Sanity check my upgrade plan

[Theutrich]

Thanks, yeah I get the theory that kv is the back emf in volts of a motor at an rpm if used as a dynamo, and as such is the theoretical output rpm when a volt is applied with zero load. And that kt (torque) is the inverse of kv for a given motor constant km. It seems like it's basically an "electrical gearing" (where you are trading speed for torque) before actually getting to physical gears, which then can further exchange speed for torque. I just don't have experience with how the actual numbers (2850kv, 2280kv) anchor them to relative performance.

In theory whatever kv I pick, I could adjust the speed/torque with gearing. But in reality pinions can only get so small, and spurs can only get so big while fitting in a gearbox. I'd hate to get too fast of a motor and be forced to put the smallest pinion possible and the biggest spur possible for decent lowspeed control -- and then have no wiggle room, or worse, just run out of gear range and it's still too fast. I'd rather have a motor speed that gives me some wiggle room to gear in either direction until I like it. Since there's a lot more room to gear up than down, I think I should err on the low-kv side, if that makes sense?

For that thought process, I'm looking at the castle 1406-2280kv motor. (I would get a puller pro, but castle is out of stock on everything so I have to get the mamba x through amazon and amazon only sells them paired with castle motors) Since I have no experience with these motors, or for that matter adjusting gears, I hope the 2280kv isn't too fast and I end up wishing I went with the 1900kv. I just worry that's TOO slow. It's a very scientific guess of, "slow but not the slowest thing there is, so second slowest".

 

[DRED805]

I went with similar logic, and decided on the 2850kv, but I also got a 9t pinion. I can let you know how slow that is in a few days when my driveshafts show up.

 

[23drumerboy]

Thanks, yeah I get the theory that kv is the back emf in volts of a motor at an rpm if used as a dynamo, and as such is the theoretical output rpm when a volt is applied with zero load. And that kt (torque) is the inverse of kv for a given motor constant km. It seems like it's basically an "electrical gearing" (where you are trading speed for torque) before actually getting to physical gears, which then can further exchange speed for torque. I just don't have experience with how the actual numbers (2850kv, 2280kv) anchor them to relative performance.

In theory whatever kv I pick, I could adjust the speed/torque with gearing. But in reality pinions can only get so small, and spurs can only get so big while fitting in a gearbox. I'd hate to get too fast of a motor and be forced to put the smallest pinion possible and the biggest spur possible for decent lowspeed control -- and then have no wiggle room, or worse, just run out of gear range and it's still too fast. I'd rather have a motor speed that gives me some wiggle room to gear in either direction until I like it. Since there's a lot more room to gear up than down, I think I should err on the low-kv side, if that makes sense?

For that thought process, I'm looking at the castle 1406-2280kv motor. (I would get a puller pro, but castle is out of stock on everything so I have to get the mamba x through amazon and amazon only sells them paired with castle motors) Since I have no experience with these motors, or for that matter adjusting gears, I hope the 2280kv isn't too fast and I end up wishing I went with the 1900kv. I just worry that's TOO slow. It's a very scientific guess of, "slow but not the slowest thing there is, so second slowest".

My only suggestion in the case you present....is order two separate motors of differing kv ratings (one-2200kv, and one-1200kv (or as low your experiment will want to go, ))and i believe even the tallest-geared rigs with some 800kv will have you endo-ing to your heart's content! If you ran a solid 12+lb rig, may be different story??

Read-Up! Mod-On! Crawl EXCESSIVELY!

 

[lonleycreeper]

To give you an Idea of what 2200Kv is able to do...

https://youtu.be/mA3ojsPYApc

The Ryft comes with 2200kv motor and is geared high giving it a lot of wheelspeed... aka 35 ish mph on 3s...

 

[Theutrich]

Appreciate all the input!
I went forward with the mamba x + 1406-2280kv. I'm going to experiment with the gears.

I went with similar logic, and decided on the 2850kv, but I also got a 9t pinion. I can let you know how slow that is in a few days when my driveshafts show up.

