GP video

Made a new Ground Pounder video .

Fixing the stiction on Redcat Racing's Ground Pounder shocks

Stiction

Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the term "static friction", perhaps also influenced by the verb "stick".Wikipedia

The stock shocks on the Ground Pounder have seem to have issues out of the box with shocks wanting to stay in one position instead of reacting to forces that should make them expand and contract . The severity of this issue seems to very greatly as my step fathers truck shows hints of it but my rear shocks where down right horrible .

So what is the fix for this . Some people buy new shocks from other brands such as HPI . Others fix the stock ones . 

I elected to Fix the stock ones so here is what I did .

Depending on the condition of your shocks your's may require more or less work than mine did my rear shocks where the worst and took 2 hours to do both . My front shocks took ruffly 1 hour .  

Remove the shocks from the model . Always rebuild / maintain your shocks in front or rear pairs so they preform equally

Remove the spring and lower and upper spring retainers.

Remove the upper cap and drain fluid in a clean container if you plan to reuse. Buying a bottle of fresh shock oil in the 20-30 wt rang is recommenced to insure you have enough to fill the shocks completely.

Remove the lower eyelet / ball link . Use pliers with a padded jaw or protect the shaft with a soft material if using normal pliers to prevent the shaft from becoming scored .

Slide the shock shaft out of the body and then remove the lower cap from the shock . There will be two seals in the body under the lower cap as shown in the picture . Set the smaller thinner o-ring / seal to the side as it will not be used during reassembly.

The inclusion of the small o-ring and the hole in the lower cap being undersized is the cause of the sticking in many of these shocks . 

Many people drill hole out to a larger size . Since it helps keep the shaft running parallel in the bore of the shock body I elected to use rubbing compound to increase the clearances but still keep slop at bay.

Just add a little bit and work it up and down the shaft .

After a while the compound will became gray- black wipe the shaft down test fit the cap on the shaft it should be just loose enough that it will slide down the shaft  by just gravity. 

Next clean the shaft up with polishing compound it will remove most if not all scratches on the shaft .

Apply just a bit 

Polish till it shines. 

Now reassemble for a test fit .

Insert the large o-ring back in the housing covered in plenty of silicone based grease.

lubricate the shaft with silicone grease and slide it though the body and the seal install the lower cap and tighten a few threads at a time while working the shaft back and forth to allow the seal to seat . When cap is snug move shaft through its full motion . If it moves  smoothly refill the shock with oil bleed out the air , re-install the upper cap lower eyelet , spring and the spring retainers .

If everything isn't silky smooth :

First loosen the lower cap a bit and see if the ruff spot is now in a different spot if so the hole in the lower cap is probably of center a bit and the drill bit method might be the best way to go .

If there is no change by loosening the lower cap inspect the shock piston it may have a bit of flash not removed at the factory . Light sand the outer diameter and retest .

If your still having problems there may be a flaw with the shock bodies bore it's self .

Role up a small piece of sand paper and rotate it in the bore . Start with a large grit piece and work down to a fine grit like 1000 . Do another test fit if you feel a improvement move on to using rubbing compound and then polishing compound . Test fit once more when the bore is nicely polished .

Motor's I have tried in the Ground Pounder

This list will grow with time.

Below are a few tables showing the Spec's of the Mabuchi equivalents of the stock motor and a few others that may be of interest .  When looking at the chart's the last 2 digits of the part number denote how many turns the motor is . 

MODEL		VOLTAGE		NO LOAD		AT MAXIMUM EFFICIENCY					STALL
		OPERATING RANGE	NOMINAL	SPEED	CURRENT	SPEED	CURRENT	TORQUE		OUTPUT	TORQUE		CURRENT
			V	r/min	A	r/min	A	mN·m	g·cm	W	mN·m	g·cm	A
RS-540SH	7520(*1)	4.8 - 7.2	7.2	23400	2.40	19740	13.0	30.6	312	63.2	196	1998	70.0
	6527(*1)	4.8 - 9.6	9.6	23400	1.60	20040	9.55	31.0	316	64.9	216	2202	57.0

