Puller Build - Gen7 Pro Slider

[TheseusOfTroezen]

I'm going to be building a scale pulling truck based on the Gen7 Pro. Currently have a slider and a few parts en route, and I'm going to be using thread to share the build.

RC pulling isn't super popular, so finding info on what works and what doesn't has been and will continue to be somewhat difficult. But that means there will be lots of testing, trial and error, and breaking/rebuilding. Which is honestly half the fun!

GOALS:

• Be competitive in the NRCTPA Dirt Crawler Class
  
• Make it "dual duty" (i.e. still able to crawl well enough to have some casual fun, with minimal changes)
  
• Keep within a somewhat reasonable budget...no set number specifically I'm just trying not to go too crazy.

CLASS RULES:
NRCTPA Dirt Crawler Class

• Motor: Brushed or Brushless
• Chassis: Any 1/10th scale 4WD crawler/scaler kit
• Battery: 2s Lipo
• Weight: 8lbs Max
• Hitch: At the frame rail or below
• Suspension: Must be funtional suspension on all 4 corners
• Tires: Must be street or trail type, no agricultural or V tread tractor tires
• Other: All weights must be under body

Parts on Order

• Redcat Gen7 Pro Slider - from eBay
• Redcat Steel Transmission Gears
• Aluminum drive shafts (probably should have gone with steel, we will see)
• Aluminum C Hubs
• Aluminum Steering Knuckles
• Castle Copperhead 10 ESC
• Castle 1406 5700kv motor (supposedly wheel speed is king when pulling! Planning to gear down from stock 18t pinion to 12t to start out)

Parts still needed/researching

• Upgraded diff gears, do they even exist? (want to make the drivetrain as bullet proof as possible)
• Servo, probably going with a cheapy high torque ecopower or something similar
• Tires (still need to research, looks like local pulling track is pretty hard packed)
• Wheels
• Body
• Pinion gears (12t-18t)

 

[ferp420]

i would swap out those axles and trans asap they wont hold up to the abuse your gona put them trough
ar44s or portals would be the way to go the lower the gearing the better for a puller
the gears wont be your week point though that will be the axle shafts and the drive shaft needs to be steel the tangs on the aluminum ware real fast with a big load

for motor brushless would be best just cause they handle the heat better and again the lower your gearing the better and i wouldent go above 3500kv no torque on the low end and someware around a 10t pinion

other than that i think your good lol

 

[Steve g]

Higher kv the better. Can gear down lower and have more power

Sent from my SM-G970U using Tapatalk

 

[ferp420]

to pull you need torque not horse power
spining tires dont get alot of traction and when pulling a sled your not gona go vary fast so wheel speed is worthless
and you can only gear down so much so if the kv is to high you wont be able to gear down enuff to get to the torque
personaly if i was building a sled puller i would use a big outrunner but being limited to 2s makes the choices that much harder

 

[TheseusOfTroezen]

i would swap out those axles and trans asap they wont hold up to the abuse your gona put them trough
ar44s or portals would be the way to go the lower the gearing the better for a puller
the gears wont be your week point though that will be the axle shafts and the drive shaft needs to be steel the tangs on the aluminum ware real fast with a big load

for motor brushless would be best just cause they handle the heat better and again the lower your gearing the better and i wouldent go above 3500kv no torque on the low end and someware around a 10t pinion

other than that i think your good lol

to pull you need torque not horse power
spining tires dont get alot of traction and when pulling a sled your not gona go vary fast so wheel speed is worthless
and you can only gear down so much so if the kv is to high you wont be able to gear down enuff to get to the torque
personaly if i was building a sled puller i would use a big outrunner but being limited to 2s makes the choices that much harder

I appreciate the input, but from the research I've done this seems to not be the case. Most rc pulllers are running relatively high kv motors, and wheel speed is king.
I've also spent a good amount of time at 1:1 pulling events and used to be close to one of the teams. Wheel speed is king there as well.
I'm not saying to send the wheel speed to the moon, but they definitely aren't sitting there with their tires barely spinning as you implied was best....



