Yardracer28753

This is a fantastic thread! I was wary of building my first ball diff on my new 22, but after reading through this I put it together and had tremendous success at its first two race outings. Thank you very much for the information.

gelshocker

iTrader: (1)

Was wondering if there is a (urgent) need to replace thrust washers after a groove has developed in them. I use ceramic thrust balls (B-Fast).

I understand diff rings need to be replace/sanded/flipped after each rebuild.

There are thrust ball bearings where the thrust balls are seated anyway, so is it necessary to replace grooved thrust washers?

Thanks,

K. Wood

iTrader: (2)

On the old Losi XXX-T we would tighten the diff screw all the way down, and then back it off 1/8 of a turn. Do it again after a couple of runs and check it from time to time. My diffs lasted forever and were very smooth that way.

rcmodelswiz

Wow. Pretty comprehensive. Thanks for the great videos. This certainly help me a lot.

archerwin

iTrader: (10)

Hi! After failing at building my first ball diff, I followed this guide and it solved my diff barking problem after rebuilding it! Thanks a lot.

Just a question, I'm running stock motor and when I follow your procedure in setting the slipper clutch I can't get the frot wheels to go up to about 3 inches. I tried tightening the slipper clutch already but after a few tries my motor became very hot and some smoke started to appear (good thing I stopped as soon As I saw this, my motor is still good).
So what I did was to just tighten it so that it doesn't slip when I throttle and hold both wheels.

I checked the diff and i think it is tight enough (when I hold the right wheel and spur gear, the left wheel can't be rotated w/ moderate force). The diff is smooth when I do counter rotation on the wheels too.

Did I do something wrong? Or is this expected for a 17.5 motor (=no wheelies)?

Thanks

Silverexpress

iTrader: (1)

Hi. Sounds like your motor is geared to high. What make and model is this, and what spur and pinion teeth are you using?

archerwin

iTrader: (10)

I'm geared 70/32 for a 17.5 motor

Silverexpress

iTrader: (1)

Is this 2wd or 4wd? Do you know what your differential ratio?

archerwin

iTrader: (10)

It's the TLR 22 2.0 2wd buggy

Silverexpress

iTrader: (1)

Sorry for all the probing questions, but Im trying to calculate your rollout ratio. The rollout ratio is the ratio between your motor rpm and your rear tires rpm. It should be 1:1....one turn of the motor should equal 1 turn of the tire. Anyhow since I dont know your motor, I'll just assume it's roughly at 2500 kv which is common for a 17.5T motor. Knowing that TLR kept the same diff as version 1.0, this gives us a diff ratio of 2.43 (see your manual).

Finally, let's just add to the assumption that your tires are 3.35" in dia, and with a 70/32 gear combination this gives us a rollout ratio of 1.98. At 8.3v your 22 will hit 38 mph. Unfortunately, you want a rollout ratio of 1.0, so the bottom line is your overgeared for that motor. Ideally a 17.5T motor will be very happy with a 76/18 combination and this roughly provides a rollout ratio of 1.02 at a top speed of 20 mph. Now this can be stretched with either a taller pinion, and or timing via the endbell or the esc but doing so you will need a temp gun. Because once you start to deviate from 1.02 you'll start raising the temp of the motor/esc/ batteries. A temperature of 180 degrees F seems to be the accepted upper limit. Beyond this temperature you start to cook the glue that holds the magnets inside your motor.


Bottom line, you will have to upgrade your motor to give you that top speed of 38 mph. It's surprising that the manual gives a 70/35 combination since that's a rollout ratio of 2.16!!!! With a top speed of 43 mph!!! It's got to be a typo. For that type of performance your looking at a motor with 8.5T or a 9.5T geared down for torque to keep things nice and cool. The version 1.0 manual calls out a 76/30 combination, and that gives a rollout ratio of 1.7 at a speed of 34 mph. That's more believable, but I'd still take a temp gun to it just to be sure. It is really strange to see 70/35 for the v2.0 since they added so much weight to it also.

Do a google search for "rc rollout calculator"....

Have you taken the temp of your motor after a 6-7 minute run through a course? If so what did you get?

archerwin

iTrader: (10)

Thanks! That was informative! I'll be running it this weekend. I'll report back the temp after.

I use a speed passion 17.5 V3 motor w/ sp club spec esc.

Thanks again!

Silverexpress

iTrader: (1)

Ah...a little more info. I took a quick glance at SP's motor chart and for the 17.5T v3 it has the recommended range of 4.6 to 6.0, and I think that this is the final gear ratio. A 70/32 with a 2.43 diff comes out to 5.31 = ((70/32)*2.43) so that's well within the range. Now that we know the true kv, 2700, you will have a top speed of roughly 40 mph. Maybe this combination is at the cusp of overstraining the motor, and holding down the rear tires put it over the edge - especially with a heavy battery, along with the added weight of upgraded aluminum parts at the front, and a 70/32 that provides top speed in place of torque.

Let us know what the temps are....remember moving forward on the track at speed helps cool the motor, as oppose to it just sitting in one place with the rear tires held down.

archerwin

iTrader: (10)

I just want to report back that the motor temp is ok. Not hot when I touch it (i don't have a thermometer). Thanks for your help

Henry#40

iTrader: (9)

76/18 with a 17.5?
Sounds like a rockcrawler setup.

asc6000

iTrader: (15)

The 1:1 ratio is not the golden rule of gearing. 76/30 IS the correct starting point for that vehicle, temp/tune from there.
Please post in the vehicle specific thread for additional gearing info. Has virtually nothing to do with setting the diff or slipper.