OD in the transmission vs ring & pinion in the pumpkin

[swerv512]

Thinking about my trip down the LCG rabbit hole and I see alot of transmissions (Salinas, TGH, etc..) have various OD ratios built in. I may end up using my TRX4 axles in the build and I already have the OD & UD installed in the ring/pinion in the pumpkins. Is there a benefit to having OD in the transmission vs the pumpkin. I think I read some pumpkins can't accommodate OD/UD but for those that can (TRX4) should I choose a Transmission with a lower OD since I have it already in the pumpkins. I should probably learn to do the math to figure out what my final OD ratios would be and what's appropriate....

Speaking of which- how does one determine how much OD to actually use? Is there such a thing as too much ?

Probably should have put this in the newbie section.... thank you everyone.

 

[mikemcE]

OD in the transmission vs ring & pinion in the pumpkin

My advantage is 25% OD up front . With both the tgh and OD gearset I have 25% OD .

As I’ve done by adding two you can dial things in to what you want.


What you need/want is really the terrain and your driving style

Hang up and Drive

 

[lonleycreeper]

So... Od in the trans vs Od/Ud in the axles.

Advantage of the trans is as mentioned tuneability, the disadvantage is Torque Twist. Lowering the gear ratio in the axle minimizes the amount of TT you observe.

 

[ScaleLifeNewbie]

Re: OD in the transmission vs ring & pinion in the pumpkin

As far as too much, if you are crawling 100% of the time, no trailing at all, I would say 40% OD is pushing it-It adds a lot of unnecessary stress on the driveline, and I cant see someone even remotley needing anything above 45-50%.

I would say the sweet spot would be 12-30% range. Enough OD to pull you up, but also not a ton of extra stress.

______________________________________
AR60 VS410
TRX4 Sport
coming soon..

Veterans deserve a whole month too...

 

[swerv512]

Thanks for all the good information. I'll look for a Transmission that has close to zero OD since the TRX4 portals will get me 27%(?) total OD including UD on the rear pumpkin. Since i still have the stock ring and pinion gears I could always go with a lower final OD ratio since side-hilling performance could be improved as is. I could always reach out and see the availability of alternate transmission gears if I switch axles, I'm sure.

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[MOguy]

Thanks for all the good information. I'll look for a Transmission that has close to zero OD since the TRX4 portals will get me 27%(?) total OD including UD on the rear pumpkin. Since i still have the stock ring and pinion gears I could always go with a lower final OD ratio since side-hilling performance could be improved as is. I could always reach out and see the availability of alternate transmission gears if I switch axles, I'm sure.

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If you are using the TRX axles why not the TRX trans. Portals are geared different than strait axles so other trans will require more gearing research.

The TRX trans sits lower than many other transmission and sets the motor forward for good weight distribution.

As far as side hill? Get a controller so you can control your selectable lockers independently. If you unlock you front axle on a sidehill the upper front tire will be light. Power follows the path of least resistance. The front upper tire will lift, than that tire will spin faster than the other side. When it comes spinning faster than the opposite side it will pull you back up the side hill.

 

[twade984]

One thing I always consider is cost.. o/d and u/d gear sets for the Trx4 axles are $40 each irc. That’s $80.

Since you have to buy a transmission either way, getting one with o/d included can save you money.

An element trans is $50 and includes 10%, plus you can add aftermarket higher % gears

A vfd is $120, but only has 6.5%, but can be upgraded to 20% for $50 I believe.

A TGH 2.low is $170 and includes 30%

Not saying one is better than the other, just something I would consider.

Also, since you’re using portal axles with extra reduction, I wouldn’t be too concerned with excessive torque twist due to o/d at the trans vs the axles.


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[swerv512]

If you are using the TRX axles why not the TRX trans. Portals are geared different than strait axles so other trans will require more gearing research.



The TRX trans sits lower than many other transmission and sets the motor forward for good weight distribution.



As far as side hill? Get a controller so you can control your selectable lockers independently. If you unlock you front axle on a sidehill the upper front tire will be light. Power follows the path of least resistance. The front upper tire will lift, than that tire will spin faster than the other side. When it comes spinning faster than the opposite side it will pull you back up the side hill.

