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Collin

Bump steering, or what I am dealing with?

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Hi guys.

I am tinkering around on my Dyna Storm Mid motor buggy using different lenght of front damper and shock towers. Goal is to make the Dyna flat and hard for high speed tracks with low jumps.

Now there is one phenomenon, which I can't really spot yet. its alway when steering is 100% to left  AND right damper is fully compressed. on the last 30% of damper traveling it starts to pull against the steering direction. Also the opposite way around, steering right and compressing left damper.

Now I was trying to shim the steering rod on one and the other side, but they are in okay position regaring suspension arm.

Does this phenomen sound familier to anyone of you? All hints highly welcome : )

Greetings.
C.

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Never had a Dyna Storm or had this problem on another car. Sounds like it must be something purely mechanical. I would try to remove the steering rod on the right, "steer" the right wheel as far left as you can and then compress the damper to see what happens. If the wheel stays full left it's probably about the steering rods...  

Does the Dyna Storm have steering with the servo saver directly on the servo horn (like the Grasshopper) or is there a steering "system"? (like the M-05)  

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Yep, servosaver mounted directly on the servo.

Will try your suggestion tomorrow.

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Hey Tom, will check mine today! 

@Tamiyastef: Dynas have a steering crank system like M05, so almost the same length of steering rods and upper wishbone links!

@Collin: What about pushing the front down on in parallel until the chassis sits on the ground? Do the wheels turn in the last cm?

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@ruebiracer on my original Dynas there is no effect like this. In my case, imagine a Dyna with VQS short Hicaps at the front & short shocktower. Until the front is bottoming out everything is fine, even if I raise the one arm its okay until the very last moment. It seems like the steering rod is then pushing against the steering mechanism.

Probably this is a position you never actually have when racing but I am a bit perfectionist saying, this is not legit.

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Sounds like you might just be bumping up against the limits of what's possible with the geometry. Suspension systems are only designed to work within a certain range of movement, and if you exceed that, then weird things start happening. I would suggest just setting it up so that the suspension stops just before you get to that point.

To quote a mechanic who knew a thing or two, albeit in the fictional world: "Ye canna change the laws of physics."

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3 hours ago, markbt73 said:

Sounds like you might just be bumping up against the limits of what's possible with the geometry. Suspension systems are only designed to work within a certain range of movement, and if you exceed that, then weird things start happening. I would suggest just setting it up so that the suspension stops just before you get to that point.

To quote a mechanic who knew a thing or two, albeit in the fictional world: "Ye canna change the laws of physics."

Hi. This sounds very reasonable to me. Indeed am trying to get maximum travel out of the construction. I think I can put another spacer into the damperbody and its still a lot of up/down travel.

Whise guy your friend : )

Thanks.

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Hi Tom, thanks for the vid! Just responded to your mail!  I also think @markbt73 could be right and you reach the limit of the ballcups!

Just make a check with taken off steering link to see the effect!

Cool car, by the way!:wub:

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Very good point. Accidently I used short ballheads and this effect was even worse. I figured that out yesterday and  now with the standard 5mm ballheads and gray frictionless adjusters its eleminated but maybe not completely.

Will check it out later or tomorrow.

 

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Gentlemen, it was the tyres. : )

It drove me so crazy and obvious things are somtimes not seen. Additional I was using Star Dish rims for the last summer and switched to TRF flat disc ones, which have a bit of an offset.
Sooo stupid, this cost me some nervs but I can loudly lough about myself.

Thanks to all of you pointing my head to the right direction. :D

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Dyna Storm has a relatively impractical and outdated steering mechanism. The tie rod balls are attached to the bell cranks instead of a steering bridge like all modern cars.  I remember distinctly that this causes a very sudden change of angle on the inside tire at full steering lock.

Try removing the balls and drag-link and fitting a custom steering bridge cut from frp or carbon fiber. This will allow you to test various pivot point locations for the tie rods and see what fixes the problem.

 

X-Steering 1_zpsdp1tiifl.jpg

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8 hours ago, 94eg! said:

Dyna Storm has a relatively impractical and outdated steering mechanism. The tie rod balls are attached to the bell cranks instead of a steering bridge like all modern cars.  I remember distinctly that this causes a very sudden change of angle on the inside tire at full steering lock.

Try removing the balls and drag-link and fitting a custom steering bridge cut from frp or carbon fiber. This will allow you to test various pivot point locations for the tie rods and see what fixes the problem.

I have already been there and tested dozends of steering bridges. My thoughts was, this very extreme steering change on the last bit was, what made the Dyna Storm so much easy going around sharp corners? Maybe I am missreading this behaveor.

ku_ds_051.jpg

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So every steering as about the "Ackermann principle". Racer really alter the angle setup of each tire while steering with shims on the steering bridges on most modern Touring cars, even M-chassis. You can measure the angles of the wheels on a proper setup station and compare to each other. While there is a theoretical Ackermann principle for every steering angle, when just looking at the different circle diameters the tires are driving on, in the real world there´s a "dynamical" Ackermann value, which also includes the slip angle of the tires. It´s a long time ago I learned the maths behind this, but I guess that´s the reason why racers (no matter buggy or onroad) play with these parameters for their driving style and the chassis characteristics of the car to suit their needs.

As Colin said, I also think there is a reason Tamiya designed it this way on the Dyna. "Modern" Steering layout with a bridge was already invented on the Avante in 1988. This principle is still 90% of all modern RC touring cars I´d tend to say.

