Lawsy

DB01 - Only the essentials build decisions

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yes your suspension is to soft, you should be able to drop the car from between 1 and 2 foot off the ground and not have the chassis slap the ground, above that and the chassis should start to kiss the ground, get the suspension to stiff and the car will be so twitchy as to be uncontrollable.

I don't run a mah cap on my charger, as the amount put in over the stated amount is wasted bringing the cells back in balance, I also only ever balance charge my lipos.

I run shorty pack lipos in my 2wd sct, both are 4500 mah 100c batteries, for my 8th scale truggy I'm running 8000 mah 100c batteries in series as a set of saddle packs.

your choke points for power are first battery, then esc, then motor, what ever the motor wants as it's nominal amperage should be, for the safety aspect, 5 amps below what the esc will handle nominal, oh and my batteries are from rc concepts

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Ah, you've found the limit of the kit CVA dampers.  The pistons don't seal against the bodies very well, and the holes in the pistons are too large to generate "pack" when landing jumps.  They're fine for tarmac and basic dirt driving, but not great for jumping.  Basically, if you buy the TRF buggy dampers the pistons seal very nicely against the aluminum threaded bodies, and the holes in the pistons are sized so the oil flow transitions from laminar to turbulent when landing jumps.  This creates a huge change in damper characteristics racers call, "pack."  You can try thicker oil in the CVAs, but they'll be too stiff for normal driving and they'll never really land jumps well.  The cure is TRF big bore buggy dampers.

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Kit oil should be 900cst (clear). Options are quite limited for anything thicker.

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There is a lot of slop in the front end, specifically the front axles and bearings. In contrast, the rear bearings press into the hubs firmly, whereas the front bearings fall in, and fall out with ease - no pressing required. And even still. This is making the front end clang about making terrible noises when steering at anything more than half-lock - like a car that needs new CV's. I shimmed the wheel hexes with a single 0.2mm shim, thinking that might help a little, but it didn't help at all (it cannot be shimmed further).

This is my biggest disappointment on the car and I'm not sure how to fix it... The bearings would need to be 0.5mm larger in diameter to fit properly into the hubs, that's how bad it is. I'm looking at breaking the budget and purchasing the WO front universal joints because they come with new uprights and 950 bearings as well, which I think will mostly solve the problem. I'm just annoyed because this shouldn't be an issue to begin with. Part of the problem is also that there is about 3-4° too much steering, and there's no way to mechanically adjust the steering throw. Will the WO UJ's fix this issue? A feel as though buggy of this price and performance shouldn't have this much steering slop, and it especially shouldn't have any axle slop.

Everything else seems great still, though I'm thinking about moving the lower and upper shock mounting position out one space. This should provide a firmer spring and damper rate, with approximately the same progressiveness. With greater shock speeds, I might gain a little pack (of what little pack can be gained from the stock shocks). That's given me another thought - when I build shocks, I tend to slightly loosen them again to bleed some of the air above the bladder out, neutralising the spring effect. I found this makes the shocks less likely the leak and stay more consistent over time. Maybe I shouldn't do this on the front? This would certainly increase the spring rate and bound rate slightly, but to maintain this might require constantly rebuilding the shocks and that's going to be annoying...

 

 

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Cut some strips off an old decal sheet and lay them into the opening for the bearing as shown below.  Then press the bearing in.  Cut the remaining bit of decal that's hanging out of the hole.  You can do both bearings so long as the strips are placed at the same clocking.

TapeShim_zps7a834a34.png

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1 minute ago, 94eg! said:

Cut some strips off an old decal sheet and lay them into the opening for the bearing as shown below.  Then press the bearing in.  Cut the remaining bit of decal that's hanging out of the hole.  You can do both bearings so long as the strips are placed at the same clocking.

TapeShim_zps7a834a34.png

 

Mate, you're a genius - and the adhesive will prevent it from falling out while get the bearing in place. I'll feel much better running a quick motor once this slop has been taken care of.

Cheers!

