More BK issues. Am i doing something wrong? - RC-Monster Forums

Mightytaco · **More BK issues. Am i doing something wrong? -** 06.18.2007, 10:03 PM

I just got done setting up my 9920 on my brushless buggy. Programming went perfect.. I set it up foreward only by holding full throttle after the first and second beep, plugged in the 4s lipo and headed out to the street. I get about 30 feet away after 2 seconds of half throttle, turned around and it cut off and on like the battery pack was going dead, which i think it was. Problem is, the esc seemed hotter than it should have been for that few seconds of running. Any ideas or thoughts? I dont want to fry this thing!

Mightytaco · 10:54 PM

Update: I charged two 2400 cheapie nimh packs and hooked them up in series. Hooked everything up and threw my fluke amp probe around the + in to the ESC. On the bench freewheeling, i did a couple quick 1/2 throttle bursts, then one quick full throttle burst. According to the amp probe, the peak draw was 93 amps. Isnt that a bit much for not even having the wheels on the ground? gearing is 14/46 on an 8xl.

silentbob343 · 06.18.2007, 11:42 PM

Quote:

Originally Posted by Mightytaco

Update: I charged two 2400 cheapie nimh packs and hooked them up in series. Hooked everything up and threw my fluke amp probe around the + in to the ESC. On the bench freewheeling, i did a couple quick 1/2 throttle bursts, then one quick full throttle burst. According to the amp probe, the peak draw was 93 amps. Isnt that a bit much for not even having the wheels on the ground? gearing is 14/46 on an 8xl.

That does sound high for no load, what size wheels/tires are you running?

MetalMan · 06.19.2007, 01:01 AM

How's the gear mesh between the spur/pinion? Is there any binding, does the buggy roll smoothly without the pinion on?

06.19.2007, 01:58 AM

Your gearing sounds right. Is that a new motor? Had it been overheated at some point? What are the odds that the cheapie batt packs are dropping voltage so badly that the amp draw is getting that high?

Mightytaco · 06.19.2007, 08:07 AM

I didnt think of the voltage drop issue. I'll retry my tests later with my good lipo pack. The motor is used, so who knows what temeratures it has reached. A motor thats gotten hot could draw more power? I did notice the wires to the motor were a bit warm, could a bad solder joint between the motor connector and wire cause excess amp draw? Everything else looked good. It rolls real nice and the mesh is good. Tires are just standard 1/8th scale tires/rims.

Mightytaco · 06.21.2007, 08:44 PM

Ok, here is what i did. I charged up my new 5000mah lipo packs (2x 2c packs in series) and ran some tests. Even with the good packs, i was getting up to a 135 amp peak draw with the wheels off the ground doing a couple quick full throttle bursts. Now that may have been for only a split second as my amp probe was set to display the max drawn. I swapped in my mamba max and was still getting a peak of 125. For the heck of it, i pulled out my ofna 9.5 conversion ( Fiago 8xl finned can with Mamba Max esc) and got a peak of 55 amps with the wheels off the ground which seems more like it. Id like to just throw it on the ground and not worry about it, but these esc's are expensive! Any thoughts?

Can i make a cable myself to interface the bk with my PC or is that something i have to buy? If it has the options the mamba has, i figure that it would be a good idea to to turn some things down. :)

sjcrss · 06.23.2007, 01:27 PM

Bk does sell a program cable, I have one that im not using...that I can let go for a small price, along with the program software as well....drop me a PM andwe can discuss this further if you like

06.23.2007, 01:51 PM

Don't know. It sounds like a bad motor. 125A peaks are about what you should see when the wheels on are the ground and you're doing wheelies.

Mightytaco · 06.23.2007, 10:41 PM

lol, my thoughts exactly. I did find out though that the motor is not an 8xl like i thought. Its a nemisis XL3T which i have no specs on. Im gonna order up an 8 or 9xl here soon and just throw that in. It probably wont be as fast, but at least ill be able to use it!

zeropointbug · 06.23.2007, 11:25 PM

I can see it drawing very high peak amps, but only for as long as it takes to accelerate the wheels up to speed (free wheeling). But like you said, it went from 135 amps to 55 amps in your other R/C buggy. Are you sure there aren't any binding? Are the rotating mass the same on both buggies?

06.23.2007, 11:35 PM

Oh, it's one of those FineDesign jobs. You might want to try something. If you can, put a 3S lipo pack on it or just the nimh equivalent and see what happens.

I know that a few of his setups, especially those meant for buggies, are "designed" to be run on 3S rather than 4S. It might just be a really high kv motor and you have it way overgeared.