Slash 4x4 Buggy 1717 6s

[Dr_T]

Hi Lizard, how's it going? Got the ESC working properly now?

Could you do me a favor and measure the base part (outer diameter and length) of that 8mm bore mod 1 Kershaw pinion you have please? I'm wondering what diameter "motor mount hole" those pinions would require to work properly.

I decided get a Kyosho GT2 to put the Turnigy 5682 in (I know... GTs suck in real world, but I'll figure that out how to deal with that later :)) and am looking what gearing options there are. I would need around ~50/34 (pinion/spur) gearing to gear for ~100mph... I will probably replace the center diff with a spool with Revo spur, but pinion is still a bit of a question. Kershaw has these huge 48, 53 and 60T pinions, but they're going to be very heavy, and I think I would want to try a plastic pinion first given those sizes; the standard Revo spur-to-pinion adapters could work, but those Revo spurs come in 40T max I think. Might see if I can get an adapter for some standard 4-screw spurs, or 1st speed nitro gears as sold here on RCM. A spur-to-pinion adapter for the XO-1 spurs would be cool too, but I don't know really how feasible that is. Don't you have the same problem finding pinions for your XO-1 with the Turnigy motor, or are you going to run 8S on it?

Cheers!

EDIT:
Sorry to clutter your thread Lizard, but I know you have one and are likely able to help me out :). Do you know the diameter of the center hole of the XO-1 "cush drive key"? Wondering if it can be used to have XO-1 spurs as pinion, with the added bonus of having "Cush Drive": http://www.rc-monster.com/forum/showthread.php?t=32150

[Lizard]

Not sure about the ESC yet, need to test the sensors first and then try if it runs. Weather is nice and I have finally received my new transmitter, will probably find out later today...

Diameter of the base is 14mm.

Regarding the low-kv motor and the XO-1: Will only run 6s on it with that motor. It's not that bad on the XO-1 because it has 2.85 diff ratio and 4.29 inch tires. I went with a Revo 3.3 Slipper that can run 34t to 42t spurs, that gives me enough gearing options.

[Dr_T]

Hi Lizard, how's it going? Got the new suspension dialed in yet?

I was wondering if anyone here has some recommendations for diff fluids for on-road speeders. I read on-road racers typically use heavy or locked front diff and around 10k cSt rear diff. I'm working on an Inferno GT2, 5682 motor, center spool, RTR weight will be about 4.5 kg, geared for 90 mph and up (depending on what motor will be happy to pull for continuous use). I'll be running 2° rear toe (instead of stock 3°), as Mike suggested below, to free up some speed, but have no idea if I should compensate that with a bit of a lighter rear diff fluid in order not to lose too much rear end stability. Any ideas?

What would be a good starting point for rear and front diff fluid, yielding good balance between straight line stability and handling (I'm not talking about serious track use, I just don't want it to be a straight line speed runner only that does not turn well)?

Originally Posted by RC-Monster Mike

Rear toe does create some scrub, but adds straight line stability(pretty important for high speed). If the rest of the setup is pretty rigid(minimal flex and play in the linkage, etc.), I like 1-2 degrees rear toe for high speed straight line work(3 degrees is the norm for off-road).

[Lizard]

Haven't done anything on the suspension yet, the motor/ESC doesn't run smooth anymore since the BEC died, it's stuttering, even with external BEC. Bruno wants me to send in the motor and ESC, but haven't had the motivation to do so yet. I'm getting fed up with wrenching lately :)


Regarding diff fluids:
From what I have read, for onroad straight-line hard acceleration it's better to go for a quite thick diff fluid in the rear because it helps to maintain the same wheelspeed on each side. With thin fluid it can happen that one side has more grip and then the other side just spins which will throw the rear around as soon as it gets traction again.

I think I have experienced that effect when trying to achieve maximum acceleration from a standstill. When you look in the the video at 0:57s you can see how the car at first runs straight, then the rear steps out a little, I get scared, let off the throttle and after that the rear passes the front.
http://youtu.be/EVJkGJpTDKI?t=57s


At 1:46 in the video I managed to keep it straight, I think that was because I didn't let off the throttle which allowed the spinning tire to get grip gradually again (by the "natural" reduction of torque with higher RPMs).
http://youtu.be/EVJkGJpTDKI?t=1m46s

Always wanted to try a thicker fluid in the rear, but haven't done that yet. The diffs have the XO-1 stock filling with 100k front and 10k in the rear.

[Dr_T]

Sorry to hear of the troubles with your Alien stuff :(. Was really looking forward to seeing Godzilla Slash in action a bit more.

Hoped the Alien stuff would be a nice alternative 8S option, but given your experiences, I'm really leaning towards XL2 now. I read the concerns you mentioned of Ub3r on rcgroups, about the long distance between drivers and FETs, but it seems it's still the best option. Seems the reported cogging issues, like the one Othello posted here could be heat related, so with a bigger fan, in a ~4.5 kg car, and with a bit of luck :), I'm hoping it'll work fine.

Thanks for the XO-1 set-up as reference. I'm using 20k/10k (FR/RR) in my Truggy, but the 10k is a bit light and it seems to be leaking, probably due to getting hot. I also have some 40k cSt and 500k WT (Traxxas stuff, read someone reporting it to be actually thinner than his 300k cSt FG fluid), so I think I'm gonna rebuild the diffs with the 500k WT front and 40k cSt rear.