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17 hours ago, Lawsy said:

There is a lot of slop in the front end, specifically the front axles and bearings. In contrast, the rear bearings press into the hubs firmly, whereas the front bearings fall in, and fall out with ease - no pressing required. And even still. This is making the front end clang about making terrible noises when steering at anything more than half-lock - like a car that needs new CV's. I shimmed the wheel hexes with a single 0.2mm shim, thinking that might help a little, but it didn't help at all (it cannot be shimmed further).

This is my biggest disappointment on the car and I'm not sure how to fix it... The bearings would need to be 0.5mm larger in diameter to fit properly into the hubs, that's how bad it is. I'm looking at breaking the budget and purchasing the WO front universal joints because they come with new uprights and 950 bearings as well, which I think will mostly solve the problem. I'm just annoyed because this shouldn't be an issue to begin with. Part of the problem is also that there is about 3-4° too much steering, and there's no way to mechanically adjust the steering throw. Will the WO UJ's fix this issue? A feel as though buggy of this price and performance shouldn't have this much steering slop, and it especially shouldn't have any axle slop.

Everything else seems great still, though I'm thinking about moving the lower and upper shock mounting position out one space. This should provide a firmer spring and damper rate, with approximately the same progressiveness. With greater shock speeds, I might gain a little pack (of what little pack can be gained from the stock shocks). That's given me another thought - when I build shocks, I tend to slightly loosen them again to bleed some of the air above the bladder out, neutralising the spring effect. I found this makes the shocks less likely the leak and stay more consistent over time. Maybe I shouldn't do this on the front? This would certainly increase the spring rate and bound rate slightly, but to maintain this might require constantly rebuilding the shocks and that's going to be annoying...

The clanging you hear may be due to the dogbones -- if the ball of the dogbone is not centered relative to the axis of the kingpins, the dogbone will chatter or move from side to side.  To a certain extent you can help the situation with O-rings in the axle stubs to space the dogbones out, and sponges in the diff outdrives to maintain a little pressure, but the ultimate solution is CVDs as the joint stays relatively in line with the kingpins all the time.  I assume the noise is the worst when holding the car, or placing it on a stand, and you squeeze the throttle while steering from side to side.  The dogbones are just not consistent like CVDs are; that said, I ran my Durga on dogbones for a long time and didn't experience any unexpected wear.  Also, driving it on pavement puts a little preload on the dogbones, so they don't make as much noise as when the vehicle is floating on a stand.

Adjusting steering throw mechanically can be done by buying a new servo horn with more holes; Kimbrough makes several good one for about $5 a pop.  The holes closer to the servo shaft will reduce the throw of the connecting linkage, which will in turn reduce the maximum steering angle.  Most people just reduce their EPA settings on the transmitter, though.

For a treatise on shocks, check out:  https://sites.google.com/site/rccarengineering/home

 

 

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Thanks for confirming for me, Speedy. Always helpful to know you're not crazy sometimes when you can "hear voices", I mean noises...

I'll be using 94's solution until a pair of WO UJ's arrive - I bit the bullet yesterday and found a very good deal from a hobby store in QLD. You don't think I'll regret getting the wide operation version? Are there any negatives associated with the WO version? (As I was typing this, I got notification that they will attempt to deliver today - that was fast!)

And I should have clarified my post regarding the steering adjustment - what I should have said was, there is no out of the box mechanical adjustment of the steering throw. I've got a tonne of other servo horns that I could use, however, this is the nicest servo I've ever owned (I know, I know, it's only $25 worth...), so I don't want to kill it. It deserves to be protected, I am that pleased with its performance and accuracy. Therefore, I want to keep running a servo saver, but I don't want to yet again, have to buy something to fix a problem that shouldn't exist to begin with. My old 5 channel Futaba flight transmitter is both accurate and what I am used to (I don't like wheel transmitters - I grew up on F1 games for Sega's, then Gran Turismo on the PS1/2 - I drive with sticks!), but being old means it does not have end point adjustments.

I'll just drill a hole where one would otherwise be if the standard servo had five holes. Because I'm cheap. Also because this allows me two oportunities to drill the hole with a finer adjustment than otherwise, as I only want a very small decrease in throw to keep the steering blocks from hitting their end points. At a full 60°, the DB01 can turn in a diameter less than twice its wheelbase, and this is pointlessly tight.

