As an RC-system newbie, I encountered some confusing choices, and now that I've found some better info, I wish to share it. Several builders have used a Servo-Tester (ST) as the basis for a throttle, and as luck would have it (for us), RC manufacturers have also been using servo wire and connectors to make the connection between the Electronic-Speed-Controller (ESC) and the radio signal reciever on the model airplanes that these components were originally designed for.
Its my understanding that a servo is a device that takes an electrical signal and moves a device (such as a rudder, or a retracting landing gear). For the enthusiast who wishes to test and adjust model servos in his garage, demand has produced inexpensive servo signal adjusters. The industry standard seems to be a servo signal that usually operates somewhere between 0V and 5V.
It is useful to understand that some ESCs have a Battery-Eliminator-Circuit (BEC), which is a tiny DC/DC converter. This reduces the main pack voltage (18V and 22V are common, among others) down to 5V for the servos. The battery that is 'eliminated' is the need to have a separate 5V battery to power the models servos.
If you wish to use an ST as the basis for an RC-Ebike throttle, you should select an ESC that has a BEC, or...when using a BEC-less ESC, you either add a separate universal-BEC (UBEC), or a small 5V battery to power the servo supply wires. EVTodd has enjoyed success with 4 NiMH batteries of AAA-size in series for servo-supply 5V power, and Recumpence has employed UBECs with great performance reported.
I purchased a Turnigy ST, and also an E-Sky ST. The Turnigy is quite small, and the E-Sky unit is so tiny, the diameter of the knob in its pic is only 1/2"
http://www.hobbyking.com/hobbyking/stor ... oduct=8296
http://www.esky-heli.com/esky-esky-serv ... th=432_433
The Turnigy 85A ESC I had purchased has a 3-wire signal cable that had a confusing Orange/Red/Brown color scheme. This caused me some frustration, as many types of electronics can be immediately fried when plugged in wrong. I made sure the battery was dis-connected, and attempted to see if the plug was polarised in some way to ensure it could only be attached in the proper orientation. A fried component would take 2-3 weeks to replace from HK.
Much to my annoyance, the plug could be inserted in several ways. Also the STs had a square 9-pin arrangement that allowed the servo-plug to be attached either vertically or horizontally! With the assistance of several helpful ES posters, the issues were sorted out. There seem to be two fairly common plug and wire-color standards (among several other obscure standards):
It is my understanding that the Futaba/J female connector can accept both common male plugs, and the JR/Hitec-S male plugs can be used on either female plug. If you look closely at the graphic, you can see a rail alongside the Futaba male connector that attempts to ensure the plug is polarised, and can only be inserted one way. This ridge can easily be shaved off by a razor, if needed.
I'm told the JR/Hitec-S male connector is sometimes capable of being plugged in backwards. However, since the red/positive wire is the center wire on both standards, it has been reported that no damage will occur from a reverse plug-in. Since I will be purchasing raw connectors, I will use all Futaba/J's, since they are polarised, but can easly be modified if neccesary.
[in the pic above] The column of pins that the Futaba/J connector is attached to is "S2", the middle column is labeled "S1" (you can test two servos at once), and the nearest column is labeled "Batt" to allow adding a battery to test servos with.
Concerning the wire, there seems to be 3 common sizes. Ultra-light 32-AWG, the common medium weight 26-AWG, and the thicker 22-AWG. Long runs of wire may encounter a small amount of voltage drop. This would be where a 5V full-speed signal from the throttle ends up being only 4.5V when it reaches the ESC. I don't know how bad this issue will be, or if it is no issue at all for the common medium weight wire at a distance of 3-4 feet.
I have chosen to test the thicker 22-AWG wire, which is three individual wires that come in a "twisted" bundle rather than a 3-wire ribbon. One web-catalogue suggested that the twisted wire is somehow more resistant to radio static interference, plus it will eliminate voltage-drop as a possible issue at the beginning of my build. Rather than string several short pigtails together, I will buy a roll in order to have no extra connectors between the rear wheel drive and the handlebar ST-throttle.
Here is Hobby-Kings servo wire + connectors page:
http://www.hobbyking.com/hobbyking/stor ... tegory=376
Here is "Servo City's" wire and connectors page:
http://www.servocity.com/html/wire_conn ... cess_.html
I would like to take this opportunity to encourage everyone to AVOID the "Brown wire as Negative" standard. The Red/Black standard for Positive/Negative is one of the few standards that are consistently used around the world, regardless of language.
Since the Tech-Ref area is a "no discussion" section, please PM me with any helpful suggestions and links to additional suppliers. Corrections are also gratefully accepted.