Seeking help to confirm what I believe to be true - is the SparkFun Servo Trigger board only compatible with Analog servo motors, or can it also support digital ones?
I have a project that utilizes the trigger board and due to size constraints, I need to use a 2g 2502 size servo (GS2502MG). Upon connection and modulation, the servo becomes hot to the touch, and my initial test motor has melted. Even in the resting position it would remain hot.
Input voltage is 5 volts, DC. Servo is rated for 4.8 - 6volts
The only variable I can conclude is the analog vs digital servo. The servo size is a key factor in my model, making this now a challenge. I don’t see a servo small enough from Sparkfun, unfortunately.
Is there any way to utilize a digital servo with the current trigger board, or is there a different board option available?
Any servo with the standard 3-pin header (GND, power, signal) should work with the Servo Trigger Board. Almost all servos have the same input voltage range (4.8V to 6V) and accept the same kind of PWM signal. There is some variation in the exact pulse width ranges, but most servos have a “middle” pulse width of 1500us, with a common minimum and maximum pulse width of 500us and 2500us. Some fancy digital servos also accept a UART-like communication over the signal pin, but they still accept the standard PWM signal.
I don’t have experience with the GS2502MG specifically, so I can’t say for certain why it became hot and melted (sorry to hear about that!). The fact that it got hot implies it was drawing a lot of current for some reason. Are you certain the servo cable was not flipped? Was the output shaft free to spin, or was it connected to something that the servo was unable to move? Were you sending a pulse width outside of the 500us to 2500us range?
It’s also possible there was a defective device. Do you have a second servo and/or second Trigger Board to test with?
Thank you for the reply. I appreciate knowing that either servo type (digital or analog) should work with the trigger board. I did purchase two trigger boards (nice to have a spare), and achieved the same results with either board.
Servos have been connected correctly with the three wires -
Brown - GND
Red - VCC
Yellow - SIG
The GS2502MG overheated and melted. I tried another model I had available, FH-2502. Similar spec and size. This one also unfortunately began to get hot so I removed power to avoid burning it out.
I tried a 3rd servo, purchased from Sparkfun - the Generic (Sub-Micro Size). I can’t find specifications to confirm analog or digital, but I noted this one does not heat up, and functions normal. Is that one analog or digital?
I’m not a servo expert yet, so I’m hoping to understand how these vary in performance (aside from size). I’m still suspect of Digital vs Analog, and I’m also unsure about the question related to current draw.
Not sure the best way to describe, but each of the A and B pots are turned inward to set limits of the servo range - Servos have 90deg available, but I’m using less than that. Does that make sense?
Thank you for confirming the specifications with links to the datasheets to note the analog.
Please correct me if I’m wrong, but I seem to understand that digital servos will respond differently than analog versions while in the resting state (starting position)? I’m curious if that has something to do with the issue of overheating with the digital ones.
Good suggestions - I’ll give that a try. I picked up a couple different servos today that might be analog, so hopefully I can do more testing with a successful outcome. I’ll report back what I find.
Thank you again for the help and suggestions. I’ve had some time to continue testing, with a few different servos and some successful outcomes. Here’s what I believe to be true:
The Sparkfun Trigger Board does appear to work with Digital or Analog servos. If Sparkfun supports this, I would imagine others might benefit from this call out on the product detail page. *I’d love to have a smaller version of this product for future use!
I tested the board with various 2g servos and found the metal gear versions to perform better than nylon (as many might expect). Their performance and accuracy allowed me to fine tune the trigger board better.
Adjusting the A and B pots was critical, but unfortunately more precise than I would have expected. I had to set the A pot slightly inward to prevent any (and I mean any) tension left on the servo mechanism during the “closing phase”. The slightest tension would trick the servo into thinking it hasn’t reached it’s resting point, thus causing the motor to achieve stall current and excess heat
On my initial design I had wiring with heat shrink tubing attached to the door. The heat shrink tubing was just stiff enough, that it was applying tension to the door’s movement and full closure. This tension was great enough to force the servo motor to work harder than it should, likely challenging the torque. (We’re talking wires smaller than 36awg).
While some of that doesn’t make sense considering how strong the servo is, and how little the wires were, upon redoing my wiring approach, skipping the heat shrink tubing and leaving flexibility for wire movement, the tension issue was resolved
So to summarize this unique situation, using servos this small requires a much more precise and delicate approach to the mechanical side of things. Having the trigger board set perfectly appears to be crucial as well. Upon further analysis and observations, servos this small are super quiet, and if careful, you can hear them turn on / off at their respective A and B points. (This audible noise was initially missed by my lack of hearing and their low volume).
Hope this information and learning experience for me, provides advice for others!
