A Newbie's Guide To Bottlenecks

Horshu · #1 03-01-2005, 04:55 PM

I've been thinking a bit about the inner workings of my car more and more as I slowly but surely start checking off the various improvements, preferrably consisting of "ultimate" solutions, I want to make to my car to bring it to a state of completion. Along the way, I started identifying the various bottlenecks that limit the XMOD's speed as well as solutions to the various bottlenecks. These are discussed in varying levels of detail elsewhere, but I wanted to bring together a succint guide for the newbie that in interested in tricking out the XMODS to the upper limits of its physical design (my XMODS design philosophy is along the lines of Formula 1 or Koenig/Callaway, so I'm aiming to answer the question of "How far can an XMODS go without altering the outer body asthetic?"). If anyone would like to add to or dispute any of my conclusions, please feel free to do so.

1. Drive train friction -> Solution: replace nylon bushings with ball bearings. Radio Shack BBs a start, but TinyRCs are excellent here (although I'm going to eventually test it against some of the VXB ceramic ones, as the VXB wide tracks are expensively bad-ass). Possibly grease the drive shaft, as my CF one shows marks from rubbing the ESC assembly

2. Power supply -> Solution: add lithium ion, although my car's setup has swappable battery harnesses, so I can drop in 4 AAAs or 2 AAs.

3. Weight -> Tricky one. Is light good? I actually like the extra weight of my aluminum a great deal, as it handles like a dream. If you want light weight, keep the plastic and buy a lighter (Zero CF or AtomicMods Switchblade) chassis. If you want the extra weight for stability, aluminum parts do the trick

4. Loose suspension -> Caused by crappy RS lugnuts, play between dogbone & cup joints, servo play, and tie rod-to-knuckle play. Solutions -> two wide track bearings per wheel covers dogbone play(most people say just 1 on the outside per rear wheel, but I use 2 per on the back as well) + wheel shims to fit the wheel on the inner bearing track better. Replace stock steering knuckles with aluminum. Have found no way to remove servo play.

5. Turning restrictions -> Replace surface mount resistors with lower-resistance parts to allow for full range of steering, although this may increase steering jittering

6. FET limitations -> Extra power can overload the onboard FETs. Solutions -> stack FETS to distribute the workload, although it results in more power going to the entire board, affecting braking/reverse (good) and steering (bad). External turbo -> because space is no longer an issue, as the power FETs are placed offboard, bigger FETs can be used for a greater range of allowable power. Also, newer turbos are sending a regulated 5V back to the board, which reduced steering jittering

7. Motor limitations -> Standard XMODS motor size is 130 and can handle 4 AAAs fine. However, lithium allows for more power being thrown at the motor, which means more heat. Also, lithium allows for longer running times, which enhances the heating problem (heat can shorten magnet life and fry the motor, although I'm not sure if a fried motor means the wires are melted or the armature/commutators are damaged). Solutions -> motor with thicker-gauge wiring to handle higher volts/heat, silver wire for better conductivity & less heat dissipitation, ball bearing motor can, carbon fiber brushes, added motor heatsinks, & using a 180 motor instead of a 130, although it won't fit in chassis configurations.

8. Wire/solder limitations -> Yep, even these bad boys can be overloaded. Solutions -> thicker gauge wiring (I'm using 18g superflex, but even that is "only" rated at 5A sustained, so throw enough power at it, and you could theoretically melt wires and/or soldering points, although with a turbo board, the ESC should be safe.

broke ess supra · #2 03-08-2005, 10:22 PM

Good job horshu...nice compilation'll try to add something(first one is ghetto but it works

drivetrain friction--->raising the motor a little bit off of the gear works. if you raise one end of the motor mount with a a tiny shim 1 or 2 mm on only one of the screws you'll get a few more km/h on the speed checker...try to find the height just before the gear starts grinding in reverse and you'll be satisfied with the addded torque, top speed

Power supply--->a 6 cell can supply more current for low wind motors (although it weighs a ton and kills handling even if you put it in the back bumper )that would require an fet upgrade...just 2 lithiums will not be able to give you more than (guessing) an amp or two...but you can series/parallel 4 lithiums although its bulky

Horshu · #3 03-19-2005, 05:08 PM

I've also given some thought to taking a dremel to the diffs and shave off unnecessary internal plastic to lighten things, as that goes through a lot of RPMs, so it could benefit from less weight. A tricky part would be ensuring that it's still balanced after cutting out whatever plastic you do wind up taking out.

arch2b · #4 03-20-2005, 11:56 AM

very well put together review.

