DT-01 double wishbone

[Vrooom666 31]

has anyone seen this and used it?  

 

https://www.thingiverse.com/thing:2377087

[GregM 1109]

This looks interesting! Thanks for sharing.

I wonder about the strength of the shock tower with the integrated camber link mounts. Good thing you won't have to cut the body for clearing the camber mounts. I have doubts about the 2mm thin rod camber links, but this can be remedied with regular 3mm links. I wish these parts would be available on Shapeways.

Here's another thread discussing how to equip the DT-01 with front double wishbones: Either by modifying the stock parts, using DT-02/03 arms and a DT-03 front suspension mount, or by 3D printed parts:

 

[Vrooom666 31]

I have DT-03 parts but you ruin the front bumper by drilling / cutting into it...    DT-03 parts may be better but im loving those addtional mounts that website links offers.   no mods to chassis that is what sold me.  

[nowinaminute 2815]

I decided to be a guinea pig and try these out.

I had the same concerns as greg about those upper link mounts plus the overall design hasn't been done with consideration to fdm printing. I've already been taught that harsh radii are baaaad and that it's better to chamfer/fillet to take away stress points. I can also see various wasted opportunities where there was ample room to simply bulk vulnerable areas up and give them a better chance of sustaining impacts.

Saying all that, it's still a really neat and thought out design and considering that I'm useless at 3d software I can't really be too critical!

I ordered the parts in PETG with 100% infill via Treatstock. This was about the best compromise between the parts having half decent strength and not spending too much money on what amounts to an experiment.

The parts came back looking pretty nice although I did overlook the fact that the vendor only had transparent PETG on hand so the results were a little more like cherry drops and sherbet lemons than I anticipated!

[nowinaminute 2815]

The parts integrate nicely with the chassis without modifications which is very satisfying.





Unfortunately, I could instantly see that the shock tower isn't going to work with the steering link mod. There's barely enough room for the stock wire to pass underneath which is a shame because the mod is really needed here because there's so many sources of wobble and play. The arms themselves fit loosely, just like the stock ones and although adding some heat shrink to the arms helps, there's a limit to how far you can go before they begin to bind. The next source of play is the uprights, it's quite common with 3d printed parts to have looser tolerances than Tamiya parts and it's no different here. I can certainly shim them to make a significant improvement but again, it will be a juggling act between removing slop and introducing binding. Then you have to consider that there is no upper wishbone and only a camber link so there's an asymmetric force working on the uprights which isn't a flaw in its own right but it will provoke any sloppiness elsewhere.

So overall, the wheels still have a lot of play and undesired freedom of movement just like in stock form but at least the suspension is now fundamentally superior, gotta look at the bright side!

[nowinaminute 2815]

For the camber links, I decided to try two different approaches. Both use plain old m3 threaded rod but on one side I used those little Tamiya brass ball studs and Tamiya connectors. The advantage is that they only have m2 threades which means a minimum of material being removed. The downside in my experience is that they are prone to stripping the threads, even if you take the time to tap the holes first (which itself is easier said that done with a 3d printed part)

For the other side, I tried some combined ball connectors and larger m3 self tappers.



I originally wanted to just put machine screws and nuts on but for the upper link, there's no clearance between the tower and the shock even for a screw head, it catches on the shock spring and binds it up so I've had to resort to a self tapping screw which is not what I wanted at all. Besides having to make a larger pilot hole and remove more material, I now have the force of the screw pushing outward and stressing that area too. I would space the shock outwards slightly but the bottom mount sandwiches the shock eye so there's no potential to move the bottom outwards. I'm not sure if there's enough freedom of movement there to allow me to add enough spacing at the top to clear a screw head or not. I will report back when I try.

[nowinaminute 2815]

So here it is all in place. Looks pretty nifty if I do say so myself!





