B-MAX4iii 'thermaling' indoors; advice please

[andrewc]

Hi all

Not a newbie to the sport, but I am to the BMAX4iii, so thought I'd put this in here and hope for more specific advice/experience than in electrics/1/10th off road.

Bought a used BMAX4iii before xmas, great chassis with everything on it, PSM upgrades, lightweight chassis, YZ rear end etc, all the gear. Rebuilt it completely, renewed all bearings etc, chassis rolls a treat, no bind anywhere.

Running indoors, sports hall (20c probably?) on a large 28x17 carpet track with jumps etc, 1066 Racing on FB if you want track pics for an example.

G-Force 160 ESC and 5.5 motor; I'm aware that's running a quick motor but struggled with thermal cut out ON MOTOR all day. Got thermal cut off set at 105c, can up it to 125c but that seems crazy hot??

MOTOR temps/set up from day, (ESC ran at under 60c all day) in brackets my thoughts...EVERY RUN ZERO BOOST ZERO TURBO ON ESC

Practice: geared 18/87, 10% drag brake, 0 timing on motor, thermal 109c at about 3.5 mins. (Figure this was under geared? Also G-force supplied motor at 20 degrees, and I've learned since they possibly don't like running low timing? It wasn't negative timing, I checked electronically, actually read 7 degrees at zero)

H1: geared 19/87, 5% drag brake, 20 timing on motor, ran the 5 minutes came in hot, 98c BUT no warm up/wind down lap. (better gearing? Timing? Drag brake?)

H2: geared 19/87, 0% drag brake, 20 timing on motor, 1 warm up lap, thermaled on 'wind down' lap after 5 mins, 108c (extra laps the problem?)

H3: geared 20/87, 0% drag brake, 20 timing on motor, 1 warm up lap, thermaled about 4 mins 40, 109c. (over geared?)

H4: geared 19/87, 0% drag brake, 10 timing on motor, 1 warm up lap, steering screw dropped out at 4 mins approx... was at 96c at that point. (obviously inconclusive but less timing might have helped?)

Apologies for so much info, just keen to get some answers...had a 6.5 in a B44.2 previously and never had heat issues on longer runs than this.

Could it be a duff motor? (brand new)
Temps are normal and I should suck it in/up the thermal cut off?!
Put a fan on motor? How much temp difference could this make? (I've noticed this on some EOS pics but not all...why would some need it and not others? G-Force known to run hot?)

I did have a very tight to chassis trim on shell but have opened rear up a little for airflow. Not keen on holes in shell...looks crap and want to be able to run on wet astro.

Ideally need to be able to run a couple of warm up laps and not be running the temp gauntlet. Any thoughts/experiences appreciated, Thank you.

[ayske1]

I suspect it's your esc. I'm currently running the 160a toro and I believe the g force may be similar. I have an ORCA fan on it and the esc stayed within 40 degrees. The indoor track I was at was maybe 23 degrees.

Running g2 v10 6.5t motor, 20/87 gearing. My suspicion is that even if you had a fan the esc would still be very hot, maybe 20 degrees cooler... So I think there's something wrong with your esc. I would return it asap if you run out of ideas and under warranty. I am with mine with my toro...

I'm also running blinky on my esc, stock timing on can. Good to see ppl running the bmax 4 iii on carpet

[K-Brewer]

Pretty sure (someone will correct me if I'm wrong) but I'm sure u can go to about 160F. I pull mine off the track at 135 an don't have any issues

[K-Brewer]

Just seen your talking about C, yeah that's bloody hot. I know u don't like holes but if ur running indoors with a 5.5 on carpet indoor ur gonna need to. Cut a couple round holes in the front using a reamer to let the air flow through

[neallewis]

What are your cells? how old are they? could they be high resistance and you are hitting the low voltage cut out on the speedo, not the thermal cut out?

I had this myself with the BMAX4iii and a 5.5 with some cells that were not up to the job. Thought it was thermal cutout, but it was low voltage cut out. Disable it and try it again, or try a new battery pack.

Honestly though a 5.5 is a bit mad for indoors. You will go quicker with a tamer motor. I use a 7.0 in my yz4, and did in the bmax4iii during the summer outdoors.


Edit - I just re-read.
Also put motor timing to 0deg. Gearing, you'd want to be about 18-19/87. Under or over gearing isn't that critical between 1-2 teeth in a healthy system.
This issue reminds me of mine with the low voltage cut out. You can run a motor fan, (the orca or MR33 fan mount works great), but it won't fix this.

[neallewis]

OK a bit more. I really must learn to read properly first time...

The thermal cut out temp isn't read from the outside of the speedo (heatsink) its from inside via a component on the circuit board, but also sometimes inside the FET substrate. This is why it might seem hot.

oh, you mention that the speedo is warm, not hot, but the motor is hot. how are you reading the motor temp at point of cut out?

Where are you reading the cut-out temp from, plugging the progbox in after its shutdown?

by the way, what's the motor?