Looking for a buggy project

You should be pushing over 50+ mph with the 2d; you think the quark could handle such a hot motor? Also, was it a shipping error that got you the 2d or you mistakenly ordered it?

BTW your buggy looks really good!

Bye:018:

[BrianG]

Thanks! No, I ordered the 2.5. I think it was a simple shipping mistake (I verified my order). Unfortunately, I didn't notice it until I started questioning why it was going so fast. lol. I obviously soldered it up and ran it so I can't just exchange it. No biggie really.

I think the Quark will be just fine, especially since I've added a little extra cooling. I'm more concerned about the batts heating up under the extra load in the heat of summer. I emailed Mike asking what he thought. If it will run a little hot, I'll just see if I can order a smaller pinion to reduce the motor load a little.

Edit: Wow, I already got a response from Mike! He says I should be fine. He's running the Quark with the 1515 1y in his Maxx with no pack heat issues. So, I think I'm all set.

[jnev]

Sounds good. So about how much did this system set you back... like the 125B and Neu 1512/2d. Also, are you using a UBEC? And from what cemetary said, it'll be pushing 50mph, what kind of run time(s) are you getting?

Mike is making a motor mount for me right now for my 1/8 buggy, so I am still deciding what system to run in it.

Thanks

[BrianG]

I don't even want to think about how much this cost me; I'd have to shoot myself! :002: You can probably get a pretty close figure by adding up the parts from the RCM store, then add the base kit. Then, there's the metal stock used for some of the custom parts. Not to mention the time. Ugg. Makes me cringe just thinking about it.

Yes, I'm using a UBEC. The UBEC, capacitor (for the UBEC), and any extra wiring is located in a custom box under the ESC to keep everything tidy. :)

I haven't run it enough in one shot to get a runtime figure yet. I was outside for about 10 minutes at a guess and the batts didn't dump, and they were at a storage charge of about 3.8v/cell. Hard to say. I'm hoping for a solid 25 minutes. If not, I'll just pick up the 2.5d later and use the 2d in my Revo since it has more gearing options.

[jnev]

Cool. Once you do get a full run time, do you think you can PM me the run time, or post it here? One last question, lol (sorry for so many)... with the 2.5d and everything else the same, do you think that the speeds would be able to remain between 45 and 50mph? Will the run times also be significantly longer than the 2d? I was tryign to use your speed calculator, but wasn't sure what to put for gearing, or tire diameter of a 1/8 scale buggy tire.

[BrianG]

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.

[skeeler]

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.

[skeeler]

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.

[neweuser]

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

[BrianG]

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. :)

[skeeler]

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?

[BrianG]

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. :)

[skeeler]

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?

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

[BrianG]

Originally Posted by Aragon

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

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