It was dark and wet out by the time I finished so I only gave it the briefest of drives but it seemed to work pretty well. In all fairness, although it's not a great handler in stock form, it is pretty stable due to how low and squat it is so I wasn't expecting much benefit there. It did seem a little more planted and less bouncy though, at least at the front end!

One thing I did notice is that the articulation is reduced now that the wheels don't do the back to the future thing. I always prefer when a car can bottom out on the chassis so the force doesn't go through the suspension components and I prefer it twofold when the parts are 3d printed so that's another area I would address if I knew how to do 3d modelling. I'm currently running mini CVAs at the front and short at the rear. I think a slightly taller shock tower and shorts all round would be about perfect.

I will have to wait till I have some spare time in the daylight now before I can drive it more. I'm probably not going to try doing massive jumps or anything to stress test it but I won't baby it too much either.

I'll probably try it on the carpark down the road which is heavily weathered tarmac. My Lunchbox used to have a similar thingiverse front end conversion and that seemed to manage ok once I went to 100% infill. If it holds up as well as the Lunchbox did in the same circumstances I'll be happy because it means it should do ok in dirt and at the beach which are my favourite places to bash.

 

[nowinaminute 2815]

The first half proper test drive has concluded!

Positives:

Nothing broke! I wasn't exactly brutal but I did do some small jumps and suffered a roll over from cornering so hard one of the tyres pulled off the rim! ( note to self: use Mad Bull body for tarmac and testing, mad bull shells are available and cheap, RX shells are not!)

Ride quality was notably improved, there's definitely a more planted feel at the front end although sometimes the suspension runs out of travel.

Handling seems sharper. It still has the same basic behaviour of under-steering on the throttle and tightening up when you lift off but it seems to turn in a little sharper and grip slightly better.

Bump steer greatly reduced!

I think the full potential for the handling is a little way off due to the one major issue though. The wheels are literally all over the place. In particular the outside wheel just bounces up and down when you corner hard. There's so much play and slop that the tyre just judders along the road. It might be exasperated by the the more consistent camber allowing for more grip too.

I'm going to have to just try and shim the lower arm/upright pin as best as I can. There's nothing I can do with the camber link to stop back and forth play so it's all on that lower mount. I'll probably risk carving some material away too so I can do the servo linkage mod and probably make up some metal steering links too and get rid of the plastic ones. I'll shim the front wheels too so they can't move along the axles. I'll just do pretty much anything I can to cut down on the slop.

You might be wondering how bad it is?
 

You can see there's enough play for the wheel to begin to fold over on itself but then the play runs out and it's forced to bounce back into place and the cycle continues over and over. Factor in all the play inherent in the the steering linkages and there's really not much there to keep the uprights in check at the moment.

Now before I shimmed it, my Lunchbox did the same thing when I first fitted printed front suspension but it was nowhere near as bad as that! Not even close. Hopefully by doing as much as I can to remove play I can get it down to an acceptable level.

I'm definitely pleasantly surprised by how well the parts held up though. That wheels wobbling around must have put quite a strain on them!

[nowinaminute 2815]

Right, ok. So you may have read in the "what have you done today?" thread that despite making a massive improvement to the amount of slop, the juddering wheels were not cured. There was some improvement but not 100%. So the play appears to have been a bit of a red herring. No doubt it facilitated the wheels in wobbling but it wasn't what was setting them off.

It was at that point that I had a flashback to when I first ran my Re-re Blackfoot and I had to turn down the EPA because if the wheels turned too far they just kind of dragged along the ground and juddered as the rubber scrubbed the tarmac.

So I tried turning down the EPA on the DT01 and boom, instant cure! I guess I could feel a little silly now for spending all that time shimming it but on the other hand, it did improve the issue quite a lot so it definitely tightened things up. 

Just to make totally sure, I put the stock arms back on and tried to replicated it and lo and behold, it did the same thing. Not to as great an extent but it was certainly there in certain situations with the EPA on max.

