Kagama Lee Spring Servo Saver Spring - What you need to know

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Jeffwazz said:
Thought I'd better join the Springers Club! Lee Spring, UK site, despatched my order of 9 (carefully chosen to avoid the handling charge) and I received it in a couple of days.
First impressions - bloody awesome 👍 I'm able to steer around small areas around my lawn and patio. Thanks to everyone involved in finding these 😁
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You've set the pre-load perfectly I see! It makes such a difference. Fit and forget. 👍

I'm waiting for all the Kagama LE drivers to come out and look for these. You'll have no problem selling your surplus ones. 👍
 
The springs shipped so I can get you guys the cost for them with shipping. Sorry for my delay doctor day again with not so good news. I’ll message you guys who reached out to me tomorrow with cost break downs again guys not making any money exact cost that I get and will provide pics of shipping and the spring
 
shortround9191 said:
Amazing how much better they steer even with a stock servo. Was thinking on replacing stock with the spring I’m happy for what I’ve been doing
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Stock servo will be perfectly alright until it isn't. 😝🤣

Until then, you'll probably find the standard servos are good enough - through a Lee Spring.

My Savage scoots around on a 13kg Servo, with a speed of 60°/0.15 seconds. Low performance by modern standards, but it was considered a strong servo in its day. Through a good servo saver setup, however, it out-steered rigs with top-end KO and Sanwa servos.

Here's the OFNA monster pirate servo saver with beefy spring. Note the alloy system I tried for a couple of runs was sloppy and weak, so the old one went straight back in! 😅 You'll have to excuse the Phillips screws. Ahem. It was normal back then! 😅

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Horatio said:
Stock servo will be perfectly alright until it isn't. 😝🤣

Until then, you'll probably find the standard servos are good enough - through a Lee Spring.

My Savage scoots around on a 13kg Servo, with a speed of 60°/0.15 seconds. Low performance by modern standards, but it was considered a strong servo in its day. Through a good servo saver setup, however, it out-steered rigs with top-end KO and Sanwa servos.

Here's the OFNA monster pirate servo saver with beefy spring. Note the alloy system I tried for a couple of runs was sloppy and weak, so the old one went straight back in! 😅 You'll have to excuse the Phillips screws. Ahem. It was normal back then! 😅

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You’ve seen my pics always a mess working on this that and the other. If I was doing serious racing or until the stock servo bites the dust I’ll probably leave it be. The Kagama4 turns so much nicer now along with the Spark but the Kagama was the steering I really didn’t care for now it’s ❤️
 
Dunno how people are installing these without tools. I had to use a bench vice to get the spring installed in the servo saver arm and a strip of cardboard around the thumb nut with a set of shock pliers to tighten it (the cardboard to protect the aluminum from being chewed up)
 
Atomic Skull said:
Dunno how people are installing these without tools. I had to use a bench vice to get the spring installed in the servo saver arm and a strip of cardboard around the thumb nut with a set of shock pliers to tighten it (the cardboard to protect the aluminum from being chewed up)
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I have a fairly typical grip strength of around 55kg (per hand) and I fitted mine by hand. I describe how to fit them on numerous threads here on the forum. When I sold the springs on eBay, I also detailed how to fit them.

You just have to apply and maintain sufficient force to compress the spring whilst ensuring the screw is correctly aligned so it doesn't cross thread. It helps if the threads are given a smear of oil to aid torquing down the nut. Once the first few threads are engaged - just tighten normally.

The only tools required are the ones you use to remove the servo saver steering assembly out from the rig. There's certainly no need to use a vice, but where you do, it makes sense to use jaw protectors to avoid marring your work.

However you choose to install it, they're fit and forget. The thumb screw will never back off and your steering will work. Upgraded servos will unleash their potential and your rig's turning radius will be noticeably improved on any surface. Win-win!

Now we wait for all the new Kagama LE drivers to fit theirs......
 
It goes without saying, but once this spring is fitted - for the love of christ don't bother trying to adjust the nut with it assembled in the rig - not by poking a screw driver up through the chassis - it isn't going to happen! 😅🙏
 
I did my Spark by hand the Kagama4 the o-ring was jammed over a thread so I used vise grips for remove the stock spring but did both of mine by hand also. I do have old mechanics hands though finger tips been cut off reinstalled skin is like leather
 
A 40kg-cm servo can overcome the lee spring with the steering immobilized so would anything beyond that torque amount be wasted potential? Or would an e.g. 50kg-cm servo still be more effective than a 40kg-cm one?
 
