My BL Revo project - Page 8 - RC-Monster Forums

BrianG · **It's Done!!! -** 04.06.2006, 08:49 PM

Yay! It's finally done!

I have a Strobe slipper on back-order from Mike, but was able to snatch the last one at hobbyshopnj.com and now my Revo is finally complete. When Mike's arrives, I'll just have a spare for maybe another version, or if I somehow mess this one up. :)

All I have to say is: Wow! It's crazy fast and powerful! I'm using 51/14 and it's pretty quick - way faster/stronger than the stock Nitro 2.5R, even with the fact that this Revo is heavy. Count me as a brand new BL convert!

I may need to order some more slipper pads though. :dft001: I thought they were tight, but they weren't and now have some wear to them. I have the slipper quite tight now and even lightly sanded the plates so they grab better. And yes, I cleaned the grease out of the bearing. :)

Runtime isn't bad either. In my yard doing general bashing, I got around 25ish minutes on 14 GP3300 cells. Doesn't cog unless I try to go REALLY slow (<5mph).

Temps of motor and ESC was warm at about 120*F, the batteries at about 90*F. I noticed everything was cooler when running at high speed. Only at low speed (5-10mph) did things reach those temps. Is this normal?

I'll try to snap a final picture and post it later tonight.

04.06.2006, 09:12 PM

it is normal for a motor to heat up a good bit when only running on partial throttle especially the ones without segmented magnets

BrianG · 04.06.2006, 09:32 PM

Quote:

Originally Posted by boss 302

it is normal for a motor to heat up a good bit when only running on partial throttle especially the ones without segmented magnets

Cool, thanks! So, if I read other forum posts correctly, the fact that my motor and ESC are about equally warm means I have the right gearing ratios, right?

HotnCold · 04.07.2006, 05:32 AM

Yep - sounds spot on...

BrianG · 10:01 PM

Well, I took it out for a while today and had a blast. Runtime is still right around 25-30 minutes and I can't figure out why it's so long. The truck is heavy and is using GP3300 cells. :032: That calculates to 6.6A average current draw. And I'm not really easy on the throttle either...

I got a wheelie bar and it was working good until I landed on it from a jump and bent it. Oh well. Now I have to find a new one that will last more than one bashing session. Is there a good one that someone can recommend? I also bent the roll bar I made all to hell. Hmmph. That'll teach me to run without the body.

Man, the thing is hard to control! The power is almost too much. I ended up reducing the throttle to 85% and the brake/reverse to 60% on the transmitter. Otherwise the tires break loose when I goose it or it does forward flips when I brake. Seems like a waste to keep the EPA so conservative. Kinda makes me think I should have gone with a 9XL or 10XL instead of an 8XL? Is there a way to program the ESC so it will take longer to go full throttle if I "floor" it? According to the manual, it says there is a pre-programmed 0.3 second ramp-up time for the throttle. I was thinking maybe a 0.5-0.75 second ramp-up might help.

maxxdude1234 · 04.10.2006, 03:34 AM

I believe you can adjust the throttle curve on some transmitters, so that there will be a smooth progression when you floor the throttle.

Sylvester · 04.10.2006, 05:44 AM

I think you need the programming cable for that? Ask mike, he should know.

squeeforever · 04.10.2006, 08:26 AM

not sure about your transmitter but im pretty sure the m8 has a feature like this. ill try it out and let you know later. i kinda had to be a little easy on the trigger last night. i have the 10xl on 14 cells for now (soon 16 or 6s lipo). i ran it last night for th first time on my new ib 4200s and it was INSANE. top speed was about 40 to 45ish with 20/51 gearing. lets put it this way...i had no problem ketching up with the cars going by at 35 to 40 mph....

BrianG · 08:40 AM

Maxxdude: I have the Spektrum DX3, which I don't think has that feature.

Sylvester: I thought I heard there was a programming cable, but when I looked, I only saw the Castle link. I just went there again and saw the one for BK in the controllers section. I must have looked in the "motors" section before for some reason, which only lists the Castle link. Doh.

Something else I noticed, but not sure if it's the batteries. I also have two 6-cell packs that I was using and it seemed to reduce the speed to about what I'm looking for, but runtime was half of what I had with two 7-cell packs. All four packs are GP 3300 cells, but the two 6-cell packs are packaged differently. Does it make sense that runtime is reduced using a lower voltage? I would think that a lower voltage on a relatively constant motor resistance (impedance not included) would create less current, increasing runtime.

Assuming 1.2v/cell (I know they start out a little higher), what is the minimum number of cells recommended to use with the 8XL? For max cell count, it seems like 18-20 cells will keep it in the 45k rpm range, but that would be wayyy too fast for me. 14 cells equates to 31,500 rpm.

coolhandcountry · 04.10.2006, 08:54 AM

Well you have a tendency to run the motor with more throttle on the 12 cells than the 14. You have more power to use so you accually are easier on the trigger so you get more run time. If you launched it the same every time the 6 cells would or should last longer.

squeeforever · 09:01 AM

i was under the impression the higher the voltage the better the runtime up to a certain point when the efficiency falls? maybe im loosing it :confused:

BrianG · 04.10.2006, 11:56 AM

CHC, what you say makes sense, but then Squee's response sounds right too.

04.10.2006, 01:30 PM

i also think that what squee said makes sense and sounds right

maxxdude1234 · 04.10.2006, 01:36 PM

In short, they are both right! CHC's is right from a scientific view. In that a higher voltage will increase current. However, in the context on rc cars it is slightly different. Because when we add voltage we 'gear down' (ie. use a smaller pinion) the motor has to work less hard, and hence we draw less current. This is how squee is also right.

BrianG · 02:08 PM

Ah, but I didn't gear down...

There must be a point where the ESC sends an "ideal" signal of pulese where the BL motor operates with the most effieciency, and this ideal range is based on voltage and wind. I'm sure the AC reactive properties of the coils must have something to do with it, but without inductive ratings, and the frequency of the ESC pulese, it's pretty hard to tell.