Man, I am tired of frying HSR-5995TG's

Lynxmotion
31

This is for Kondo KRS788 10.8V servo 10Kg.

I know its not Hitec but these are uprated and heres what mines survivedā€¦

Standing with full weight on 1 leg for 3+ minutes quite happily.

20 minutes (full battery life) of activity, some of it extreme but mostly just standard moves.

The recovery move from a fall requires the 2 hip servos to lift the whole upper body through 90deg. I would say thats almost 1Kg moving rapidly from Horizontal to Vertical. Probably ranks as the most strain I can apply.

And it survivesā€¦

The only 2 servos I have blown are the Head which has no load whatsoever and the forearm which at most is used doing pressups, Possibly about 1Kg maxā€¦

So the answer is not No or Yes, it very much depends on circumstances etc.

I dare so if I tried to do the extreme moves when the servos were hot they would blow

32

Just curious, is that a 9-cell NiMH? Thatā€™s quite a lot of voltage for a standard size servo.

33

Yep, 9 of AAA rated 800mAh NI MHā€¦

the AA would give a longer life but the weight and volume are a problem

34

Guys take it easy. Ribotson is a very smart guy. He singlehandedly reverse engineered the Hitec digital servos, a feat not to be taken lightly. I am a big fan of his work! So there may be a stepper solution that will perform as well as or better than servos. I personally have my doubts, but whateverā€¦ But the majority of folks in hobby robotics are using servos due to lots of reasons.

**The fact is no one should design any mechanical device using the stall torque. **

Manufacturers have been publishing stall torque values forever knowing full well the motor canā€™t perform at this capacity at 100% duty cycle. Iā€™m talking motors, not servos. Lots of places list ā€œtheoreticalā€ torque values (motor torque x gear reduction) even though the gears canā€™t handle the torque. I have done my best to make sure what we publish is accurate!

When you are ready to build the cool robot of your dreams, you need to have realistic expectations, and um, wellā€¦ hopefully have some fun in the process.

35

Apologies if my posts appeared to be flaming, thats not what I intended. I was attempting to sympathise as I have been watching comments both here and at Robosavvy about blown servoā€™s and can understand where he is coming from. Specs are specs and phrases like ā€œtheoretical limitsā€ and ā€œwithin acceptable limitsā€ are too often used to cover up inadequacies in the design.

Normally thats enough to put me off a product and go looking elsewhere but as you and Ribotson have pointed out budget and other limitations make the super-servo the best option.

Again, apologies if Iā€™ve appeared offensive, compared to many on here Iā€™m a newbie and an amateur one at that and I wouldnā€™t force my opinion on any situation. Usually coz Iā€™ve jumped the gun or mis-understood it myself and Iā€™m miles off targetā€¦

I get it right sometimesā€¦ I thinkā€¦ :laughing:

36

AMEN! I could not have said it any better. :smiley: Iā€™m going to be posting assembly pictures of one of my dream (or was it a nightmare?) robots soon. :smiley:

8-Dale

37

Which robot?

38

Iā€™m not sure where the take it easy part came from actually because I was mostly just talking numbers. Iā€™ll admit I played on words a little bit to make some humerous innuendo but it wasnā€™t really intended to be overly disrespectful. I also believe there are several very smart people frequenting this board with a diverse set of background, life experience, and personal interests. In my opinion Mr. Ribbotsonā€™s post didnā€™t reflect his technical skills applied to decrypting the digital servo protocol. I did see a request to see my "calculations on the stepper motor so I banged out something straight forward and to the point. Really though he made a marketing pitchā€¦ kick butt servos living on the edge learning and burning. Enthusiasm is great but weā€™re in a thread the topic of which is Iā€™m tired of throwing away $100 servos when I didnā€™t do anything wrong, another contributor is concerned about the (sounds like) two grand he just sunk into servos for his new project, and yet another person is examining the question of at what design threshold do we accept that we have exceeded the practical design limits of even ā€œathleteā€ servos and start to examine alternatives. Even you yourself Jim are in the process of designing a servo product to replace even exotic class ā€œnormalā€ servos because the application you want to develop is limited by those normal servos by either performance or outright cost. Why bother if there isnā€™t a need? Because there IS a need and your own learn and burn has identified it.

You just also happen to be in the excellent position to do something about it. :slight_smile:

No harm meant by my posts in this thread. I just tend towards taking more of an engineering approach to figuring things out then a try it and go from there one. That IS the world I live in but I am also trying to relax a bit so I might enjoy this stuff as more of a hobby than yet another extension of my job. I do still have that tracked ROV being built on my bench downstairs with the WAG gear motors on itā€¦ hoping it does more than sit there and smoke the first time I get to put power to it all. :open_mouth: :stuck_out_tongue: 8)

39

Thanks for all the informative responses guys. Just to clarify. Iā€™m aware just how much of a marvel these little servos are. There is alot of power packed into a tiny package.

