Rustler 8s/9918: gearing/cells?
 

Howdy!

I finally bought the 8s! Now I have a quick couple of questions:

(I've done a bunch of research on this site, but I haven't really figured out a definite answer to my exact situation, so here goes:)

1) For high speed runs, what's the hottest gearing (32P) and highest cell count I can use without blowing anything up? (I figured out that I'm pretty much limited to a 60T spur due to space limitations. Correct me if I'm wrong. Maybe I should switch back to 48P?)

2) Same question about gearing and cell count, only for bashing and long runtimes.

(Background info: I run GP3300 cells, and my Rustler is stock except for: MIP CVDs, RPM bearing carriers, UBEC, Swami Wheelie Bar, Road Hawg tires, M8 radio, and an aluminum idler gear.)

Thanks a ton for your help!

Brian

Well, you might need to get back to 48p so you can use a more precise gearing. How many cells are you going to use? What speed are you aiming at?

Thanks for your reply, Cap'n! :-)

Cell counts: anywhere between 1 and 30, I just need to figure out which cell count is most appropriate for this motor on this vehicle. Coming from a 12 lb e-maxx, I know that a 9L is best with 14 cells, while a 10L is best with 16 cells. I just don't know what's okay and what's too much for this 8S on a lighter weight rustler.

(If it helps, my rusty weighs 3 lbs, 13 oz w/o cells and 4 lbs, 13 oz with a 7 cell pack.)

What speed? Good question. I pretty much want to find this part out by pushing this motor to its limit, but without going over. I regularly hit 45mph with my e-maxx/9L. I'd love to see 55 w/ my Rustler.

Thanks!

Brian

Okay, use 9-10 cells with a gear ratio 11.8:1 and watch the temp of the esc and your motor. The motor should not go beyond 100 deg. Cels. and the controller would stay cool by using a 12 volt fan. Your 8s will take you beyond 58mph easily at 12 volts, so maybe 9 cells will keep your truck at high speed and under control as well.

Thanks again! I am definitely headed in the right direction now.

Got another question:

What gear ratio should I be aiming for with more conservative cell counts like 6,7, or 8 (for general bashing purposes)?

Should I stick to the 11.8:1 regardless or is that only for 9-10 cells? Is the 11.8:1 the tallest I should attempt regardless of cell count?

I don't mind experimenting to find out, but I'd rather learn from others' experience if it's already been determined what's best for this application.

Thanks again!

brian

lol, 9918 is overkill for ur setup! good luck though! If u wanna get a diff esc, u could always sell me ur 9918! lol

Well, with brushless you can always gear higher, but you can only do that if you are mostly bashing and not racing. Once you notice that the esc is thermalling( does not work or deliver power) you must try things like cooling fans or lower gear ratios to keep the esc and motor in a moderate temp or slightly lower than -very hot- this way you will keep the setup safe and far from wrekage. BTW, the gear ratio that I gave you is a suggestion, but not a recommendation. I'm currently using 9:1 in my T4 with the 9918 and Lehner 1920/8 motor and 11 cells. My gear ratio should be gone a little lower, however.

If you want to hit 55mph, you need A LOT of space and good radio range. Back when my BL controllers weren't burnt up, I was using 4s Lipo (14.8v) on a Feigao 12s motor (so at full throttle the motor was spinning ~40,000RPM). I did many speed runs, and in a space of about 200ft., I got to 56.6mph (this distance included braking distance), and was GPS tested. So, if you want your Rustler to go really fast, you need a huge open area to it in where your radio won't glitch.

With the 8s, you should not exceed 9 cells for bashing. For better efficiency, 8 cells would be best. Whenever you change cell counts, you should change gearing to keep the motor in its good temperature range. To find the best gearing, it is best to just experiment, as differences from Rustler to Rustler can make gearing of one motor could make another motor heat up too much.

Thanks a ton for all the great info!

Today I tried 10 cells at 18/84 (12.7:1) and 20/84 (11.4:1). After several high speed passes at 20/84, the motor was 170F, while the 9918 was 130F.

