Lowering BL Revo CoG.
 

After getting back from the race weekend I have decided to lower the center of gravity on the truck. First by using dual 3s packs instead of one on the right side, in their own lower batt mounts/trays lowered about an inch down; moving, and flipping the transmission around and lowering the motor on a separate motor mount in front of it, and moving down more than an inch as well.

I don't know where to put the speed control, and maybe I don't want to move it, but as for the receiver box, I am totally open to suggestions as to where to put it. The Rx box will be a RPM unit, maybe above the rear shocks?

As far as I can see it, this way, there will be the perfect front/rear distribution, as well as near 50/50 side-side balance.

Does anyone have any experience modifying a Revo chassis for lower CG, and dual packs? I have two weeks to fabricate the mounts and do all that is needed.

Another.

The OG 50/50 revo.....lol

http://www.rc-monster.com/forum/showthread.php?t=19479

http://www.rc-monster.com/forum/showthread.php?t=218

Try that, or have a glance through the build in this thread:

http://www.beatyourtruck.com/forum/s...ad.php?t=58732

Nice setup. What does OG mean? :smile::neutral:

So you say that setup will keep up with the truggies, that's great. The current setup, I can get a better average lap time than half the truggy drivers on our track, and that's with a HIGH CoG setup as well.

I'm kinda seeing where this is going, the whole trying to lower the CG, where does it end? You know?! At some point, it's just a truggy really, and can run with the truggies.

What battery trays are those? Impakt RC? I am thinking of using 1.5 inch carbon fiber angle on each side.

I am just wondering if it's better to lay the packs down for lowest possible CoG, or to stand them on edge to keep them more center lined?

What packs are you using these days, btw? As you can see, I am using a pair of 3s, 4200, 35C G3 packs, love em, getting another pair soon.

Does anyone know of a good source for carbon fiber products? Such as angle, sheets, tubes, etc?

I found robot marketplace, but not the best selection of sizes.

hobbycity has some carbon fiber... alot actually

OG=Original Gangster

Have you thought of making some type of bottom tray like the GorillaMaxx chassis incorporate?

FullForceRC sell CF sheets too:

http://www.fullforcerc.com/Carbon.htm

As for stuff like angle, I would google for it- lots of obsure companies turn up that should be useful.

OG, right, I knew that, just testing you guys. :whistle:

Checked out hobbycity for angle, nada. Too bad, the CF there is inexpensive.

Nitrostarter, I thought about a bottom plate, but I am just not sure how I would attach it, and the battery mounts would not be angled up, which you need to protect them, and to reduce snagging on jumps, bumps, and large lumps if they were on the track. But the idea really interests me as it would provide a skid plate effect, and even protecting the steering servo when landing on a spike in the cribbing off a jump (don't ask ;) ).

K, now that I have several CF sources... it's either a bottom plate, or twin angle CF off each side, which just might work better, but who knows.

Is there a place that you can order CF with custom bends in it? Shapes? Cuz you need those batt trays to angle up to reduce snagging when landing off kilter.

Any ideas are welcome, and pics as well!

cheers

You can heat up CF and reshape it (over a wooden mold for example), though its not as good as a piece that was laid wet into a mold and pre-formed to the required angle. Still, worth thinking about, maybe even prototyping with a cheap piece of CF, test it and see how it holds up, before deciding on a more expensive piece of CF etc..

Hmm, I don't think I would come up with anything aesthetically pleasing if I heated and bent it myself. :oops:

I really like the way Dafni did his batt mounts, only with CF like with Serum's Revo 2.5 conversion.

How low does the GM Revo chassis go, was it all the way down to skidplate level? I wonder why they stopped selling them? Just because the E-Revo came out?

HERE is the CF angle I was looking at, looks like a good size, although I would prefer a 2" size, this is 1.5". So if this is the biggest CF angle I can find, I would have to set the batteries on edge as to avoid the packs sitting over the edge and getting abused. Then all I would need is sticky velcro where the pack would sit, and two velcro straps, and that should do the trick.

What do you think of this motor? I know Sike should be here now to give a brew some experienced suggestions.

http://www.scorpionsystem.com/catalo...s40/S-4025-16/

Scorpion outrunner:

332Kv.
14 poles
2000watts continuous? seems high for cont.
8s max

Would run 6s, that works out to 47mph, not a whole heck of alot higher top speed than it is now, ~42mph, but non the less, should be less, maybe around 280 - 300 Kv. would be nice.

