R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 06-23-2011, 09:09 PM   #1
Tech Rookie
 
Join Date: Jun 2011
Posts: 4
Questions?? RJ Speed Digger - Got some issues

Hey all! Just recently, I got bit by the bug to get back into RC. Back in the day I had a Bolink Digger, and I go the urge to see if I could track one down. Found out that RJ Speed was making them again, and the rest is history.

I've got some issues with this car now (mostly my own doing ). I got crazy and put a 3900kV Reedy / XP SC450-BL combo in the car, and man that thing is sick! Obviously, I've broken some stuff pretty quickly with a setup that quick, but I expected that.

What I didn't expect is the way the motor ran. Granted this is my first brushless setup, and I quickly realized that a BL motor does not behave the same as brushed. What I didn't expect was that after several runs, it would get real jumpy when going full throttle from a low speed. Did a bit of research and it seems that the motor is cogging. I'm running the car on a Duratrax Onyx 4200 NiMh; is this likely the problem, or could there be something wrong with the electrics?

The second issue I've got is with the tires, but that's simpler. The rears chunked out pretty bad real quick, and I've managed to run them almost clean down to plastic in no time flat. I run the car primarily on semi-rough tarmac for the most part and I could use a recommendation for what foam compound would be a bit more durable.

Any insight and suggestions are welcome!
SpideR W is offline   Reply With Quote
Old 06-25-2011, 09:04 PM   #2
Tech Rookie
 
Join Date: Jun 2011
Posts: 4
Default

Any thoughts at all?
SpideR W is offline   Reply With Quote
Old 06-26-2011, 04:36 AM   #3
Tech Fanatic
 
BrodieMan's Avatar
 
Join Date: Oct 2009
Location: Ontario, Canada
Posts: 761
Trader Rating: 3 (100%+)
Default

Cogging is likely due to the battery not being able to put out the Amps that the Motor is demanding continuously. I had some minor issues with cogging with an old 3200 20C LiPo. Swapped LiPo's and the 'cogging' went away. I would recommend ditching the NiMh and go LiPo, 30C or more.

For tires you probably want a treaded rubber tire for bashing around as they will last way longer than any foams.
__________________
Mark Richardson
Kawartha Radio Controlled Racers
Lakefield Hobby & Game. ExtremeRCforum
Schumacher Mi4cx CRC Gen-X 10 LE
BrodieMan is offline   Reply With Quote
Old 06-26-2011, 04:57 AM   #4
Tech Master
 
pejota's Avatar
 
Join Date: Apr 2008
Location: Vero Beach, FL
Posts: 1,022
Trader Rating: 12 (100%+)
Default

Purple fronts, pink rears is a pretty common combo for pan cars on asphalt. RC4Less is a great source.

You may also want to look at some BSR Spec fronts/rears.
pejota is offline   Reply With Quote
Old 06-26-2011, 07:43 AM   #5
Tech Fanatic
 
ozzy-crawl's Avatar
 
Join Date: Aug 2009
Location: Forde A.C.T
Posts: 990
Trader Rating: 14 (100%+)
Default

yea i run purple fronts,magenta rear on asphalt with 2s a lrp x12 10.5t (3600kv) with boost/turbo esc and get good tyre life
__________________
MST XXXD vip
MST FS-01d
Xray T4
Xray T3
AE Sc10.2 AE SCB

Last edited by ozzy-crawl; 06-26-2011 at 08:00 AM.
ozzy-crawl is offline   Reply With Quote
Old 06-27-2011, 07:45 AM   #6
Tech Rookie
 
Join Date: Jun 2011
Posts: 4
Default

Quote:
Originally Posted by pejota View Post
Purple fronts, pink rears is a pretty common combo for pan cars on asphalt. RC4Less is a great source.

You may also want to look at some BSR Spec fronts/rears.
Out of the box, the car came with BSR Specs; blue front and green rear actually. So the purple/pink combo should last a bit better? Oh, and thanks for the source tip!

Quote:
Originally Posted by ozzy-crawl View Post
yea i run purple fronts,magenta rear on asphalt with 2s a lrp x12 10.5t (3600kv) with boost/turbo esc and get good tyre life
Not really knowing foam tires very well, what's the difference between the magenta and the pinks that pejota mentioned?

Quote:
Originally Posted by BrodieMan View Post
Cogging is likely due to the battery not being able to put out the Amps that the Motor is demanding continuously. I had some minor issues with cogging with an old 3200 20C LiPo. Swapped LiPo's and the 'cogging' went away. I would recommend ditching the NiMh and go LiPo, 30C or more.

For tires you probably want a treaded rubber tire for bashing around as they will last way longer than any foams.
That's what I was thinking really, though I wasn't really sure why it was getting worse each run. Could that be a result of very small changes in a an already marginal battery? Oh, and I was thinking about treaded tires too, but I think on a car as light as Digger with no diff or suspension that would a be a recipe for disaster!
SpideR W is offline   Reply With Quote
Old 06-27-2011, 10:23 AM   #7
Tech Elite
 
mkiiina's Avatar
 
Join Date: Jul 2007
Location: Frisco TX
Posts: 2,334
Trader Rating: 69 (100%+)
Default

I'm glad you brought this up as I have an old Digger sitting on a shelf with dry-rotted tires and was looking for something that would last well on concrete.

I also have 2 legends that need tires....

How do you like the 3900kv motor? I was trying to decide what would be a good motor and not overpower the crap out of the chassis....
mkiiina is offline   Reply With Quote
Old 06-27-2011, 11:17 AM   #8
Tech Rookie
 
Join Date: Jun 2011
Posts: 4
Default

Quote:
Originally Posted by mkiiina View Post
How do you like the 3900kv motor? I was trying to decide what would be a good motor and not overpower the crap out of the chassis....
Honestly, it's way too much power for it. When it isn't cogging (see above), there just isn't any way to use all the power. I've got the throttle EPA on my radio set to 60%, and when the battery is fully charged, that's still enough to instantly flip the car backwards by stabbing the trigger. Once it's moving, it's hard to keep it a anything above 75% of the trigger just because little bumps move the thing off course so easily. One pebble at that speed causes cartwheels!

All that said, be careful with the throttle and that little car is an absolute blast to drive. The 3300kV would probably be overkill too (just not quite as much) if the 3900 wasn't available.

Some of the general characteristics of the BL motors though don't seem to fit though, and I'm toying with the idea of going back to brushed. For example, you can get the car into a beautiful pirouette, but with no diff the axle can sometimes bind, and when that happens, the motor will often just stop. Also, you cant exactly slam it into reverse at speed either.

Just thinking out loud there... Anyways, with careful controll and tweaking the 3900 is rediculous fun that will put an equally rediculous grin on your face, but it's also serious overkill.
SpideR W is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 05:47 PM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net