At 170F, I couldn't keep my finger on the motor, but that's still less than 100C, so that's okay, right? If these temps are okay, does that mean I could possibly go to a higher pinion like 22 or 24T?

With that said, how hot is too hot for the motor and controller? What is a good temperature range to make these things last me a long while?

Thanks!

Brian

Hey kulangflow, how do you like that 9918? Can you post some pics of your setup? I have the 8s too and I am running the MGM 8012.

Josh

I really like the 9918. I've been running it with a 9L in my e-maxx for about a year now. The 9918 has never thermalled or given me any problems. I also have a Schulze 18.97KWF, but it seems to cog a lot more than the 9918, so I'm just going to sell it.

I'll have to come up with some pics.

Word.

No, dont go higher in gearing at all, but try to drop a teeth or two from the pinion and measure the motor and esc heat once again.

pics granted! :-)

http://hondahunter.com/videos/Brian/PDR_1764.JPG

http://hondahunter.com/videos/Brian/PDR_1766.JPG


http://hondahunter.com/videos/Brian/PDR_1767.JPG

Hey, Kulang, these are the Acer Racing battery connectors, right? does it feel any better than the deans connectors.

I've never heard them called Acer before ... usually Anderson or PowerPoles.

I really like them though. I've used Deans for a long time, but I'm converting everything over to PowerPoles. They're much easier for my fat fingers to connect/disconnect.

Also, they're ideal for brushless applications, because you can connect red to black to change cell counts in series without needing a y-harness. Like, for this Rustler, I have an 8 cell pack and a 2 cell pack built for it. When I'm just bashing, I use the 8 cells, and when I want to do a speed run, I can throw the other two in there in mere seconds.

Another great advantage is that they're cheaper than Deans, and you can buy as many as you want in one package. Also, I can solder them on much quicker and don't need to use any heatshrink.

Can you tell that I love these things? :-)

Can you offer me any suggestions on my set-up? Like, should I shorten the blue wires from the controller, or will that make a difference? Can I bend the three hard wires from the motor a little more, or can that cause damage? Also, is there a better way to mount my controller?

Thanks!

Brian

Well, probably shortening the blue wires is a good idea, but honestly, everything looks neat.

PowerPole connectors are the best for me. I use them in all of my applications now. Best part about it for me is that I don't have to solder them :)

How much amps can it tolerate?

It's nearly impossible to get accurate data from either WS Deans or Anderson, but as near as I can find both connectors are actually only rated for 35 Amps. However, we know that Deans can handle more than that.
Alternately, I've seen several references to PowerPoles handling over 60 Amps continuous and up to 200 Amps burst.
Here's a great article to help understand PowerPole connectors:
http://www.flyrc.com/articles/using_powerpole_1.shtml

I have read that Deans are rated at 60amps cont. and much higher in bursts. Powerpoles are good connectors, but they are rather bulky, and crimping the wires on will create higher resistance than soldering.

Not to be argumentative, but a crimped connection has less resistance than a soldered connection, all other things being equal. This is the best way i can describe it:
With a crimped connection, all of the strands of wire either touch each other or touch the connector directly, offering a direct path for the current to travel through.
With a soldered connection, the solder gets between the strands and connector as well as between the strands themselves. This puts a higher resistance substance (solder) between the current and it's destination.
If soldered wire was better, we'd put solder inside short lengths of wire to increase their capacity. Strand-to-strand is a better conductor and, generally speaking, the more strands the better. A soldered wire essentially turns all of the strands into 1 at the connection point.

However, you are correct in that the PowerPoles are larger connectors.

Yes, I have also read that the Deans are rated at 60 Amps. It's just impossible to get information from WS Deans themselves. Their website hasn't been updated in years and none of their products come with spec sheets, so all we have to go on is what other sources say.
As far as PowerPoles, since they aren't specifically designed for R/C use there are many, many people using them for a large amount of different applications. This makes quite a bit of data available about them. Here's a quote from the article I linked earlier: The actual rating for a 30-amp Powerpole is for a 30° Celsius (54° Fahrenheit) temperature rise at 30 amps (and 110 volts) using 12-gauge wire. This temperature rise spec is published in the National Electrical Code for building wiring and is more of a wire gauge rating than it is a connector rating. The power level noted in that standard is 3,300 watts.
I think the 30A rating on the PowerPoles themselves generally makes people think they are weaker connectors than Deans.

