clw

Ray:

Just picked up a new, well new to me B4.2. In your tuning chart, which BTW is the best I've seen in RC!, you mention under high temperature conditions to use a 3hx1.4 optional piston. When I search Google (not that Google's perfect) for 3hx1.4 it only finds your tuning chart. What are the part numbers of these babies please?

Normally under really hot conditions you would just increase the viscosity by 2.5, can you elaborate on the type of improvement gained between the old way and using the optional piston?

Thanks

ray_munday

iTrader: (4)

I ended up with 37.5 front / 32.5 rear. Would like to drop front to 35 for next test.
Hopefully this Sunday I will get a test at Knox which generally needs a lower pack setup, so I will let you know after that. Id also like to try dropping a spring rate there. The B5 is surprisingly lighter than the B4. I will try a black front / green rear as the next step.

Glad you like the tuning chart!

A 2.5wt increase helps, but I found the 1.7s seem to be more sensitive to warmer temps and the car starts to feel too soft (if the grip is aggressive). The 3hx1.4 dont ride the bumps quite as well, but are better than the 1.6s and seem to handle better than the 1.7s on warmer days when the track is grippier.

The 3hx1.4s are available in flat and tapered. Tapered good if bumpy, flat if track is smooth.

http://www.teamassociated.com/parts/details/91352/

http://www.teamassociated.com/parts/details/91349/

clw

Thanks for the detailed answer from an engineering brain. Just figured out your nomenclature! You are saying 3 holes at 1.4mm (3hx1.4)....I thought it was ASC's model number!

Does bumpy refer to the overall track surface and not the jump size? I tend to overjump the downramps on the back side of the jumps and hit bottom. Should that be tuned out? or allowed?

In your guide is the highest level of traction a sugared track (bar codes)? And the standard Australian track (left column) one that you would use Double D's on?

clw

One more question please

I see you are a design engineer for 1:1 vehicles. Why don't RC engineers use a lighter weight suspension fluid like a dirt bike suspension? The only time I need to worry about the temperature with my KTM is only when setting spring preload, it's set cold, so not to be influenced by the nitrogen expanding as it warms. But, the damping is consistent with 5wt oil as the day warms up. Is it because the RC shocks are built to lose tolerances to fight stiction is these light weight vehicles? Or just a cost to produce?

Thanks

ray_munday

iTrader: (4)

Bumpy refers to the track surface, not the bumps. If your jump has a good downramp, then its better to try and land on that, but sometimes 'flat landing' cant be avoided. if so, you generally need to increase the 'pack' (using smaller hole pistons) or heavier oil, but this can hurt the handling on the surface bumps so there is a compromise. On the B4 Ive always preferred the 1.7 pistons if the track is bumpy, but it will bottom out more when landing from big bumps. The 1,6s help the bottoming a lot, but they don't feel to absorb the surface bumps. This is where the 3 hole x 1,4 seem to be a reasonable compromise, but it really depends on your track.

The highest level is a grooved track where you would use Bar Codes. A sugared track fits that description, although the B4 is not as comfortable in these conditions as the mid motor C4, even with that setup.

Basically with a full size car / motor bike shock, a lot of the damping comes via the use of shims which are mounted on each side of the shock piston. These are made of spring steel and are quite thin. At rest they sit against the shock piston with only very small bypass ports to control the low speed shock damping; as the piston moves faster, the oil forces the shims oout of the way. At very high speeds, the holes in the piston create the high speed damping force.

These shocks are very tuneable, and can run lightweight oil as the shims are doing most of the work. At high speed, its actually the density of the oil that has the most effect (as its the mass of fluid being accelerated at very high speed through the holes that causes most of the pressure drop).

With rc shocks, getting the tolerances correct with these shims is currently not practical without having $1000 shocks. We need to have very thick oil to give enough low speed damping whilst still having big enough holes for the shocks to absorb the bumps.

So basically a full size shock is less dependant on viscosity. Viscosity varies with temperature (density only a small amount), therefore our RC shocks are more sensitive to temp changes.

Im in 2 minds about shock tech. The engineer in me knows the potential that higher tech shocks have and could bring (especially in terms of position sensitive shocks to prevent bottoming for large inputs). But the pragmatist in me knows that the current shocks do an amazing job for being so simple and cheap, and wishes that IFMAR / ROAR etc would basically mandate that shock pistons be one piece to prevent the inevitable technology arms race that would occur with the massive cost increase that would accompany it (starting to need shock dynos etc).

Hope this explanation makes sense.

Ray

ray_munday

iTrader: (4)

New parcel arrived today from Team Associated

All things going well, shakedown and first run will be at Keilor this Sunday. Hope to see some of you there!

ray

bk2racer

iTrader: (32)

Do I have double vision??