Sike, would you recommend an outrunner for racing? Are you still using the outrunner in your truck?

All the conversions i have done i have used 4 electronic kitchen scales put one tyre on each and than moved stuff around to get as good a weight balance as i could.

I dunno if an outrunner for racing would be ideal- the spool up time is much slower compared to an inrunner I believe, so that would mean poor acceleration down the straights and out of corners, just when you need it most. I might be lying though...

Hmmm, all I need is 4 digital scales now... :neutral:... I have one legal for trade 10lb unit, which I just weight the components and place them on the chassis and hold the truck in the center of the skidplates and see if it holds level. I do it by eye as well. There has got to be more to weight distribution than just static balance me thinks... a sort of 'dynamic' balance, where even though it is balanced for weight, components might be all wonky all over the place that it causes certain 'inertial' effects when in action, thus not being 'truly' balanced.


Neil, true, that might be a valid point... it might be unbearable going from a fast spooling 1512 to a high inertia outrunner. Although, I don't think it would affect it in the straight, I would think more in the tight technical parts where you need quick power to the wheels for mere milliseconds.

Sike! Calling Sike on this one!

If I could get an outrunner to work well in the Revo for racing, and lowering the batteries... I am pretty sure I could beat all the truggy drivers except two at our track.

Hi Guys,

Always glad to lend a hand when I can.

Here's some reference material. http://www.rc-monster.com/forum/show...ect+drive+diff

Am I still using the outrunner in my truck? No, but I still have all the parts here.

I ran into two problems with the direct drive to diff setup:

#1. 4.6:1 final diff drive ratio gears would NOT hold up to the torque being made. The diffs use ball bearings not thrust bearings on the pinion gear. I could trash the pinion bearings in less than one packs runtime. Yes, they were shimmed properly. It would always punch the center race right through the outer race. Little balls everywhere. LOL

#2. In an effort to get the kind of speed/power I wanted, a custom wound outrunner was created. An AXI 4130 was made into a 4 turn motor. Hot Thing! but would pull HUGE amp spikes on startup.

It still wasn't too shabby:

http://www.youtube.com/watch?v=dFDrYXLkcGg

Check out the video, then ask yourself if this has "spool up" problems.

Spool up time is required or negated by final drive ratio. It all depends on how much torque the motor makes. High Revving motors use very low gearing to make up for their lack of torque. The same applies in reverse for outrunners.

How do you plan on gearing your setup Seth? And what voltage do you plan on running?

Thanks for the PM Seth. Please feel free to include me on ANY discussions of this sort. I LOVE it. LOL :yes:

More Reference Material:

http://www.rc-monster.com/forum/show...light=axi+maxx

Check out the setup and the vids in this thread.

Such Torque from such a small outrunner. :yes:

beauty, thanks for posting Sike. :smile:

I would run 6s, so the 330 Kv. of the scorpion motor would equate to 45mph, not too much faster than the 40mph it's geared for at my track, which is perfect. (we have a long straight section)

If they have a 300Kv., that would be ideal, but they have a big gap in their Kv's to choose from.

I was also thinking about a truggy center diff, but the Revo diffs are too high of a ratio to be used with one, you would need hybrid diffs.

Q1: What diffs were you using to blow the bearings? And how would an inrunner/trans setup be any different in that respect?

Q2: Simply, what do you think of the motor in question? Think it will be suitable?

If this did work, then the handling on the truck would be in short, sick. I would be able to keep up with truggies no problem, as I can keep up to most of them even with the high CG as it is now.

Q1. I was using the RCM v2 Hybrid Diffs. Difference = Direct Drive. No Slipper. Diff Torture Chamber!

Q2. Scorpion Motors are well built, but they have little or no fan. This makes it harder for them to shed their heat, especially in a rolling application. Flyboys mount them behind the biggest fan possible, so it works well.

Any Motor makes heat especially when pushed. If your mount and frame are aluminum, you might have enough mass to shed heat.

This is why I went with AXI. They do sell a fan that mounts to it's rotating endbell. It moves alot of air too.

