From: FrryFox
Subject: Servos
Servos for the fursuit enthusiast
Servos: What are they?
Servos are special DC motors with gearing and a mini-controllers built in. Most servos have 180 degrees of motion with 90 degrees being “neutral.” Controlling the position of the out of the servo is done by sending a small DC pulse at low frequencies. 99% of all servo manufacturers use the 1500us neutral standard. This means a pulse where the signal is “high” for 1500us will hold the servo at the neutral position. (Futaba uses 1520us). And as a general rule to go all left is 1000us pulse, and full right is 2000us pulse, with all positions in between between 1000-2000us pulse.
Servos come in all sizes and powers from the sub-micro variety to the “giant” scale, and powers from as low as 17 in-oz torque to 400 in-oz torque (and higher). 4.8V is the standard power requirement, but most giant scale are 6V. If you need a specific servo, there is someone out there that makes it. A local hobby shop is a good (but expensive) place to get servos as RC airplanes and cars use the same servos as fursuits do.
A couple of notes on torque numbers: 400 in-oz of torque means that with a 1-inch lever arm, the servo can provide 400 oz of lifting/pushing force. A 1-inch lever arm gives 2 inches travel. So if you need 8-inches of travel, you need a 4-inch lever arm and on the servo mentioned in this paragraph, would get 100oz of lifting force. (Just over 6 lbs).
Servos: Safety
Servos are nice in that because of the lower power requirements, risk of electronic shock are very low. You are more likely to hurt yourself on the output side of the servo than anywhere else.
Servos: How to use them on a fursuit
Servos are fantastic devices for adding life-like movements to fursuits. Excellent examples are Sir Karl (a deer with servo powered ears) and Teddy Ruxpin. Hollywood uses servos extensively for animatronics, the close ups of the wolves from the movie Wolf (with Jack Nicholson) had dozens of servos in the muzzle and head for the realistic movements.
Unfortunately for the fursuiter, we have silly things like space and power constraints and don't have half a dozen people working the servos for us. Generally the fursuiter is limited to 2 to 4 servos (or 1-2 sets of servos link at the controller) based simply on the fact that there are only so many thing you can control while wearing a suit (i.e. in real-time).
There are ways to increase the number you can have a suit, but as for interactive control, 2 to 4 is about the upper limit. One way to increase the number is add a random pulse generator to a servo say on a tail or an ear for a random twitching of the tail/ear. Another is to have a microcontroller running a program do a pseudo-random program that controls a servo. Or add a HF receiver and have your friend in the corner controlling them (not very likely as the HF hardware is costly and bulky)
Servos: Controlling
Most of the talk on the fursuit list is about servo controllers. These are the small electronic chip(s) that generate that 1000-2000us pulse that physically controls the position of the servo. There are several approaches to using a controller:
COTS: Commercial Off The Shelf
Go buy one from a hobby store.
Pros: Easy to use. No electronics knowledge required.
Cons: Expensive! Tough to customize. Bulky.
ASICs: Application Specific Integrated Circuits
Unless you have ALOT of VLSI design knowledge and have a fab lab, don't even think about it.
Pros: All on one chip. No extra wires. Exactly what you need and nothing else
Cons: Requires in depth knowledge of chip design and a facility to make it. (I have designed some of my own ASIC's before, and for something like fursuiting, unless you are really bored I would recommend against it)
MicroControllers: Micro Code! YEAH!
Microcontrollers are fabulous little chips than can be sent a program and will happily execute it for ever. Better yet, the program can be erased and re-written. Few if any external parts required (maybe an oscillator and a few capsitors). Sounds like the ultimate answer…almost. Sir Karl used this approach and it worked fantastic for him. The product he used was the Basic Stamp. (http://www.rentron.com) It is a nice, semi-simple to program micro-controller. They do also offer some upgrades and enhancements, but watch the price tag.
Pros: All-on-one chip. Reprogrammable. Low-Mid price range. Control multiple servos
Cons: Sharp learning curve. “Perks” can cost extra. (I have yet to use this method personally, but others have with varying but usually good results)
PLA: Programmable Logic Array
These are very simple microcontrollers. They can be programmed just like the Basic Stamp, but have less internal circuitry. The programs are much simpler and require some off-chip pieces to get them to work.
Pros: Reprogrammable. Cheaper than MicroControllers. Control multiple servos.
Cons: Requires more external parts. (I have tried this route before, and IMHO its more work than its worth. Although it did lead my to build my own homegrown controller)
Homegrown PWM: Pulse Width Modulator
Thanks to the miracle 555/556 series of chip, home building a servo controller is quite easy. Radio Shack has a mini-notebook on the 555 chip, and the second design shown is a pulse width modulator. With a few more additions to the design it becomes much more robust and with a 556 you can control 2 servos at once. The difficulty is building the board and having the knowledge to build the circuit to behave properly.
Pros: Extremely cheap. Parts readily available at RadioShack. Can control 2 servos simultainously or independently
Cons: Requires some electronics knowledge and some soldering skills. (This is my personal favorite because of the amount of control it provides. If something dies, its really easy to fix/replace. http://soli.inav.net/~fox/fursuit/electronics.html)
Servos: Great, I know what they are, but what are the limits they can do?
Just about anything. I am currently developing a set of wings that use servos to expand and compress the wings. At last check, Legend was also planning to adapt his design for servos. Ruxpin uses a cassette player to record the control for his servos so the voice being played matches the eyes and mouth movements. I have had a servo in the tail for twitching. Sir Karl's ears. And I'm sure I have left out a bunch but you get the idea. Its limited only by your imagination (and the size of servo you can afford).
Servos: Where can I get some?
As mentioned a local hobby store carries them. I buy online from FMA Direct (http://www.fmadirect.com). I have been pleased with FMA quality but they aren't the “Cadillac” of servos. That would be Futaba. Futabas cost more, but they some of the best performance and low noise servos I have ever used.
And when all else fails, search the web for RC sights. See what they recommend for servos.
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