Atomic Skull said:
A 40kg-cm servo can overcome the lee spring with the steering immobilized so would anything beyond that torque amount be wasted potential? Or would an e.g. 50kg-cm servo still be more effective than a 40kg-cm one?
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Essentially, a 45kg servo is massive overkill in a 1/8th rig. 👍

The spec of the Lee Spring we detailed states a spring rate of:

24.343 N/mm

So to compress the spring 1mm requires 2.482 kg.

If the spring is already preloaded with 2 visible threads clear of the thumb nut/collar, to compress the spring another mm would require another 7.446 kg.

Load at solid (with the spring fully compressed) is 242.99 N, which is a total loading of 24.778 kg. So in theory, a 25kg servo should be able to overcome it.

Your conclusion is correct. A 50 kg servo wouldn't be able to produce more force at the wheels through the servo saver than a 25 kg servo - unless the spring was locked solid.

So for the kind of servos we use, the spring is well within the limits of the servo. The only time your spring would get compressed anything like 10 mm would be in the event a heavy crash or impact.

A stock spring locked up close to solid (the way most of us ended up) offers no real protection at all. 👍
 
This calculation doesn't account for leverage though. If the servo is rated 25kg-cm that 25kg is only accurate if your steering linkage is attached 1cm from the center of rotation. Then from the linkage to servo saver introduces more leverage. I'm not completely sure if you could add up the distances servo-linkage and linkage-saver and calculate with that, or if the linkage changes something else aswell. The way the servo saver works it also has quite a bit of friction which would make it harder to compress. If you really wanted to know you could reconstruct the servo-linkage-saver assembly and hang increasing weight from the saver.
 
Niekname said:
This calculation doesn't account for leverage though. If the servo is rated 25kg-cm that 25kg is only accurate if your steering linkage is attached 1cm from the center of rotation. Then from the linkage to servo saver introduces more leverage. I'm not completely sure if you could add up the distances servo-linkage and linkage-saver and calculate with that, or if the linkage changes something else aswell. The way the servo saver works it also has quite a bit of friction which would make it harder to compress. If you really wanted to know you could reconstruct the servo-linkage-saver assembly and hang increasing weight from the saver.
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That's a good point - the forces required to compress the spring are known, but leverage and linkage position weren't discussed.

Friction between the saver cam would add to the force required to compress the spring.

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Most of us have their linkage about 2 cm out on the horn, but then the linkage mounts a similar distance out from the pivot point on the servo saver. So that cancels out.

People could set up a rig and measure it to get real world numbers, if they felt the need.

But: Comparing the Lee Spring to the stock spring by actually test driving the rig has already been done by many of us, and it works so much better. It tells us everything we need to know.

Better steering response, better static steering lock, faster lock to lock, better low speed steering response, better straight line holding, and greater high-speed steering authority.

I would happily challenge anyone still running a stock spring to a race around a track with a mixture of low, medium and high speed corners. Running the stock spring, they are 100% going to lose - and lose badly.

As for 30, 40, 50 kg servos - they are definitely huge over kill in our 1/8th rigs. Especially if they're running a floppy servo saver. 🤣
 
I've read this thread from end-to-end several times, I'll probably take the plunge and upgrade soon but I do appreciate the efforts and meticulous detail that you guys have put into this. It's comforting and reassuring to know there are so many technically minded members on this forum.
 
Horatio said:
That's a good point - the forces required to compress the spring are known, but leverage and linkage position weren't discussed.

Friction between the saver cam would add to the force required to compress the spring.

View attachment 9410

Most of us have their linkage about 2 cm out on the horn, but then the linkage mounts a similar distance out from the pivot point on the servo saver. So that cancels out.

People could set up a rig and measure it to get real world numbers, if they felt the need.

But: Comparing the Lee Spring to the stock spring by actually test driving the rig has already been done by many of us, and it works so much better. It tells us everything we need to know.

Better steering response, better static steering lock, faster lock to lock, better low speed steering response, better straight line holding, and greater high-speed steering authority.

I would happily challenge anyone still running a stock spring to a race around a track with a mixture of low, medium and high speed corners. Running the stock spring, they are 100% going to lose - and lose badly.

As for 30, 40, 50 kg servos - they are definitely huge over kill in our 1/8th rigs. Especially if they're running a floppy servo saver. 🤣
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I definitely agree, I would just run the upgraded spring with a ~25kg servo. But since @Atomic Skull was asking at what point a stronger servo would be wasted potential, he could calculate or test it out if he really wanted to.
 