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Did you buy #54118?  It seems like there are new front uprights included/required to use the WO shafts.  There shouldn't be any downsides to the WO version vs. #54015.

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8 hours ago, speedy_w_beans said:

Did you buy #54118?  It seems like there are new front uprights included/required to use the WO shafts.  There shouldn't be any downsides to the WO version vs. #54015.

Yes, 54118, which comes with new uprights.

Much fo the slop has been reduced with the new uprights and the 950 bearing, but there's still enough there for me to detest. I want this slop to be all but gone, and I'll figure out how to get rid of it. I'll also be doing the same with the rest of the steering linkages, as there's far too much slop in all of that as well...

Thankfully, though, the UJ's are drastically smoother, so I'm very pleased with this aspect of things (though I haven't actually run it yet, just turned by hand at this point at full lock, and instead of nearly binding as it would with dogbones, the resistance hardly increases - brilliant).

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Took it out for a bash with the new UJ's and they were squeaking so badly I had to stop... There is also enough slop to annoy me still, so I rebuilt the UJ's using the graphite powder. Basically I filled the cup a little and ground it up using the ball end, to try and separate the finest particles so they stick around a little longer. 

Put it back together, shook out the loose particles and the squeaking has gone. Lovely.

While I was at it, I tightened the bearing slop, and drilled a hole in the servo horn, which went rather nicely. The wheel rattle has gone, and it no longer tries to over extend the steering (and I don't seem to have lost much turning radius at all since the extra movement of the steering rack at either extreme resulted in negligible turning of the wheel).

Now comes the strange part.

At part throttle and then holding steady at low speed, the car will not always centre itself to track straight (but this isn't consistent). When the steering hasn't centred properly, the turning radius is equivalent to moving the trim on the radio a little more than about a quarter of the adjustment range. Then, if I apply power, it will straighten rather suddenly and track normally again (including when under braking).

I don't get it - is there so much bearing slop to purposely keep this thing straight? I can't determine the cause yet, but I going it could be the small amount of slop that's developed in the main hinge pin of the lower suspension arm. It could also be the servo mount. The outer servo bracket screw, even though I was incredibly careful, I'm sure is stripped. The screws holding the servo brackets to the chassis are half the length required, in my opinion. This is a bigger problem because finding a longer screw that is so flat in this diameter is difficult. The consequence of the basket not being fixed as securely as if like is that any lateral movement in the servo results in a change in the steering angle, but under acceleration, the vibration combined with the force produced by the caster angle at speed, could be centering things again.

I'm just getting a little annoyed at these minor issues as they are distracting me from just enjoying things.

Any ideas? 

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I also added a little more toe-out to ensure the tracking issue wasn't the base wheel alignment, since neutral toe settings can sometimes make straight line tracking a little vague. This doesn't seem vague however, it feels like something is slightly sticking, but everything moves freely, so I can't think of what that could be...

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Oh, check the linkage between the servo horn and the bellcrank -- I think a few people have had issues with it hitting the belt cover.  If there is any interference that could cause the steering to not center.  Also check your servo horn for slop, and check if your servo centers consistently from either left or right turning.  Some servos don't center as well as others, and friction in the servo saver may mask any slop it has.

It's really a process of elimination.  I can tell you with a stock Durga build and running a Futaba S3305 servo I had no issues with steering wander.  So you'll have to evaluate it piece by piece -- servo, servo saver, ball connectors/adjusters, link/cover interference, bellcrank movement, front uprights, bearings...

Just a little toe out in the steering (like 1 degree), and about 1-2 degrees of negative camber, and maybe 2-3 degrees of rear toe in should work fine.

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The new uprights were a little tight, but a little time will free them up and it seems much better after quickly pulling them apart and putting them back together with a minuscule amount of grease, after coating the hinge pins with dry lube...

Motor should arrive any day now, can't wait!

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Still no motor... Hmmm, slightly concerning.

In other news: I needed to rebuild the rear diff yesterday.

I think I over tightened it, and I suspect tightening beyond a certain point has no real benefit, so this time it will be tight enough to not slip before the slipper clutch, and that's it...

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