MODEL		VOLTAGE		NO LOAD		AT MAXIMUM EFFICIENCY					STALL
		OPERATING RANGE	NOMINAL	SPEED	CURRENT	SPEED	CURRENT	TORQUE		OUTPUT	TORQUE		CURRENT
			V	r/min	A	r/min	A	mN·m	g·cm	W	mN·m	g·cm	A
RS-550PC	8019(*1)	6.0 - 9.6	7.2	15300	1.40	13540	10.8	41.7	425	59.1	363	3700	83.0
RS-550VC	7525(*1)	6.0 - 14.4	12	17600	1.20	15730	10.1	58.3	594	95.9	549	5596	85.0

Stock 20 turn  540 motor 

On flat ground it has a reasonable amount of speed but has unsatisfactory torque and high temperatures with the stock 23 tooth pinion. Installing a 17 tooth pinion improved things but still wasn't to a level I felt was appropriate .


Pinion Tooth Count: 23
Total Voltage: 8.4
Motor KV: 3216
Top Speed (MPH): 25.73


Pinion Tooth Count: 17
Total Voltage: 8.4
Motor KV: 3216
Top Speed (MPH): 19.02


27 turn 540 Mabuchi  

With a 17 tooth pinion temperatures where good top speed was mild but enjoyable . The boost in torque was noticeable.


Pinion Tooth Count: 23
Total Voltage: 8.4
Motor KV: 2437
Top Speed (MPH): 19.49



Pinion Tooth Count: 17
Total Voltage: 8.4
Motor KV: 2437
Top Speed (MPH): 14.41


550 19 turn Redcat Racing part # 28446

Don't ask me why the motor is listed as a 19 turn when the code on the can states its a 20 turn all I can say is close enough.

This motor to me is a good first mild upgrade if you can find it on Ebay or such for less than $15 bucks. If its over $20 there are other options out there that can get you essentially the same motor or better for the same cash.

To be honest this is the motor that should have shipped with the Ground Pounder from the factor as it provides a reasonable top speed " but slower than stock" and plenty of torque with the included 23 tooth pinion . If you want a bit more speed you could easily install a bigger pinion and sacrifice a bit of torque for more speed. Or you up the voltage which would be what I would do .


Pinion Tooth Count: 23
Total Voltage: 8.4
Motor KV: 2125
Top Speed (MPH): 17

Pinion Tooth Count: 33
Total Voltage: 8.4
Motor KV: 2125
Top Speed (MPH): 24.39

Pinion Tooth Count: 23
Total Voltage: 12.60
Motor KV: 2125
Top Speed (MPH): 25.5

Leopard LBP3650/3.5D 3900KV 4-Poles Inrunner Brushless Motor RTR

Pulled this motor and the ESC from the Redcat Twister I am No longer running . All I can say is wow complete over kill Currently Running this with a 10 tooth Mod 1 pinion and the 43 tooth Mod 1 spur gear . After twisting  2 driveshafts I have lowered the punch level of the HobbyWing / Lansu ESC to 2 and am now lowering the timing to make it more drivable and to help safeguard the fresh shafts till upgraded ones are installed . 

Spec's

	Max Amps	Max Voltage	Max Power	KV (RPM/V)	Resistance		Dia. x Length (mm)		Length of Extend Shaft	Shaft Dia.	Weight
	86A	15V	1300W	3900KV	0.0075		Φ36.0×50		16mm	5mm	185g

Pinion Tooth Count: 10
Spur gear tooth count: 43
Total Voltage: 8.4
Motor KV: 3900
Top Speed (MPH): 25.55

(Not attempted yet )
Pinion Tooth Count: 10
Spur gear tooth count: 43
Total Voltage: 12.6
Motor KV: 3900
Top Speed (MPH): 38.33

Redcat Racing Gound Pounder Quality .

Well at this time I still like the Ground Pounder but I do have a few words of warning .

Construction quality of 1 I received and the one my step father have has proven to be vastly different.

Examples :

Several screws on my  truck are longer than they need to be .None of these are in places were they are a issue but it seems like they ran out of the right length screws and substituted what ever would work from what they had.

My step dads trucks shocks has had a mild amount of sticktion where the shocks hangup after not being cycled for a bit .

My shocks were horrible after a lot of work the rears are smooth as butter and the fronts are waiting there turn ( expect a post with pictures showing a tear down when I do the fronts ) .

His motor has 30-40 packs minimum through it and despite a hiccup its still chugging along my motor is junk after 5 packs . The arm that holds and applies tension to the brush broke off.

So am I mad NO I bough this RC to modify to my taste.