Hmmm, at first I thought it was made by acer racing, but it does say it is a powerpole connector. Check this page if you want: www.acerracing.com/connectors.html I also heard that the bullet type connectors like the ones made by Trinity and Orion are capable of handling up to 80 amps cont. The 3.5 mm like the Schulze ones are 50 amps or something like that. Also Chris Fine just imported a new type of bullet connectors that can tolerate up to 200 amps cont. Check it out here: www.finedesignrc.com/motors.asp

So, today I did some GPS testing. Here are the results:

10 GP3300 matched cells

18/84: 35.3 mph
20/84: 38.0 mph
22/84: 40.5 mph

9 GP3300 matched cells

18/84: 31.2 mph
20/84: 34.6 mph
22/84: 36.7 mph

8 GP3300 matched cells

18/84: 27.5 mph
20/84: 31.9 mph
22/84: 33.2 mph

The hottest my motor ever got was 115 F, and the hottest the controller ever got was 91.9 F (This was on 8 cells at 22/84).

What do I need to do to get to that 58mph you mentioned? Are these gear ratios correct?

18/84 = 12.69:1
20/84 = 11.42:1
22/84 = 10.39:1

I'm thinking that I'm gearing it way too low.

What do you all think?

Thanks ....

Sounds like your undergeared. 10 cells on the 8s should in theory fly. I run 8 cells on my 6s and it'll fly faster than any of the speeds you've posted with the right gearing. Your setup should rev the same as mine on 10 cells, but have more torque.

I have no experience with the rustler, but in theory, you need to run 25/84 (assuming normal 3.5" diamater tyres, adjust accordingly if your tyre sizes are different) giving a ratio of 9.14 and approx 55mph.

You should use something closer to 26/84! A 22t pinion just isn't big enough if you want a lot of speed! Also, if your slipper clutch pegs are worn down, replace those.

More like a 30 tooth pinion or higher. The max efficiency at that voltage occurs at over 80 amps!

Wow, those sound pretty slow. I gps tested my Lehner 4200 on 6 matched cells in my stampede reached 39.6mph. It was geared 18/84 I believe. I have the 8s too now. Maybe it just doesn't have it. I've been disappointed so far as well. I'm thinking of gps testing mine on Sunday.

Hmm. As the others suggested, go for higher gearing and replace any worn out slippers and fully tighten your diff.

Right on ... thanks for all the help!

I'll try 24, 26, 27, and 28 tooth pinions sequentially while watching the temps of everything, then I'll report back to let you all know what happens.

It might be awhile though, 'cause my Integy 16x4 Pro went up in smoke again for no apparent reason. It worked perfectly for 6+ months, and now it's smoked twice in the past two weeks. I wish it didn't take so long to get it fixed, although mostly it's time spent in travel to and from Integy.

Word.

you could get the Power polese which are 45 amp rated from robotcombat, since I had a whole bunch of the black and red covers.. I decided just to order the contacts....

the pole conectors 15 amps, 30 amps, and 45 amps both use the same housing.... And I do agree taht deans are good for 80 amps... but the solder is the week part... my Crimped 45 amp power pole stays cooler than my soldered Deans 80 amps...

So the batfish is correct, the solder is the week part.. well.. that's my opinion.. :)

These are the 5.5mm plugs from BK. I carry these as well-not a new product, actually.

does the 5.5mm gold plugs have a housing?...

No, they are just regular gold connectors. To keep them from shorting out, you can use heat shrink tubing.

I wouldn't trust myself... with my luck, I'd probably short it out.. .I fried an 18.149 like that..

That's why you would use heat shrink tubing to cover the exposed plugs :).

Yeah, I guess so.. but I was using power poles.. and I put the black in the red housing.. I'm glad it was only a $50 repair...