Yet another Customised Optima Mid Custom Special

[alcyon]

I went for a beach vacation. This time the missus let me have my mids with me.
took several videos too. For the swb mid look on youtube. I posted 2 vids of that car.
as for this car i will post a link here .

URL=http://s185.photobucket.com/user/alcyon2sp/media/20140914_180958_zpscyjhfal9.jpg.html][/URL]
URL=http://s185.photobucket.com/user/alcyon2sp/media/20140914_104840_zpsbbtewiai.jpg.html][/URL]


[youtube]5P47RJF9lfs[/youtube]

[alcyon]

I raced my car on Monday. There were 2 Durango DEX 410 V4, a caster Racing S10B, My Mid LWB, and a 1/8 car. We ran together but were timed separately. It wasn't an official race per se, but to work out the kinks in the system as this track operator is new to this sort of thing. I broke 2 arms on that day, both because of my mistake. On the first arm I broke, I chamfered the edge near the gearbox too much causing it to become really thin at that area, so it broke there. Then I replaced another arm, which also broke, but this time at the area where the C hub is attached. My CSI skills pinpointed the problem of the sharp edge on the corners. After I went home with a 5.5mm milling bit and a drill, I radiused the sharp edges, now these shouldn't break.

See where the new arm broke

This is my solution

Ok, how did the car perform. The track was slightly damp in the morning, and during practice the fast guys were even beating me with their Durango 210s. with their 4WD Durangos I was left far behind. But when the track became dry, and with lots of loose sand, the Mid gave the dingos a hard run for their money. It seems the mid really shines on low traction surfaces.
Here is a video of the mid doing its best.
[youtube]OeLpzcsBevI[/youtube]
http://www.youtube.com/watch?v=OeLpzcsBevI
The first heat a rear hub upper link screw came off so I only managed 11 laps, the top pro was doing 16.
In the second heat I improved my lap times , between 29s to 31s. The Top pro with his DEX 410 V4 was doing 27s. Really not bad.
In the final My arm broke when I cased a jump, shown in 1st the pic above.
My rear ZXR wing mount also cracked, so I devised a plate to mount Durango wing mounts.




I look forward to the next race, and to lower my lap times even more, without breaking the car or making mistakes.

[alcyon]

another video taken today.
[youtube]ZLmbeIjyyvQ[/youtube]

[alcyon]

Another new video but not of my car per se, but includes it. Whats special about this video is the clear picture and professional editing and slo moing.
Have a look at it.
[youtube]Vd9WW5XpoCY[/youtube]

[rccars4sal]

WHat kind of plastic are the arms? Acetal or nylon? Im surprised they broke like that. Were they hard hits?

[alcyon]

WHat kind of plastic are the arms? Acetal or nylon? Im surprised they broke like that. Were they hard hits?

They are made of delrin. They broke not hecause of the material but because of stress concentration at a sharp edge. Thats why i am radiusing all the inner edges. Yes the hits were very hard..hitting on the edge of the landing ramp.

This broke at the hingepin area also because of stress concentration. I am now removing the whole cutting from the hinhepin area as its not really needed. We shall see if this breaks again.

[foampervert]

Hello Alycon!

Delrin is not a suitable material for arms. Why not consider purchasing nylon instead? it's softer but much tougher. Delrin is great for low impact stuff like pulleys, gearboxes... things that need a higher lubricity.

-Alexander

[alcyon]

Hello Alycon!

Delrin is not a suitable material for arms. Why not consider purchasing nylon instead? it's softer but much tougher. Delrin is great for low impact stuff like pulleys, gearboxes... things that need a higher lubricity.

-Alexander

Thanks for the suggestion Alex. Welcome to the forum. I see that this is your first post ?
However I feel the problem is the design of the arm not the material. I have revised the design like this.

I removed the gap in between where the inner hinge pin sits. And added relief radius on the c hub sharp edges. I tested the car for 3 packs yesterday and cased pretty hard many times because of lack of traction, and stability because of low caster, and so far still have not broken yet. I will be changing to TA05 4 degree caster block as suggested by coeclanth , lets see if it improves handling.
If these arms break I will change material to blue nylon.

[Coelacanth]

I have a feeling that the outer, trailing edge of those arms will snap too. 1 post or not, I'll have to agree with Alexander. Sometimes it's not about how much material there is, but what the material is made of. Maybe Delrin is too brittle of a material for a high-shock application like control arms; nylon or glass-filled nylon are more commonly used because they have more give, that bit more flex before fracturing...while aluminum may have almost no give, but is that much stronger.

