Servo / ESC / other RC tester (scratch kit build)
08-15-2009, 02:18 PM
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Servo / ESC / other RC tester (scratch kit build)
Here is another from-scratch / kit build I did recently, for something unrelated to RC, but I just realised it might be a useful thing to post here for fellow RC'ers.
For RC'ers, the use of this device is to test or diagnose problems with servos, ESCs, and other devices that normally rely on a receiver pulse. For instance if you have have an electric truck that won't go forward / backward, or a servo that seems to power on but not move, it's sometimes hard to tell if the problem is the servo itself or something else, ie. the transmitter, receiver, RF interference, etc. This device generates the same pulse a properly functioning receiver does, and then you can move the servo slowly throughout its range with the up and down button. It even has a calibration mode for ESCs, and an alternate mode for aicraft ESCs.
Just like the LiPo balancer kit I posted in an earlier thread, there's no reason anyone else can't build one also (that's why I'm posting it here). The component cost is around or under $5. at digikey in small quantities. The board is a standard 2-layer board, no surface mount parts, all through-hole, so no fancy soldering is required. The board once again is from expresspcb. The only catch is that unlike the lipo balancer build, this uses a microcontroller so you also need a atmel AVR programmer. I think the cheapest ones are about $40. on digikey. The microcontroller code is very adaptable to difference devices, as some servos apparently have more range than others.
#define POS_TRUE_CENTER 95
// for servo
#define POS_OFFSET 30
// for aircraft ESC
//#define POS_OFFSET 22
#define POS_MIN POS_TRUE_CENTER-POS_OFFSET
#define POS_MAX POS_TRUE_CENTER+POS_OFFSET
// for servo
#define POS_CENTER POS_TRUE_CENTER
// for aircraft ESC
//#define POS_CENTER POS_MIN
#define CYCLE_MAX 4
Took only a couple of hours to code and test, though I'm planning on making a few more changes in the near term. It actually has 2 3-wire inputs and 2 3-wire outputs, so you could for instance make it into a simple mixer or even a 'dig' control for a crawler with a multiple-motor drive (ie. a dual motor-on-axle drive), etc.
For RC'ers, the use of this device is to test or diagnose problems with servos, ESCs, and other devices that normally rely on a receiver pulse. For instance if you have have an electric truck that won't go forward / backward, or a servo that seems to power on but not move, it's sometimes hard to tell if the problem is the servo itself or something else, ie. the transmitter, receiver, RF interference, etc. This device generates the same pulse a properly functioning receiver does, and then you can move the servo slowly throughout its range with the up and down button. It even has a calibration mode for ESCs, and an alternate mode for aicraft ESCs.
Just like the LiPo balancer kit I posted in an earlier thread, there's no reason anyone else can't build one also (that's why I'm posting it here). The component cost is around or under $5. at digikey in small quantities. The board is a standard 2-layer board, no surface mount parts, all through-hole, so no fancy soldering is required. The board once again is from expresspcb. The only catch is that unlike the lipo balancer build, this uses a microcontroller so you also need a atmel AVR programmer. I think the cheapest ones are about $40. on digikey. The microcontroller code is very adaptable to difference devices, as some servos apparently have more range than others.
#define POS_TRUE_CENTER 95
// for servo
#define POS_OFFSET 30
// for aircraft ESC
//#define POS_OFFSET 22
#define POS_MIN POS_TRUE_CENTER-POS_OFFSET
#define POS_MAX POS_TRUE_CENTER+POS_OFFSET
// for servo
#define POS_CENTER POS_TRUE_CENTER
// for aircraft ESC
//#define POS_CENTER POS_MIN
#define CYCLE_MAX 4
Took only a couple of hours to code and test, though I'm planning on making a few more changes in the near term. It actually has 2 3-wire inputs and 2 3-wire outputs, so you could for instance make it into a simple mixer or even a 'dig' control for a crawler with a multiple-motor drive (ie. a dual motor-on-axle drive), etc.
