy the S3004 deal and end up with cash in your pocket to get a PIC board :wink:

Ivancho

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