RCCrawler Forums

Toyo496 · 02-28-2010, 05:24 PM

So for those of you who thought (myself included) that the HPI reduction box was going to be the perfect gear ratio for your WK: here is my improvement that I came up with.
When I first installed the GRU it was cool for the first 15 minutes, I could crawl up anything I had the traction for (including alot of furniture). And as some of you have stated "has the torque to pull down sky-scrapers". But over time I found that I needed a little more speed to get the truck from point A to B. The .02 miles per hour kind of sucked for anything but techinal steep climbs. I was looking for a little more general speed and the ability to add some more wheel speed when I just didnt quite have the traction to make it up and over. So I took my motor plate off and extended the groove that alows for pinion adjustment both upwards and downward. I then re-installed my GRU and 27t motor, and headed down to my local hobby store to find a better pinion/spur gear setup. After a couple of different combos, I went with the stock 90t spur and a 32t pinion. I know, sounds wierd, but it seems perfect for the type of crawling that I do. It has low enough speed/torque to still climb steep stuff with the stock Saturn 27t motor and it has far better top end speed to get around the flat parts of the courses. Best of all, because it still uses the GRU, I still have good roll control. Versus having a low pinion gear that dosent offer the gear reduction against the motor and rolling backwards off every obstacle you release the throttle on.
Hope this helps some of you who had higher hopes with the HPI reduction box.
Anybody have any ideas what my gear ratio is now?? If the box makes it 174:1......then the addition of the 32 tooth pinion should make it like 130:1 ???? Just guessing??

norbyx · 03-01-2010, 12:57 PM

Well let me tell you I am on the same boat you are. I installed the GRU a few days ago with the stock 55T motor. I think that the torque is even too much... the speed on the other side is way too low. I feel that in some ocasions if I had more wheel spin I could go over some obstacles that now I just get stucked. I am planning in changing the motor soon but can't say if just this will solve the problems or if I will have to change the pinion as well.
One thing I wouldn't want to loose is the drag brake that I achieved with the GRU, wich is just amazing, rock solid. I don't use a ESC that has a brake function so I can't rely on that....

rottenbelly · 03-01-2010, 01:14 PM

I have all the wheelspeed and torque i need for crawling with a 35 turn motor.
If you really want torque and wheelspeed look into a holmes handwound and throw that extra weight of the gru in the parts bin.

wanantrdsc · 03-01-2010, 07:44 PM

Quote:

Originally Posted by norbyx

Well let me tell you I am on the same boat you are. I installed the GRU a few days ago with the stock 55T motor.

That would make your speed 0.0002mph. Definately get a lower turn motor if you are going to use the GRU. I love it, but I could go for some more speed myslef.

wanantrdsc · 03-01-2010, 07:48 PM

Toyo496 -

Just wanted to verify. You are running the stock 90t spur, and using a 32t pinion. So you have increased wheel speed - excellent. Wasnt sure if I followed part of it though. Does the GRU with the 27t and 32t pinion still prevent the rig from rolling back? How about temps? Im running stock everything with the GRU, and I can run over an hour with no noticeable heat increase.

Thanks

looking forward to more wheel speed

Toyo496 · 03-01-2010, 08:48 PM

sorry forgot about the temps question....the motor spins up very easily, with no hesitation unlike in the stock form at 23:1 while trying to crawl. I still get really good run times, probably around an hour as well. I have NOT noticed any excessive heat at all and have NEVER experienced the thermal shut down.

Hope this helps.

wanantrdsc · 03-01-2010, 09:00 PM

Does the GRU with the 32t pinion still prevent the truck from rolling backward?

Toyo496 · 03-02-2010, 12:40 AM

Sorry I posted and it hasn't shown up yet. (maybe I didnt hit "quick post") ?

So to clarify what I am running: I have a WK with a flipped chassis, HPI crawler kit, locked front and back, 55 weight oil, Traxxas 2075 in stock location, garage built tierod and drag link, stock tires grooved and sipped, stock axles, 3600 venom battery, stock Saturn 27T motor, HPI GRU, stock motor plate modified to have more gear mesh adjustment, stock 48 pitch 90T spur, 48 pitch 32T pinion, stock electronics, stock controller, and one heavily cut body.
After running this GRU and 90T/32T gear combo a bit more this week, I am still very pleased with the increased wheel speed. It almost feels like a new motor swap because with the GRU alone I was full throttle every where ! Where as now I find myself using more throttle control down low and then hammering down when in need of wheel speed. To address the roll control topic a bit more: it is far supierior than the stock 90T/22T setup, although it is not as "ROCK SOLID" as just the GRU it self. From time to time it will roll backwards very slightly, well within my acceptance. I think that the wheel speed increase is well worth the trade off of losing some roll control. I have a 87T that I was thinking about trying with the GRU and 32T combo just for kicks.... How ever keep in mind that the 90T/32T combo does fit under the stock gear cover, a 96T spur will not fit with out cutting the gear case heavily which defeats it's use. I am not sure but I think a 93T would fit under the gear cover...

