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Quinster

Monster Beetle Steering

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Hi,

I’ve built a MB and it was driving straight to begin with but now it’s swerving to the right. Putting the trim on adjusts it’s for a bit but then it starts swerving again. I’ve stripped it down a few times and can’t see any problems.  I have a metal gear 9kg torque servo in it and a torque tuned motor(not sure if I should have these in either).  It wheelies like mad - the number plate has been off 3 times.

I centralised the servo, it looks straight on the stand and the steering looks fine when I test it on the stand too.

Anyone got any ideas  as to what could be the cause?

I’m not too experienced so any help would be great.

Cheers.

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It could be a number of different things, but assuming steering arms are in good order as well as their associated connections, it will generally either be an issue with your servo or an issue with your servo saver. When I've had this type of problem it is usually because of one of the following;

1) the servo has become defective and  no longer centres 100% of the time, resulting in steering off in one direction or the other;

2) the 'teeth' on the servo spline have stripped, meaning the servo horn/saver  that attaches to it slips, resulting in off-centre steering;

3) the opposing teeth in the servo horn/saver have stripped, with the same result (or the servo saver has 'stretched' and become loose, inducing slippage - although this only really applies to the standard kit supplied tamiya jobs. It's the thick 'C' shaped bit that acts to absorb sudden shocks. Unfortunately, over time this will stretch and separate, resulting in the whole thing becoming very imprecise).

4) some random thing such as the screws holding the servo to the chassis becoming loose or something obstructing the servo arm that isn't immediately obvious.

If you are sure that all screws etc are tight and where they should be and that nothing is bent or out of whack then I would try a different servo saver/horn if you have a spare first. If it cures the problem, great. If not, it will probably be the servo that is at fault. Again if you have a spare, swap it out to test it. Trial and error is usually the only way to solve these sorts of things I'm afraid. 🤞👍

Good luck.

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My Stadium Blitzer was doing similar thing, I then discovered that the kit supplied servo savers had a habit of ‘slipping’ and easily fixed with a small zip tie around the servo saver. I did this on a Blackfoot and didn’t have any problems.
Most just upgrade the servo saver.

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6 hours ago, Quinster said:

9kg torque servo

I use a 3kg in mine, is it possible this is overpowered and distorting something? Or as @Silver-Can says stripping teeth? Have you put it on a stand with the servo cover off to see if something distorts when the wheels end stop? I’m actually also interested in some of the more experienced guys opinions of which strength servos should be used in which machines, I thought the MB all felt a little bit flimsy for anything greater than the 3kg, mine drives ok, but then... I’m a novice driver never race and only run on perfectly flat grass...so what do I know :)

 

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2 hours ago, Lee76 said:

I use a 3kg in mine, is it possible this is overpowered and distorting something?

My Blackfoot, Monster Beetle & Brat all have Power HD 15kg metal gear servos in have been fine. 

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Astounded by the help here.  I’ll respond In more detail after work.  Cheers.

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do not know if this is the problem BUT I have found anything with big tyres needs the standard servo saver upgraded. Kimbrough are pretty much straight swap. The Tamiya standard is very soft.

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1 hour ago, Re-Bugged said:

My Blackfoot, Monster Beetle & Brat all have Power HD 15kg metal gear servos in have been fine. 

Correction.. Just double checked, mine is 4kg.. even so.. 15kg! I could drive my SUV with those :) 

Good to know though.

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It’s actually a 15kg servo - metal toothed, I just checked.  I replaced the servo yesterday before posting this and the problem was still there.  I have another servo saver on order but will give the cable tie trick a shot as that should tell me if that’s the problem.  I wasn’t sure if I bought the right servo so tried to reduce the end points in case that was the problem.  I may buy another servo after trying the advice here - I just touch the trigger and it pretty much backflips :) 

I had a similar problem on my Midnight Pumpkin and that ended up being a servo mounting bracket thing being the wrong way round. Checked that too.

Cheers again and I’ll let you know what works after trying the points above.

How helpful is this forum!

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+1 for kimbrough servo saver too. My usual go to when needed.

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Post pics of the lot of your car and TX.  That could be caused by several things-

Sloppy servo saver

Unequal length tie rods

Toe out

1 damper/suspension binding

Drive line drag on 1 side

Glitching radio gear

Bad pots in the servo

Broken gear in the servo

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Well I’ve got a pretty long list of things to check - this is fantastic.  Thanks everyone.

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Engine ShotAstounded by the help here.  I’ll respond In more detail after work.  Cheers.

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So I centred the servo and put a cable tie round the servo saver C shaped bit. Tested it and it was still the same.  I could see from looking that the front right wheel was facing inwards more than the right so I shortened the steering rod a fair bit so that it looked straight to the eye (it won’t be the recommended length in the manual for sure).  Tested it again, tweaked the right trim and it’s running pretty straight.  Straight enough for a novice anyhow.  I’ll pop my new servo saver on when it comes.  Delighted.  Thanks for the help.  It will be useful for future too.

