Heat/Friction of 775 + Versaplanetary

[timytamy]

Hi all,

We've been experimenting with various motor + veraplanetary combinations for our shooter, and with the higher power 775pro, we noticed a lot of heat (presumably due to friction) being generated. It got to the point where the gearbox was too hot to hold.

We then ran the same combination through our power meter, and saw the 775 was drawing a whopping ~150W (on a ~300W motor) just to overcome the friction. We saw this consistently across two motors, and multiple gear ratios (inc 1:1)

Interestingly, with no gearbox the motor was still pulling on the order of ~30W, more than triple what the maths says it should be.

For comparison, a similar setup with a BAG motor resulted in 30W w/ gearbox no load, and 15W with nothing at all.

We'll do more experimenting tonight, we could well be just putting the versaplanetary together wrong, but what has everyone else's experience been?

[JesseK]

Need some context: What manipulator? Does the manipulator free-spin well without the gearbox attached? Is there any chatter in the gearbox when you back drive it with your hand? You greased the gearbox, right?

[Nuttyman54]

I can't comment on the 775pro yet since we just ordered them, but I do recall in 2014 we encountered a similar problem with our VP's running RS550s. It wasn't quite to that extreme, but they were very touchy with how they were assembled as to how much friction they had inherent to the gearbox. I would suggest disassembling the gearbox (or at least loosening the screws a bit) and trying it again.

[Paul Copioli]

Originally Posted by timytamy

Hi all,

We've been experimenting with various motor + veraplanetary combinations for our shooter, and with the higher power 775pro, we noticed a lot of heat (presumably due to friction) being generated. It got to the point where the gearbox was too hot to hold.

We then ran the same combination through our power meter, and saw the 775 was drawing a whopping ~150W (on a ~300W motor) just to overcome the friction. We saw this consistently across two motors, and multiple gear ratios (inc 1:1)

Interestingly, with no gearbox the motor was still pulling on the order of ~30W, more than triple what the maths says it should be.

For comparison, a similar setup with a BAG motor resulted in 30W w/ gearbox no load, and 15W with nothing at all.

We'll do more experimenting tonight, we could well be just putting the versaplanetary together wrong, but what has everyone else's experience been?

How are you calculating power?

Is the 150W you are referring to the electrical power or mechanical power?

I can tell you the 340ish power that is on the VEXpro web site is at max power and is mechanical power. There is a big difference.

I assume you are referring to electrical power and, if so, you were probably pulling 12 amps from the power source if it was at 12 volts. This is definitely not normal.

We are running 5:1 VP with the 775pro and they are only pulling 2.4 amps, which is about 30ish Watts of electrical power.

I pulled all of these numbers from motors.vex.com/775pro. If you click to expand the motor curve, then all of the data is there.

Paul

[timytamy]

No manipulator, just gearbox. We've greased on assembly of the stages (except 1:1)

We are measuring electrical power (using http://www.powerwerx.com/digital-met...owerpoles.html), under these no-load conditions we expect to see all of that converted to heat (and some sound), which is consistent with what we're seeing.

You're correct that the max power isn't really a valid comparison as we're measuring power at a completely different stage, I included it more to give a sense of the scale.

We expected to see ~30W like the BAG, and like your tests. We're unsure of what has gone wrong. We're interested in what other people's experiences have been.

Originally Posted by Nuttyman54

I can't comment on the 775pro yet since we just ordered them, but I do recall in 2014 we encountered a similar problem with our VP's running RS550s. It wasn't quite to that extreme, but they were very touchy with how they were assembled as to how much friction they had inherent to the gearbox. I would suggest disassembling the gearbox (or at least loosening the screws a bit) and trying it again.

Do you recall anything that can indicate the order of magnitude you experienced? No-load power (or current) measurement? Could you hold onto the motor/gearbox after running it for a little while?

[RoboChair]

Too much grease? You don't want too much in there if you are spinning that fast.
Wrong size planet and/or sun gear pairing?
Ring gears not lining up well or unevenly tightened?
Motor to sun gear hub mounted too far on or not on far enough?

[MetaEngineer]

Something is certainly wrong.

The 775pro we wired up a few days ago would pull less than 1 amp at 12 volts (<12W) unloaded. With a lightly greased 3:1 versaplanetary and a small shooter wheel, current draw was around 14 amps at 12 volts (~168W).

Wheel speed was 5340 RPM and motor speed 16020 RPM. After a few minutes of launching boulders, motor case got to maybe 38 C (~100 F) and outside of gearbox got to around 41 C (~106 F). Warm, but to be expected with the high speeds involved.

Tomorrow I could get better data on RPM and power consumption of motor + gearbox without the wheel, which wastes quite a lot of power moving air.

