Wider suspension arms

[fredswain]

Awesome. I'm just making sure. You don't want to wait 3 weeks for something only to accidentally ruin it.

[MCKNBRD]

Question...I've looked through the first 400 or so posts on the 'tuning with camber links' thread over at R/C Tech...and I'm blown away by the info provided by fredswain over there. Coming over here and seeing fred post about stuff on the good ol' RC10 and talk about these arms and stuff, I'm curious about a couple of things.

First, is there such thing as 'too long' for the suspension arms? Why couldn't someone just make a narrow front bulkhead and use SC10.2 arms or similar? Is there a point of diminishing returns where it gets too 'crowded' up front?

Second, has anyone played with changing the kick-up on the nose? Fred mentioned that backing that down to around 20* or so could help tremendously with controlling weight shift under braking... And the RC10's nose is aluminum, so it could be bent and flattened out a little, right? (fully acknowledging that it would be hard to get it precise & even...)

Or, combining the two ideas...why not have a front bulkhead that incorporates a 10* droop in the inner hinge pin holes? (yes, I have access to a CNC milling machine...I just don't have a lot of CAD experience to translate it into a chunk of delrin or nylon yet. YET!)

Thoughts?

Thanks-
Byrdman

[mk-Zero]

Funny you mention changing the front kickup angle, I've been playing with the idea of making front arm mounts with angled pin holes to change the effective kickup angle for a couple months now. Once i design them I'll have some made at Shapeways. I was thinking of making them 5 degrees, which would result in a 25 degree kickup angle.

[fredswain]

I just got the latest revision of my arms in from Shapeways and I'm disappointed in them. I think they are trying to print faster and it shows. I'm getting more loose powder in the screw and hinge pin holes than I have before and there are some weird angles that shouldn't be there. The quality of this pair isn't what I want people associating with me so I hope no one else has the same issue. I have a local source for 3D printing that claims they have higher quality than Shapeways (would you expect a company trying to get your business to say otherwise?) but they are about 50% more expensive. 3D printed parts are already quite costly but I may try them out anyways. They have a faster turnaround time.

[fredswain]

MCKNBRD thanks for the kind words. I think so differently than most that many just think I'm plain nuts! Whatever.

I think there's a point where the arms can be too long. They can definitely be too short. I'm not sure what that point is though. It's probably going to be based on a combination of surface smoothness and vehicle speed. I don't know if anyone has posted or published a true comparison.

[mk-Zero]

My arms have shipped from Shapeways, hopefully the quality is good. Guess I'll find out in a few days...

[fredswain]

Mine do fit just fine. Looking at them closely, this set just isn't up to my standards.

[MCKNBRD]

When the parts are printed, what material are they using? Is it more like a nylon, or delrin? I know so little about 3d printing...

I'm getting my mill up and running and plan on playing around with front bulkhead designs; I don't think it would be hard to import the 3d models you have for the arms into Mach III and see if I can get my machine to make them, if you'd want to try that. No guarantees on speed, though...I'm missing some parts that are backordered, so I'm stuck twiddling my thumbs until I see them.

Fred, any ideas about reducing the kick-up on the nose? What are your thoughts?

Thanks!
Byrdman

[fredswain]

The parts are a kind of plastic called PA 2200. It's a powder that gets sintered and is commonly used in 3D printing because it is supposed to approximate the durability of injection molded polypropylene and abs. Those materials however are also a bit flexible and this material is no different. This gets you their description for the product, "strong and flexible plastic". Strength isn't only determined by material but also by how well it was sintered in the manufacturing process. One that was printed slower will most likely be stronger due to less free material leftover inside that didn't get sintered. The fine powder that I've mentioned is a good example.

I have a 3 axis cnc at home but I've never set it up. I need to get on that at some point. The material that was used for parts at Bullet Racing was a version of Nylon called Nylatron which is what I'd prefer to use over standard Nylon 6/6. There are 3 grades of it but one is more suitable for rc parts than the others. I've got some ideas for stiffening Nylatron parts as I wouldn't just cut out an arm shape and run it. It would be too flexible.

