Using a 775pro in Dusty Conditions

[Ginger Power]

Since the 775pro is a fan cooled motor, is it possible to run it in very dusty conditions? For reference it would be used on a mining robot built for NASA's Robotic Mining Competition. The mining material is called regolith (not the horrible FRC kind) and it is made up of very small particles of volcanic ash called BP-1.

We are thinking about using a system of fans and filters to keep the motors cool and sealed. The logic behind using a 775pro or just a fan cooled motor in general is the weight savings vs. a cim motor for example.

So can a 775pro survive these conditions? Is this a stupid idea? Does anybody have any motor recommendations that would be better suited than the 775pro?

[EricH]

Not a pro, but I have used a 775 (RS-775-18) in the same competition. Used drink cans (empty, of course, and missing one end...) around the back end of the motors and plenty of tape to seal the dust out. No motor problems, but the speed controller safeties gave us trouble... (not motor-related). This was in the drivetrain; I want to say I uploaded a photo to CD-Media some time ago of that robot. There was no cooling on the robot--remember that there is no air on the moon, so fans aren't exactly useful (FRC 2009 aside). Judges just might call ya on that.


I'm not sure I'd use a 775-Pro in that application, offhand, but if it seems to work out powerwise that might do the trick.

[ctt956]

I think it would work, but it may not last long if dust stops the fan or impedes airflow. Motors will work if they're filled with dust, but they will probably run hotter. How fine is this dust? Maybe you could put a screen or filter over the 775's vents and just clean it every run. Is there anything electrically conductive in the dust?

Originally Posted by EricH

There was no cooling on the robot--remember that there is no air on the moon, so fans aren't exactly useful (FRC 2009 aside). Judges just might call ya on that.

True. I wonder what would happen if it stalled on the moon... Also, the temperature of the moon would help make up for the lack of cooling at night. In the day, not so much...

[EricH]

Originally Posted by ctt956

I think it would work, but it may not last long if dust stops the fan or impedes airflow. Motors will work if they're filled with dust, but they will probably run hotter. How fine is this dust? Maybe you could put a screen or filter over the 775's vents and just clean it every run. Is there anything electrically conductive in the dust?

This is really, really fine dust. As in, tyvek suit, dust mask, and safety glasses just to enter the operation area (see next to my WAI photo), and a respirator if you're in there longer than a couple minutes. I don't remember the exact size, but that's pretty fine...

Oh, and the robots get vacuumed on exiting, trying to get all of the dust off or out. I don't think there's anything conductive, but it's hard to say for sure.

[ctt956]

Originally Posted by EricH

This is really, really fine dust. As in, tyvek suit, dust mask, and safety glasses just to enter the operation area (see next to my WAI photo), and a respirator if you're in there longer than a couple minutes. I don't remember the exact size, but that's pretty fine...

Oh, and the robots get vacuumed on exiting, trying to get all of the dust off or out. I don't think there's anything conductive, but it's hard to say for sure.

In that case, I doubt it would do well. I think I've seen motors permanently damaged from fine sheet rock dust, but I have also seen some full of household dust at a pretty fine size that continued to work. I did once accidentally send a small amount of baking soda through a vacuum cleaner motor, and it survived. Still, I probably wouldn't try it without a filter. You don't want it to fail during a competition match/run.

[EricH]

Originally Posted by ctt956

In that case, I doubt it would do well. I think I've seen motors permanently damaged from fine sheet rock dust, but I have also seen some full of household dust at a pretty fine size that continued to work. I did once accidentally send a small amount of baking soda through a vacuum cleaner motor, and it survived. Still, I probably wouldn't try it without a filter. You don't want it to fail during a competition match/run.

I added a link to my previous post, but I'm not sure you'll be able to see the motor shields through the frame. They'll run, but you want 'em shielded pretty well.

[Ginger Power]

Thanks for all the advice Eric! Good to know there is precedent for something like this. We'll obviously do some testing before implementing anything.

The 775pro is just such a powerful motor for the weight that I think it's worth the trouble to filter and cool it. Given how fine the BP-1 is, would filtration even be possible? I haven't taken the time to look into that yet.

Also, NASA allows fan cooled motors despite the fact that there is virtually no atmosphere on the Moon/Mars. This is because NASA can afford much nicer motors than us

[Aren_Hill]

If I were you I would venture into brushless land, an Inrunner is already sealed, or an outrunner doesn't really care that much, but could be sealed without too much work.

-Aren

[pilleya]

Originally Posted by Ginger Power

The 775pro is just such a powerful brushed motor for the weight that I think it's worth the trouble to filter and cool it.

If your looking to reduce weight a brushless inrunner will be more powerful for the same weight and will be sealed. The resources you need such as flashing brushless ESC's with SimonK is quite well documented and is reasonably straight forward.

Is power important or is it more weight reduction that you are wanting? If you wanted to reduce weight and don't need a lot of power a small sealed motor like a BAG motor could work.

[asid61]

Originally Posted by pilleya

If your looking to reduce weight a brushless inrunner will be more powerful for the same weight and will be sealed. The resources you need such as flashing brushless ESC's with SimonK is quite well documented and is reasonably straight forward.

Is power important or is it more weight reduction that you are wanting? If you wanted to reduce weight and don't need a lot of power a small sealed motor like a BAG motor could work.

Out of curiosity, would the ultra-fine grit get through the bearings? How would any motor be safe for long?

[OccamzRazor]

Let me brutally honest about this from our competition experience down at Kennedy in '13. They will not survive past the competition unless your motor enclosures are above excellent. See my link below about this.

https://www.youtube.com/watch?v=DaodHQC_MIo

We had an enclosure that was large enough to allow for some air to move around our rs775s but you will not have that in a lunar/martian environment. In testing, we wrapped our motors in several different materials but even with sand we had thermal issues because heat was being generated quickly in those wrappings. We ended up going with enclosures that had dust barriers around the drive shaft. The encoders we used were also protected with an enclosure that was a bit taller if you look in the video.

We had to replace 3-4 motors out of 6 because this material is so fine that it actually went through two military grade dust barriers and into the motor. I would recommend using CIMS if possible because if any of that dust gets in the rs motor it is done for. We even had melted fans in the motors. If we had the weight we would have went CIM motors for sure.

The challenge is a lot harder than it looks. We qualified in 6th place I think which was the first time UNCC ever qualified.

Also, do not get that stuff on your skin!!!! Clean your rover really well when you come out.

[Cory]

Originally Posted by OccamzRazor

We had an enclosure that was large enough to allow for some air to move around our rs775s but you will not have that in a lunar/martian environment.

As a point of reference, brushed motors wouldn't function on the moon at all, or would fail very quickly if they did. They can work on Mars because there's a thin atmosphere, but they cannot handle the vacuum on the moon. Outgassing of all the lubricants occurs, the brushes can be damaged (the presence of water vapor essentially lubricates the brush-commutator interface. Without it, damage rapidly occurs of graphite brushes), and the outgassing causes increased thermal load which cannot be transmitted to the surroundings well due to lack of atmosphere.

Regolith simulant is also INCREDIBLY abrasive. I would be very surprised if a 775pro held up to it for more than a few minutes here and there.

[kaliken]

Way back in 2007- 2009 when the Regolith competition was one of NASA's centennial challenges, myself and a couple other industry folks decided to enter a couple of robots in our free time. Ended up placing 2nd and 3rd.. We ended up right behind Paul back when he was at WPI doing robotics then (and now with BiteForce).

To the best of my memory, all of our drives were fully sealed, both motors and gear trains. Just like FRC we really wanted to keep our drivetrain as bullet-proof as possible. If I recall correctly we used fully sealed Maxon motors as well. I believe they were brushless as well however that part i am not remembering as well.

Plus as Cory mentioned you really are not going to have the ability for convection to cool your motor out on the lunar surface.

My thoughts that the 775pro would likely meet a relatively quick death with the amount of dust kicked up. To my knowledge, the simulant is designed if to have relatively sharp edged particles that would replicate the lunar surface and not the water eroded particles that we typically see here on earth and thus be much more abrasive than normal sand, dirt etc...

Good luck!

[Ginger Power]

Originally Posted by asid61

Out of curiosity, would the ultra-fine grit get through the bearings? How would any motor be safe for long?

The competition consists of two 10 minute runs and a 10 minutes practice run. Hardly enough time to ruin a sealed motor. I'm sure most motors within our price range would have trouble in the long run, but that's one of many reasons the Mars rovers cost a lot of money

Originally Posted by Aren_Hill

If I were you I would venture into brushless land, an Inrunner is already sealed, or an outrunner doesn't really care that much, but could be sealed without too much work.

-Aren

Thanks for the recommendation Aren. I'll be sure to do my research on brushless motors before buying anything. Do you have any motors in mind?

[OccamzRazor]

Originally Posted by Ginger Power

The competition consists of two 10 minute runs and a 10 minutes practice run. Hardly enough time to ruin a sealed motor. I'm sure most motors within our price range would have trouble in the long run, but that's one of many reasons the Mars rovers cost a lot of money

We smoked 2 of ours after the first official run but we had practiced with them for many hours prior to that. We smelled something burning and we opened up the box to find that lovely burnt plastic smell. 20 minutes between the practice and first run was all it took for the regolith to make its way into the boxes and wreck a couple of the motors.

It did plow into a boulder and go right over it though!