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On 8/4/2020 at 2:34 AM, Lee76 said:

Correction.. Just double checked, mine is 4kg.. even so.. 15kg! I could drive my SUV with those :) 

Good to know though.

I run 35kg in my Wraith and UMG-10 Unimog!! 😲😲

ANYTHING that makes Power, will only output as much as you ASK it for. These BIG Servos require a programmable 2.4GHz Radio. WHY? So you can make vital adjustments - especially end points. On the Power HD 35kg, I had the end points set beyond the stops.... On any light powered Servo, it will just buzz and hum.

With MINE, it RIPPED the C-Hub right off the Front Axle!!!- 😖😲😲😲  With absolutely NO Damage to the Servo! 

This also explains why I haven't used a Servo Saver in over 10 years! Seriously, with today's modern Servos, Ball Raced, all Metal Gears, higher voltage Electronics... You don't NEED a Servo Saver. They were from a time when Servos were WEAK and had brittle Plastic Gears! Not any more. 

For those who believe that they absolutely HAVE to have a Servo Saver - Kimborough is the ONLY way to go!! 👌  They have virtually NO SLOP.

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On 8/4/2020 at 6:15 PM, Lee76 said:

I use a 3kg in mine, is it possible this is overpowered and distorting something? Or as @Silver-Can says stripping teeth? Have you put it on a stand with the servo cover off to see if something distorts when the wheels end stop? I’m actually also interested in some of the more experienced guys opinions of which strength servos should be used in which machines, I thought the MB all felt a little bit flimsy for anything greater than the 3kg, mine drives ok, but then... I’m a novice driver never race and only run on perfectly flat grass...so what do I know :)

 

Off topic from the original question, but a very torquey servo won't damage anything, unless its going beyond the required travel in  which case it can twist the chassis, break uprights etc. Just check the end points to make sure its not going too far.

My cheap servos are 9kg with metal gears, they seem bulletproof compared to the old S3003 etc of old

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Yeah I'm going to concur with the Kimborough servo saver. I use them on a few of my buggies. My MB has one, I also mounted my servo in the center and used aftermarket cups, balls and steering links. It works really well.
The kit servo saver is trash. It was one of the first things I changed on my MB.

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Could someone post a link to the kimborough servo saver, I had a look on a EBay but there was no size reference and a few to choose from.  

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5 hours ago, Quinster said:

Could someone post a link to the kimborough servo saver, I had a look on a EBay but there was no size reference and a few to choose from.  

I get the mid size ones. They are the ones you want.

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7 hours ago, Jonathon Gillham said:

Off topic from the original question, but a very torquey servo won't damage anything, unless its going beyond the required travel in  which case it can twist the chassis, break uprights etc. Just check the end points to make sure its not going too far.

My cheap servos are 9kg with metal gears, they seem bulletproof compared to the old S3003 etc of old

Staying off topic.. including @Carmine A

I've only built a few Re-Re's and have no driving experience or history of how fragile servo's used to be.. But reading your posts It strikes me that the consensus is that servo's can be as powerful as you like (within reason) and there's no need for a servo saver provided your travel isn't exceeding the mechanical range of the steering.

Here's my take on it.. Having thrown together some builds I've never actually thought to measure servo angle required, nor do I remember seeing it stated on the instructions (though if I'm honest I don't read 'every' word in instruction books :) ) I checked my cheap servo (£7 4kg).. It only states voltage, force and speed on it, there's no mention of angle.. Also I've never measured these. once all together I turn the wheel and the wheels go to end stops and nothing breaks..

I've got a reasonable radio, but I've only used this to trim the centre position.. I don't even know if it's possible to vary the end points, but even if it is.. I have now more than one car and would be too lazy to set up the servo every time.

So.. do you think the purpose of a servo saver is now less about saving the servo and more about making sure the servo doesn't break the linkage/chassis if you have more servo angle than required? So really we should be picking a servo saver that is slightly less stiff than the linkage? (you'd think the kit designer would have factored this into the saver supplied but that's designers for you)

This leads me to another stray thought... I have a more powerful servo in my Avante,  It has a quick reaction time. I'm only ever driving on flat very short dry grass. If I snatch the steering as quick as I can the car will roll, too much grip I assume and too aggressive a turn. So.. I can adjust my handling to not be as aggressive or back off the throttle (driver skill based control) or alternatively you could select a servo by reaction speed effectively lower power so that at your fastest turn at top speed the steering will only turn at the surfaces grip allowable limit..(and snatch the steering to my hearts content)  I'm sure the high end transmitters must allow programmable reaction speed? at the other end of the spectrum is my 4kg servo monster beetle, which will not roll at high speed cornering on the same surface, so perhaps I should be increasing the servo power till it does roll (or just before) to get a sharper turn out of it.. I might buy a Carmine A rated 35kg servo, stick this in the beetle and test this out.. see if she rolls.

I know most of you already have all the answers, but as I'm just starting this hobby it helps to air my thoughts out loud and suck up all the feed back you helpful guys throw back!

