xah
Newbie
Posts: 5
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Post by xah on Dec 6, 2011 11:59:17 GMT -6
We're running on a plastic track (supertimer) with no center rail. I have a few questions:
1) Will the Derby Worx pro body tool allow me to drill the axle holes higher up the body so I can get a lower center of gravity (less clearance)? it doesn't look as though it will.
2) if it will, what ground to body clearance should I go for? strikes me that the less clearance (obviously without catching) would be the best.
3) Obviously we can't rail ride with no center rail, but should we still aim to ride on 3 wheels? if so, does it make sense to shape the body with the majority of the front weight towards the used wheel (so an unbalanced front end)?
4) given there is no center rail, should I even consider camber? I think toeing is out with no center rail, but cambering to only have the inside edge of the wheel make contact seems to be a reasonable option still.
Thanks guys!
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Post by RacerX on Dec 6, 2011 12:18:16 GMT -6
Lets see if this is any help.
The Pro Body Tool 2 will not make your car any lower than the provided slots because it is designed to work for both making axle holes and drilling straight axle holes in the slots (its the same height as the slots) this also allows room on the bottom of the car for stick or screw on weights. If you want to lower your ride height, we recomend the Pro Body Jig. This will get you close to the min on ride height for a lower cg, but you will need to pocket your weights in. Lower is better.
I'm not a expert here, but we have been told if you reverse the Rail Rider process and reverse your front dominant wheel (smooth inner edge out) to ride the outter edge of the track, it works well.
I would set your weights and alignment so the car is neutral and then steer out with the wheelfor the outter guide strip.
Let us know how it goes.
Racer X
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Post by *5 J's* on Dec 6, 2011 12:29:42 GMT -6
when considering how low you can sling the weight - make sure you consider the curve
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xah
Newbie
Posts: 5
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Post by xah on Dec 6, 2011 23:06:09 GMT -6
If you want to lower your ride height, we recomend the Pro Body Jig. This will get you close to the min on ride height for a lower cg, but you will need to pocket your weights in. Lower is better. Do you mind just clarifying the body jig for me? as I understand things, it will make the axle holes exactly 5/32" from the bottom. Is that understanding correct? On a side note, you haven't considered renting your tools out have you? I'd gladly pay say $12-$15 to rent the Pro body jig, but not so sure about $38 to buy it......... thanks for the feedback so far.
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xah
Newbie
Posts: 5
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Post by xah on Dec 6, 2011 23:11:11 GMT -6
when considering how low you can sling the weight - make sure you consider the curve Given the curve is concave, and as long as the wheels are near the ends of the car I should be good I think, as mid curve, the center of the body will be at its furthest distance from the track, or have I got that the wrong way round...? It works in my head!
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tkp
Pine Head
Posts: 65
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Post by tkp on Dec 6, 2011 23:32:14 GMT -6
I can respond more tomorrow however, here is what I can quickly provide regarding this track:
In general: Very fast track- we ran 2.9's this year for 42 feet. Running straight on this track is key- sand outside wheels The edge of the track is smooth but the lip of the track goes directly into your wheel The end garage is deadly. Like a concrete wall- in fact at Pack this year- big bent axle Cars that do not have weight low or too aggressive on com will spin off or wobble
Things that have worked for my sons: very low and centered tungsten- 3.75 oz with 3/4 COM testing 5/8 com next month- will let you know... straight runner 3 wheeler canted rear axles- to keep weight low- as this track can produce the wobbles!! tight wheel spacing- ie 1/16 to 1/32 lightly sand the lettering on the outside of the wheel- very light can help with walls Hob e lube the heck out of the outside wheels, body, axles etc On the raised front wheel- he prep's it big time- axles, wheels etc- it's in great shape very smooth and no need to be conservative on COM move .3 from back to front
Will share more tomorrow...
But sons now run 2.9's every year and have won pack and districts many times on this track.
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Post by Murph on Dec 7, 2011 1:00:19 GMT -6
Shawn and I tried to run an "inside out" rail rider on a plastic track. Darn car was slow. They had an adult division and our "straight runners" were clearly faster than the inside-out rail rider.
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tkp
Pine Head
Posts: 65
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Post by tkp on Dec 7, 2011 11:00:59 GMT -6
Additional Clarification:
2- Yes, we actually slightly increase the depth of the axle slots on cars. As you can imagine, this allows the axles/wheels to allow the car to sit even a bit lower to add for some increase in stability. Since the track is very smooth and the slope is typically not too concerning- we have gone pretty low on our cars- IE- made 1/8 deeper axle slots.
