Hardened Steel Pinions?

[BrianG]

I've read various discussions on using the hardened steel pinions with the stock steel spur found on center diffs and the general consensus seems to be that the spur and/or pinion will be eaten. Well, I would like to keep the steel spur on my center differential for a few reasons and was looking into why it would be so bad. I mean, Nitro trucks use a steel clutchbell and they hold up fine, so why would a hardened steel pinion be any different?

I have an extra 14T regular pinion laying around so I tested the mesh. I noticed right away that it seems to bind as it turns.

In the picture below, there is a stock 14T clutchbell that came with my Hyper8 and my 14T pinion. The pink arrows point to the peak of the tooth and you can easily see that the pinion is definitely wider. Also, the clutchbell tooth seems to have a wider base, which makes the tooth slope not as steep, as seen in the green circles.



The picture of the hardened steel pinion in Mike's store is a little too blurry to see how it compares to the picture above, even after attempted enhancements to it. I'd like to get a clear picture of this so I can see if it has the same look as a regular pinion. That would explain the problem.

I really don't want to accept the fact that it's just "bad" to use hardened steel pinions with steel spurs without some type of explanation. How is it that clutchbells work fine and the steel pinions don't?

[jhautz]

I agree that the shape of the tooth will have alot to do with how well it holds up.

I'm interested as well to find out how to make the steel on steel work. It just opens up so many more grearing options.

[BrianG]

In my first post, it's easy to see the teeth have different geometries; not only is the top and base of the tooth different size, the general shape is different too.

I wonder if the pinions in Mike's store are simply hardened versions of regular pinions? If any one has a clear close-up of one of Mike's hardened pinions, could you post that picture? Please?

I know that using the Delrin/plastic spur with a regular pinion is cheaper than using a few hardened gears. However, if a diff "goes" and you just want to replace it to keep racing, you can simply get the whole diff at more places and install it in a matter of minutes. Otherwise, you'd have to have the diff ahead of time pre-installed with the plastic spur.

I would think (please correct me if I'm wrong here) that a steel setup would be a tad more tolerant of a slight momentary mis-mesh. If you take a large jump and land hard, the weight of the motor coupled with inertia may flex the aluminum a little and the mesh might not be perfect. At that point, less of the teeth are in contact. The very tops of a few teeth of a plastic spur would probably have some shearing.

[glassdoctor]

I have a hardened gear that looks to be made from a nitro clutch bell... I think that is what Mike's are... genuine clutch bell gears.

But I'm sure I recall reading that someone destroyed these too... don't forget that nitros do not have the startup torque and they don't use the gears for braking. So the nitros are much more gear-friendly than bl.

But I agree that it seems like hardened steel should hold up to bl anyway...

[RC-Monster Mike]

The tooth width variance pointed out by Brian is called the pressure angle - Traxxas Revo spurs use a 14.5 degree pressure angle, as do my standard mod1 pinions with 12-15 teeth. The 16,18 and 20 tooth mod1 pinions that I make use the stronger 20 degree pressure angle(same as the clutch bells on most nitro vehicles). The 14.5 degree pressure angle has slightly less rolling resistance, while the 20 degree pressure angle(which is the "standard" for most gears) has slightly stronger teeth. My hardened pinions were made from real live clutch bells - I just chose a lighter weight method vs. FD.
The problem is, there is a wide spectrum of quality on the clutch bells, and mesh is probably the largest factor for the gear's survival. As Dustin pointed out, the electric conversions also "use" the gears much more harshly. Nitro vehicles also have a clutch, which effectively limits the torque transfer between the gears, along with not using the gears for braking. Also, a typical electric motor is suspended using only 2 screws at one end, with the motor hanging off the other end - most motor mounts used for this also exhibit quite a bit of flex(landing a jump, for example), which undermines the gear mesh and accelerates wear substantially. A nitro motor, conversely, typically is mounted to a flat chassis with 4 screws and on a flat plate/mount, which holds its mesh MUCH more rigidly. The high stress of a brushless sytem, along with the lack of any clutch/slip and a relatively flexible motor mount typically leads to the demise of these gears. Metal on metal is far from ideal in the real world anyways. To illustrate the importance of a rigid gear mesh, and the effect it has on wear, consider the hardened idler gears used in the emaxx tranny - these gears last a very long time, even though they mesh against a hardened top gear. The largest factor is the RIGID mesh. Both gears are supported on both ends and the mesh doesn't change in use, which results in much longer lasting gears(metal on metal will always wear, just much more slowly when proper and rigid gear mesh is present).
Nylon and delrin(common materials for plastic spur gears) are plenty strong for the application, along with having much higher natural lubricity(less rolling resistance), and less rotating mass. They also have the benefit of allowing almost any material to be used for the pinion, resulting in a less expensive and wider availability of gearing. Maintaining the mesh is still important, of course, but a metal pinion on a plastic spur is much closer to ideal in many respects.
I still have quite a few hardened pinions, but I took them out of inventory simply because I was not thrilled with the consistency(varied quality mentioned earlier)/quality of the product. In short, I would rather lose money than my reputation and I wasn't satisfied with the product in the end. they were made from clutch bells, but in harsh situations, they still failed occasionally - not up to my standards. This is a major reason I developed the slipperential setup, and will adapt it to different applications. The performance of a center diff, with the durability/reliabilty of a slipper. My personal opinion is that direct drive without a slipper should be avoided. Sure, it will work for a while, but without the outlet for extreme stress relief(slipper), the diffs take a beating, as does the motor and speed controller(high amp spikes at the controller, and eventual dislocation of the motor shaft/rotor).

[BrianG]

Thank you Mike!! That was a very thorough and easily understood explanation.

Just the fact the emaxx top gear and idler work fine under BL (thanks for pointing that out - I hadn't even thought of that!) makes me think it should be fine IF, as you said, the mesh remains perfect.

Maybe you could sell those hardened pinions on a case-by-case basis? Maybe put a bold-face note or disclaimer on the product description which summarizes what you said above? Even if people still ruin a few pinions, everyone here KNOWS you don't offer shoddy products. It's a shame to have spent capital on making a product and not selling it simply because of a customer's proper use.

[Serum]

Mike, the pinions you used on your hardened pinions; those where originally screw-on models?

[RC-Monster Mike]

Nothing would please me more than to sell the gears, Brian - but I won't list them. Drop me an email if you want a couple and we can work it out. Even at the $25 selling price, it is no "get rich" scheme. I had to buy the stainless, buy the clutch bells and have the stainless turned precisely to size, cut the gears and press them together. Cost me about $18 per unit to make! It was a lot of work for $7 and I have sold 20 times more ofna and Kyosho spurs than I ever did the hardened pinions(customers are smart!), which is a better material choice to begin with.

Rene - I used Ofna, HPI and a couple Mugen clutch bells - not the screw on type, though. The teeth are cut off the clutch bell(or the clutch bell cut off the teeth) and pressed with a 14 ton press over a precision turned stainless steel "adapter"(pretty much guarantee it won't spin off the adapter). It looks like a pinion in the end, doesn't weigh a whole lot (steel isn't light, but it is similar in weight to a standard pinion) and is made from a real live clutch bell that was designed to run against a hardened spur. It sounded so good on paper! Just doesn't account for all the User variables out there I guess.

very good info... comming from the world of 1/8 nitro and never having an issue with spurs or clutch bells i was inclined to go with an all steel setup... now i will wait for the sliperential and use the ofna plastic gear and figure out a better way of mounting the motors... anyone though of drilling and tapping the rear endbells of motors to have another point to mount the motor to the chassis... ?

[jhautz]

One question I have is... why does it seem that the pinion is the part that fails in a hard steel pinion and hard steel spur application? I have seen many pictures of gnarled pinions, but never hear that the hard steel spurs were damaged. If it is truely a mesh issue I would think the spurs would be mangled just as much as the pinions.

[BrianG]

Maybe since the pinion has the power behind it?

[Serum]

No Brian, the power is equal on both.

Quite simple neweuser;

a pinion has got less teeth.. it's 51 against 14.. And besides; the teets are cut in a different angle when the gear is smaller, meaning less material.

[BrianG]

I really meant instantaneous power, but the tooth count makes sense!

[RC-Monster Mike]

Simple math, really. A 12 tooth pinion realizes almost 4 times as much wear as the 46 tooth spur it rides against.

[squeeforever]

So I'm assuming that is why the pinion is always some sort of metal and the spur is plastic instead of the other way around, correct?