NXT servo motor robustness

[rghansen]

What's the consensus on the robustness of NXT servo motors?

Will they overheat if we run them at full power for extended periods?

Will their gears fall apart if we drive them much harder than we would ever drive our cars?

Will a little gentleness go a long way to extending their useful existence?

[mattallen37]

I have only heard of a couple (one?) that wore out/broke.

Unless heavily loaded, they will not get warm. Based on what I have read, it appears that they have an internal electrical/motor/heat protection.

The gears can handle much more torque than the motor can provide, so they shouldn't fall apart, even in almost stalling loads (obviously even in stalled situations).

I my opinion, they are very, very good. I haven't tried to test the limits, but from what I have done, I would say there is nothing to worry about (as long as you don't give it a higher voltage than 9V). I know that they seem to be okay at 12V, but do that at your own risk.

[rghansen]

Thanks for the info. You've taken the worry out of pushing them a little harder.

[doc222]

I have been loading these servos for years. Many times i stall them, this is not as easy as it seems as well. Like Matt has said they are built alot tougher than most people can build a drive train that can handle this amout of torque. I have about a dozen of these and the newest ones are about 3 years old, the oldest are now almost 4 years of very hard use. Now the way i can see this is a "shock load". example if one put say a long bean on a motor then spun it up to full power and then grabbed the beam in a way that stopped it dead, then all the force goes to the motor. This would be the extreme end. But since most people build a reduction gear train this puts the load there and it is much easier to break Lego gears and twist axles( i have twisted many like a pretzel). Just to show how much one can load these little motors was a old contest at out last forum(nxtasy-no loger on line). The contest was to build a bot that would lift a weight and carry it 1 meter. The winner lifted over 100lbs!! this is very extreme and can break things, but showed off the power of properly built leg bots. Also they are 18$ or less to buy.

My latest bot has stalled motors a few times(my programming error), in NXT once you over load the program will stall it then try again to finish rotation. If the bot can handle this it will keep trying to finish untill you cancle the program. To stall these with out the drive train breaking takes a very robust drive train of many redundant gears. Still these motors work like the day i bought them. Very well made for the money you wont find a better product. Lego stands behind them as well. I have heard of people even after a year getting replacment parts free. Though if i ever do break a motor i would bear the cost since I tend to push anything Lego to its limits and beyond.

Doc

[rghansen]

Thanks for the additional confirmation.

But I started to have my doubts when I read that Lego was offering replacement linear actuators to some of their unhappy customers. (You also mentioned this problem in your bided topic). I was thinking about buying a set of these. How can I be sure that I'll get the new, improved ones and not the old ones?

[doc222]

Thanks for the additional confirmation.

But I started to have my doubts when I read that Lego was offering replacement linear actuators to some of their unhappy customers. (You also mentioned this problem in your bided topic). I was thinking about buying a set of these. How can I be sure that I'll get the new, improved ones and not the old ones?

The Lego Linear actuators: This is a new issue. I am not sure still how to tell: Are these the new ones or the old ones by any visual means?

But mechanicaly yes. The new ones have alot of "slop" meaning that when extended the feel loose when lateral forces are applied. This is do to the loosening of the metal rod gear to the plastic sleave.

I have 5 "older versions" 4 are in use in my Biped right now. As i talked about in my Biped thread I pre-lubed these with #30 weight pure silicon oil(this stuff is common at any R/c hobbie out let that sells these R/c cars), they use this oil in there shocks as the damper fluid. This I use to see if it extends the life of these rams. I have been testing this Biped alot up stairs and walking and so far so good. The added oil has made them very smooth as compared to the stock(no lube at all) ones. These rams must balance the whole weight of this bot, each foot has two and to lean the weight is on them.

Since other making your own( I have a very good design too) the only other are these non-Lego ones. Mindsenors http://www.mindsensors.com/index.php?mo ... tion=11:11. But they are expensive, why i have not bought any yet.

Remember if you buy these Lego rams from say Lego Education you get the 1 ram and the two parts that add on to them. But 15$ each. If you get them at say Bricklink(thats where i did) You also have to buy those "other parts as well seperatly. I only bought the main one that has the prongs, about 9-10 bucks each for the two parts. Or you can buy a new thechnic kit that has them as well(may be the better option if you need parts as well since in total you are paying the least per part. I just did not want to spend 200$ on the new trackhoe that has 4, since i only needed two and that was 20$.

If they fail/ break, I am sure Lego would replace them as well.

Doc

[philoo]

I have 5 "older versions" 4 are in use in my Biped right now. As i talked about in my Biped thread I pre-lubed these with #30 weight pure silicon oil(this stuff is common at any R/c hobbie out let that sells these R/c cars
Doc

How did you get oil inside without making a mess of it outside?

[doc222]

I have 5 "older versions" 4 are in use in my Biped right now. As i talked about in my Biped thread I pre-lubed these with #30 weight pure silicon oil(this stuff is common at any R/c hobbie out let that sells these R/c cars
Doc

How did you get oil inside without making a mess of it outside?

Well its not a mess free job. First take a paper towel to hold the ram, extend the ram, The oil I have has a bit of a nipple on the bottle( A syringe would be best) afew drops at a time and cycle it through. After afew cycles you will notice right away that i gets smooooth.

I plan to use grease( pure silicon ONLY) next but i will need to mode the ram( right now i am bit leary to do this). My plan is to drill a small hole and then inject the grease. What I am not sure is where to dril this hole? Top bottom? I have not taken one apart since it will ruin it. I should write the guy at Tecnickbrick he has taken them apart and was the only guy I know that tested the older to se whats wrong and has pic showing the "plastic dust" from wearing out fast. he may have a good idea on where tdrill these for a injection hole?
OR I know Philo has a reputation taking things apart and I could defer to you

[philoo]

Well its not a mess free job. First take a paper towel to hold the ram, extend the ram, The oil I have has a bit of a nipple on the bottle( A syringe would be best) afew drops at a time and cycle it through. After afew cycles you will notice right away that i gets smooooth.

I see... thanks, doc!

My plan is to drill a small hole and then inject the grease.

That's what I considered too...

he may have a good idea on where tdrill these for a injection hole?

According to this photo http://2.bp.blogspot.com/_MBEVlUMi9kI/S ... s+%232.jpg I think the best bet would be to drill the hole on top of the LA near the piston. Drilling on side is chancy because you might reach internal sleeve, make a burr and have a hard spot in rotation. Moreover it's the best spot to reach the metal screw and add grease on it.

OR I know Philo has a reputation taking things apart and I could defer to you

Do I have this reputation ??? Well, I didn't felt the urge of opening it since someone already posted good photos...

[jojo60]

Hello,

One of my NXT motor is worn out.
The motor does not turn freely anymore by hand. I have to put a high power to make it turn.

Is there a way to repair this ?
I though I could partialy open it, and spray silicon grease on the gears ? Any better idea ?

I must say that LEGO customer service already sent me a replacement motor for free but I would like to give it a try...

Thank you in advance
Geoffrey