Anyway, it would really be interesting to collect data from different cars, which tire angles they reach on full servo throw. So you would be able to compare your individual car to steering / Ackermann layouts to other cars...

But in the end it´s great, that nothing was wrong with your TRF Prototype Tom!:) What I have already seen of it is kinda mind blowing! It will be a legendary project!

Have fun,

Matthias

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I'm certain Tamiya did that on purpose. From photos of  the 1992 TRF211x it appears Tamiya developed this system for competitive racing.  However.....when they finally returned to competitive 2WD with the TRF201, they had switched back to more common style steering bridge.  I think they stuck with that through the TRF211XM.

I'm not saying one is better than the other (I never raced 2wd off road). I'm just pointing out Tamiya abandoned the Dyna Storm system for whatever reason.

Trying to piece together the history of engineering choices always fascinated me.

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BTW I believe real Ackerman is created by the angle between the steering knuckles axis of rotation and tie-rod pivot.  The shimming of the steering bridge common in RC plays more of a secondary role of modifying the curve of the difference between the two wheels.

I believe this why the Avante series will always have relatively awful wobbly steering. It effectively has no true Ackerman since these two pivot ponts are parallel with the centerline of the car.

r0qZt.png

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We'll a quick sketch in CAD revealed something very interesting. A Dyna Storm style steering system makes WAY more wheel angle difference than identical static geometry with a steering bridge in it's place.

These are drawn with bell cranks at 0, 30 and 60 degrees.  Cyan is Dyna Storm storm style and yellow is the steering bridge style. No actual measurements taken, so this is only for theory.

thumbnail.png

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I totally agree, once I printed arond 30 different steering bridges in all variations and I never got such a extreme steering angle for inner wheel like Dyna Storm had it. So I went off but something mad drove me to think I need it for my actual prototype project.

But since one of the main goals was to keep the DNS of TRF211x / DS it will stay with an idear of the originl steering arms and no steering bridge.

Great you guys came with so impulsiv tech content. Cant thank you enough.

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That's amazing you did actual rapid prototype testing of custom steering components. I've always wanted to try making custom Ackerman c-hubs for the Avante series. I feel that chassis still has a bit of room for creative improvement (plus I'm a fanboy I guess).

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@94eg!

I started with this:

steering_mod_01.jpg

and finally this:
steering_mod_02.jpg

That photo is a bit dark but in general DS arms with carbon bridge. Have alot more of that 3D printed bridges, its cool becaus in 3 miuntes you can test the next one. But at the end your graphs show exactly what I figured out in reality checks.

The 211X / DS steering might be vintage or something, but they have this excessiv cornering. On speed shure it will still push the car off steering radius but if you are slow and a nice accelerating motor, its like beeing a rabbit. Maybe it was that time and that tracks which needed this layout, still dont know...

What I did at the end is a adjustable outer ballends on the steering arms, where you can lower the ackerman by moving them forward (more) or to the rear (less ackerman).
steering_mod_03.jpg

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For some reason it just popped in my head that altering the length of the drag link between the 2 bell-cranks might also be an Ackerman tuning tool. I'll play around in cad and report back.

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Blah, nevermind. Imediatlely found out that if the bell cranks aren't perfectly parallel, then it completely throws off the steering angle of the right bell crank.

In fact, I would say getting the length of the drag link to perfectly match the center spacing of the bell cranks is of the utmost importance.

I lengthened that rod +9% and it throws off the right bell-cranks by 1.5° in either direction (3° total).

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5 hours ago, 94eg! said:

We'll a quick sketch in CAD revealed something very interesting. A Dyna Storm style steering system makes WAY more wheel angle difference than identical static geometry with a steering bridge in it's place.

These are drawn with bell cranks at 0, 30 and 60 degrees.  Cyan is Dyna Storm storm style and yellow is the steering bridge style. No actual measurements taken, so this is only for theory.

thumbnail.png

thumbnail.png.01c336945c9ae6f4987f2ad063de6553

Wow. The geometric effect is obvious enough in principle but this illustrates the (very large) extent of it. If this is as much as the outside wheel turns in, that's disastrous, surely? Yet, we hear above that the car cornered well. Seems very odd to me. 

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The graph is comparing the angle difference between the inside and outside wheel at 3 different points.  Essentially the stock Dyna Storm steering setup provides a huge amount of Ackerman.....which, in theory, provides much more accurate control in extremely tight turns (as Collin has confirmed).

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2 minutes ago, 94eg! said:

The graph is comparing the angle difference between the inside and outside wheel at 3 different points.  Essentially the stock Dyna Storm steering setup provides a huge amount of Ackerman.....which, in theory, provides much more accurate control in extremely tight turns (as Collin has confirmed).

I can see how it would up to the point that the Ackerman exactly reflects the path of the front wheels on the ground at full lock, but what I struggle to grasp is how it would be beneficial once it goes beyond that, which I would think it has done here by some margin. 

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If there is excess Ackerman for a given vehicle path, it would act as added front toe-out.  If there was a lack of Ackerman, it would behave as added toe-in.

With so many other variables, one must test setup changes on-track to fully comprehend these effects in various scenarios (every turn on a given track). If on-track benefits are discovered for given conditions, then this data is added to the arsenal of "set-up" options.

This was team TRF was for.

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