Rat Rig Community [Unofficial]•14mo ago

MG995 Servo causing error and beeping

Ya’ll. Struggling to add an mg995 servo to my rig.
Using the BLTouch pins, the servo initially moves to the initial_angle set position but the MCU (octopus) then disconnects and beeps constantly. I’ve tried using one of the endstop pins for the pwm signal instead (PG11) and got the same result. Have crimped and recrimped the connectors. There’s no error per say in the Klipper logs either. Just get an ‘EOF’ error.

16 Replies

blacksmithforlife•14mo ago

How do you have it setup in your config?

zesty-coffee•14mo ago

My bad should have posted that:

[servo servo_wiper]
pin: PG11
#pin: PB7
maximum_servo_angle: 180
minimum_pulse_width: 0.0005
maximum_pulse_width: 0.0025
initial_angle: 90
#initial_pulse_width: 0.0025

[servo servo_wiper]
pin: PG11
#pin: PB7
maximum_servo_angle: 180
minimum_pulse_width: 0.0005
maximum_pulse_width: 0.0025
initial_angle: 90
#initial_pulse_width: 0.0025

Just tried a second servo, same thing unfortunately.

zesty-coffee•14mo ago

As you can see, it powers on, moves to initial angle and then screams continuously. The MCU shuts down which makes me wonder about some kind of electrical issue.

zesty-coffee•14mo ago

FWIW I've decided that it must be something relating to the servos, having tried the second one that came with the order. I've tried a variety of pin combinations and even checked if the GND/SIG wires have somehow been swapped internally. There's only an issue when the servo actuates. The constant beeping is -- I believe based on a BTT reddit thread -- due to a short on the 5V rail. So my assumption is the servos suck. So I've ordered some alternate servos, this time MG996R's as I believe they're essentially updated/better versions of the MG995's. Will report back...

ptegler•14mo ago

the bulk of what is sold as MG995 servos are garbage! If you paid less than $15 per servo it's not a 'REAL' MG995 (btdt on too many of them) That whine, is the servo not quite centering the potentiometer in the servo gear train to get it to stop moving (match the input pulse width) so the motor in the servo is oscillating/or the H bridge is not passing enough current to move the gear train) Only other option...the pulse out (driving the servo) is noisy as hell! Using 5V? (servo supply) that is just barely enough for the ckts in the servo. They prefer 6V for stability. They'll work at 4-6V but with issues. One of my Hexapods here (uses 18 MG995s) ...one by one every servo had to be replaced.

zesty-coffee•14mo ago

Thanks! That’s super useful info. Update: MG996R's didn't work. Just to be clear, the high pitched noise is almost certainly the BTT Octopus Pro 429 making a constant high pitched beep. I've come across this video: https://www.youtube.com/watch?v=VAtnU_rXLFg in which a chap uses 9g SG90 servos. I've ordered both a cheap one from Amazon, and a more expensive one that was recommended by multiple people on an RC forum (Fubata S3114) so hopefully one or both of these options work. I bought the cheap one out of curiosity really as I'd simply like to know if the cheapies in that size work. Part of me wonders if the Octopus is getting upset because the MG99X's are asking for too much current at the lower 5V voltage, and therefore that the lower torque ratings seen in the smaller servos may require less and operate OK. Guess I'll use all these spare servos for an RC hovercraft project in future..

blacksmithforlife•14mo ago

maybe you could try a 5v PSU directly to the servo to test that theory out

ptegler•14mo ago

valid point (close enough anyway) a DC motor in servos has almost no filtering. so you're placing a brushed motor (noisy as hell) across your 5V supply

zesty-coffee•14mo ago

Hopefully the higher quality servo is better? Who knows. 😅 For now I’ve snapped the Euclid probe arm clean off the printhead front plate. It never rains, but it pours. 🌧️ @ptegler @blacksmithforlife 🇺🇸 So, cheap SG90 9g servos arrived and work just fine. https://www.amazon.co.uk/dp/B07MY2Y253?psc=1&ref=ppx_yo2ov_dt_b_product_details <-- these specifically. Working on the BLTouch header (5V/GND/PB7) on an Octopus Pro 429. This leads me to think that it's something relating to what ptegler said, with the electronics inside the cheap MG995/6R's either not playing nicely at 5V, or perhaps trying to draw too much current. It's odd, as the Octopus 1.1 Wiggy has seems to work just fine with the MG's.

ptegler•14mo ago

possibly a real 995? As simply a probe mount there is little to no load on the servo, so have to believe it was simply the cloned 995 they stuck you with. most 90s are real, just different vendors slapping their label on them.

zesty-coffee•14mo ago

No they’re definitely clones. But it’s all four of them. Do you know of any brand names or anything that would help make sure it’s a ‘real’ MG995.

ptegler•14mo ago

From what I last saw/remember...the MG995 isn't even made anymore. Most are 996's with 995 labels just applied. IIRC...TowerPro was the original. 'IF' it's a real 995.... you can get a true 180° rotation out of it. All other bogus units are 60-90° (115° max?)

ptegler•14mo ago

just went looking..... wow!...it's STILL on line! https://servodatabase.com/servos/all I use to use this back in the late very late 80s'-90's

All RC Servos - Servo Database

An organized chart of specifications for thousands of RC servos. Sortable by torque, speed, weight, dimensions, and more.

zesty-coffee•14mo ago

Thanks. Ordered a TowerPro MG996R from what appears to be a genuine RC hobby shop via ebay (though he has two independent websites). Was £12.50 for one, so hopefully it's a genuine/decent unit. So, wanted to come back and give an update ... again. The TowerPro MG996R servo from a more reputable source than Amazon random sellers appears to have done the trick. Thanks to @ptegler for the information. With the unit linked below I can reach both 0 and 180 with zero whine, and the Octopus doesn't poop out either. https://www.ebay.co.uk/itm/175288731929 https://servoshop.co.uk/index.php?pid=TPMG996R180&area=SERVO There was also another issue, which is my 'DuPont' connectors. They just suck. I've never liked them anyway as they're easy to pull off the board by mistake, but I didn't think they were actually bad. They are. I've moved all of the wires to an endstop port (J33 -- 5V/GND/PG11) and it appears to operate just fine from there, with the added bonus that it's more secure/tidier/uses all the connections on that single port. So, summary pro tips for anyone reading this in future (yay forum functionality):

- Buy a branded servo (TowerPro MG996R seems good)
- Buy from a reputable RC shop as you're more likely to get genuine quality parts
- If the servo price is really cheap, it's probably a clone. My working unit cost £12.50/$16 without shipping.
- Use a JST port where you can or make sure you have high quality DuPont style connectors.
- Don't waste £30 on junk servos like me :)

- Buy a branded servo (TowerPro MG996R seems good)
- Buy from a reputable RC shop as you're more likely to get genuine quality parts
- If the servo price is really cheap, it's probably a clone. My working unit cost £12.50/$16 without shipping.
- Use a JST port where you can or make sure you have high quality DuPont style connectors.
- Don't waste £30 on junk servos like me :)

zesty-coffee•14mo ago

zesty-coffee•14mo ago

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MG995 Servo causing error and beeping