Well, as you know, runtime depends on a lot of factors, but with all else being equal, I could use the 2.5d and gear up and get the same runtime and speed as what I have now because the motor would be loaded more.

What I was shooting for was about 35mph for track use. With all the gearing (standard buggy diffs, 46T spur, 14T pinion), and with 4s batteries, I chose the motor that would get me near 35mph, which was one with a kv around 2000rpm/v. Since this motor spins faster, I'll probably get a smaller pinion to compensate. This will reduce the top speed closer to what I want, help unload the motor a bit, help runtime, and keep things cooler.

I use 4.25" as the tire size.

And yeah, I'll post runtime. But it will be closer to actual race time before I take any serious measurements. That's assuming I get good enough to even try racing this year.

Ubec?
 

Stupid question: Is a UBEC anything like a BEC? If so, why do you need one, since the Quark 125 comes with a BEC? If not, what the heck is it? And why do you need a big capacitor to go with it?

Sorry to trouble you with such elementary questions.

Nice Buggy!
 

By the way, I'm very impressed with the factory-quality conversion of your buggy, BrianG. I'd like to do something similar myself, once I learn more about brushless motors and LiPo batteries. I'm sure I'll have more ignorant questions for you soon.

A bec is a battery eliminating circuit and only allows so much voltage. A UBEC converts the voltage from your batt pack to send 6v to the rx, thus eliminating using a rx batt pack.
With disconnecting the bec circuit and running the ubec, you can run a higher voltage at cooler temps through the esc without frying the bec in the esc...make sense? lol

Good answer newe! :)

To add to what he said, the BEC in the ESC is "linear" and can generate a lot of heat depending on load (servos) and main cell count.

And the term "BEC" just means "Battery Eliminator Circuit". The "U" in UBEC is "Universal". Really, the terms BEC and UBEC are interchangable, but when the people here say "BEC", they usually are referring to the ESC integrated one, while if they say "UBEC", they mean the external switching one.

The capacitor is not required, but it does help filter noise out from the power lead, which may help stop potential glitching. And, it also provides a little extra current boost if the servo(s) need it (especially when they begin moving from a stop).

And thanks for the comments. :)

Thanks!
 

Thanks for your replies. BrianG, now I see your (U)BEC explanation on your RC calculations site. I guess I needn't have asked. Here's a follow-up question: how does one determine the capacitance required? At what frequency do you find most of the noise?

I usually just use a 1,000uF rated ~10v. If you are using a heavy duty servo, you could go up to 4,700uF, but the cap will be physically bigger.

Most of the noise will probably be at whatever the BEC switches at (I've seen anywhere from 20kHz to 250kHz) and will be most evident at higher loads. And since this BEC also supplies DC power to potentially sensitive receiver circuits, I take no chances. :)

Weight Distribution
 

BrianG,

Thanks for the reply. What weight distribution did you strive for when assembling this buggy? I assume you wanted equal port/starboard, but did you aim for equal fore/aft, or did you want more weight on the rear wheels?

I was shooting for almost perfect right/left distribution than fore/aft. But the amount of space under the canopy was a limiting factor in front as well. The ESC and receiver are about as high as I can go before it starts hitting the shell. I figure I can tweak the spring preloads for the weight and then compensate for less-than-ideal jumping attitude by tappign the brake or whatever.

Looking forward to the vids, Brain. *hint* :D

Looking forward to receiving a video camera. *hint* :dft012: :027:

How are those ofna gaskets for the center diff working? Any problems?

I'm working on a Hyper 7 - yes, one rev. behind conversion right now... Does anyone know if that motor mount that is used in the Hyper 8 conversion in this thread would fit the Hyper 7?? The designs look VERY similar.

I like the center mounted motor, gives the car a much more balanced look, and I'm sure "feel" on the track.

Also, if I can just use your expertise. I've got a Quark125b controller, and a Lehner 1940/7 Hi-Amp motor that I'm planning on running... will that fit be ok? Or is that under-powered?

@lydiasdad: The gaskets seem to be working well for now, but I really haven't run it all that much. I'll probably end up getting a Kyosho center diff and the Kyosho spur as a spare in case I run into any problems with leaking.

@hunter306: Actually, I was originally looking at getting the 1940/8 but they were out of stock, so I got the 1512 Neu instead. From what I understand, they are comparable power-wise, and the Neu has PLENTY of power. The 125B may be a tad difficult to squeeze in there. I had trouble getting it to fit while allowing proper wire routing and clearance on the shell.

Since the Hyper 7 and Hyper 8 diffs are interchangeable, I would think the mount would work.

The center-mounted motor does look/feel balanced, but a layout with the motor on one side and the batteries on the other frees the area over the CD for all the electronics.

Hey Brian, Thanks for the help.
Couple more questions!

Where did you get your hands on that Center Motor Mount assembly?
--What online store or place sells that part?

Do you still have those 2 unfinished lipo trays? What are the dimensions?
--If you do, I'd like to take them off your hands, let me know where to paypal the shipping money!

Also, I see what you are saying with the Quark125b... it is huge, I've got one in my Electric LST2 and it was a pain to fit, but I think it'll work. These cars have some decent sized trays on them!