I plan to gear down to a 12t pinion (from 18t). I also plan to run 4.1" tires which is equivalent to another 12-13% gear down when compared to 4.7" tires. This combined with a 5700kv motor should be a good starting point from what I've read.

I could be wrong but this is where my research has lead me. I'll be testing, making changes, and testing some more. And will definitely keep this post updated with results. So we will see what the outcome is!

 

[ferp420]

tires need to be in contact with the ground to get traction end of story you want to put a 100mph motor in your rig thats fine but it aint gona pull

my 1450kv outrunner has enuff torque to snap axle shafts on 2s with a 11t pinion why the hay would you want 5700kv
with 5700kv crawling is out of the picture you will fry that motor that is if you can keep from snaping axle shafts left and right
i have 3 gen7 axles here from one of the guys i built rigs for we.tryed everything to get those axles to hold.up to a brushed motor on 3s had to swap to axial axles even the og scx10 that the gen7 is cloned after had week axle shafts so there are no posable way to get a stronger axle shaft for that axle

 

[TheseusOfTroezen]

tires need to be in contact with the ground to get traction end of story you want to put a 100mph motor in your rig thats fine but it aint gona pull

Tires will be firmly in contact with the ground. Wheel speed is going to be higher than ground speed, but that's what you want, from what I've gathered. Go watch any rc pulling event, or even 1:1 pulling, guys with wheel speed higher than their ground speed are making it farther than guys with wheel speed at or near their ground speed.

Let's do a little napkin math:
2s lipo max voltage = 8.4v
5700kv motor max RPM would then be 47,880 (I know motors don't 100% follow this rule of thumb, back emf and all that, but let's roll with it)
With a 12t pinion total drivetrain gearing ratio is 56.16:1
That's a max wheel rpm of 852.
With a 4.1" tire that's 10.4mph

10.4mph wheel speed doesn't seem all that unreasonable to me. Ground speed will undoubtedly be slower, but like I've said pullers that are actually doing well have wheel speeds faster than their ground speed, by a decent amount.

And this is all without a load. Add a load and rpm will come down some. To what exactly? Not sure, but I will be able to log motor rpm with the ESC I have and will be able to extrapolate to wheel speed.

Also I plan to run a different motor for crawling, probably in the 2200kv range, but that's still TBD.

Shoot, now that I'm thinking about it, I can run both the low kv "crawling" motor and the high kv "pulling" motor and we can see what will work best. I'll report back when that happens! Should be some good data.

my 1450kv outrunner has enuff torque to snap axle shafts on 2s with a 11t pinion why the hay would you want 5700kv
with 5700kv crawling is out of the picture you will fry that motor that is if you can keep from snaping axle shafts left and right
i have 3 gen7 axles here from one of the guys i built rigs for we.tryed everything to get those axles to hold.up to a brushed motor on 3s had to swap to axial axles even the og scx10 that the gen7 is cloned after had week axle shafts so there are no posable way to get a stronger axle shaft for that axle

I'm guessing you're snapping axles when you're in a bind and are trying to get out of it?

 

[ferp420]

nope

 

[ferp420]

snaped one climbing a small snow mound with the wheels mostly straight thats how bad they are

 

[ferp420]

the first rule of older redcat cralwers is dont over power them and like i sead even the axial vertion redcat copyed isent much stronger

 

[TheseusOfTroezen]

the first rule of older redcat cralwers is dont over power them and like i sead even the axial vertion redcat copyed isent much stronger

I'll keep that in mind! Will have spares at the ready and if it does prove to be a problem then I'll axle swap it.

 

[TheseusOfTroezen]

Parts have arrived!

 

[high plains drifter]

So cool! Looking fwd to seeing this come to life.

 

[Goro Majima]

Sounds like a fun build. Sub'd.

 

[ScaleLifeNewbie]

This outta be awesome, I’ll be sticking around to watch it unfold!