HiTec Servos

I use HiTec servos a lot. They are common, inexpensive, and well made for hobby servos.

These are good quality and inexpensive hobby servos. I use HS-422 in fluffy. They are not very powerful, and so I replaced HS-422s on the back leg to help carry the weight in the back. They are fine servo, but probably not adequate torque for all applications.

The HS-485 is a very good inexpensive servo. They are very similar to the HS-422/425, but with more torque. In Fluffy I exchanged HS-485s for more expensive HS-645s that had gotten a worn gear. They worked great. For the cost these are terrific servos.

This servo has been around for a while, I think because it is popular. It is small, strong, and fairly cheap. What is not to like? If you are making a lynxmotion robot this is a good choice. I have had these servos strip their gears more than once. I think it is because they are among the more powerful servos you can get in such a small package. The small package means smaller gears. You can get replacement gears for them.

This is a quarter scale servo with good torque. It fits into Lynxmotion servo brackets and has durable metal gears. It is a little heavy, but it is powerful and durable. I have seen discussions of whether servos really perform up to their specifications, with these I think they really live up to their specs. I have used this servo with absolutely no problems on Sterylite6000.

A quarter scale servo with amazing torque for the price. Unfortunately they do not fit into Lynxmotion brackets. I use them for the leg lifting motors in Sterylite6000, in RobotZone brackets. That is fabulously strong.

The HSR-1425 is a servo that rotates continuously-- in other words it turns around like a conventional motor. You control it by pulse width so that you can adjust the speed and direction.

The HSR-1425 is great value that I highly recommend. For $16 you can buy a geared motor that is easy to mount and easy to attach a wheel to. It is not only reversing, but it also can adjust its speed. It can be controlled by most microcontrollers with no additional circuitry. It isn't as strong as some gear motors and you can't run as much power through it as a motor with an H-Bridge or a an electronic speed controller. But for quick light robot they work great.

I use HSR-1425s in the Peanut Tin of Terror. I considered using gear motors. Good gear motors cost $25 a pop, and the cheapest are probably $10 each. Once you have a gear motor you have to control it with an H-Bridge or electronic speed controller. The H-Bridge is cheaper, but it doesn't give you any speed control. An ESC can easily cost you $40 and up. So I could have spent $80 for a two wheel drive system ($20x 2 for motors, $40 speed control) but instead spent $32 on two HSR-1425s. You can definately get a lot more power or speed with other solutions, but the HSRs are cheap and they just work.

Dynamixel

Dynamixel servos are made for robots and seem to offer some clear advantages over hobby servos. Because they use serial communication they require fewer wires to the microprocessor, and less computational babysitting. They also can report back their position.

I have read that dynamixel servos have great holding torque but otherwise don't always live up to their torque ratings. Their are enough really good walking robots using Dynamixel servos that I am comfortable saying they are a good choice for a robot.

They do require very fast communication, so not all microprocessors are going to work well with them. In particular, I think you could have a problem using a BASIC Stamp and some Arduinios. Check ahead of time if your microprocessor can handle the communication speed required.

When you look at the features vs. the cost, these are terrific servos. When you consider the cost of brackets (which are usually included with these) they really do not cost a lot more than good hobby servos like the HS-645. But they have a lot more features, such as position reporting and heat detection.

Position reporting lets your controller read the position of the servos. This means you can pose a robot and have the controller remember the pose, which is really useful. It also means you can detect when the servo isn't going where you planned, such as when it overshoots a particular position.

These just came out and seem like a stronger version of the AX-12, with a faster coreless motor. They seem to be about twice the cost of AX-12s, without a doubling of performance. It doesn't mean they are not worth it, it just shows what a great deal the AX-12s are.

I only know of this servo from the robots that use it. But they are great robots made by talented builders. If you really want to spend a lot on servos, this is probably a very good choice. Google Giger, or the RNSL hexapod.

Where to Buy Servos on the Internet

Lynxmotion is a good source for robot kits, robot brackets, and robot servos. They tend to only sell servos that are appropriate for robots.

Servocity has a great selection of servos, R/C and mechanical bits. Not all of them are good choices for robotics but the selection is good.

Crustcrawler sell good quality high end robotics components. This is a good place to get AX-12s and brackets for them.

Trossen is a good site for a wide variety of robotic components.