RCCrawler Forums

RNUOVR · 10-15-2011, 11:23 AM

I am looking to swap out the sensorless motor I have in my scaler for a sensored motor. I have decided I am going to go with a tekin redline (as I've always run all tekin setups in my race trucks as well as the scaler currently has a Tekin RS esc in it) & I was planning on also swapping to a bigger rotor. Right now I'm running a holmes crawlmaster 0n 87/15 gearing on 3s and I find it a little quick for smooth crawling. Plus the clogging makes it a little challenging sometimes.
As I have limited experience with 3s/brushless I am not sure if the 17.5 or 21.5 is more comparable to the crawlmaster I have right now. Wondering if the 21.5 on 3s would give me the throttle "snap" when I need it or if the 17.5 would better suit what I ma looking for.

Charlie-III · 10-15-2011, 04:17 PM

I don't know the equivilant KV rating of the HH motor (I'm will to bet it's on his site) but the lower the KV usually the better for a crawler.

Since it spins slower, you have to gear it up for the speed, this usually gets it into a better operating RPM to reduce the "cogging" that sensorless brushless motors can exhibit.

Sensored is better than sensorless, but the lower KV rating still has a bearing in crawling.

skid · 10-15-2011, 06:32 PM

If you're set on a bigger rotor, I would go for the 17.5. The bigger rotor will tone it down some while adding torque. But the 21.5 is no slouch either, especially when you start playing with the timing advance and boost.
For ultimate low end, 21.5 with the big rotor at a slight sacrifice of top end speed.

RNUOVR · 10-16-2011, 09:19 AM

I know that the kv rating on my current holmes motor is 1000kv and the 21.5 tekin is 2100kv. I know that it can also get a good deal on a comparable 21.5t novak ss motor at 1800kv. Knowing hte the lower the kv number the better, but again pardon my ignorance with electric motors but I am not sure how much of an actual difference those higher kv numbers on the sensored motors would have an end effect in my rig...would it really be that noticable?
I will give up top end for more low end control...even though I am a speed guy I'm really loving the low speed technical crawling right now with my scaler...anyone can get through something with power and wheel speed, it just looks so much better when it's done slower

PowerCrazy · 10-16-2011, 11:26 AM

My advice is to do the 17.5 if you are using 3s ore 21.5 for 4s. I had the 21.5 or 4s and it was pretty awesome. I would get the mmp esc though. I played with the advance timing at high rpms and whatnot and you can get some rediculas snap when you want it for jumping gaps or high wheel speed

10-15-2011, 11:23 AM	#1
RNUOVR Rock Stacker Join Date: Jul 2011 Location: Ottawa, Canada Posts: 90	21.5 vs 17.5 brushless motor - which size? I am looking to swap out the sensorless motor I have in my scaler for a sensored motor. I have decided I am going to go with a tekin redline (as I've always run all tekin setups in my race trucks as well as the scaler currently has a Tekin RS esc in it) & I was planning on also swapping to a bigger rotor. Right now I'm running a holmes crawlmaster 0n 87/15 gearing on 3s and I find it a little quick for smooth crawling. Plus the clogging makes it a little challenging sometimes. As I have limited experience with 3s/brushless I am not sure if the 17.5 or 21.5 is more comparable to the crawlmaster I have right now. Wondering if the 21.5 on 3s would give me the throttle "snap" when I need it or if the 17.5 would better suit what I ma looking for. Last edited by RNUOVR; 10-15-2011 at 11:33 AM.

10-15-2011, 04:17 PM	#2
Charlie-III I wanna be Dave Join Date: Nov 2010 Location: 07456 N. NJ USofA Posts: 8,314	I don't know the equivilant KV rating of the HH motor (I'm will to bet it's on his site) but the lower the KV usually the better for a crawler. Since it spins slower, you have to gear it up for the speed, this usually gets it into a better operating RPM to reduce the "cogging" that sensorless brushless motors can exhibit. Sensored is better than sensorless, but the lower KV rating still has a bearing in crawling. Last edited by Charlie-III; 10-15-2011 at 07:39 PM. Reason: added a missing word...

10-15-2011, 06:32 PM	#3
skid Rock Crawler Join Date: Nov 2004 Location: in a basement in Kalispell, MT Posts: 857	If you're set on a bigger rotor, I would go for the 17.5. The bigger rotor will tone it down some while adding torque. But the 21.5 is no slouch either, especially when you start playing with the timing advance and boost. For ultimate low end, 21.5 with the big rotor at a slight sacrifice of top end speed.

10-16-2011, 09:19 AM	#4
RNUOVR Rock Stacker Join Date: Jul 2011 Location: Ottawa, Canada Posts: 90	I know that the kv rating on my current holmes motor is 1000kv and the 21.5 tekin is 2100kv. I know that it can also get a good deal on a comparable 21.5t novak ss motor at 1800kv. Knowing hte the lower the kv number the better, but again pardon my ignorance with electric motors but I am not sure how much of an actual difference those higher kv numbers on the sensored motors would have an end effect in my rig...would it really be that noticable? I will give up top end for more low end control...even though I am a speed guy I'm really loving the low speed technical crawling right now with my scaler...anyone can get through something with power and wheel speed, it just looks so much better when it's done slower

10-16-2011, 11:26 AM	#5
PowerCrazy Quarry Creeper Join Date: Apr 2011 Location: United States Posts: 226	My advice is to do the 17.5 if you are using 3s ore 21.5 for 4s. I had the 21.5 or 4s and it was pretty awesome. I would get the mmp esc though. I played with the advance timing at high rpms and whatnot and you can get some rediculas snap when you want it for jumping gaps or high wheel speed

Sponsored Links

RCCrawler Forums

Thread: 21.5 vs 17.5 brushless motor - which size?