Hope you'll be wrenching again soon man, looking forward to seeing twin truggy updates :).

[Lizard]

After I have been pretty de-motivated last year (system was stuttering after a few testruns and on top of that my transmitter broke ...) I finally found the motivation to send the motor+ESC to Bruno :)

Just heard from him, that one sensor on the motor is defective, he's going to replace it now. Well, let's see ...

[Lizard]

Some news.

The Alienpower ESC and the TP5670 are still not returned to me (despite me asking several times), but Bruno promised that I'll get it this week. At first he told the ESC will be repaired, now it'll be a new one because the old one was too heavily modified by me (?) Not sure why that is, I didn't do anything beside cutting the heatsink a bit and applying Plasti-Dip. Well, getting a new one is nice, but now I'll have to redo all the soldering and cutting the heatsink :(

Since the weather was getting better and I wanted to drive, I put the Mamba and the 1717 in again. Runs reliably, as always. Springs/Oil seems a little on the hard side now with the lost weight compared to the TP5670, but it was driveable.

Also tried out the new black-spoke GRP slicks. They look really nice, but traction is not as good as with the treaded ones. Ran it for a few minutes with a lot of throttle, after that the rear tires were almost too hot to touch. Clearly a sign for not enough traction :) Somehow I have the feeling, they are a different rubber compound.


And the VESC finally arrived and was installed in the car. Started the software, ESC gets recognized by the software, nice. Then started the "motor detection" routine and nothing happened. Fault eventlog gives:
Fault : FAULT_CODE_DRV8302
Current : 1.9
Current filtered : 0.2
Voltage : 23.09
Duty : 0.01
RPM : 0.1
Tacho : 5
TIM PWM CNT : 3872
TIM Samp CNT : 3878
Comm step : 2
Temperature : 27.31

Looks like the FET driver chip is broken. Still unclear why that happened, I'll send the VESC and the 1717 to Benjamin so that he can have a look at it.

[Dr_T]

Nice to see you got the Slash out again!

Crap to hear the GRP slicks have less traction (which compound do you have?)... :( I haven't tried mine and hadn't realized it yet, but reading your post and comparing the two compounds, the slicks indeed feel like different material, not with the "stickiness" of the treaded ones. Are those treaded ones in your comparison pic above also from this year, or from last year (just wondering whether they migh have changed all compunds for this year)?

Seeing your car again also reminded me I still have some work to do on my front wing :). I got a couple of wing options and I think I'll use a small lexan 1/10 ST wing. Looks most natural to me size-wise and is actually a very good copy of your design :). Still have to do a little trimming of the sides and will have to add some foam behind it for rigidity, but below is how it is going to look. Did you experiment with different angles of your front wing? Have you had issues with the car scraping the ground when on speed?

[Lizard]

Yeah, really sucks with those GRPs. I tried the S3s and had the feeling they have less grip than the treaded S5s I bought last year and also this year a few months ago. Maybe the S1 slicks come close to the S5 treaded ones, but I think I'll just stick with the treaded ones, they always worked well for me in S3 and S5.

With the frontwing I seem to have gotten it right (or atleast good enough) the first time, did not experiment with angles so far. It sits pretty high, no problems with srcaping the ground at all, I also can go up lowered curbs in case I need to get out of the way when real cars approach. (BTW, it's really funny, I would estimate about 95% of car drivers actually treat my little car as a normal car that's bound to traffic rules and give right of way to it etc.) When the front suspension is fully compressed, there are a few millimeters left.

[ruudxd]

Offtopic : @ Dr.T, what car is that in the background, with the Badlands?
Kyosho Scorpion?

[Dr_T]

Yeah, I don't really understand why they would use different rubber for the Revos and the Slicks in the first place and then also not provide any indication that they do... Italians... :D.

Oh, I actually meant whether the front wing downforce would be high enough to compress suspension to the point the chassis/ front skid plate would touch the road; I think that would a good recipe for crashes, so I really want to avoid that... Anyway, maybe I'm just overthinking and should just get it out and test a bit.

I think it's cool how you just drive with traffic, I don't really have the guts to do so, which does limit driving options a lot. Not so many empty, long, straight and smooth roads out there :).

@ ruud: yes, new toy! :) just getting started with it, some more info here.

[Serum]

Love those scorpion (XXL) buggies. The 1/10 looks like a sweet retro kit too.

That XXL is a tempting buggy, i've seen your movie on youtube, in a quest for the XXL, without knowing it was you.

An overpowered 1/10 2wd can be tricky, but this 1/7 looks like pure fun, it's like it's running in slomo. Very predictable so it seems.

[Dr_T]

Video isn't mine, it's not driving yet, needs some mods first :).

[Dr_T]

I just got a reply from GRP about the tire compounds:

in January when we have put on the market the new line 2015 of 1:8 Gt we have make same little change to all the compound for works this better and also have more time life.

So the compound of 2015 season it is little differnt from the 2014 tyres. But the REVO 2015 and SLICK 2015 compound are the same.

[Serum]

'More lifetime' means harder compound, which equals less traction, right?