philtSF505 · 03-02-2010, 02:02 PM

alright i have mine gear at 48 pitch 96t spur, 13t pinion and its pretty slow can make some kinda steep obsticales and i just order the GRU,
that comes with a 15t pinion (i'm still very new to this) is this gonna slow me down to much?and if i put the stock spur gear and the 13t pinion and the GRU that may help but what does that make my ratio?

sorry for the super novice question

i have a crawler king rtr and just started to mod it

EeePee · 03-02-2010, 02:24 PM

Quote:

Originally Posted by Toyo496

Sorry I posted and it hasn't shown up yet. (maybe I didnt hit "quick post") ?

Needed moderator approval, you hit a keyword somewhere.

wanantrdsc · 03-02-2010, 02:46 PM

I was told that there would be no math in this!

wanantrdsc · 03-02-2010, 11:45 PM

Well, I tried the 28T pinion, as I did not modify the motor plate (so I cant used the 32T pinion). I really like the speed, but could use a tiny bit more drag brake. Ran for a bit, and motor was not even warm. Definitely a marked improvement over the 21t. Going to give a 26T a whirl and see if I get a bit more brake.

Good thread Toyo!

Toyo496 · 03-03-2010, 03:54 PM

philtSF505: I will attempt to answer your question without doing ANY math... LOL

Stock WK gearing: 90T/22T = 23:1 ratio
WK with GRU and 90T/22T = 174:1 ratio
WK with GRU and 96T/13T = Really SLOW !! I would GUESS at 200:1 ratio or more !!

I am sure there is a formula to figure this out, maybe some of the gurus here can helps us out with this trivia.

philtSF505 · 03-03-2010, 04:05 PM

hey thanks toyo, it slowed down alot with the gear i put in but...i am looking for more torque too....thinking that the GRU may help but if it slows down to much im gonna have to play with the gearing, i broke a dog bone on sunday just waiting for the replacements and the GRU so we'll see i'll try and post videos. thanks again

Toyo496 · 03-03-2010, 04:23 PM

I broke my first dog bone in the rear on Monday...LOL ! I was doing some urban wheeling in the office parking lot planter boxes and the manager came out and gave me the stink eye, so I picked up my rig and headed over to my chevy pick up. Thinking that I wanted to continue to play I threw my WK in the bed of my chevy and started to crawl on the bedsides and up the tool box, well apparently I still need to learn throttle control because I bound up the rear tire crawling over my goose neck hitch and broke the dog bone ! WHOOPS. So now I am trying to decide wether to go with stainless steal dog bones or an axle lock out kit???

In regards to the GRU, you will definately see a huge increase in torque ! Definately if you still have the stock Saturn 27T motor, which is NOT a torque monster by any means. Your rig will have no problem crawling the front tires straight up a wall, it will not roll back at all and the Saturn 27T motor will very easily power it straight up anything it has the traction for. It was just to slow for my style of crawl-bashing... so hence why I moved up to the 32T pinion on the GRU to gain a little more wheel speed.

wanantrdsc · 03-03-2010, 11:52 PM

Well I tried a 23t, 26t, and 28t - now I need to find some rocks!

philtSF505 · 03-04-2010, 09:29 PM

I have the crawler king, 55t this was my first rig, lookin to pri getone for the wife and kids

philtSF505 · 03-06-2010, 11:49 AM

Sososo slow gotta work on gearing. I'll go to the hobby shop soon. Tourque is crazy just to slow

wanantrdsc · 03-06-2010, 05:49 PM

You arent running a 55t motor with the GRU are you?

philtSF505 · 03-06-2010, 06:23 PM

yep, should i not be? didnt know what it would do so i tried it, lookin to change the gearing.

still very new to this and i'm still learning so if you got any to help i'll take it.