I also realize that servos canā€™t be operated at stall continuously. And that they will never actually produce their stall torque for more than a few seconds before burning out. What I think, is that servo manufacturers should be displaying their specs the same way Lipo batteries do. With a continuous and a burst rating. A 300oz stall servo should probably be called a 200oz continuous or 300oz burst. Since that is the reality. To assume that people will only be using their servos for short bursts is not realistic. Hitec posts their specs in such a way for the purpose of putting the highest numbers they can out, then adding some fine print somewhere saying ā€œposted torque at 7 volts for 2 seconds on the surface of marsā€.

I was running my 5995 on an SES style arm, with 5 inch long segments and a 5 oz motor on the end of the hand. The servo was in the elbow joint, no restricted movement and very little load. I was running through some very basic movements in RIOS for about 4 to 5 minutes. Then poof, up in smoke. Iā€™m using just 1 HSR-5995 on the base of the arm, it was barely warm. And at 6.0 Volts!! The last one was at 7.2 Volts and burned up about 30 seconds into some load tests where it was near stall, not stalled.

Iā€™ve used and abused HS-645ā€™s and 805ā€™s where they are repeatedly being stalled for extended periods and never had one fail. So why is it that me, and others, keep smoking the 5995 when it is pushed as being so powerful and wonderful. Especially when the price reflects that.

I canā€™t help but feel like there is nothing special about this servo at all. They tossed titanium gears and a metal arm onto a servo and said ā€œthe super robot servo, 417oz of torque!!! Wow, come buy oneā€ When really they could have just said ā€œrun your HS-5645 at 7.2 Volts and you get loads more torqueā€¦[size=75]for 10 to 15 seconds[/size].ā€

If the chips and motor canā€™t handle a moderate load current for more than a couple minutes or a stall current for a few seconds, then they are pretty useless. I mean thanks for the heatsink and the thermal shutoff on the HS-5990 but I think you can keep it. Especially if itā€™s the same servos with a shutdown and heatsink added. So I should buy some so that instead of smoking the servos, they just constantly shut down from overheating. Thatā€™s alot less frustrating. :unamused:

I love Hitec servos. But come on. The HS-5995ā€™'s are a joke. They labeled them something they are not to set the bar in the market for a powerful servo. When really all they had was a moderate servo that they recommended everyone overvolted. I have notice some vendors donā€™t even post the higher torque spec at 7+ volts. Some advertise them as a 333oz/in servo at 6.0V. Which is what they are. Almost.

And this is not an attack on you Jim. You always put the customer first and I love that. Itā€™s not like you made the servos. You have to sell whatever they offer. We are all at the mercy of that. I just wish Hitec would realize that I would pay $200 for a servo that could do 333oz/in indefinitely and reliably, as apposed to a 417oz/in servo that only works for 30 seconds then commits suicide.

40

I had one blow up running at 6vdc with no load, just sitting there. Of course they replaced it. I just do not know what the real problem was. We may never know. The fact that they discontinued the servo speaks volumes. Curious, did you ever contact Hitec about the servos you blew? Itā€™s one thing to complain, but if they are willing to make it right somehow, it may be much to do about nothing.

Um, a heatsink would effect how long it takes to go into shutdown eh? All of these ā€œsuper servosā€ no matter who makes them MUST dissapate heat. So this falls under the reasonable expectations I was talking about earlier. Do you really think this isnā€™t a significant improvement over the 5995? :unamused:

I appreciate that! Hey, nobodyā€™s perfect, but I can say without a doubt, that my list of faults DO NOT include trying to cover up product faults to make a buck. :wink: I am only interested in providing the most accurate information I can so people can make intelligent purchasing decisions.

41

I just though the replys were a bit much, but it could have just been me, no harm, no foul. Sorryā€¦ whistles casually, take a few steps backā€¦

I just couldnā€™t resist. It seams like a lot of the ā€œsuper servoā€ problems are due to trying to keep everything in the tiny standard servo case. I figured the performance will increase dramatically if a ā€œrealā€ gearhead motor is used, thinking outside the box, lol.

Np really, sorry again. Canā€™t wait to see that tracked ROV going!

42

Hmm. Why do my worst posts give the best feedback ?

I guess my comments were not all approporiate to this thread.

Though badly expressed in my post, I do stick to my premise that safe operation and reliability is a design parameter, that we be adjusted in accord with other objectives, and I prefer that to be in my control. As a consumer and engineer, I too was very upset when I started losing servos a year ago. I had not factored healthcare costs into my budget. Maybe myself and fellow robot users are too soft, but frankly it is still great value hobby at 20% per year approxā€¦ Sure as an engineer and consumer I still feel affronted by this high failure rate, but it does not worry me like it did. Maybe best to leave further thoughts on this to a less technical thread.

On the stepper Vs. Servo, looks like I was wrong. As soon as I saw the example you posted, I wanted to build a robot with them. I think your math is wrong, and these are still slightly less capable than the servos, but they sure are contenders, and have changed my view on steppers. Will someone build with these and give us some information on their dynamic capability.

I apologise for any marketing bias in my posts. I just feel that Hitec are getting quite a bashing, and I already find them rather conservative. I fear they will become more so. They appear reticent to release the programming cable for the HMI servos, maybe, because this will enable users to make unsafe settings on the servos. Indeed, I also am cautious to release the full HMI programability of the 5990 for this reason.

