Running a brushless set-up on the LRM

[pmathews924]

How much is too much for the LRM gears, and how much do I need to be competitive? I have a slipper so I can control some of the power going to the gears, but I've been reading some horror stories about newer brushless systems melting older plastic gears. I know that you can roughly estimate RPMs by taking your motor KV x battery voltage (example: 7.4v LiPo battery x 1900 KV motor = approx. 14,060 RPM)

I'm going to start out with a 17.5t stock set-up...probably one of these three because of the price...anyone running a brushless set-up in their old Losi? Insight appreciated...

Speed Passion - $100
http://www.amainhobbies.com/product_info.php/cPath/1_221_911_1949_2930_2931_2935/products_id/248309/n/Speed-Passion-Reventon-Stock-Club-Race-ESC-V30-Motor-Combo-Fixed-Timing-175R

Novak - $119
http://www.amainhobbies.com/product_info.php/cPath/1_221_911_1949_2930_2931_2935/products_id/225313/n/Novak-Club-Spec-Brushless-ESC-Club-Brushless-Motor-Combo-175T

HobbyWing - $119
http://www.hobbypartz.com/07e-combo-js5.html

Slowly but surely I'm getting caught up on all this new tech...2 months ago I'd never heard of 4000mAh LiPo batteries, 2.2" wheels, low voltage cutoffs, and brushless motors...lol.

[dldiaz]

I use the Novak Club Sensored 17.5T setup,
exactly like the one you referenced above,
in a 5-link JRX-2 with a stock LRM transmission.

((I got it through Tower for $109))

I am very happy with the setup.
It's not super fast, but it has good torque and is extremely smooth, hassle-free. My only minor complaint would be the lack of reverse. You have to step up to the "Edge 2S" ($159) to get reverse.

[knixdad]

I got a Novak SS5800 back when it was first released and I found out very quickly that it could totally destroy the tranny if you didn't set the slipper right or had the diff too loose.

I melted at least 2 diff gears and chipped the teeth off an idler or two. I traced part of it back to a previously undetected crack in the tranny case but there was also the brutal power on tap from that early brushless system.

But if your slipper is too tight or the diff is too loose and you have good traction, it won't last too long.

[FasterLouder]

The most power I've put through a JRX2 with the LRM tranny was an Orion 5.5 turn,it handled it no problem...With no slipper!
The case and gears were used,but in good condition and I rebuilt the diff beforehand,too.
Gil Losi Jr. has a masters degree in plastics and injection moulding,I've always found Losi trannys to be the best around.

[knixdad]

My big problem was the ball diff slipping. The throttle on the early Super Sport had no tip in or ramping. So if you pinned it, it just opened the floodgates.

Once I straightened out the diff I was fine. You are correct, the tranny can take a lot of abuse.

[pmathews924]

Right on...I think I'm gonna get my feet wet with that Speed Passion, and if I feel like going bigger the ESC that comes with it handles up to a 9.5t brushless. Here's another question I thought of...

If your RPM formula is motor KV x battery voltage, is it the rating of the battery, or the voltage reading when it's fully charged?

7.4v rating x 2200kv = 16280rpm
8.4v reading x 2200kv = 18480rpm

That would be the rpm range I'd be running through the tranny, so either way I think from what y'all are saying the LRM will handle that. Probably gear it around 86/20 (4.30) to start and gradually dial in the slipper. If it fails I've got a handful of spare diff gears and a lot of time on my hands, lol.

[matt1ptkn]

I've had a Venom brushless system on my Jrx-T with the stock LRM transmission and race carpet oval with it. I cleaned the teeth off one diff gear from braking too hard and too often, but my bigger problem is with the driveshafts. They kept twisting off the universal joints. I was running the stock gray plastic ones and recently changed to the white super sliders. I'm hoping that helps. Just my couple cents to add.

[knixdad]

I've had a Venom brushless system on my Jrx-T with the stock LRM transmission and race carpet oval with it. I cleaned the teeth off one diff gear from braking too hard and too often, but my bigger problem is with the driveshafts. They kept twisting off the universal joints. I was running the stock gray plastic ones and recently changed to the white super sliders. I'm hoping that helps. Just my couple cents to add.

That's a thought as well, all my brushless runners have MIP CVDs, so I never ran into that.

[DerbyDan]

My LRM equipped JRX2 runner has done half a dozen or so meetings now (+ some general fun running between heats) with no gearbox issues so far with an Orion 8.5 brushless on an an old LRP Sphere TC spec ESC. I am running a twin disc slipper which I think is a 'must' - not so much to save the gearbox but to stop the thing from pulling wheelies!

The only issue i've had so far is with the old roll pins in the driveshaft joints gradually working themselves out - I first noticed when one partially fell out & chewed up the outdrive from the gearbox... so now i'm keeping an eye on all the others after each race. When I replaced the output I quickly took the gearbox apart & inspected it & all seemed OK

[DerbyDan]

Ohh & I forgot to say that i've been running it on high grip Astroturf - which must be the worst surface for drivetrain shock & wear?

[pmathews924]

Right on...thanks for all the input.

I ended up going with the Speed Passion Reventon Pro ESC with a 17.5r Speed Passion Competition motor. It's a pretty mild brushless set-up from what I understand and not many people run that motor, but I guess the ESC is one of the better ones out there. Everything else I found in that price range had a turn limit that wouldn't allow me to upgrade later, didn't have reverse, didn't come with a program card, etc. This unit has an intercooler and fan so it's advertised as running 20% cooler than previous models (common issue with the reventon R and reventon S).

http://www.rcmart.com/reventon-brushless-with-free-competition-motor-175r-shipping-p-36868.html?cPath=1100_1252

Best part...RC Mart was having a fire sale on them so I picked it up for $125 shipped. Only crappy part of this deal is that it's coming from Hong Kong so I have to wait, and wait, and wait. Their emails have said shipping can take "7-30 days" and they're all written in broken English so I'm not really sure when it's gonna show. I read the sensor cable is too short so I tried to order another one through them, but when I tacked it onto my order it added shipping charges so I decided I'll just buy that locally if I need to.

One thing I'm not really understanding...if all of these brushless set-ups make your car so fast off the line it's uncontrollable, why would people think there's such a difference what motor you run? If you have enough torque to make it do a wheel stand, then to me, the key factor would be more about your car's handling and your ability to dial in the transmission...at least on the course I'm going to race it would be...longest straight is about 25-30ft.

[knixdad]

Slipper and Punch Control. And your own trigger finger. Sure you can set it up to do a backflip but you tweak the throttle profile so you get a nice ramp up to full power.

[pmathews924]

That's what I'm thinking...if all brushless setups can reach a level where the car lifts or flips, between the ESC adjustments, slipper adjustments, and transmitter adjustments you should be able to tune your car to a point where it has the maximum desired power for the track.

Dial it in and take as much trigger finger/human error out of the equation as possible, so if you get a little excited coming out of a turn you won't be waiting on a marshal to flip you back over.

[knixdad]

Exactly. I have my XXX-SCT setup so that it almost has "turbo lag" to keep me from breaking loose the rear if I pin it. It's very slight but it helps with how I tend to drive it.

[highwayracer]

The problem with the LRM is the case. Check the part where the top shaft exits the gearbox. The bearing seat will eventually wear out causing some play between the pinion and spur. As you compensate by bringing the pinion closer to the spur, the space between the top gear and diff gear becomes greater. Eventually, it will cause this the gears to skip..and grind.

This even happens when running stock motors...so running a hotter motor will make this failure occur quicker.