Notices
1/16th, 1/18th, Mini & Micro RC Cars Discuss 1/16, 1/18, Minis, Micros & any RC Cars smaller than 1/10th scale in this forum

Brushless motor questions...

Old 08-02-2011, 11:28 AM
  #1  
JustHover
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: Pekin, IL
Posts: 23
Likes: 0
Received 0 Likes on 0 Posts
Default Brushless motor questions...

I know there is a place for robotics specific questions, however this is an unusual request, even for robots... I know there are folks here who use CC brushless motor controllers...

I'm wanting to use a couple 1/18th scale brushless motors for a differentially steered mini sumo robot. I'm looking at the CC Mamba Micro Pro or the Sidewinder Micro. I need the forward and reverse to be symmetrical, and I'd like the thing to break when not commanded forward or reverse. The problem is I don't want to drop a couple hundred just to test the feasibility. They tell me everything is adjustable, but I can't see through the hype for the information I really need. I even wrote Castle Creations support but they blew me off. Anyone who has experience with these motor controllers wanna help a guy out?

I also see they package these controllers with motors. They have 4200kv, 5400kv, 6800kv 8000kv motors. Which to choose? Run times are very short, 3 minutes. I want the most torque possible and will need to make gearboxes to get the rpm's down to usable levels, around 750 to 1000.
Old 08-02-2011, 01:07 PM
  #2  
thehuntingterminator
Senior Member
 
Join Date: Jul 2010
Location: Tyler TX
Posts: 3,549
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Brushless motor questions...

for that braking under no power, you need a drag brake that is used on crawlers.
Old 08-02-2011, 05:37 PM
  #3  
BigTb17
Senior Member
 
Join Date: Feb 2008
Location: Perrysburg, OH
Posts: 1,167
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Brushless motor questions...

The KV option you go with will depend partly on what voltage you are going to run, but since you only need 750-1000RPM you would probably be best with the lowest KV. A lower KV motor will draw less power for a given voltage input and torque output.

The Castle micro controllers have a drag brake setting, which will automatically apply a braking effect at zero throttle input. Just make sure you get the Castle Link so you can access the full programming options.
Old 08-03-2011, 06:55 AM
  #4  
JustHover
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: Pekin, IL
Posts: 23
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Brushless motor questions...

Hi thanks for the feedback. While I waited for a response I found the Mongoose Micro 1/18 BL System 8.5T (9000kv). It's cheaper than the CC options and it has a robot mode which has the symmetrical response if forward and reverse. And it does not require a programmer. Because in robot sumo we need speed and torque, my idea was to use the higher kv motor and gear it down for the optimum rpm. That would give me the most power available for the weight of the system. I will be using 11.1vdc lipos.

I'm totally fine with borrowing parts from RC cars. I like Losi stuff. Anyone happen to know the gear reductions available in these small RC cars, or the rpm of the above system at the motors shaft?
Old 08-03-2011, 07:28 AM
  #5  
BigTb17
Senior Member
 
Join Date: Feb 2008
Location: Perrysburg, OH
Posts: 1,167
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Brushless motor questions...

ORIGINAL: JustHover

Hi thanks for the feedback. While I waited for a response I found the Mongoose Micro 1/18 BL System 8.5T (9000kv). It's cheaper than the CC options and it has a robot mode which has the symmetrical response if forward and reverse. And it does not require a programmer. Because in robot sumo we need speed and torque, my idea was to use the higher kv motor and gear it down for the optimum rpm. That would give me the most power available for the weight of the system. I will be using 11.1vdc lipos.

I'm totally fine with borrowing parts from RC cars. I like Losi stuff. Anyone happen to know the gear reductions available in these small RC cars, or the rpm of the above system at the motors shaft?
The KV rating is the unloaded RPM of the motor shaft per volt applied. If you are running a 3S Li-Po you will be getting over 46,000 RPM even at the battery's nominal voltage on a 4200KV motor. Gearing that down to get 750-1000 RPM would require something like a 45:1 transmission ratio. For that type of reduction ratio I would look at rock crawlers. The 9000KV motor would be twice that fast, around 100,000 RPM unloaded. The motor will be screaming and drawing more power than necessary, wasting energy because the RPM would be just too high.
Old 08-03-2011, 08:06 AM
  #6  
JustHover
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: Pekin, IL
Posts: 23
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Brushless motor questions...

Ah I see. That's a lot simpler than I thought. lol Even a 45:1 gear reduction will be challenging enough. I will go ahead and get the lower kv motor option. Thanks for the help!
Old 08-03-2011, 05:27 PM
  #7  
hands without shadows
Senior Member
 
hands without shadows's Avatar
 
Join Date: Nov 2005
Location: Lakeside, ON, CANADA
Posts: 6,934
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Brushless motor questions...

I think the gearing will provide enough of a drag brake, no?
Old 08-04-2011, 11:39 AM
  #8  
JustHover
Junior Member
Thread Starter
 
Join Date: Jan 2011
Location: Pekin, IL
Posts: 23
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Brushless motor questions...

Just ordered the BL systems (2) will see how it goes!

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.