RC10T pinion advice

[highflier]

I have a old RC10T pretty much stock everything except Power train.

I put a Lehner 4200 basic and a bk 7018 controller in it.
For batteries 3s A123 cells.
I'll be adding a parkbec to it for reciever power. I want to run stock tires on it and on short grass. What pinion do you think I should run. I have no idea what the drive ratio is on a stock rc10t.

I have run it on the streat and it was fast, but the motor got pretty damn hot also.

Highflier

[highflier]

I found a thread that said the Tranny ratio was 2.25 and with 21 tooth pinion and a 87 spur, it would be 9.3 finial gear ratio. Does this sound right and does it help me figure out what I need for a pinion with my setup?

I will be using 2.2 tires

highflier

[highflier]

Sorry for post after post.... I am adding to this as I learn more.

I currently have 87 spur and a 14 pinion on it. Using the rc calculator, I am way undergeared and over volts for the motor...

It says the lehner is only good to 40,000 RPM's and I am driving voltage to 50,000 RPM's
However I think that is the unloaded KV and I am assuming that 4200KV is the loaded value which puts me right on the edge. of 42000 RMPS

Using the 14 tooth it says max speed of 32 MPH, I have a 16 tooth I can put on that would get me to 38 MPH. I am thinking I should be gearing for about 45 MPH which would be a 19 tooth Pinion.

So will increasing the Pinion up to 19 tooth actually lower motor temp, This goes against my natural instinct.

Highflier

[What's_nitro?]

Yes increasing the pinion size will lower the motor temperature. I know it seems wierd but it is true for brushless motors. The motor spins a little slower since there is a bigger load on it, and so there are fewer current pulses through it and less power is dissipated to the case. OTOH the ESC will heat up more. This is true when gearing up with brush motors OR brushless motors since each pole of the armature remains energized for a longer period of time. Since the armatures of the motor are basically short circuits, powering them for longer periods of time is harder on the FETs of the ESC. The Lehners are very efficient motors so they will run well up to 40000 RPM. I think your getting so much heat because the motor is just taking so much power to run. Probably 70A at WOT with that motor in a 1/10 ST. You may want to try a 4S A123 setup and a higher wind motor like a Basic 3100. It will be more efficient since it draws less current for the same power output as the Basic 4200, so the temps overall (motor, esc, batteries) will be lower

The Lehner motors are rated with an unspecified load. So the 4200kV may be 4300kV unloaded or it may be 5000kV unloaded. I don't know and there is no way to find out unless Lehner publishes the load they are rated with. Be careful using the Warrior controllers with the high RPM because they can only handle 42000 RPM max. They cog like mad if you exceed the limit and that's bad for the motor AND the ESC. Not to mention, your drivetrain. The good news is that A123 cells drop voltage more under high load than other Lithium based batteries. So your guess of 10V under WOT may be high. This is GOOD news since it means you wont hit the RPM limit on the BK- just don't revv it up with the wheels in the air or you might be sorry. Hope this helped a bit.

[highflier]

Thanks,
I want to stay 3s since I am zip charging and it only takes 10 min for a charge :)

I also don't want the weight or size of the packs to grow at all. I just had to reconfig the layout to get the 3s A123's in. Now I got to find a good way to secure them if I cartwheel. I am sure they will say in place with Velco for the normal bumps and jumps.

I'll pick up a 19 pinion. That should help quite a bit. I think the ESC will be fine since it is rated 70Amps at higher voltages. I'll probably set the throttle on my radio to 90% or so anyways. The slipper will not be able to handle that much power. I already destroyed the diff once when I was using 3s lipo's.

Highflier

[What's_nitro?]

Hmm 10 minute charge sounds nice. Almost worth reconfiguring all my cars to use A123's and buying another charger/balancer....nope. Maybe in future vehicles, for me. Definintely make sure the cells are properly held down. We don't need any accidents now. Although the cells ARE fireproof if you DO crash bad.

I would be careful with the ESC that close to the limit. Exceeding either the amperage OR the voltage rating of an ESC can blow it up.

In case you were wondering how to tell the difference: Voltage makes it "pop" whereas amperage makes it "fizz".

[highflier]

A123 are much safer then Lipo's They have a metal can and do not explode/flame up like Lipo's.
My charging method refered to as Zip charging, does not require buying new changers. You can make one in about 10 min for under $10.00. I use the same balancer as what I have on my lipo's. (LBA10) I balance after the charge not during. This is OK with A123 cells.

I certainly hope I am well within specs of the controller.
A stadium truck on 10 volts (under load closer to 8)

The controller BK, is a 70 amp 20 volt rating. 1400 watts.
Of course I will be at 8 Volts thus 560 watts.

A123 Cells will start to really sag voltage before they hit 70 amps. So I should be plenty safe on Voltage and Amps unless I 3s2p the packs. I have no intention of adding that kind of weight to the truck.

For secureing the batteries, I am thinking about drilling 4 holes in the bottom fo the tub,
2 on each side of the battery, then installing a velcro strap tiedown. This way I can use both velcro on the bottom of the pack and a strap on the top of the pack. I expect that to be plenty strong.

Highflier

[highflier]

Well I just test ran it with the new pinion. I ran for 10 min in 35 degree weather, Just did WOT laps in my backyard, Ok not all Wide open it kept lifting the front tires and spinning out

After 10 min I broke a A-Arm it was 20+ years old, So now I am waiting on parts from Tower, I am replacing it with a RPM A-Arm set.

Everything was nice and cool. I did not temp the items as I was inpecting damage to the vehicle. But I did touch them , I would say the ESC was 60, the Motor 70, and the batts were cold. So I am hoping that I have fixed the motor temp issue, Even if I raise everything by 40 degrees for summer weather I should be plenty fine.

I recharged the battery and it took 1900 MAH. I guess I had about 1 more min left in the battery.

Highflier