3- Yes- a 3 Wheeler on this track definitely produces a faster car. Our son's cant/camber the rears at about 2 degrees to reduce wheel to track percentage and ensure that wheel runs on axle head and never the body, and on the front DW we use slight toe in. The cant also allows the car to sit even slightly lower. Net is- 3 wheeler is a must have and to your question about leaving more body on one side in order to allow for 3 wheeler in which the 4th wheel will never touch the track- I would simply recommend to use weighting and slightly shift your weight to one side instead of adjusting your car body. I can let the other experts here chime in, however, even when I use 3 wheeler, I slightly shade weight to one side to ensure the lifted wheel never touches- but truly, its not much as I want to ensure it has some affect here, but not too much weight on one side which will potentially put additional forces on axles/wheels on the heavier side of the car. There may be some formula that someone has come up with and related topics may be titled Triangulation- you can search that and see what you come up with. However, again, I use weight, not body and "slightly" leverage this shift away from raised wheel. I never put weight up front- all in the back.
4- Camber/Cant- as mentioned above- yes this puts the car lower and argueably, reduces wheel to track friction. But on this track Camber has seemed to produce slightly faster cars with no wiggle/wobble. If you use Camber and increase the depth of the axle slots, the car will most definitely sit lower than your competition. However, no need to be over the top aggressive here, as mentioned 2- 2.5 degress on camber and perhaps 1/8 inch deeper axle slots all in an effort to keep car/weight low and provide a slight increase in stability.
I would also mention that we actually slightly steer our cars to the side with 2 wheels touching as hitting the raised non-rolling wheel on the side of the track takes a bit of energy and impacts speed as opposed to the two rolling wheel side of the car hitting the wall. Generally speaking, if the car hits the wall- and it will, we would rather it hit the side that has spun up wheels. We typically steer about 1 inch in 10 feet to that side. This is your call, but it's what we have found.
As also mentioned to increase stability we move .3 from back to front. At the end of the day, see if your car can have "very close" to 4 oz weight on back wheels and 1 oz weight on front wheels.
In review:If you have a car that has at least 3.5 oz of tungsten at 3/4 com, with canted axles and slightly deeper slots, 3 wheeler, either very straight runner or "near straight runner" as mentioned above, move back to front, keep weight low, don't graphite the wheel tread as produces opportunity for track slippage, tight wheel spacing to avoid any shimmy starting at all etc you will have an awesome car for this track. These specs are pretty much what we do about every year and as mentioned track times are 2.9's and no wobbles. We are testing 5/8 com this year and will let you know next month how that goes.
Lastly, please check your axles after every race as almost every year the fast cars hit the garage and bend axles. We have been lucky as most times it was the raised wheel!! ;D
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xah
Newbie
Posts: 5
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Post by xah on Dec 7, 2011 13:53:41 GMT -6
This is really helpful, many thanks. I'll update with progress (and almost certainly some more questions) as I go.
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tkp
Pine Head
Posts: 65
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Post by tkp on Dec 7, 2011 14:12:29 GMT -6
No problem and good luck. I didn't want to go down any bunny trails but also should mention we also spend a good amount of time on sanding, polishing, burnishing, etc on wheels and axles as well. Again good luck and I'm sure you and your son will be all over it!