02-28-2010, 05:24 PM	#1
Toyo496 Quarry Creeper Join Date: Feb 2010 Location: Nevada City, CA Posts: 301	HPI Reduction Box gear ratio change So for those of you who thought (myself included) that the HPI reduction box was going to be the perfect gear ratio for your WK: here is my improvement that I came up with. When I first installed the GRU it was cool for the first 15 minutes, I could crawl up anything I had the traction for (including alot of furniture). And as some of you have stated "has the torque to pull down sky-scrapers". But over time I found that I needed a little more speed to get the truck from point A to B. The .02 miles per hour kind of sucked for anything but techinal steep climbs. I was looking for a little more general speed and the ability to add some more wheel speed when I just didnt quite have the traction to make it up and over. So I took my motor plate off and extended the groove that alows for pinion adjustment both upwards and downward. I then re-installed my GRU and 27t motor, and headed down to my local hobby store to find a better pinion/spur gear setup. After a couple of different combos, I went with the stock 90t spur and a 32t pinion. I know, sounds wierd, but it seems perfect for the type of crawling that I do. It has low enough speed/torque to still climb steep stuff with the stock Saturn 27t motor and it has far better top end speed to get around the flat parts of the courses. Best of all, because it still uses the GRU, I still have good roll control. Versus having a low pinion gear that dosent offer the gear reduction against the motor and rolling backwards off every obstacle you release the throttle on. Hope this helps some of you who had higher hopes with the HPI reduction box. Anybody have any ideas what my gear ratio is now?? If the box makes it 174:1......then the addition of the 32 tooth pinion should make it like 130:1 ???? Just guessing??

03-02-2010, 02:02 PM	#9
philtSF505 Rock Stacker Join Date: Dec 2009 Location: santa fe Posts: 81	alright i have mine gear at 48 pitch 96t spur, 13t pinion and its pretty slow can make some kinda steep obsticales and i just order the GRU, that comes with a 15t pinion (i'm still very new to this) is this gonna slow me down to much?and if i put the stock spur gear and the 13t pinion and the GRU that may help but what does that make my ratio? sorry for the super novice question i have a crawler king rtr and just started to mod it Last edited by philtSF505; 03-02-2010 at 02:07 PM.

03-06-2010, 11:49 AM	#18
philtSF505 Rock Stacker Join Date: Dec 2009 Location: santa fe Posts: 81	Sososo slow gotta work on gearing. I'll go to the hobby shop soon. Tourque is crazy just to slow Last edited by philtSF505; 03-06-2010 at 11:52 AM.

03-01-2010, 12:57 PM	#2
norbyx Rock Crawler Join Date: Feb 2010 Location: costa rica Posts: 705	Well let me tell you I am on the same boat you are. I installed the GRU a few days ago with the stock 55T motor. I think that the torque is even too much... the speed on the other side is way too low. I feel that in some ocasions if I had more wheel spin I could go over some obstacles that now I just get stucked. I am planning in changing the motor soon but can't say if just this will solve the problems or if I will have to change the pinion as well. One thing I wouldn't want to loose is the drag brake that I achieved with the GRU, wich is just amazing, rock solid. I don't use a ESC that has a brake function so I can't rely on that....

03-01-2010, 01:14 PM	#3
rottenbelly Just jump it! Join Date: Aug 2008 Location: Cedar City, Utah Posts: 1,947	I have all the wheelspeed and torque i need for crawling with a 35 turn motor. If you really want torque and wheelspeed look into a holmes handwound and throw that extra weight of the gru in the parts bin.

03-01-2010, 07:48 PM	#5
wanantrdsc Quarry Creeper Join Date: Mar 2009 Location: Peoples Republic of Kalifornia Posts: 240	Toyo496 - Just wanted to verify. You are running the stock 90t spur, and using a 32t pinion. So you have increased wheel speed - excellent. Wasnt sure if I followed part of it though. Does the GRU with the 27t and 32t pinion still prevent the rig from rolling back? How about temps? Im running stock everything with the GRU, and I can run over an hour with no noticeable heat increase. Thanks looking forward to more wheel speed

03-01-2010, 08:48 PM	#6
Toyo496 Quarry Creeper Join Date: Feb 2010 Location: Nevada City, CA Posts: 301	sorry forgot about the temps question....the motor spins up very easily, with no hesitation unlike in the stock form at 23:1 while trying to crawl. I still get really good run times, probably around an hour as well. I have NOT noticed any excessive heat at all and have NEVER experienced the thermal shut down. Hope this helps.

03-01-2010, 09:00 PM	#7
wanantrdsc Quarry Creeper Join Date: Mar 2009 Location: Peoples Republic of Kalifornia Posts: 240	Does the GRU with the 32t pinion still prevent the truck from rolling backward?