It might be worse with the printed parts because the camber and hence grip is a lot more consistent whereas with the stock setup, the camber chance is quite severe, especially that outside wheel when the car is leaning during a corner.

The obvious cure for this would seem to be to keep the EPA turned down, right? Well unfortunately it's not quite that simple. The car turns more going right than it does left so if you set it up so the that turning right is the optimum balance between turning circle and not juddering and you end up with the turning circle of a barge going the other way. 

Why? That awful linkage between the servo and bell crank. The cause of the slack, the link being able to move in the holes on the servo horn and bell crank has a different characteristic at the extreme of each direction. This is a terrible drawing but it illustrates the issue. Depending on which way you turn, the link is effectively a different length!



The logical thing would be to fit a proper linkage to get rid of the slop but the 3d printed shock tower was designed by someone who apparently had no idea the linkage mod was a thing because there's just no clearance there for the link, even the stock wire link rubs against it. The new tower actually has material directly over most of the crank whereas the stock one doesn't.

So I have two options now. The first is to use my Flysky gt3 so I can set different endpoints for each direction. This should work but it's more of a short term solution that hides the symptoms rather than curing the problem.

The other thing is to remove some material away from the shock tower so that the linkage mod can be carried out. I'm not sure how badly this will effect the strength of the tower though.

That issue aside, It is honestly driving really nicely! The rear end is still pretty much locked up and bouncy under heavy throttle but the front end seems much better. It seems to stick to the surface better and the turn in seems crisper when you corner. 

Hopefully I can iron out the crazy tyre issue.

Oh, and those PETG parts are holding up perfectly so far!

[nowinaminute 2815]

Whoops....

To be fair to it, I was giving it badword when it happened. It went into a full on cartwheel and that was the result. 

Unfortunately the little patch of old coal dust I like to bash on (it's in my recent blackfoot video) has been driven over repeatedly by workmen from the water company so a lot of it has been squashed into big rock hard tyre tread imprints which I don't think helped matters. It's gone from a lovely pit of soft dust to a lumpy assault course that's had loads of mud introduced into it. I might have to take a rake down there and try and restore it (pesky kids and their plant machinery!)

I decided to go for it anyway and it held out for a good hour but the cartwheel finished it off. It manged tons of jumps and bumps etc so I guess it must have just hit at an awkward angle. It's also possible I hit a bit of rock or brick lurking in the undergrowth. The area is a former coal washer plant so there's all kinds of stuff like that laying around but when I actually saw the damage, it was tough not to make a conclusion.

Having a quick look at the wreckage, I can see the print quality was pretty **** good, the layers are so well bonded that it just looks like solid plastic in most places.

I think the most blame rests on the original design, there really is only a feeble amount of material hold that part in place.

It's frustrating because there's tons of room at the front where extra material and or support could have been added:

Maybe it was a fluke and I could go another 50 years before the same thing happened again but once you have gotten a few sets, the cheap experiment ain't so cheap any more. Likewise, sending it off to shapeways to be sintered in nylon would undoubtedly be stronger but do I want to invest the greater printing cost on a design that I feel isn't optimal?

Oh well, back to stock for now. Maybe one day I'll work out how to use the software and make something myself.

I think until then, one of the solutions that utilises existing Tamiya parts might work better. At least for worry free bashing.

I do have another set of parts so might use them at the beach, I think they are tough enough for that environment. 

It was great fun while it lasted at least!

[xSyReKzZ 13]

 

Apologies for reviving an old thread, 

 

I recently bought a DT01 Chassis which I plan to modify heavily into an R-Spec (Race Spec) Variant. 

I came across this Front double Wishbone Conversion on Thingsverse and I had planned to print it in PA12 MJF on Shapeways, my concern is durability as I plan to "use" the chassis with standard buggy wheels. 

What 3D Material did you print yours in? Also do you think the monster wheels might have caused more stress on the 3D Shock Tower?