Outcast 8s Slower with Spectrum 5687 than stock

[Gelatocat]

Hi fellas,

I have had the Outcast 8S RTR for about a year, but don't post much because I have been with RC since 1983, so I generally know what I'm doing. But I'm stumped right now. I had been running the Outcast with Stock 1250kv motor with a 25t pinion, and it screamed, with plenty of speed and torque. In pursuit of more performance, I swapped out the stock motor for a Spektrum 5687, which I gather is the same as the Hobbywing 5687. I swapped the 25t pinion for a 34T pinion to increase top speed. I put Duratrax Bandito belted road tires on it for tarmac. With Zee 60c 4s batteries it went from being a screamer to being a slow, non torquey truck. Also the brakes now have no resolution and it goes immediately into reverse. In other words, the truck just stops dead when I braked. I ran just a few passes in the street and motor wasn't hot. Did I use too big a pinion for that motor. Any help would be much appreciated.

Just picked up a Limitless when it was on sale recently. I have a Castle X8S and 1717-1650kv motor so that's my next project. Also have an Infraction 6s.

Jonathan

 

[jkflow]

Spektrum 5687 is 1100kV, which is 'slower' but that isn't your problem.
You have 2 major issues and a maybe. I'm surprised you haven't blown anything up.
a) You need to immediately remove the deans connectors and throw them in the garbage. Those are 60A connectors, and are be consistently in the 100+A range. Nothing less than EC5 and those are already stressed.
b) Jumping to a 34T pinion is a huge jump with a huge jump in current, i.e. back to a) and you are killing your rig.
c) The 60C Zeee might not be up to the task on this motor.

 

[Roy-187]

I think the batteries are too low c-rating, for a truck this weight and size 100c is the absolute minimum in my opinion.

Also the deans connectors.......

 

[Gelatocat]

Hi JKflow and Roy,

Thanks for your feedback about my Outcast 8s build. Regarding the Deans connectors, believe me, I know that the plugs offered these days can pass more current and may also provide a more secure, positive/reliable connection. But, I'm an old guy with 7-8 RC cars from the past 10 years (and another 10 that are shelf queens) that I still run on occasion, and Deans used to be the plug of choice--replacing the antiquated Tamiya plugs. That said, I have never had a problem with them when soldered correctly. That includes a highly upgraded, 8s 1/7 Axial Yeti XL. With all heavy aluminum parts, the original huge Castle XLX ESC and a big Leopard motor geared for speed. They never heat up, short, etc. And my batteries all have Deans on them. That said, for my Limitless build, I will definitely use the latest plugs. And I may switch them out.

On the 34t pinion, I installed it for speed runs on asphalt with belted on-road tires. I would not use it to run in grass or any conditions that would increase current draw. I ran it yesterday, zipping up and down the street. After 6-7 min of running, the motor hit 150 degrees. That was with no heatsink or fan (on order). The truck was flying, and still had enough torque for a pseudo-wheelie. That said, there was an occasional pause here and there, which was likely the batteries low-volting. I probably do need 100c batteries.

I previously ran a 25/47 with the stock Spektrum 1250kv motor and it was great. How many teeth do you think would you guys think would be idea with the 5687 1100kv, for a mix of speed/torque.

Many thanks.

JC

 

[jkflow]

On road or off-road?
All depends on surface and tire diameter.
Let the temperature of the motor be your guide. 150F is about as hot as you want to get i.e. with fans the 34T should be fine for on road.
Off-road (gras), drop about 4-6T and see how that goes.
My guess would be that your ESC will heat up as well.

 

[stevenwm]

Arrma recommends at least 100c rated batteries for the 5th scales

I know that’s not the real issue here
But just wanted to mention that

 

[LTErene10$]

Gearing it to a 39 spur 25 pinion will wake it up. Battery’s are a big deal also. Ec5 connectors minimum