 

 

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There's no such thing as a servo that's too powerful! Big servos are one of the best things about modern RC. You always have enough power to move the tires around, they're fast and consistent, and center accurately. Proper adjustment is key, though, because they can be strong enough to bend or break parts, and can burn up if stalled for a long time.

A 600 oz. servo makes a RTR crawler into a real beast, and a 150 oz. .09/60° servo makes a buggy or touring car drive like a racecar. Good steering servos are one of those overlooked "best upgrades", especially with the RTR guys. The performance increase is huge.

Off topic a bit, quality electronics really add to my enjoyment of the hobby. Having fought with crystal sets, fast brushed motors, weak and fragile servos, mechanical speed controls and unreliable ESCs in the olden days, the advent of LiPo batteries, brushless motors, 2.4 GHz radios, and digital servos still seems like a miracle. My electronics are essentially maintenance free, and my cars are so much more controllable than they used to be. A nice electronics package costs about the same as it did in '90 (RX, ESC/motor, servo, battery) and is infinitely better in every way. Now, I can go to an event and not worry about radio impound or run time, and I don't have to keep as many spares around. We can all run together without frequency conflict, so we can have big bash sessions or trail runs. 

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@Lee76 It's been a long time since I've had an ORV Chassis Vehicle, but I do really want a Subaru Brat! 

Being practical, 35kg is OVERKILL for such a Light Vehicle. 😲  It is often better to have too much Power than too little. But as I mentioned, if you don't have a Radio with adjustable end points and dual rates.... You'll do more harm than good. 

You DON'T need to spend a fortune either!! My $32 (USD) FlySky GT3B Radio does all that and more! 😁  It's got 3 Channels, and stores 10 Vehicles. I've only got 5 RCs left, after having to sell 3/4ths of my collection about 6 years ago, due to horrible circumstances..... 💔😞 

But those 5 RCs, run on the ONE Radio, each with its own set of individual adjustments!!!  Plus, new Receivers are only about $10-14 USD, depending on where you find them. It outperforms many Radios costing 4X as much! 

You Sir, have done a LOT of thinking. 😲

Servos not only have varying degrees of Torque - but also varying degrees of Speed. Racers like the speedy ones, Crawlers like the Torquey ones! Your Avante is a great candidate for a high speed Servo. You just need to watch how fast you turn the wheel!! 😲  Exactly like driving a Sports Car after driving the Family Sedan.

You made another VALID point! You don't really need a Servo Saver to protect the Servo itself anymore.... But using one to protect the Front End components is a great idea!! 

The Servo Savers in Tamiya Kits, with Rare exception, are pure RUBBISH. SO much off-centre play, that Steering can get imprecise!  That's why so much fuss over the Kimborough Servo Savers. They're sprung to prevent impact damage... but there's no back and forth play when driving normally.

Thank you! That was a very insightful Post. 💯👏👏👏👏👏👏👏

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@Big Jon 2.4 GHz has been a modern miracle, even beyond never having to impound your Radio!! 

And I agree - 90% of the time... Über Powerful Servos are the way! I'm so glad I was able to get a Reefs 550 Servo (550 in. oz.!!) for my SCX10 II UNIMOG! I had to get Aluminium Rod Ends, because I kept ripping out the plastic ones. 😲😲  But I get the piece of mind that no matter how gooey the Mud or how soft the Sand, I've ALWAYS got full Steering, that always returns to center when I'm done turning. 

I started in 1984..... 1000 MAh NiCd was considered an UPGRADE!!  It's a great time indeed to be in the Hobby!!

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@Quinster this is the sort of thing you're looking for Kimbrough servo saver

As an aside, I agree with the argument that servo savers are as much to save chassis/servo mounts and other parts of the car as the actual servo however, also bear in mind how much faster cars are today, with their lipo and brushless setups compared to back in the 80s and 90s. I think they still have a role to play in protecting the servo, just not as prominently as years gone by.

I also agree that as a consequence, servos need to have properly adjusted throw to prevent them twisting, stretching or otherwise breaking stuff. I've just finished a schumacher cougar 2000 refurb and installed a new 25kg servo with .07 speed. It can also travel through around 180° (but is set to 60 by default). Without setting the steering endpoints it was causing so much flexing and warping of the front end assembly that I thought was going to snap something. On the 0 - 120 points of adjustment on my tx (with 120 being max throw), I have it set to 70 and the steering assembly just touches the maximum limit of its throw.

/derail. 😁

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5 hours ago, Carmine A said:

The Servo Savers in Tamiya Kits, with Rare exception, are pure RUBBISH

I assembled the one in a re-re sand scorcher and did find myself wondering if the designer of the saver and the entire linkage was on some sort of acid trip at the time.. the whole thing is bonkers It’s a bit like thinking I’d get better control with my chainsaw if I dangle it with some fishing rod. Still, I bought it for the looks anyhow :)  I’ll do some background reading on the Kimbrough ones mentioned, see what it’s all about. One things for sure, If and when I buy my next project (I’d love to get into crawling) I know I won’t buy anything without asking here for recommendations first! As always thank you for the support and feedback!

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