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Post by RacerX on Dec 7, 2011 21:23:23 GMT -6
If you want to lower your ride height, we recomend the Pro Body Jig. This will get you close to the min on ride height for a lower cg, but you will need to pocket your weights in. Lower is better. Do you mind just clarifying the body jig for me? as I understand things, it will make the axle holes exactly 5/32" from the bottom. Is that understanding correct? On a side note, you haven't considered renting your tools out have you? I'd gladly pay say $12-$15 to rent the Pro body jig, but not so sure about $38 to buy it......... thanks for the feedback so far. The Pro Body Jig makes the holes .188" from the bottom of the body or 1/10" lower than the Pro Body Tool 2. The accuracy of having them tied together in one fixture makes it even BETTER!!! No, we do not rent tools. besides, by the time you payed rent and freight both ways, you just about bought it. Racer X
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Post by dnd720 on Jan 17, 2012 22:39:24 GMT -6
Additional Clarification: 3- Yes- a 3 Wheeler on this track definitely produces a faster car. Our son's cant/camber the rears at about 2 degrees to reduce wheel to track percentage and ensure that wheel runs on axle head and never the body, and on the front DW we use slight toe in. The cant also allows the car to sit even slightly lower. Net is- 3 wheeler is a must have and to your question about leaving more body on one side in order to allow for 3 wheeler in which the 4th wheel will never touch the track- I would simply recommend to use weighting and slightly shift your weight to one side instead of adjusting your car body. I can let the other experts here chime in, however, even when I use 3 wheeler, I slightly shade weight to one side to ensure the lifted wheel never touches- but truly, its not much as I want to ensure it has some affect here, but not too much weight on one side which will potentially put additional forces on axles/wheels on the heavier side of the car. There may be some formula that someone has come up with and related topics may be titled Triangulation- you can search that and see what you come up with. However, again, I use weight, not body and "slightly" leverage this shift away from raised wheel. I never put weight up front- all in the back. 4- Camber/Cant- as mentioned above- yes this puts the car lower and argueably, reduces wheel to track friction. But on this track Camber has seemed to produce slightly faster cars with no wiggle/wobble. If you use Camber and increase the depth of the axle slots, the car will most definitely sit lower than your competition. However, no need to be over the top aggressive here, as mentioned 2- 2.5 degress on camber and perhaps 1/8 inch deeper axle slots all in an effort to keep car/weight low and provide a slight increase in stability. I would also mention that we actually slightly steer our cars to the side with 2 wheels touching as hitting the raised non-rolling wheel on the side of the track takes a bit of energy and impacts speed as opposed to the two rolling wheel side of the car hitting the wall. Generally speaking, if the car hits the wall- and it will, we would rather it hit the side that has spun up wheels. We typically steer about 1 inch in 10 feet to that side. This is your call, but it's what we have found. As also mentioned to increase stability we move .3 from back to front. At the end of the day, see if your car can have "very close" to 4 oz weight on back wheels and 1 oz weight on front wheels. In review:If you have a car that has at least 3.5 oz of tungsten at 3/4 com, with canted axles and slightly deeper slots, 3 wheeler, either very straight runner or "near straight runner" as mentioned above, move back to front, keep weight low, don't graphite the wheel tread as produces opportunity for track slippage, tight wheel spacing to avoid any shimmy starting at all etc you will have an awesome car for this track. These specs are pretty much what we do about every year and as mentioned track times are 2.9's and no wobbles. We are testing 5/8 com this year and will let you know next month how that goes. Lastly, please check your axles after every race as almost every year the fast cars hit the garage and bend axles. We have been lucky as most times it was the raised wheel!! ;D I am new to the forum. This is a great source of info with people willing to help other competitors, nice to see. Our pack races on this same type of track. We have never tried a 3 wheeler or adding any camber, although our wheels always migrate to the axle heads on our alignment board (I think there is a small amount of unintentional camber due to polishing of axles and the axles being slightly smaller diameter near the head). A few questions based on what TKP wrote: 1. You state using camber on the rear axles, ever tried any camber on the front axles? 2. Our rules state that all 4 wheels must touch the track, this is partially why I am wondering about camber on the front axles. Also wondering about trying to make a NDFW that just barely touches the track. I am concerned that this may result in wheel wobble as the wheel will have nearly zero pressure on it and would essentially be "hanging" from the axle. I am thinking it may intermittently touch the surface as it goes down the track. Anyone have experience with a "barely touching" NDFW for a pseudo 3-wheeler? 3. Regarding having "at least 3.5 oz of tungsten at 3/4 com". Does it really matter how much tungsten you have and where it is located fore/aft as long as you obtain 3/4 COM? It seems you can still get 3/4 COM with a different amount of weight and with the weight positioned differently. With our current car we are going to have ~2.5 oz of tungsten behind the rear axle and ~0.3 oz just in front of it in order to get 3/4" COM with the car design we chose. I just want to make sure I am not missing something here. Thanks in advance for any help. I look forward to the responses.
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Post by Murph on Jan 18, 2012 23:27:38 GMT -6
You can certainly use camber on fronts to keep wheels out on heads. When you tune the car, tune with just one front wheel (one with most weight) and than add other front wheel and tune.
That extra wheel that is just barely touching can be tuned to not be a hindrance. Just play with it for a period of time. Get frustrated, leave and come back later.
You are correct, strive to attain 3/4 to 1" COM. Do it your way but try to keep the weight low.
Hope this helps! Murph
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tkp
Pine Head
Posts: 65
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Post by tkp on Jan 26, 2012 0:13:41 GMT -6
Tried camber on the rears however not the front. We have found that the track is too slippery and we now go flush with front on the track having a good contact for driving the steering. Again, not on front, however technically one could toe in the front DW and determine is this assists with speed. We have found no delta to date.
