Unfortunately, ~13mm is a bit too tall. The batteries have to be mounted at an angle so they fit lengthwise, but then that brings them close to the edge of the body where there isn't much room height-wise. So, I have to keep the tray as close to (but not touch) the dirt guards so save as much height for the batteries as possible.

That's a good idea though - I'll have to keep that in mind if I see something that is small enough to work. I was planning on drilling some ~10mm holes in the bar to help cut down on the weight, but you have the right idea. How would I secure the bar to the chassis and batt tray - locknuts? As you can see in my crude drawing, I'm using the thickess for the "meat" for the threads.

If only the actual chassis was wider with smaller dirt guards! I know it's for weight considerations, but still aggravating!

I don't know if you are familiar with my PRP Swift buggy, but I too ran into a similar dilemma. I couldn't mount the batteries on the mud guards, and I didn't feel like raising the batteries. My solution was to get smaller batteries - they're about 35mm wide x 105mm long, and 40mm tall. They fit on the chassis behind the center diff, with the motor on the front-left floor of the chassis. Would this type of setup be feasible for your, or would you rather use the standard 6cell NiMh size batteries?

Actually, I was shooting for two 2s2p 8Ah Maxamps Lipos. Nothing else will give me the runtime I want, with the size and weight I need. Plus, a continuous discharge of 120A will ensure the voltage won't drop much at all when I anticipate peaks of about 100A. which will be better for the batteries and I can squeeze more of that 8Ah out on each cycle.

According to the site, each 2s2p pack is 44mm X 137mm X 26mm. I figure if I make the trays adjustable from 130mm up to 150mm long, it should allow me to use pretty much anything within reason. I also plan on making the tray 50mm wide to again allow room for future packs and/or a little extra side padding. 26mm high is just right so it won't touch the body - even with the raised platform.

I also thought about moving the diff forwards more, but that would mean cutting a new groove in the chassis for the bottom of the spur, moving the steering servo, modding or getting new bones, etc. I'd rather keep it looking nice without too many extra holes and such.

I made little 150mm X 50mm cardboard cutouts (to simulate the packs) for test fitting. It's tight, but I think it will work.

Do you have any pics to post of the car/layout etc?

I'm having the same battery fitment issues on the 8ight project... as I expected. ;) I have some options that will work, just can't decide...

I will snap some pics after work tonight.

I remember seeing yours - that 8ight is MUCH narrower! I can fit the cells I want; but the rear corner of the pack will stick out of the body/chassis a tad. No matter what, a battery platform will be required since I refuse to mount anything to the dirt guards. I suppose the batts could be mounted on edge, but that would raise the cog and the motor will be bad eough since I plan to mount it over the diff.

very cool, I really want to see....

Not really much to see since it's basically en empty chassis.

The two attached pictures are the two battery placements I was looking at. I figured on worst-case battery size of 150mm X 50mm. The battery tray will be a smidge bigger (~4mm width and height). Either layout leaves a little bit of the pack off the edge (red circle) although the angled one is not quite as bad. The straight layout looks better though.

The only option i see is to move the steering servo to the other side and use the bell-crank on the opposite side

Yeah, I was looking at that option, but as you can see, the shaft really isn't that far off center. I'd only gain a couple of mm's. I'll probably just make the battery holders and see how they look.

this is what i did to work around that problem.

Hmmm. Something to think about...

OK, I came up with the battery trays. I just have to either find a metal shop with a nice cutter and bender or do everything with a dremel and vice (ugg). So now I'm looking for batteries. The buggy as seen in the pictures above currently weighs 5.28 lbs. I plan on using a Neu motor with a kv ~2000 on 4s Lipo, total gear ratio of 11.1:1. I was looking at the Maxamps 7.4v 8Ah packs, but am not sure if those will be big enough to get at least 30 minutes of racing runtime.

As a comparison, my BL Revo gets 14 minutes of track runtime using 14xGp3300 cells. The Revo weighs 10.78 lbs loaded with batts. That's an average current draw of 14.14amps. If I were to use 8Ah packs, the runtime should be around 34 minutes.

I'm thinking the buggy will (hopefully) be lighter and therefore require less power to accelerate/run, but I thought I'd ask the experts here. :)

With my 5s lipo 8Ah on my 11lbs gmaxx, i'm getting 30-34min of runtime. Does that help?

Well, for as far as i can tell; a buggy is relative heavy. (at least daniels mbx5, Nieles his ofna mbx and my my MBX4)

Yes, it does. Although, you're probably using a lower kv motor on that 5s, so average current draw will be less than my Revo. It looks like I'll be right at the edge of 30 minutes.