Niekname said:
I definitely agree, I would just run the upgraded spring with a ~25kg servo. But since @Atomic Skull was asking at what point a stronger servo would be wasted potential, he could calculate or test it out if he really wanted to.
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Yes, I suppose he could - and Atomic Skull likely has the mindset to actually do it, too.

I reckon all sorts of horror would occur if we actually hung 45kg off our servo savers, with a servo attempting to hold it. 😝🤣

But I'd love to see a YouTube video of it! 🤣

I still reckon 20kg - 30kg is plenty, more importantly with a decent speed of 0.05 - 0.10 sec/60° would be in the fun zone.

My 81BHMW servo is rated at 45kg, but when I run it on 6v rather than 8.4v that it's specced for, it's more like 35kg - still overkill TBH. But it's responsive and controls the rig at 70mph with ease.
 
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This is turning into proper engineering now 😁
My view is that whilst a 25kg servo is enough for the SS spring, a 35kg might just give a little more reliability - stronger gears, case, motor etc, and it's not being run at full capacity.
With a LeeSpring upgrade, the stronger servo would mean that the spring is hopefully still the weakest bit of the steering rack.
 
Jeffwazz said:
This is turning into proper engineering now 😁
My view is that whilst a 25kg servo is enough for the SS spring, a 35kg might just give a little more reliability - stronger gears, case, motor etc, and it's not being run at full capacity.
With a LeeSpring upgrade, the stronger servo would mean that the spring is hopefully still the weakest bit of the steering rack.
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A 25kg-cm servo should hold against the servo saver when you force the wheels but that's only holding torque, stall torque (the servo's ability to push against a load when commanded to move) is usually around half that and servo manufacturers almost always list the holding torque not the stall torque because it's a bigger number. I have a 35kg-cm servo in my Asuga and the servo saver tightened to three visible threads and it can hold position against the lee spring just fine when the wheels are forced to turn but it struggles a bit when the wheels are locked in place and the servo is made to push against the servo saver (it moves visibly slower than normal). A stronger servo is also likely to be able to better handle being worked hard because the motor and electronics are made to handle larger currents and dissipate more heat and the speed will be less affected by load (servo speed specs are almost always given for no load conditions)

Also, when taking corners at speed I have noticed that the wheels sometimes appear to not turn as far as they "should" be able to which is why I tightened the servo saver another thread. It still does this though though not as bad. I'm going to get a stronger servo and tighten it another thread or two and see what happens.
 
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Atomic Skull said:
A 25kg-cm servo should hold against the servo saver when you force the wheels but that's only holding torque, stall torque (the servo's ability to push against a load when commanded to move) is usually around half that and servo manufacturers almost always list the holding torque not the stall torque because it's a bigger number. I have a 35kg-cm servo in my Asuga and the servo saver tightened to three visible threads and it can hold position against the lee spring just fine when the wheels are forced to turn but it struggles a bit when the wheels are locked in place and the servo is made to push against the servo saver (it moves visibly slower than normal). A stronger servo is also likely to be able to better handle being worked hard because the motor and electronics are made to handle larger currents and dissipate more heat and the speed will be less affected by load (servo speed specs are almost always given for no load conditions)

Also, when taking corners at speed I have noticed that the wheels sometimes appear to not turn as far as they "should" be able to which is why I tightened the servo saver another thread. It still does this though though not as bad. I'm going to get a stronger servo and tighten it another thread or two and see what happens.
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Protek are one of the few servo manufacturers that state both dynamic and stall torque. 👍

In reality, it doesn't really matter that the servo struggles to turn against the spring when the wheels are locked, because it's not a scenario your rig is going to experience during real world driving conditions.

We're not actually looking for servos that are strong enough to overcome the rate of the servo saver spring - we're looking for servos that can happily manage turning our selected wheels and tyres on the surfaces we typically run.

With the spring, we're speccing a rate that can hold all the typical dynamic loads on the surfaces we normally run, so as to maintain authority, but with enough 'give' when unexpected forces are put through the system - in the event of a hard landing, impact with terrain or crash into something solid, to prevent damage to any of the components in the steering system. We want the spring to deal with it, not the servo.

I notice on my Losi 22X-4, there is no servo saver at all. If you crash, you run the risk of killing a servo. Thankfully modern servos are so much stronger than they used to be, that in a 1/10th scale rig the chances of the forces being great enough to kill one are very low.
 
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