you should apply the same logic to a mini-z/iwaver, etc

btw, where are you buying the superflex wire? it's not easy to find apparently

Horshu · #5 03-20-2005, 12:49 PM

I get the superflex from atomicmods.com. He ships out real fast, always getting to me in a couple of days. I'd recommend getting the 3 foot lengths, as it can go fast.

arch2b · #6 03-20-2005, 04:42 PM

here is another place i know of that has speghetti wire
http://www.nyblimp.com/superior/wire.htm

rssjib · #7 03-22-2005, 09:05 AM

The aluminum steering knuckles and tie-rod should help with some of the steering slop. It is a far better fit than the plastic. For an inexpensive(temp) solution, you can slip a small piece of heatsink over the tie-rod end to help alleviate the looseness in the steering knuckle. Does that make sense?? LOL

I also trim the steering knuckle to help with tire rub. You will definitely need to do this if you do the aforementioned steering resistor upgrade.

Another thing I do is slip a small washer in between the wheels and the bearings. This helps with the play there as well. I already had bearings, and didn't want to spend more money on wide-track bearings, so I bought the alum washers at Lowe's for about 30 cents for a pack of eight.

broke ess supra · #8 04-03-2005, 04:42 PM

i was thinking the other day if i could increase the top speed of my xmod in terms of more torque... some of my hotter motors don't really have a good top speed with my 11 tooth pinion because of the lack of torque. the stock stage two almost has a higher top speed...soooo...i added spinbrush magnets to my hot motor and it helped a lot in the top speed area i guess because of the added torque...
with this in mind i was thinking the 180 motor would have a nice top speed with the proper gearing...since it revs pretty low a 14-16T pinion would probably make up the difference and with the right setup it would even be faster than a hot motor with the 11t pinion...

My question is do you think my theory is sound and where do you find the proper pinoin and gears?

Horshu · #9 04-11-2005, 07:18 PM

Quick update: after wrestling with the format of this all-encompassing optimization guide (how do I delve into an optimization guide while only addressing one particular path), I came up with writing an instruction manual for my car (I'm calling it "QuickSilver" basically because it can go from stock power up to 30v with a really cool turbo assembly that is almost completely polished or woven aluminum and I needed a name for the car and all its accessories). This thing is an EXTREMELY detailed so far (the section on the turbo unit itself is 2 pages) and delves into both general optimization (in what I call a "form integrity" or basically running with any mod so long as the motor is 130 and the body isn't cut) and optimizations particular to GPM/Zero Products-based cars. I'm including detailed sections on how the car is painted and how the remote is built (my remote has a turbo button for Lo throttle driving, custom molded rubber handle, and multi-paint paint job...I detail how to do every step). I am also including every DWG I've done, including the foam briefcase patterns for water/laser cutting and turbo heat sink as well as performance notes, parts weight comparisons, and general price lists. It's basically both a How-To-Build and Tune my car as well as a collection of every non-extreme tuning tip that I can think of. I'll be posting links to versions of it as I get it nearly complete (perf #s will be the only major holdup) for those looking for a formal, comprehensive XMODS guide.

rssjib · #10 04-11-2005, 11:45 PM

Sounds detailed... I cannot wait to see it.

broke ess supra · #11 04-12-2005, 09:21 PM

I love reading about do it yourself modifications...please do release this soon...and to get on topic...

Power supply--->racing aaa batteries...they can discharge a lot more current(good if you have a hot motor!) and of course they have more mah meaning longer runtimes...I need to buy some...my friend has some 800 mah and they are much better than the rs rechargeables...it was almost like adding another battery when i tried his batteries on my six cell

rssjib · #12 04-12-2005, 11:04 PM

C'mon, broke....get some Li-Ions and feel the power!!

broke ess supra · #13 04-13-2005, 05:41 PM

DUDE I WANT LITHIUM IONS!
just....don't have the money...

Technically speaking though in races(miniz,xmods,etc) don't they restrict you to the type of power you use?

rssjib · #14 04-13-2005, 08:54 PM

Hmmmm...don't know............

I probably should race mine a little...there is a hobby shop that I know of in Houston where they have an indoor track set up for mini-z's and the like. Maybe I should go by...

Horshu · #15 04-13-2005, 10:01 PM

You're thinking of M&M over on Chimneyrock. Let me know how it is if you go. I was just asked about that track today, although I've never used it.
I'm taking my 2 Wide Ls over to San Antonio to race this weekend. Hopefully should have my lith/NML SSv3 combo running by then vs. my friend's 6 NiMH SuperStock 130.