[EvolutionRevolution]

I have a feeling that the outer, trailing edge of those arms will snap too. 1 post or not, I'll have to agree with Alexander. Sometimes it's not about how much material there is, but what the material is made of. Maybe Delrin is too brittle of a material for a high-shock application like control arms; nylon or glass-filled nylon are more commonly used because they have more give, that bit more flex before fracturing...while aluminum may have almost no give, but is that much stronger.

Delrin seems to be just fine for touring car arms. However, I think alcyon's redesigned arms are going to break, right at the three-quarter holes. Probably, rounding the corners like they do on chassis cutouts would work better - so you first have to drill the holes, then cut the straight lines.

[jwscab]

also want to say that delrin is probably not the best. 6/6 nylon will get you a tougher arm. Delrin has a high notch sensitivity, meaning it will crack around any sharp edges. Ideally formed, it will make a tough arm, but nylon is more forgiving for prototype fabrication.

[alcyon]

Ok heard you guys. The reason i chose this material is because i wanted a white arm like the rc10. And the only white material available from my supplier is delrin.
i actually wanted the relief cuts like the one showed in an earlier pic above. My supplier misunderstood me.
And a inner radius cut does not work on lazer arms because the inner radius will interfere with the c hub edges. Thats why i got these cut more inwards.
Next on my priority is adding caster to the fronts because on low traction surfaces my rear end is swinging around on power even with ball diffs.
about the 1 post thingy, i did not mean anything like that. Everyone is welcomed to say something on my thread. I was actually flattered that his 1st post is in my thread
So far these are holding up. If it breaks i will notify you guys.
then we see who wins the "hindsight is a wonderful gift".

seriously we all can learn something from this experiment.

[Coelacanth]

Certainly, alcyon...except for the box-art guys, pretty much ALL our modernizations and improvements are experimental! We all learn from the successes and failures of one another.

[EvolutionRevolution]

And a inner radius cut does not work on lazer arms because the inner radius will interfere with the c hub edges. Thats why i got these cut more inwards.

Then you make the indented part deeper. So the radiuses start where the c-hub ends (should I make a little drawing to clarify?). Nothing says the dimensions of the cuts have to be exactly the same as on the original arms...

Next on my priority is adding caster to the fronts because on low traction surfaces my rear end is swinging around on power even with ball diffs.
about the 1 post thingy, i did not mean anything like that. Everyone is welcomed to say something on my thread. I was actually flattered that his 1st post is in my thread
So far these are holding up. If it breaks i will notify you guys.
then we see who wins the "hindsight is a wonderful gift".

seriously we all can learn something from this experiment.

Refining prototype parts is always part of prototyping, no?

[alcyon]

tested my car yesterday at titiwangsa again , this time with Durango big bore springs which are harder than the kyosho BB gold, and the car handle remarkably well even with the jconcepts tyres. The car flipped hard several times when it was thrown by unseen ruts hidden in the grassy surface, but nothing broke within the 2 packs which was about 13mins a pack.
Coelacanth's mod to increase caster with maxxum arms, gave me encouragement to purchase the same pair of yeah racing 4 degrre hubs from dinball. However that will take 2 weeks to arrive. I suddenly remembered I bought 1 each sets of Lazer ZX5 LA-219-4 and LA219-7 C hubs, mainly for the knuckles. I just remembered I have those C hubs sitting in my box doing nothing !
I remembered isobaric doing minor grinding to fit these hubs, so after some test fitting, I managed to fit these hubs and 3racing knuckles for the ZX-5. After some creative shimming and spacing I got it to work.


This pic below shows the front area to grind , which is just below the 7 degree symbol.

I do worry doing this will weaken the hub, but it is absolutely necessary ,otherwise the suspension will not work. Grinding up to the caster angle mark will allow about 3 degrees of camber at front arms level to the ground, but you cant increase more camber because it will cause interference with the ZX arm. So I will stick with this minimal camber setting now. Besides, at 7 degree+ 3 degree in the arms, which totals at 10, it will automatically give more camber at full steering lock. Also, since the car should handle better, I should be having less mishaps.

lastly, The 62.5mm CVDs aren't long enough with these hubs, so I used my 3racings 65mm ZX5 CVDs which I bought way back in 2011 for my ZX-5 suspension experiment.
So lets see if the increase in caster will net me with a easier to drive Optima Mid.