I've been tempted to go with Mike's Slipperential. Put that together with regular straight cut gears in the diffs. An Outrunner geared properly would work very well.

For gearing, think outside the box somewhat. Go by the gearing calculator and even then, the outrunner has the torque to pull higher gearing than it suggests.

You are blowing diffs without a slipper? I have my slipper tightened all the way down and I have not had any problems yet. Just have to let off throttle at the right time I guess? It took me 2 years to blow a diff with slipper tightened 100%.

-Have you ran a scorpion motor in the direct outrunner project? If so, which one?

I am sure the outrunner will get enough cooling to keep it within the safe temp range... I don't really care about temps at this point, I just want to test the waters and see if I like the concept, as I always have wanted to do this, but am reluctant in the end.

One thing I don't get is the power rating, 2400watts cont. for a 440g motor? Come on, doesn't a 1515 weight almost that, and it has a 1500watt rating. Unless it's typo, or it's the max watts rating, I highly doubt it.

So the motor/trans that is in the truck now is 470g, I would save a small 30g, but the CG would be very low.

If I can find a way to lower the trans (G1 single speed) and make a seperate motor mount to lower the motor, then I would obviously keep using the Neu. But the outrunner just seems alot easier to accomplish this.

It's times like these when you just hate the setup of the Revo with the shocks taking up over half the room. :no:

[COLOR=[/B][/COLOR]
Yes, the Revo is VERY cramped.

It's alot to think about isn't it? :yes:

We're talking some explosive High Geared Torque coming from an Outrunner here. So Yes, the lack of a slipper is partially to blame for the problems. If there were a slipper, it could have been utilized with the setup. Inrunners don't have this type of Torque Period.

-IMO, I don't think that would matter would it? I mean if it's an inrunner of equal power is geared for the same speed, then the torque to the diffs would be the same, as all brushless motors have to the same torque curve (straight line)... and yah, it's too bad that any type of slipper can't be used with a setup like this.

There's a difference in the "flyboy" rating and our Land Vehicles. The Most Major one is airflow. The ability to shed heat is one thing that affects ratings alot.

-Completely agree with you on this one, cooling is basically the limitation to the continuous wattage rating (to a point), the better the cooling the closer the continuous rating will be to the peak rating. But still, that said, 2400watts for 440g is huge, so maybe the rating is taking into account that the components they use can handle high temperatures? However, that does not mean the efficiency would be very good at that output, if anything below average, maybe 85% or lower, whereas a Neu, IIRC, is roughly almost 90% efficient at it's rated output.


Another thought... I was just moving stuff around on the truck and was tilting the transmission 45 degrees one way and putting the motor centered in the chassis. Now if only I could make it work that way without heavily modifying the chassis to make room for it. If it could be done, then the motor would be centered, trans tilted to the left with steering servo on left as well, with Rx/rx batt on right side, and then twin packs on each side, should be 99% balanced then. Still thinkin on the ideas though. :smile:

I think what you're doing is great. Please share more and take some pictures. :yes:

Well, I don't know what you think 'kind' of power an outrunner has, all I know is that an electric motor has watts, and the wattage is a product of speed vs. torque, and every motor has 100% torque at zero rpm and drops from 0rpm to max rpm. I really don't think there is anything different in an outrunner, except for motor inertia (although it's spinning alot slower, so that is near canceled out), it has many times more torque, but spins many times slower, so power ends up being the same as well.

Unless I didn't get the idea you were trying to convey? Explain in more detail?


On a side note, I posted some pics of roughly what I was thinking of when I said tilting the trans and making a mount for the motor in the center of the chassis, and lowering it. Check it out. Looks like a pretty balanced setup?

The batteries would be mounted on CF angle mounts and will be sitting 1 inch lower than in the picture.

yep, Watts is Watts but could there be something more? LOL

KV versus gearing versus final efficiency rating. I get that.

That's an interesting way to look at tranny position. I like that, but how are you going to secure it?

This should be good.

Isn't there a website that is going to be doing dyno tests for popular motors in R/C? That would put this debate to rest I think, just to see a torque/power curve of some of these motors. Another thought, maybe it's the ESC firmware that is causing a different 'feel' or level of power between a in and outrunner type?