I've changed the kick on the nose. The aluminum nose plate is easy to bend in a vice. A light pole accidentally gave me more kick once! I like more kick (not more than 30°) for really rough tracks, which sadly we don't really have anymore, and less kick for smoother tracks that have higher grip. I definitely think the RC10 front arms should be longer. I don't like shorter front arms than rear arms. Modern cars have equal length all around but I'd argue that with a front kick of any kind, you'd want longer up front with the length based on the level of front kick. I'd have to draw a picture to explain my thought process on that.

Incidentally, I was here before I was on rctech. I'm really a vintage guy still living in the past.

[MCKNBRD]

I definitely understand the 'vintage' leaning...my first car was a Frog in 1987...I couldn't afford an RC10! Now that I can...

What I'm really wanting to do is make a gold pan competitive; assuming my driving is up to the task. My oldest son is 8 and we're building a legends car for him to play around with; I've got a TC4 that I'm setting up to run VTA now, and I want to get back into the off-road world.

I'll probably be asking a bunch of stupid questions as I'm hammering out what I want to do, specifically...then, hopefully, I'll be posting pictures of what I've done...good, bad, or ugly!

Thanks again!

Byrdman

(so, I can ASSume that wider arms need more kick? or vice-versa?)

[mk-Zero]

Parts came in yesterday. The design is really nice Fred. As for the Shapeways quality, its okay. If these are the polished finish i would hate to see the non-polished version. To me they look just like raw, unfinished sintered parts. Anyway, finish aside they are nice. I reamed out the hinge holes and tapped the shock holes, then died them off-white. They look great on the car (see my B1M thread).

Fred, the width is right at 9 3/4". How are those rear arms coming? With your front arms my front is now about .5" wider than the rear.

[romulus22]

If these are the polished finish i would hate to see the non-polished version.

I was curious of the same thing.

[fredswain]

I think Shapeways is getting bogged down with demand and their quality is suffering a bit. Out of the online 3D printing companies, they are the cheapest. I'm going to try a local company that is more expensive to compare quality. If quality is comparable there'd be no reason to change.

I have an example of a high quality 3D printed part at work. It was a prototype for our heart pump and it had to be perfect. You honestly couldn't tell that it wasn't injection molded. Instead of being sintered quickly in 70 micron layers, it was slowly printed (not sintered) in 20 micron layers. These arms would cost about $600 that way though!

[MCKNBRD]

Question on the amount of 'trail' that the arms have. All the early RC10 arms I've seen had the steering block WAAAAY behind the inner arm pivot...now, the 'prevailing design theory' appears to be pretty much even.

Other than shorter wheelbase, what does having the steering axle that far back do? When did AE go away from that 'excessive trail' concept?

One other question...and only because its murder to search for 'arm length' here...is there a comprehensive discussion of what arms are available for the RC10? Lengths, front end width, etc?

Byrdman

[fredswain]

The trail of the front arm is a geometry issue that is based on the amount of front kick as well as the rear axle height. Let's say all of our suspension arms are straight, as they are on the older cars as opposed to the newer gullwing designs. For a reference point let's place the car on a stand. Let's say the chassis is 1" off of the ground. The actual height isn't important as long as the chassis is parallel to the surface. Place the arms, both front and rear, completely level, parallel with the ground. Measure the distance from the rear axle to the ground. Now go up front and do the same. If all is done well, these numbers should match. When you add a front kick, you raise the front axle level. In order to get it back to where it should be, you sweep the arms back. With the front kick, this effectively lowers the axle. The greater the front kick, the more rear sweep the arms need. The older cars had a 30° kick. Current cars predominantly have 25° so the sweep can be decreased a bit. The only time you'd have a scenario where the arm sweep wouldn't change with nose kick is if you somehow had the center point that the front kick is rotated around equal to the location of the front axle, which they don't do. If you look at the 91 Stealth car, the arms swept forwards. This would have resulted in an excessively higher front axle location. They fixed that by lowering the axle in the steering hub to below the end of arm level.