Thermal mass being the idlers mount and really good lubricants are the only options I know of.
That’s the magic… I am proposing that you don’t need a case at all and the benefit of a case only exists if its sealed and uses lubricants. I’m trying to say, apparently not very well, that you can treat gear drives as belt drive replacements simply by swapping the motor and wheel pulleys for gears, assuming the existing motor mount will adjust to the correct distance for optimal gear contact.
Carbon/Hardened steel is a different ball game than ABS, POM Aluminum, etc. which is most people around here are using. Im not saying helical gears are bad, I’m just saying the benefits don’t justify the increased cost of manufacturing when speaking of limited runs of 100 pieces or less.
I can’t even guess what the cost of helical 12t & 36t spur gears would cost in carbon steel :).
Just so Im understanding clearly…are you saying you had issue with hardened/carbon steel spur gears shredding?
One difference though between a hard stop from a belt drive compared to a gear drive with no case that I think is how vastly different they each would respond to something getting caught in the belt compared to a gear. With the belt, since it’s got some flexibility and can stretch some, it’s not like a 100% certainty that say a pebble getting caught in the belt would cause a hard stop, but maybe just a jolt or something like that, or of course it could be a hard stop.
With gears though, I think it’s almost a 100% certainty that if anything gets caught in there, they are completely fixed in place and don’t allow for any play, so they pretty much for sure will have a hard stop from pretty much anything getting caught up in there.
Wow okay not sure what the fatboy mini drive spur gears are composed of but my guess is aluminum. The price does already burn a sizeable hole in my wallet 
but I just tell myself its gonna be worth it in the long run. I guess with carbon steel the teeth would likely be fine subjected to the stress?
would probably be a PITA to replace should anything damage the gears for whatever reason. Also a pain in the wallet lol
Respectfully, I disagree and my testing bears it out.
I don’t run belt covers for the reason that debris gets trapped and is reintroduced to the belt path over and over until its finally ejected.
I spun up an ABS wheel gear and Aluminum motor gear, with no case, using a 10s4p pack and 190kv 6374 motor and started dropping crap in to see what would happen. I used staples, nails, screws, aquarium gravel, limestone chert, river gravel, copper rivets, pennys, everything I could get my hands on. Not a single time did anything embed in the path of the gears.
Your good, the fatboy drive train is solid and I’m sure you will be happy with it. Im happy with mine and have almost 500 miles on it. My only point in this discussion is to propose a low cost alternative to belt drives. Gear drives are more efficient and just as robust as belt drive, likely more so.
Thanks @mmaner! appreciate you chiming in on the discussion. glad to have another builder running the same drive train, It’s defenitely helped me plan my own build out 
Well I’ll certainly take your word on that as I’ve never had that happen to me. That would freaking suck though!
Do you think making the idler gear larger and maybe out of a better material that dissapates heat more efficiently would be the best thing to do. Obviously, do all the things mentioned, but I imagine that would do the most in addressing that issue.
For a sealed gear drive with a lubricant, I imagine there is a specific type of lubricant that is used for high heat dissipation…
@mmaner thank you for bringing these issues to our attention, highly appreciated 
We’ve tested a bunch of different materials, including hybrid material gears made with steel cores and POM teeth. In everything we did we were able to shred the gears at a much faster rate than with helical. Granted they’re more complex to make and lots of finishing processes required to dial in the tolerances, but the benefits are definitely worth it.
I would guess there are kunticanta that have the benefit if heat disapation but I don’t know what they are.
My best guess on a properly built idler gear would be to use a hardened steel gear with the mounting poiint being at least 7mm of aluminum or more of steel.
If the case is sealed I think any decent lubricant would cool the bearing in the idler gear with a substantial amount if heat dispating mass behind it.
I’d be interested in discussing the benefits if hekical gears. Like I said, I don’t really see much benefit. I’ve totally destroyed oom and and motor pulleys, but steel seems to hold up forever.
I’m using a dyno tester as the surface, conrete blocks as weights and straps to hold everything in place. I’m then alternating the weight of the blocks with a piece of rebar as as a pivot handle.
I’m essentially running 200lbs on a deck with a single motor, alternating the weight placement and trying the break the gears.
Another diference you have between spur and helical is impact, with the later having none if designed and assembled correct
This may seem little, but surface fatigue on gears is a big problem, and helical solves that almost completely
With spur, each tooth engement is a impact, that’s where the sound come from, but with helical you have a smooth engagement. If you could plot the surface pressure of both, the helical would be a smooth curve, spur would be steps
Is the surface fatigue you’re referring to the same as what @mmaner mentioned earlier about stress points along the gear tooth? I do see that it would play a bigger role on gears made out of other materials besides metal but seeing as metal on metal gears look to perform well and are quite robust so far maybe its negligible in those cases?
Not exactly,
First for the spur, the ideal contact point would be a line, but since nothing is perfectly rigid it’s a rectangle. When two teeth make contact, this contact happens at once at all points of this rectangle of pressure, and it happens almost at once, from no surface pressure to full surface pressure. You can lower this by making more teeth being in contact at the same time, but to do so you need to decrease the pitch of the gears or increase their size, both have downsides
For the helical gear the ideal contact would be a point, in reality a circle. When designing a helical pair you should make it in a way that when a tooth is engaging, the previous one still engages, this way you can make the surface pressure smoothly go up and down at each loading cycle
Since we are discussing gears, what id like to see is someone actually designing them, from what I know nobody did that yet. By that I mean really doing the math and properly material and geometry selection, I think we can arrive at a way more compact arrangement and that most setups we see are way oversized
If I manage to have the funds to make one one day I plan do that, I already have most things implemented in a spreadsheet from other projects
I just placed an order for @kaly direct drive,m 4:1, he uses spur gears, sounds like a Boosted board even though i never had a Boosted board before
I wouldve picked that up as well if it weren’t for the fact that I wanted it on a longboard deck unless I find those Unik 35 deg risers. I believe he was using POM on his wheel gear from what i’ve seen on his instagram
Yeah definitely interested to see prototypes of it. So far I haven’t heard of anyone reporting that kind of wear from normal use on spur gear drives. It must quite cost a fair bit more to produce at this time plus add complexity. just getting the well made spurs already costs alot at least for me 
Yeah, this is more like general use, not esk8 specific, as I said, I believe most if not all designs are oversized, we probably won’t see any of that unless we reduce things and start running at the materials limit
Also this apply for steel/steel gears, most here are steel/pom or steel/nylon, unfortunately I couldn’t find a lot of references for non metallic gears, since plastics behave completely different at material level, most guidelines and formulations you find in a machine design would be useless since most of it derives from experiments
Ah I see, So I shouldn’t take it too seriously into consideration about wear and tear on the spurs then. That’s good because I don’t have the budget to replace or fix these anytime soon should that kind of tooth damage occur lol.
though the drive train that I purchased is steel/steel but they’re well made so I’m hoping that the contact point will be as close to a line as possible but like you said that may not always be the case.
I don’t think I can run the drives that hard to cause that kind of damage unless I’m always doing really hard braking or something which realistically would probably send me flying without bindings 
What do you think about POM/Steel as it looks to be what @kaly is using on his spur gear drives. Motor gear being steel in that case
Edit: sorry I re-read your last statement about POM/Steel. I suppose real world use is the quickest way to know how well these types stand up to our application.
Here is a study showing the friction and wear characteristics of different polymers including POM in contact with steel, pretty interesting results.
POM behaved better than all other polymers even with no lubricants just thin air.
Just note that POM starts to melt at 150C, but a gear drive should not exceed this temperature, we would not know that though until we test these drives, but if so, heatsinks may be needed