As for the mounting of the transmision, I was thinking about getting a small bracket made that screws into the aluminum plate on the trans and goes around and mounts like the regular plastic stand-offs. I would have to grind the plastic mounts away of course.

If there is a website like that, I'm not aware of it. I sure hope there is one in the future.

Watts is a measure of the power put into a motor. Volts X Amps

Actual work being done is HP and Torque values.

Efficiency is how well the incoming power is utilized. Watts changed into work versus watts burned off as heat energy.

I like to keep an open mind. Not everything that will be discovered has been discovered.

There is alot to be said about Motor winding also. Then there is the scale of measure for the strength of a magnet. With limiting factors being saturation and demagnetization temperature.

I've done alot of research. I get lost around the point where it gets in depth about eddy currents in the Magnetic Harmonics. I do know this also effects efficiency. Clashes or opposing forces that spend energy fighting each other instead of doing work.

Your setup will be almost dead on as far as being centered. :yes:

I really like the look.

I thought I would update the progress I have made making my Revo more and more 'race worthy'... and where I have got it at now is nothing short of amazing, performance wise. Everyone at the track comments on how it doesn't 'look' like a Revo when racing, more like a truggy they say. I would have to agree, the weight distribution and center of gravity seems like it is just right for the chassis, and really seems to shine in the handling department, compared to a stock Revo 3.3.

The battery mounts are 1.5" CF angle from SierraComposites.com, the mounting brackets (alum.) are made from 1/2" x 1/8" 6061-T6 strips, a little small, but has held up fine so far after some pretty nasty crashes. The packs actually sit 1/4" lower than the E-revo battery compartments, and are a few mm above the bottom level of the servo guards.

The Rx pack mount is made from some CF I had laying around, which I cut, and glued with some CA glue, sticky Velcro all-around, including main power packs, which take the securing to the next level, really works well.

I was worried about the CF getting quite scratched and damaged from landings on rocks, and scrapping on stuff that commonly occurs at a track.

Enjoy.

More.

Very Nice ZPB! :yes:

That Quark looks just like the original Quark that you first modded and posted about a few years ago. Is that the same one?

I see you're putting those Hyperion packs to good use.

Is that a receiver pack I see in front of the motor?

Nice progress! That's gonna be a mean one.

More.

Thanks Sike, the G3 packs have 2 extra heat shrinks on them for good measure as the packs are low enough to get rocks and stuff hitting them. Yes, that is a Rx pack, the HP G3 LiFe packs in fact, they work great, I get roughly 50 mins per pack running a 7955TG servo. I used a friends of mine iPod touch with the 'dyno' app. (very cool), get this, the 0-60mph time on asphalt now is 2.1 seconds, down from a ~3.5 second before the mods. I find the tracking and understeer and oversteer conditions are so much improved... on hard pack driveway, it has a slight oversteer condition, which is PERFECT, you can also just chuck it into corners and expect it to come out with a nice drift, and perfectly controllable too!

Well, that is all I am doing to it this year, next year I am going to do a Eight-T 2.0 build with a special weapon, and it involves an outrunner motor, while maintaining CD, and slipper action.


Oh, and just for reference, the setup is as follows:

-Quark 125 w/6s G3 lipo, 1512/3D (1700kv)
-new E-revo shocks w/70wt f/r (silver springs front, blue springs rear) w/P3 rockers
-new 13mm axle carriers front
-RPM true track rear end
-E-revo diffs f/r
-front caster angle set as far back as possible
-the toe in rear is 1.5 toe-in obviously (true track)
-front toe is approx. 1.5 toe-out (this combo provides best straight line 'on-power' stability)
-weight distribution is pretty close to 50-50 front-rear, with a slight rear bias

Just thought I would post this as it is an insane winner of a setup at the track.

Rubbish.





















:lol:

It does look extremely well laid out, and the symetrical battery trays are really well done, perfect way to get that great weight balance.

Rubbish you wish. Is there supposed to be a picture in that gap? :neutral:

Wah? I thought that was the oldest gag in the (forum) book?

1. Someone does something cool.
2. You reply by insulting them > big gap > smiley & then actually compliment them.

Its called a joke! :smile:

Yeah, I think you're right... except it is just that old that I must have not picked up on it! :lol: I think I was just tired and couldn't think straight at the time. :wink: