New HR gears for enduro trans
 

Hey is anyone using these? they're supposed to give more od or ud in the last 2 cases.


https://www.rpphobby.com/product_p/hotedr830x50.htm


https://www.rpphobby.com/product_p/hotedr829x51.htm


https://www.rpphobby.com/product_p/hotedr825x55.htm

https://www.rpphobby.com/product_p/hotedr824x56.htm

Re: New HR gears for enduro trans
 

I just ordered an OD3 we will see... due to show up tomorrow


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Re: New HR gears for enduro trans
 

So they're gonna make us do the math?

I do like that they drilled out some holes around the large gear, the stock ones are heavy AF!

Just to compile some specs:

Hot Racing options

HR UD2 24T Idler 56T Drive Gear

HR UD3 25T Idler 55T Drive Gear

HR OD2 30T Idler 50T Drive Gear

HR OD3 29T Idler 51T Drive Gear

Stock options are

26T Idler 54T Drive Gear 11.83% Overdrive

27T Idler 53T Drive Gear 5.7% overdrive

28T Idler 54T Drive Gear 1:1 (no overdrive)

Re: New HR gears for enduro trans
 

Somewhere around 19% I believe with out doing exact math lol


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Re: New HR gears for enduro trans
 

Now I'm wondering how the heck they're accomplishing Underdrive?

The 20T gear that mesh's with the rear axle gears is fixed so the only thing they could be doing is just giving us a sloppy mesh. Any other ideas?

https://i.imgur.com/pHRLW6kl.jpg

Re: New HR gears for enduro trans
 

I think by keeping the number of teeth at 80 between the two gears they should have the same gear spacing and mesh wouldn’t suffer. The concept of the underdrive is the same as the element offering but takes it a couple gears further. Where as the overdrive does the same thing in the other direction for the front axle.

Re: New HR gears for enduro trans
 

I'm looking at these gears in order to change my overdrive options. In the manual it clearly states that in all configuration the 20t top shaft mates up to the 28/52 gears. This makes sense as the gearcase has a fixed distance between all gears so you can't have an idler gear other than 28t (unless you can come up with a top shift that has an accordingly sized gear). I was kind of excited at how much overdrive you could get with the HR gear sets until I realized this. Although the manual shows the 28/52 gears always used for the front, you could use those for the rear and use the opposite top shaft for each motor mount configuration, which allows use of the HR OD gear sets for the front output. But, it seems like the best case is to use the 28/52 gears for the front with the HR UD2 gear set, giving 25.6% overdrive. Kind of a bummer as I was hoping to try at least 30% overdrive with this trans.

Re: New HR gears for enduro trans
 

Reviving this thread because I cannot find any consistent math behind these gears. Someone please correct me if I'm wrong or help me understad...

Constant ratio for the 20:52 = 2.6. Normally the intermediate gear is skipped, but in this gearbox that gear reduction is transferred to a secondary set of gears (OD or UD). Now, as i understand, all underdrive or overdrive ratios are multiplied by 1.4 (28t / input 20t gears). So, here is what I came up with using this formula: 100xA-B/[A+B/2]

Hot Racing options

HR UD2 24T Idler 56T Drive Gear = 22.73% U.D.

HR UD3 25T Idler 55T Drive Gear = 16.9% U.D.

HR OD2 30T Idler 50T Drive Gear = 10.81% O.D.

HR OD3 29T Idler 51T Drive Gear = 5.45% O.D.

Stock options are

26T Idler 54T Drive Gear 11.83% Overdrive (I got 11.25%)

27T Idler 53T Drive Gear 5.7% overdrive (I got 5.53%)

28T Idler 54T Drive Gear 1:1 (no overdrive)

Re: New HR gears for enduro trans
 

Anyone?

Re: New HR gears for enduro trans
 

Using the 28/52 ratio as a fixed constant:

HR UD2 24T Idler 56T Drive Gear = -25.641%
HR UD3 25T Idler 55T Drive Gear = -18.462%
Stock 26T Idler 54T Drive Gear -11.834%
Stock 27T Idler 53T Drive Gear -5.698%
Baseline 28/52 = 0
HR OD3 29T Idler 51T Drive Gear = 5.305%
HR OD2 30T Idler 50T Drive Gear = 10.256%

"OD" or "UD" spec is irrelevant, really it's just in how you set up the gears/orient the transmission. Technically, the stock trans changes the rear gear ratio to achieve a front overdrive. That's why HR labels it as UD2, UD3, etc. What matters overall is the difference in ratios.

Re: New HR gears for enduro trans
 

Your math is correct but Element gives the overdrive (actually underdrive) ratio as the difference between the front and rear ratios and not the average of the 2 ratios. Element’s formula is just (front ratio - rear ratio)/front ratio to get their listed percentages.

Re: New HR gears for enduro trans
 

Cool, thanks for the info. I figured there was different a different formula since the numbers were so close.


I wonder why Hot Racing even makes the OD gears since they are so similar to the stock UD ratios. Maybe for overall higher gearing? A spur / pinion or inverse top shaft are less expensive.

Re: New HR gears for enduro trans
 

I am currently building this truck and had the same questions, and it led me to here.

I dont think any of the HR "OD" gears will fit unless you are willing to compromise the mesh between the 20/28 shown below AND hog out the bearing race in the case (see clever YT vid of this below) OR change the 20T gear to a smaller one, but this would change the ratios for all of them.

I am okay with underdriving the rear only. The max UD ratio currently offered is 24/56 but they are out of stock so going with 25/55 which per the above calcs = -18.4% on the rear. With the 24/56's being OOS I'm guessing others have realized UD is the best way to go

https://i.postimg.cc/6pWpp8V7/1-10-2022-8-21-25-AM.jpg

https://www.youtube.com/watch?v=OBN6GzdwCgQ&t=206s

Re: New HR gears for enduro trans
 

You can either use OD or UD gears, not both at the same time. The 20/28/52 will always be in the gearbox. Switching the top shaft allows you to change which side of the gearbox will have OD or UD depending on the motor orientation on the skid. If you wan higher overall gearing run the 20/28/52 to the rear and OD the front. For lower overall gearing, run the 20/28/52 to the front and UD the rear."thumbsup"