Independent Front Suspension

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Ned
Posts: 369
Joined: Sun 13. Apr 2014 01:02
Location: Sedona, AZ USA

Independent Front Suspension

Post by Ned »

My outdoor track has many bumps and 2 banked tight corners. Unless some provision is made to prevent it, with a stiff rigid chassis, when one front wheel rises off the road surface, the other does too. This might happen when a front wheel goes over a grain of sand or seed. It always happens when going around a banked curve. This causes the gap between the wire embedded in the track and the magnet at the end of the steering arm to increase slightly. This often results in a crash.

The only way I can think of mitigating this effect is to make the chassis more flexible, especially make the front axle able to twist (rotate) around the longitudinal axis of the car. Then the front axle could rotate independently of the rear axle. The goal is to keep the steering magnet a constant distance above the wire, especially on banked corners. If anything, the magnet should be closer to the wire, not further from the wire, when the car is going around a corner.

Does anyone have any ideas on how to solve this problem?
kiklo
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Re: Independent Front Suspension

Post by kiklo »

Hi Ned.

In my test chassis I get 1-2 mm of play on the front axel by slimming down on material around the guide. Also using PETG when printing not PLA, helps.
Racing Regards

Kim K.
WesR
Posts: 371
Joined: Fri 21. Dec 2012 17:37

Re: Independent Front Suspension

Post by WesR »

DSCF1015 (3) (600x255) (318x189).jpg
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Maybe I haven't explained my front suspension properly. As can be seen, the lower plate is projected forward in the form of a T with 2 extra mounting holes. The front bumper plate lifts the whole suspension up by 1.5 mm allowing it to flex both slightly laterally and mainly transversally through the neck of the T by up to 1.5mm each side. This seems to work well and costs only the price of the two screws. As the guide arm is mounted in the suspension assembly, the magnet remains a constant distance from the track. If one wheel runs over a bump, the magnet lifts by half the height of the bump which is probably as much as we can achieve. I have been using this idea for over a year and it's now on all my cars.
Ned
Posts: 369
Joined: Sun 13. Apr 2014 01:02
Location: Sedona, AZ USA

Re: Independent Front Suspension

Post by Ned »

Wes, you have an interesting idea there. I suspect you are using it with your 1/24 scale cars. As I understand it, the front edge of the bottom plate of the frontend suspension assembly is mounted with 2 screws to the back edge of the front bumper plate, which is 1.5mm thick and which is attached to the lower plate. This has the effect of raising the suspension assembly 1.5 mm above the lower plate of the frame. With this air space between the lower plate and the bottom suspension plate, the latter can flex a little bit up or down and side to side, a maximum of 1.5mm. Another ingenious idea! While I have made some smaller chassis than your original 1/32 scale version, I’ve yet to build one that will handle better on my track. My hat’s off to you!

I’m still trying to improve a small chassis that will fit under my 1/32 scale Slot.it Ferrari 312 PB body. I don’t want the chassis to interfere with the cockpit and I want the car to go around a banked corner following a 0.8mm diameter guide wire in the track with an 8” radius. I’m trying to make an HK-5320 servo mounted between the front wheels work. Because you mount your servo behind the tie rod (near the middle of the chassis), instead of between the front wheels, I don’t think your idea will work for me but I'm sure it’s fine for bigger cars.

I have 2 main problems to solve. When one front wheel goes over a bump or the car goes around a banked curve, it sometimes loses the wire and crashes. That’s what this topic is about. I have been trying to make my frame so that it will twist easily, since my front suspension assembly is molded to the frame. See picture below.
IMG_20200906_143241(1).jpg
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The servo snaps in place between the front wheels. As you can see, 2 skinny rails connect the frontend assembly to the midsection of the chassis. Per Kim’s suggestion, I will try slimming down these rails. I’ll also eliminate the reinforcing ribs on the edge of the midsection of the frame. I guess trial and error will determine how thin to go. My chassis are 3D printed by Shapeways in durable nylon plastic using Selective Laser Sintering (SLS). It’s tough but flexible.

At a later date, I’ll post my other problem, under a new topic.
WesR
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Re: Independent Front Suspension

Post by WesR »

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Here's a pic of a 1/32 car which I built a couple of years ago.
Well I built 3 or 4, all with this front suspension which you can just about see. The servo is offset so technically the magnet in the track rod moulding goes up and down slightly relative to the servo but I never noticed any problems with this. In fact the cars goes very well.
The problem with flexi chassis is that, as soon as the bodyshell is fitted securely, as it needs to be for racing, it immediately stiffens the chassis. This can be largely overcome by mounting securely at the rear, by the usual two magnets say, but using a horizontal pin at the front. This can be seen on the photo. The body needs a vertical plate with a matching hole.
But it does need a little more care when removing the body.
kiklo
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Re: Independent Front Suspension

Post by kiklo »

I'm about to test an extreme version of my flex-chassis.
flex-test.JPG
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To find out when it is to flex or snap at the weakest point.
And yes the body needs to be secured with flexibility in mind.
Racing Regards

Kim K.
kiklo
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Re: Independent Front Suspension

Post by kiklo »

I'm thinking of using this as a front body-connector. Just a fast drawing.
Will allow for non destructing crash - I think.

Grey - the magnet clued horizontally to the body.
Blue - steel-screw, screwed into the chassis.
Purple - collar on screw so the magnet rest down but can twist longitudinal.
boddy-conn.JPG
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Racing Regards

Kim K.
Ned
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Joined: Sun 13. Apr 2014 01:02
Location: Sedona, AZ USA

Re: Independent Front Suspension

Post by Ned »

Kim,
How did your flex-chassis work out? How did you attach the printed circuit board(s) & servo to the chassis? Can you post a pic with PCB & servo?
Ned
kiklo
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Re: Independent Front Suspension

Post by kiklo »

IMG_20240202_164228 (Custom).jpg
IMG_20240202_164228 (Custom).jpg (42.66 KiB) Viewed 6618 times
Hi Ned and all.

My flex chassis (blue + camera+car) is very forgiving. I have not done a comparison but the flex does seems to make a softer running car.
It gives some challenges wrt. radio, so best suited for the ultra-small radioes.

Still my other chassis does giv a 1 mm play. Seems ok.

I am using a 3 point connection for the bodies to alow for the flex.
Racing Regards

Kim K.
kiklo
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Re: Independent Front Suspension

Post by kiklo »

As I remember the flex chassis flexed too much in the middle so the magnet will also move up and down.
Making it only twist longitydinal is quite difficult. But I'll giv it a thaught to see if I can com up with a solution.

Fixing the front end with only on bolt up front in the middle is maybe a thing ?
Racing Regards

Kim K.
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