dstidham

iTrader: (14)

My son purchased a losi 22 2.0 roller and it came with a 78 and 76 spur gear. We only has a stock motor. I am hoping the hobby shop will have the stock 70 spur gear, but in case I end up needing to order one is there any harm in running a stock motor with a 76 spur and 33 pinion? Should i just get a different pinion if available? Which size would you recommend?

Motor Turn Spur Pinion
6.5T 78 20
7.5T 78 21
8.5T 78 22
9.5T 78 23
10.5T 78 25
13.5T 70 28
17.5T 70 35


Losi Gearing Calculation Example with a Stock Setup:
70Spur/35-Pinion=2 External Drive Ratio
2.43 Transmission Drive Ratio x 2 External Drive Ratio=
Final Drive Ratio 4.86:1

My setup:
76Spur/33-Pinion=2.3 External Drive Ratio
2.43 Transmission Drive Ratio x 2.3 External Drive Ratio=
Final Drive Ratio 5.58:1

Not exactly sure what the difference is for final drive ratio and what affect it will have on the stock motor.

MarkA

iTrader: (21)

Final drive ratio or FDR, is the actual ratio that is being applied so to maintain the 4.86ish one you're wanting, you actually need to get to around a 76/37 spur/pinion, something I'm not sure will fit. However, there will be no harm in running a stock motor undergeared. In fact, for a newer racer with a buggy, it will be more slower and more controllable.

dstidham

iTrader: (14)

Perfect, thank you!

Mudcat981

iTrader: (4)

+1

Agree for stock you absolutely need the 70t spur. But since you do not have one yet you will have to go undergeared. I believe the largest pinon with a 76 maybe a 33 or 34. I do not think you can squeeze in one bigger.

Recommeded for most tracks FDR 5.48 - 5.67 (70/31, 70/30)

Your best with a:

76/33 is 5.59 <-- if this will fit would work.
76/32 is 5.77 <-- would have less top end, but more torque
76/31 is 5.95 <-- really slow, can jump well, great for very tight tracks.

shagino

iTrader: (57)

Wow, that 4.86 recommended is extremely aggressive.

This can get hot at some tracks. Where did you see this recommended? If I'm at a new track, I always ask around first but if I can't get a recommendation, I always start with the Novak chart and work my way up. Recommended 6.0 FDR for 17.5

http://teamnovak.com/tech_info/view_article/26

To some extent. If you are severely under geared, you can heat the motor up that way too.

Mudcat981

iTrader: (4)

I agree "4.86" is insane and very dangerous.

But 5.5-5.7 is good for 2WD.

Here check out these 2 threads on the Trinity D4 17.5 motors and you will see most people prefer this range of gearing. I run 5.48 on both tracks I currently run (one is short with several switchbacks and jumps high grip, the other is medium, long straight, high grip). I run strictly Trinity D4 now, but I even ran this with my Viper motors.

http://www.rctech.net/forum/electric...7-5-buggy.html

http://www.rctech.net/forum/electric...d4-17-5-a.html

dstidham

iTrader: (14)

I just took the recommended spur/pinion combo for stock racing from the Losi manual and plugged it into the sample formula. maybe my math is off.

Mudcat981

iTrader: (4)

Your math is not off, and yes that is what is in the manual, not sure why they printed that? I am guessing they are running a zero timing 17.5 motor?? Not sure, maybe Frank Root can shed some light.

But most 17.5's (especially the D4) love timing 45-55, even 60* and if you run under 5.4 then you really have to watch your temps. Also be careful to pay attention to available torque for jumps.

BigBadDogg

In the stock 17.5 class at my track we run.. 76/26 max... I dont see a 30 tooth pinion fitting .. good luck.

shagino

iTrader: (57)

Not exactly safe to assume for all motors on all tracks though. Err on the side of caution. Otherwise, someone is going to say that they melted down on your advice.

Mudcat981

iTrader: (4)

I asked Frank Root (TLR rep) about the different gearing options in the TLR 22 1.0 and the TLR 22 2.0 manuals. He said at the time the gearing was correct for that time of print, except 70/35 is totally incorrect.

Todays current recommendation for a starting point from Frank was 70/30.

Yes each track is different and also each motor is different. But you need to start somewhere :-)

shagino

iTrader: (57)

Which is why I recommended the Novak recommended gearing rather than online recommendations. Checking temp will show you where you should really be but I prefer to start conservative and go aggressive. Start in the middle and it's harder to know if you should go up or down. Sometimes gearing down makes me faster on a given layout.

dstidham

iTrader: (14)

Thanks for all the information everyone. The 76/33 with almost 60* of timing on his Killshot motor (that was what it was set to when we got the motor) with Just Stock ESC worked great for our track. In fact a little too good...

I have a D4, B5M and Just Stock ESC. I read the thread link above which has brought up some questions and concerns which may be better to post in that thread. If that is the case let me know.

Currently I am running 34/72 which ends up being a FDR of 5.5 (that is what came with the buggy). My timing is set to the default 30 and after running a complete battery pack its in the 130-140 range. So first question, should i be gearing for more run time or for the best 5-8 minute race run time?

There is single and table top jump together, but I struggle to land on the the top of the table top. My sons tlr has no problems. I know that is killing my lap times because I endo into the front ramp of the table top when i try to jump the gap. So i end up just slowing down over the first jump and then punch it over the table top.

I picked up a high torque rotor for the D4 which I am hoping will help.

I also noticed in the B5 manual there are two stock gearing suggestions. 69/31 and 78/23. I am assuming the higher the FDR the more torque. Should I try the 78/23 gearing option then turn the timing up on the motor?

dstidham

iTrader: (14)

Does this mean that there should be little temperature change going from 30* to 45 or 55*? I am around 5.5 fdr on my b5m but my temps are in the 140* range after a full battery run time (3500mah 2s SMC) with the default timing.

MarkA

iTrader: (21)

When running 17.5 classes, the inability to clear a jump others can is most often related to a lack of torque, not top speed and even then, much more often related to the intangible that is corner speed in the turn before the jump but that's a topic that's hard to discuss in text form on a forum. In other words, the new rotor should help but just dropping a tooth or two on your current pinion should as well.

In the B5 manual, the 69 spur ratio is a starting point for blinky, 78 would be for boosted and even then, really, really boosted to the moon.

For gearing with temps, you typically gear for a 6ish minute race run or however long your track runs so if they do 10 minute mains, you have to gear for that.