The portals are off at TRX4 sport. No lockers for me. Honestly I never really considered the TRX4 trans. I haven't posted the "How does the TRX4 trans compare in the crawling world?" thread yet, but I'm definitely prepared to takes notes. My single speed TRX4 Sport trans looks a bit clunky and clumsy compared to other units I've mentioned, but I'm glad to hear that it has its advantages.

I haven't decided on an ESC/motor combo yet, but thought I read that not all chassis can accept a 550 motor. I wasn't sure if this was because of the lack of space to mount a big can if I use a similar-sized motor so I figured a slimmer trans might help me out there

I only mention motor size because I am trying to keep this a "budget build." I am currently well-served by my HW 1080 - HH Crawlmaster 550 sport combination. I never once thought $70 of ESC & motor could be this good. That being said I am leaving a little room for negotiations on a different esc- motor combination.

But looking at the element trans, I can see how traxxas used their design to get the motor weight forward.

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[MOguy]

The portals are off at TRX4 sport. No lockers for me. Honestly I never really considered the TRX4 trans. I haven't posted the "How does the TRX4 trans compare in the crawling world?" thread yet, but I'm definitely prepared to takes notes. My single speed TRX4 Sport trans looks a bit clunky and clumsy compared to other units I've mentioned, but I'm glad to hear that it has its advantages.

I haven't decided on an ESC/motor combo yet, but thought I read that not all chassis can accept a 550 motor. I wasn't sure if this was because of the lack of space to mount a big can if I use a similar-sized motor so I figured a slimmer trans might help me out there

I only mention motor size because I am trying to keep this a "budget build." I am currently well-served by my HW 1080 - HH Crawlmaster 550 sport combination. I never once thought $70 of ESC & motor could be this good.

But looking at the element trans, I can see how traxxas used their design to get the motor weight forward.

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You won't hear much good about anything traxxas in the crawling community. The TRX trans sits lower that even the 2low, my enduro trans sits as low as my 2low. The only spur i could find for my 2low is metal is not it isn't any lighter Enduro trans. I won my 2low at an event but after having one I don't see the value. The workmanship and finish is excellent on the 2low and it is smooth.

The TRX trans is not much heavier if any than the Enduro one. It looks clunky because of the motor mount.

The downside to the TRX is its steering. Unlocking the diff helps allot with it maneuverability and can help with climbing for the rear and side hill for the front those are the advantages with the TRX axle.

Because of the portals the TRX climbs well, and you could probably get away with a shorter wheelbase to helps with maneuvering. Also, raising the rear upper links at the trans side helps with climbing.

 

[twade984]

The reason the Trx4 transmission isn’t used much outside of a Trx4 chassis is the motor plate keys into the skid plate, the trans mounting pattern is unique, and the link mounting points in the skid are unique as well.

You either have to figure out a way to use the Trx4 skid, or fabricate a new skid plate that integrates the motor plate.

There is just a little more versatility using some of the other options out there.

I don’t think it was mentioned to begin with, but what is your build plan so far OP? Do you have a specific chassis in mind?


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[swerv512]

Thanks again for the good information. Nothing against the traxxas trans- I finally figured out where and how much to shim mine to stop the tank sounds coming from it, but I'd rather have something more conventional. I'll include element in my search.

As far as the build goes. I'm undecided on a RES Pork Belly or GSpeed TGH V3 LCG chassis. I really like them both for a class II rig

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[MOguy]

The reason the Trx4 transmission isn’t used much outside of a Trx4 chassis is the motor plate keys into the skid plate, the trans mounting pattern is unique, and the link mounting points in the skid are unique as well.

You either have to figure out a way to use the Trx4 skid, or fabricate a new skid plate that integrates the motor plate.

There is just a little more versatility using some of the other options out there.

I don’t think it was mentioned to begin with, but what is your build plan so far OP? Do you have a specific chassis in mind?


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Yep

 

[MOguy]

Thanks again for the good information. Nothing against the traxxas trans- I finally figured out where and how much to shim mine to stop the tank sounds coming from it, but I'd rather have something more conventional. I'll include element in my search.