Dan Seiki

iTrader: (6)

Hi Ray, i have a question for you, i did quickly scan your thread for an answer but didnt see anything, so i was wondering do you have any experience with the Avid alloy chassis for the B44.2? If so what do you think, good or bad? I'm thinking of trying one but not sure if its a good thing. The track i run on is rather tight and hard with a dusty layer and its very loose. I'm currently running the stock chassis with the weight sitting in between the saddle packs. Cheers!

clw

Thanks Ray for the great reply on both track conditions and understanding what it means on a setup sheet.

And, the differences between a free bleed RC shock and a shimmed/valved system. It really is just cost to develop and controlling excess friction from a tightly controlled fluid path. I assume part of the alledged advantage to machined pistons is tighter bore/piston fit so less blow-by (free bleed).

Put my 4.2 on a scale and with a 298g battery it comes in at 1580g. I was getting ready to drop 14g on top of the servo. Some of the really fast guys at the track tell me they remove the AE ballast and try to run the car lighter to gain acceleration. Is your car super light (1500g) and right at the limit? Or, just add the weight as it calms and steadies the chassis. Thanks

clw

Ray:

Summer is almost here in the USA.

One more temperature question, please. Your standard setup I assume is about 15°C based on your August 2013 RC10.com setup sheet that listed the track conditions as 15°. It closly matched your spreadsheet standard. If it was hot, say 30°C, what changes would you make if all other conditions were constant.

Thanks

ray_munday

iTrader: (4)

Sorry for slow replies guys,has been a crazy week of work, building the B5M and travelling to Japan for more work...

The B44.2 chassis is very good on bumpy tracks with low traction. The AVID chassis seems to be better on the higher traction stuff as its a little stiffer and has more weight low down. In the conditions you describe, Id stay with the stock chassis. Also stick with the ball diffs. But try raising the roll centre by dropping the ball studs a mm or 2 at the inner ballstuds.

Shocks: JUST is a 4 letter word in engineering. It may be possible to create, but whether it would be affordable by racers (and offer a significant advantage) is yet to be proven. With the heavy oils we use Im not sure blow by is a big issue, but piston hole tolerances are more tightly controlled by machining and they can get a sharper edge to the hole which adds more pack.

Weight: On a bumpy track in mod, extra weight definitely helps. On a smooth track, less weight can be more responsive but I havent really found it to be faster. My B4.2 ran at about 1640g (note that the B5 is actually lighter).

Basically shock oil, tyre compound and plastic hardness are the 3 things most affected by temp (motor temps also in stock).
Shock oil: Increase by 2.5wt for 30C temps, especially if track becomes grippier. Also dont forget to re-set the shock rebound during teh day if the temp increases a lot (I try to keep my cars out of the direct sunlight down here in summer as it heats the shock up a lot).
Tyres: Use a firmer compound in higher temps (see post #2 of this thread for more info)
PLastics: Use the carbon front brace, 2 hole hubs and carbon rear arms (or B44 rear arms) if the temp increases.

Hope this helps.

Ray

clw

Ray:

You are the best!

I'll check my parts bag that came with the car an see what I have for the higher temps, thanks for the part-by-part description of each.

What's a 2 hole hub? Go easy, I've been away for awhile!

And, my car came with the ASC9873 rear hub tower. The camber link is in the middle hole on the tower. You spec out the OEM A tower, just replace it? Or, can it be made to have the same effective roll centre? Look, I spelt center the Queens way....

Thanks again

ray_munday

iTrader: (4)

The 2 hole hub is the carbon 30deg castor block. The 4.2 comes with the non carbon hub which has 3 holes for the camber link. The 2 hole means the carbon block.

I forgot to mention is use the carbon front arms pretty much all the time with the b4 unless it is arctic cold. They give the steering a much more positive feel. The carbon hubs and front brace also help in this regard but aren't as sensitive as the arms.

You are best off replacing the hub mount with the A hub. The C hub works well on tight tacky indoor tracks but on outdoor tracks it can feel less locked in when exiting corners.

Ray

cplus

iTrader: (11)

Hi Ray!

Couple of queries....

Pulse V2 - have you got one yet? Much of a step up over the old pulse?

1/10th TC - novak isn't very popular in TC circles, any reason you wouldn't use one? It would be for blinky 13.5

Where to buy - got any hookups for an Aus store with competitive pricing - or is it a case of fat chance, hunt the US?

Cheers

Clive

ray_munday

iTrader: (4)

Hi Clive,

I havent received a V2 Pulse yet. I am told the braking is a little smoother, and the packaging is easier without the mega-cap. I should have one soon but have been busy getting the B5s up and running (in addition to travelling overseas for work) so I havent wanted the additional complication of new ESCs at the same time.

To be honest, a few years ago the Novaks had a bad rep for blowing up when pushed hard. They have rectified the issues that they had but it takes a while for people to come back. Also, during the boost wars they didnt have the same flexibility as some of the others. Id say nowadays in a class like 13.5T blinky they should be more than competitive. I dont race touring car so I can comment any more than that.

I always recommend to go through your LHS who can get Novak gear through HEI. I live in Melbournes West and Traction RC or Central RC would be who I would recommend there.

Ray