Thanks, I'd be interested in your results. I'll try to follow up on mine with the 2280 for comparison

 

[Steve g]

I'm a little late here, but I'll still say my experiences. I've got 3 wraiths, all decked out and I do technical crawling, hill climbing/rock bouncing (like the ryft is designed to do), and "bashing" in the woods. I've tried almost every motor I could fit in there. Currently using a castle 1410 3800kv in one, a HH puller pro 3500kv in another, and a castle 1415 2400kv in another (my 7yr olds). All on 4s most of the time. I like the higher kv for the simple fact of being able to gear down lower then stock, and still have a nice top speed. Gearing down a higher kv motor gives you better low speed control and stronger drag brake then a lower kv motor with higher gearing to match the top end. Now this can have some exceptions, such as say a cheap generic motor verses an actual crawler motor, and a 10th scale size motor vs an 8th scale sized one. For instance, the 1415 motor, though still 10th scale, is a 3670 motor, meaning 36mm diameter with a 70mm length. Normal motors in a crawler is about 48 to 50mm long (same 36mm diameter). It's only 2400kv, but even geared up higher then my other trucks to match the top speed, it has just as good drag brake (maybe even better then the 3800kv one), and can creep just as slow too. I initially got a HH 2200kv motor for that particular rig to keep it a little more mellow for my at the time 6yr old. It crawled great, but no top end. Geared it up, and it just felt soggy. So I got a larger motor. Night and day difference. I'm rambling here. Sorry. Honestly you'll be happy with your motor choice, it will be more then enough to tear the truck apart...
Couple pointers here: you can run a 60t spur with the cover on. You have to shave the indentation where the driveshaft is. I fit a 62t with the cover on, with some more fiddling. It's also a good idea to run underdrive in at least the rear axle, or both. Helps with torque twist and in theory lowers torque on the driveshafts and transmission, resulting in a longer lasting driveline. Most just run it in the rear to help with crawling up hill,, but if you find yourself wanting to cruise around at higher then crawler speeds, it's a pain to hold a straight line. Oh look, rambling again.

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[Theutrich]

Interesting. I was considering the 1415s, but i measured my current motor (maybe wrongly?) at 57mm and with almost no room behind it because of the plastic stick up part on the skid plate that the axle link hooks onto is right there. Did you have to move/replace your transmission or otherwise modify the skidplate for a 70mm motor?

BTW what are these 1406,1410,1415 numbers? Are they castle part numbers?

I'm glad to know that with the mamba x I have enough ESC to experiment with different motors later.

 

[DRED805]

I have the 2400kv 1415 in my Rock Rey, and I can barely use it because it's constantly grenading driveshafts and differentials. It's one hell of a motor, but I thought it'd be way overkill for my wraith build. That's with zero wraith experience yet, though.

 

[Steve g]

Yeah to fit the 1415, I moved the transmission over and forward just a little. Helped shift the weight more centered too. The caslte numbers describe the rotor size. So 1406, 14mm tall 6mm long. 1415, 14 tall 15 long. It's been a long time since I thought of all this, so could be off there.
Dred, it's definitely overkill, especially if it's in a stock wraith. In reality, any brushless motor is overkill for a stock wraith. One of my first aftermarket motors way back when was a titan 24t 550 brushed motor. (Traxxas used to use 24t motors in their boats). Made my own 9 pack nihms, and that started to grenade parts.

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[Voodoobrew]

If it's too slow just up the voltage

 

[kellewriter]

Very interesting article. Appreciate all the input!

Essaypro​

 

[Steve g]

If it's too slow just up the voltage

Maybe you missed it, but he did mention buying a 4s for it. Should be plenty fast. But hey 6s would be interesting

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[Voodoobrew]

I ran my 2200kv puller pro 2200kv on 6s in my 2 speed trx4 on 6s. Way too much speed for me even with a 9t pinion. Did wheelies no problem, it wore off the hitch in just a few minutes. https://www.youtube.com/watch?v=dBbw8J0ZSnY

 

[Steve g]

Hmm, shoulda tried my 2200kv on 6s then.
More pointers for the OP:
The pinion bearings on these don't last long long, and if not caught in time will destroy the gears. Vanquish sells a housing for 85 bucks that comes with a larger bearing with it, but again hard to find. I took the stock plastic housing, dremmeled it out to fit a 5x16x5 bearing, part # 625zz (it's actually a high speed motor bearing) stock size is 5x11x4. I only changed in inner one (just like the vanquish one). I'm pretty sure the one I used is even bigger then the vanquish one. I did have to grind down some of the collar of the pinion gear shaft for the wider bearing. I'll include a picture of the pinion gear and larger bearing compared to stock size down below.
Another good idea is to add beef tubes. I used steel as I wanted the strength but not much more weight (they sell brass ones for aswell) the beef tubes make them more rigid, as well as having metal threads for the C hubs and lockouts. I also was able to add an additional bearing (5×11×4) at the end of the beef tube before installing the lockout. I'll include a pic of that too.

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