I do have to agree with other posts that the lack of accurate specification and communication from Hitec has made the situation worse. Thanks for this forum to fill the gap.

On more engineering issues, I did check the 5990 overload protection, and it does indeed power off after 10 sec of overload. I need to do further tests to determine if say a 50% load powers off after 20 sec etc. Also the 5990 does not actually measure current, like the open servo. The HMI read current value is actually the PWM value to the motor, and I guess that is the overload value too.

The heatsink is well thermally connected to the motor, where I still think any problems lie. The processor does not measure actual temperature as far as I can tell.

43

Kondo Servos have a feature called ICS on their red servoā€™s. On the earlier bots this feature was visible but not functional.

On the recent releases it is there in all its glory and boy can you reck them if you wanted to.

I shy away from it as I know very little about them but from the settings Iā€™ve seen as default, everything is hiked right up to the limit.

Not a good place to start playing

44

Ribbotson, I enjoy reading anything you have to say, so please donā€™t feel like you have to hold anything back.

I think everyone here is capable of having a lively discussion without anyones feelings getting hurt.

Carry onā€¦ :slight_smile:

45

the nagging feeling is quite possibly that I hand waved the gearbox, ignored efficiency, and generally rounded the numbers to make the math more obvious. like I said I banged out a quick reply. :wink:
Anyway, stepper based servos still have to deal with heat, the electronics are more complicated not less, there are mechanical issues not obvious like resonance, and you have similar issues with a relatively small field of suppliers addressing the small form factor and high energy density motors with quality products. I think that as you scale an application up its best efficiency will see-saw between dc motor servos and stepper servos a bit and then stay with dc motor servos up until you start moving towards pneumatic and hydraulic designs as you get really big.

46

You can pretty much forget the stepper motors for the types of bots generally described here. The steppers are used where precision positioning is the main requirement and not force. I mentioned it in another thread that I think a lot of the expensive servos are sold on hype and not necessarily improved performance. The real key to keep from burning out the servos is to design such that the servos are not under constant strain.

47

Below is an interesting design which limits the amount of force that the servo has to supply while holding the weight of the bot. It has some other potential issues, but might be worth a look.

mondo-technology.com/hexbot.htm

48

yea i was thinking 200oz.in. is probly the med for longitivity versus torque for a standard size servo ,those super servos are amazing but there too hot for most hobbiest i mean it wont take much of error in coding to break something , if u pop the clutch and floor a race car and its in neutral it goes boom while you could put a brick on the gas pedale of my pinto while u tuned it :open_mouth: but like some body said already if u buy them and moan about all the flaws they,ll build a better one next time,

P.S.
I cant see how a stepper motor could,nt have more potential power(its a bigger motor!! )dont quite know how u would package it but sounds like a winner to me :smiley:

49

The main problem with steppers is to achieve the same amount of power they have to be much larger. The motors in servos gain their power through gearing down the output speed of the motor. Steppers do not achieve the same rotational speed of a dc motor and consequently would require much less gearing to achieve the same 180 degree movement a normal servo provides. Less gearing produces less power.

Steppers do not have a built in method of positioning as a servo does. A stepper requires you to generate a known number of pulses and it will move that amount. You would need additional external rotational tracking to equal a servos accuracy.

Also, like servos, steppers suffer from stalling. You can just apply a high speed series of pulses as the stepper will immediately stall. The pulse rate has to be ramped up and ramped down to achieve the higher speeds.

To complicate this, unlike a servo, steppers can slip. If you apply a sufficient force you can actually hold a stepper stationary. Without adequate rotational tracking you will never know the stepper stalled or slipped. One possible advantage of this may be that it would act as a form of clutch although be it only momentary.

A stepper can achieve what a servo does, even the super-servos but they cannot do it in the same compact form. They become much larger and complicated. There are also very few steppers on that market that are suitable for running off a battery. Most stepper driver circuit require the use of a multitapped toroidal transformer in the power supply.

One extremely good implemetation of steppers I have seen is to fit the stepper with a worm gear which in turn drives a conventional gear. This has an inherently high gear ratio and has the advantage that because the gear is at 90 degrees to the worm rather than in the same plane it is impossible for any amount of force on the gear to drive the worm the wrong way. It would just shear teeth and completely protect the stepper motor itselfā€¦This method is used a lot in Lego to achieve a good ratio with high power.

50

Thanks for all the informative posts guys.

You know what peaves me off the most. I stuck an HS-645 into the elbow so I could continue my testing and I have been using it without a problem at 6 Volts. I have done 45 minutes of continuous movements and numerous 15 minute testing sessions. No problems with the HS-645.

Like I said, the servo wasnā€™t under much load. And the HSR-5995 was way overkill for the application which is why I chose it. I wanted to have an abundance of additional power on reserve. The HSR-5995 I have on the base is starting to get very hot as well. I might as well pull it out and put something else in before it fries too.

So far my $30 servo is out-performing my $130 one in longevity. Go figure.