03-02-2010, 12:40 AM	#8
Toyo496 Quarry Creeper Join Date: Feb 2010 Location: Nevada City, CA Posts: 301	Sorry I posted and it hasn't shown up yet. (maybe I didnt hit "quick post") ? So to clarify what I am running: I have a WK with a flipped chassis, HPI crawler kit, locked front and back, 55 weight oil, Traxxas 2075 in stock location, garage built tierod and drag link, stock tires grooved and sipped, stock axles, 3600 venom battery, stock Saturn 27T motor, HPI GRU, stock motor plate modified to have more gear mesh adjustment, stock 48 pitch 90T spur, 48 pitch 32T pinion, stock electronics, stock controller, and one heavily cut body. After running this GRU and 90T/32T gear combo a bit more this week, I am still very pleased with the increased wheel speed. It almost feels like a new motor swap because with the GRU alone I was full throttle every where ! Where as now I find myself using more throttle control down low and then hammering down when in need of wheel speed. To address the roll control topic a bit more: it is far supierior than the stock 90T/22T setup, although it is not as "ROCK SOLID" as just the GRU it self. From time to time it will roll backwards very slightly, well within my acceptance. I think that the wheel speed increase is well worth the trade off of losing some roll control. I have a 87T that I was thinking about trying with the GRU and 32T combo just for kicks.... How ever keep in mind that the 90T/32T combo does fit under the stock gear cover, a 96T spur will not fit with out cutting the gear case heavily which defeats it's use. I am not sure but I think a 93T would fit under the gear cover...

03-02-2010, 02:46 PM	#11
wanantrdsc Quarry Creeper Join Date: Mar 2009 Location: Peoples Republic of Kalifornia Posts: 240	I was told that there would be no math in this!

03-02-2010, 11:45 PM	#12
wanantrdsc Quarry Creeper Join Date: Mar 2009 Location: Peoples Republic of Kalifornia Posts: 240	Well, I tried the 28T pinion, as I did not modify the motor plate (so I cant used the 32T pinion). I really like the speed, but could use a tiny bit more drag brake. Ran for a bit, and motor was not even warm. Definitely a marked improvement over the 21t. Going to give a 26T a whirl and see if I get a bit more brake. Good thread Toyo!

03-03-2010, 03:54 PM	#13
Toyo496 Quarry Creeper Join Date: Feb 2010 Location: Nevada City, CA Posts: 301	philtSF505: I will attempt to answer your question without doing ANY math... LOL Stock WK gearing: 90T/22T = 23:1 ratio WK with GRU and 90T/22T = 174:1 ratio WK with GRU and 96T/13T = Really SLOW !! I would GUESS at 200:1 ratio or more !! I am sure there is a formula to figure this out, maybe some of the gurus here can helps us out with this trivia.

03-03-2010, 04:05 PM	#14
philtSF505 Rock Stacker Join Date: Dec 2009 Location: santa fe Posts: 81	hey thanks toyo, it slowed down alot with the gear i put in but...i am looking for more torque too....thinking that the GRU may help but if it slows down to much im gonna have to play with the gearing, i broke a dog bone on sunday just waiting for the replacements and the GRU so we'll see i'll try and post videos. thanks again

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03-03-2010, 04:23 PM	#15
Toyo496 Quarry Creeper Join Date: Feb 2010 Location: Nevada City, CA Posts: 301	I broke my first dog bone in the rear on Monday...LOL ! I was doing some urban wheeling in the office parking lot planter boxes and the manager came out and gave me the stink eye, so I picked up my rig and headed over to my chevy pick up. Thinking that I wanted to continue to play I threw my WK in the bed of my chevy and started to crawl on the bedsides and up the tool box, well apparently I still need to learn throttle control because I bound up the rear tire crawling over my goose neck hitch and broke the dog bone ! WHOOPS. So now I am trying to decide wether to go with stainless steal dog bones or an axle lock out kit??? In regards to the GRU, you will definately see a huge increase in torque ! Definately if you still have the stock Saturn 27T motor, which is NOT a torque monster by any means. Your rig will have no problem crawling the front tires straight up a wall, it will not roll back at all and the Saturn 27T motor will very easily power it straight up anything it has the traction for. It was just to slow for my style of crawl-bashing... so hence why I moved up to the 32T pinion on the GRU to gain a little more wheel speed.

03-03-2010, 11:52 PM	#16
wanantrdsc Quarry Creeper Join Date: Mar 2009 Location: Peoples Republic of Kalifornia Posts: 240	Well I tried a 23t, 26t, and 28t - now I need to find some rocks!

03-04-2010, 09:29 PM	#17
philtSF505 Rock Stacker Join Date: Dec 2009 Location: santa fe Posts: 81	I have the crawler king, 55t this was my first rig, lookin to pri getone for the wife and kids

03-06-2010, 05:49 PM	#19
wanantrdsc Quarry Creeper Join Date: Mar 2009 Location: Peoples Republic of Kalifornia Posts: 240	You arent running a 55t motor with the GRU are you?

03-06-2010, 06:23 PM	#20
philtSF505 Rock Stacker Join Date: Dec 2009 Location: santa fe Posts: 81	yep, should i not be? didnt know what it would do so i tried it, lookin to change the gearing. still very new to this and i'm still learning so if you got any to help i'll take it.

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Thread: HPI Reduction Box gear ratio change