[Bob Steele]

As Evan mentioned earlier, we had heat buildup issues a few years back when we started using the Versaplanetaries. You must attach the motor using the instructions exactly as VEX recommends. The gearboxes we used were before the removed the outside bearings. When the design changed to no outside bearings (right after the shaft connects) it was much easier to align everything properly and not get so much heat.

Some of the heat is characteristic of the gearbox for some reason they always run a little hot. I would suggest you contact VEX and ask them for advice.
If you are having that much friction there must be an alignment issue.

These are great little transmissions... so easy to mount with such great flexibility to mount and a wide choice of motors. We primarily use the 775 with all of our applications.

[Hawktobot]

Silly question. Did you lubricate the gears? Our team just assembled our 775pro and planetary as well. We noticed that the gears were partially lubricated but we added extra to be on the safe side. We have not tested the motors yet. We did notice that over torqueing the bolts when assembling affected the function.

[cadandcookies]

Originally Posted by Hawktobot

Silly question. Did you lubricate the gears? Our team just assembled our 775pro and planetary as well. We noticed that the gears were partially lubricated but we added extra to be on the safe side. We have not tested the motors yet. We did notice that over torqueing the bolts when assembling affected the function.

Overlubricating is also very bad in VersaPlanetaries. Last spring when I was working on some miniature robots for a non-FRC project, my group had to assemble 15 identical VersaPlanetaries and the the ones that have given us the most trouble are the ones that were overlubricated initially.

I'd second the advice elsewhere in this thread: make sure you don't have too much lubrication, and make sure everything is properly aligned. Given those two things, I've never had an issue with a VersaPlanetary (other than losing a few of the motor adapters ).

[R.C.]

To confirm,

OP are you using the piloted versaplanetary plates or the metal plate?

[MaGiC_PiKaChU]

My team had some pretty good experience using versaplanetaries over the past years.

I was assembling ours today with the 775s pro on a 25:1 reduction (2 stages). 8 motors and 8 transmissions total. I had 2 of them overheating more than the others. (turns out stages were rubbing on each other) Gears are mounted on shafts that tend to get loose. We always punch them to avoid them getting loose and grinding on the stage below. We also used a different grease with the 775, since it has a much higher rpm. You want something more fluid, that will not put too much effort on the gears. After tuning each motor and gearbox, I got them at 3 to 3.5 amps each on 12V. No more sounds of gears grinding or overheating, and it sounds like a jet engine

[Ryan Dognaux]

The first thing I do after assembling a versaplanetary is grab a wrench or a wheel with a 1/2" hex and just see how easily the output shaft spins by hand. I've had occasions where something wasn't right and we were getting some binding / friction that you could definitely feel by hand while turning the output shaft. As others have mentioned, I'd recommend disassembling, inspecting and re-assembling and compare the 'feel test' to your existing assembled gearbox.

[cbale2000]

This might be a dumb question, but what is the ambient temperature of your workspace? Just noticing OPs location, and given the hemisphere and time of year... Just a thought.

We hooked one of our new 775pro motors to a 36:1 two stage (plus encoder stage) VersaPlanetary last week and did not notice any excessive heat buildups during the time we ran it (which was, granted, only a few minutes).

Echoing what others have said, make sure to check your gearbox alignment and lubrication and make sure you're using the correct mounting plate for your motor. If you remove the motor and leave the rest of the gearbox assembled, you should be able to rotate it smoothly by hand at almost any reduction (assuming you're using a hex output shaft, it's a bit harder to grip the round ones).


In my experience, the only failure I've seen on a Versa Planetary was on my teams 2014 robot. The gearbox was at 100:1 reduction running a Bag motor (that stalled quite frequently) on our shooter. When switching out the Bag motor (which had fried) for the more powerful Banebots 775, the gearbox was still quite hot, and the brass(?) hub connecting the motor to the stage above it cracked in half just from trying to re-tighten the set screw. Beyond that, somewhat specific case, I've never had any issues with them that weren't quickly identified assembly user errors.

[Paul Copioli]

I just want to clarify a few things so we can all be on a similar page.

The VP gearboxes are pretty thin walled in the ring gear stages and they are made from aluminum alloy machined from an extruded block (in order to get them that thin).

This exacerbates any heat coming from the motor plus the heat generated by the gears during normal operation plus any binding due to misalignment.

The 775pro runs extremely fast compared to the other motors of its size and that is due to the ball bearings. It reduced friction by about 10-15% over the same model with bushings. As a result, the speed will cause the VP gearbox to get a little hotter than compared with the BAG, etc. This is normal. What is not normal is pulling more than 4 Amps (at 12 Volts) while running in your hand while connected to a single stage VP gearbox.

If this is happening, then you probably have some binding in the gearbox somewhere or you do not have enough lubrication.

Referencing the user guide below should help you greatly:

http://content.vexrobotics.com/vexpr...e-20151221.pdf

If you continue to have problems and you think there is something wrong with your specific VP gearbox, then please contact:

prosupport<the at symbol>vex.com


Paul