Kentucky Fried Servo (with photo)
Bill Henning
Posts: 6,445
Recently I ordered 50 TowerPro MG995 servos.
Four had a broken mounting hole, and one of them did a pretty good impression of a smoke stack:
Apparently some soic-8's just need to be soldered in wrong...
more at http://mikronauts.com
Four had a broken mounting hole, and one of them did a pretty good impression of a smoke stack:
Apparently some soic-8's just need to be soldered in wrong...
more at http://mikronauts.com
400 x 670 - 141K
Comments
"These really are the worst servos I've ever seen - bar none!"
'Nuff said.
Unfortunately, to fit the wifey approved toy budget, I had to keep the cost of servos down, so I ordered these to stay within budget for the build.
Futaba 3003's are apparently not powerful enough for the chassis.
My impression is that the reported issues are mostly due to lack of quality control, as they really are metal gear servos, and the pcb quality (when assembled correctly) is significantly higher than the Futaba's I have here.
50 MG-995's purchased (for HexPi, and in-house stock use)
- 4 had a broken screw mount
- one of the four with broken screw mount went up in smoke
- 21 of 22 passed limit/centering tests (18 undamaged, 3 with busted mount)
28 servos remain to be tested
I'll test the rest of the servos from my order, and update the "quality" table above with my final results.
The problem with all these direct Chinese imports is that the factories there know buyers aren't likely to ever return them for refund. Even if you bought from eBay (or Amazon), *that* buyer got them directly from China. Not all of the importers offer decent customer service. Of course you should see about returning all the bad servos for refund or replacement, but if you bought them direct from China the return shipping will likely be horrendous. (They're counting on that.)
Though not considered by some as quite as good as the major brands, you might see about equivalent GWS servos. If you're going to be buying these for resale you can probably get a wholesale account with them. At cost you'd be looking at about what you paid for the TowerPros.
Here's a YouTube video where the reviewer looks directly at the camera and says, "This is quite literally. The. Worst. Servo. Ever. Made."
http://www.youtube.com/watch?v=0d4qif7m6WQ
WOW that review did not pull any punches! Thank you for the link.
I'll look into GWS and others.
Meanwhile, I will try to get HexPi running with them, and I'll try to characterize them.
FYI, I originally ordered Futaba S3003's, but changed the order when the hexapod chassis supplier warned me that the chassis needs at least MG995's (for torque), so I changed the order for servos to the recommended MG995's.
Worst case - I can always use them for pan/tilt mounts.
But I don't have a watt value, the h-bridge was not installed correctly, so it was a direct short! (after the 2A diode... which can actually pass 4A with a larger vdrop).
The servo is rated for 7.2V operation, the diode dropped say 1V, so 6.2V, at a short... probably 5A+, so >31W is my best guess. No wonder smoke poured out!
out of the remaining 28 servos, one is DOA, the others tested ok for basic functionality.
Note: this does not mean they are accurate, that will take a lot more testing, which I will probably not do.
I'll take apart the DOA servo, and see what the cause is...
Total score:
50 servos
4 had mount problems
1 went up in smoke (it had mount problems)
1 is DOA
This can be summarized as:
8% had mounting issues
2% went up in smoke
2% DOA
I was able to fix the DOA servo.
The problem was the ground wire from the servo lead detaching from the ground pad on the controller pcb. I took photos, will post on my site later.
So if you end up with a DOA servo, open it up. There is a decent chance you can fix it.