As far as the build goes. I'm undecided on a RES Pork Belly or GSpeed TGH V3 LCG chassis. I really like them both for a class II rig

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If you want to use TRX stuff you need to pull out the drill and the Dremel unless you get a skid and chassis designed for TRX. I don't mind drilling and Dremeling on a chassis but mounts are often 3d printed and I don't like altering them.

Most RC off the shelf stuff will be axial based. Some they more unique stuff may have their own mount pattern for the trans to their skid but still for the most part line up with axial stuff to install into the rails.

TRX stuff is heavier and stronger than much of the axial stuff. Their axles weigh close to 2 twice the among of one pieces AR44s but soooo much stronger. The axles are unpsrung weight so not a big deal. The one speed trans is not that much different than the Enduro if you use the metal gears in the Enduro trans. I have two Enduro trans, I did strip out the plastic gears in the one, the other use from a kit and comes with metal gears. The endure trans sits higher than others, not much and you can grind away some of the skid to sit it lower.

My C3 (2.2 comp build) with 4ws and unlocking rear diff is TRX drive line. My others are axial based, much lighter and unless you have the rear locker TRX just isn't as maneuverable.

If your building for C2 I would go AR44 axles, maybe AR45 (depending on trans offset) straight and maybe portal in the back.

 

[swerv512]

If you want to use TRX stuff you need to pull out the drill and the Dremel unless you get a skid and chassis designed for TRX...

Most RC off the shelf stuff will be axial based...

TRX stuff is heavier and stronger than much of the axial stuff... The axles are unpsrung weight so not a big deal...

The one speed trans is not that much different than the Enduro if you use the metal gears in the Enduro trans. I have two Enduro trans, I did strip out the plastic gears in the one, the other use from a kit and comes with metal gears. The endure trans sits higher than others, not much and you can grind away some of the skid to sit it lower.

My C3 (2.2 comp build) with 4ws and unlocking rear diff is TRX drive line. My others are axial based, much lighter and unless you have the rear locker TRX just isn't as maneuverable.

If your building for C2 I would go AR44 axles, maybe AR45 (depending on trans offset) straight and maybe portal in the back.

This is likely just a fun rig- I dont see much comp in my future. I should change my statement to Class "1.5" right. I really like the cut away and pinched body look of Class II but I'll likely be CMS and keep a few scale goodies and proportions. Speaking of which, I need to pick a body so i can think about wheelbase and links... I actually broke down and grabbed a set of the straight axles scx10iii on sale....

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[MOguy]

This is likely just a fun rig- I dont see much comp in my future. I should change my statement to Class "1.5" right. I really like the cut away and pinched body look of Class II but I'll likely be CMS and keep a few scale goodies and proportions. Speaking of which, I need to pick a body so i can think about wheelbase and links... I actually broke down and grabbed a set of the straight axles scx10iii on sale....

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The TRX is probably more durable than most and lots of up grades and parts avaialbe. Other than less steering, non issue for most, I think out of the box, the best deal.

Brazin has a Chassis for it, I use the scattergun and there are a few others.

 

[food2000]

You guys see the OD test: https://www.youtube.com/watch?v=4KEYGLvyFnM

 

[swerv512]

You guys see the OD test: https://www.youtube.com/watch?v=4KEYGLvyFnM

That video is exactly why I subscribe to his channel! Wow... now I have to do some real world research for myself. My local spot is mostly loose rock over hard sandstone- exactly where he showed OD performed lowest... I made too many changes at once to tell if my OD/UD changes helped or hindered. I might get a low OD trans and use my ring gears to add if needed.

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[food2000]

That video is exactly why I subscribe to his channel! Wow... now I have to do some real world research for myself. My local spot is mostly loose rock over hard sandstone- exactly where he showed OD performed lowest... I made too many changes at once to tell if my OD/UD changes helped or hindered. I might get a low OD trans and use my ring gears to add if needed.

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Yeah i wondered the same too... the phoenix really is able to help show OD pros and cons since... every rig is different and even if you come back a different day.. trails can change.