4th wheel barely touching the track should not result in wheel wobble considering that all other best practices are solid and complete- IE rear wheel alignment, FDW alignment, not too heavily weighted- IE at leaset 15 grams on front end of car. etc, etc.
It does make a difference on the track in speed if you have a smaller area of mass that gravitational forces are working on. IE- smaller area and height above axle for example. However at the end of the day, while it's not perfect, remember, the simple fact that you have at all 3. 5g tungsten in the car with 3/4 cM will produce a fast car- just not as fast it it could be considering tighter CM point and location of CM point- again, at axlesl, above axles etc.
Remember alot of the weight placement and it's affect on speed are related to MOI. Moment of Inertia- transition from Potential to Kinetic Energy.
Lastly how long is the track- curious on CM placement. On long tracks we may go back to 1 inch CM.
TKP
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Post by dnd720 on Jan 31, 2012 13:55:36 GMT -6
4th wheel barely touching the track should not result in wheel wobble considering that all other best practices are solid and complete- IE rear wheel alignment, FDW alignment, not too heavily weighted- IE at leaset 15 grams on front end of car. etc, etc. It does make a difference on the track in speed if you have a smaller area of mass that gravitational forces are working on. IE- smaller area and height above axle for example. However at the end of the day, while it's not perfect, remember, the simple fact that you have at all 3. 5g tungsten in the car with 3/4 cM will produce a fast car- just not as fast it it could be considering tighter CM point and location of CM point- again, at axlesl, above axles etc. Remember alot of the weight placement and it's affect on speed are related to MOI. Moment of Inertia- transition from Potential to Kinetic Energy. Lastly how long is the track- curious on CM placement. On long tracks we may go back to 1 inch CM. TKP Thanks for the replies Murph and TKP. A few more questions: I understand how to check and adjust the front wheel alignment. What is the process for aligning the rear wheels? Could you elaborate on your statement about weight placement and its effect on speed as related to MOI? If I am thinking correctly a tighter placement of the tungsten would result in a smaller MOI, but I don't understand how that translates to speed. Is is something to do with the transition from the angled portion of the track to the flat section? Lastly the track is 35' long. Last year with 1.125" CM, all 4 touching (one front wheel was dom), extended wheel base, no intentional camber (wheels did drift to axle heads on alignment board) we ran 2.475 sec best, 2.484 ave. Our current car is close to being finished, w/extended wheelbase, we are going to have 2.5 oz directly behind the rear axle and 0.7 oz directly in front of the rear axle to get 3/4" COM. Does this setup seem resonable? Are there any issues related to MOI or anything else that this might cause that I am not seeing? Thanks!!!
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tkp
Pine Head
Posts: 65
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Post by tkp on Jan 31, 2012 16:06:49 GMT -6
A bit short on time, and perhaps Murph and others can chime in however.. Rear wheels- use a tuning board or slight decline smooth running board. Only have your rear wheels on and on the front underneath nose front, put on the slick side of tape or something simliar so the nose will slide easy. Get the rears to roll on axle head- frontwards and backwards and try a few runs down the board-(again with just rear wheels on- and slick front end) Make Sense? Does it run straight? This "skid" test will give you a real good idea of if your rears are aligned. Again, also make sure they don't touch body and go out to axle head moving frontwards and backwards. Also, you can use a yardstick and straddle that with car- this will tell you if you hit it etc and your alignment is off, or drawn lines, use strings etc to respresent a straight track alley on your running board/test plane. IE for STrack, its about 3.4 inches wide. Net- do what you need on your running board to dial in on the fact that its running straight! Lastly, canting or not, car needs to run straight and on axle head with just rears on. Once you feel good about your wheel to axle head and its straight running with just rears on- you are most likely very very close. MOI- yes you are right there. It has everything to do with transition from hill to flat- IE potentially stored energy into moving energy. The smaller area the better- But, dont get too caught up on just that point. If you use tungsten and have good CM you should be good. For reference- check out my POST about the Flaming Phantom that my son just raced. See how he did the tungsten in the rears? This is more then sufficient related to MOI and CM. Sounds like you have about 3.3 in Tungsten, that should be a fast car if all else is solid!! My humble opinion a 3/4 CM is perfect for this track and I would recommend to not go under. We have gotten to 5/8 but we have been doing this for years and have learned just about every hard STrack lesson there is. 3/4 CM with 3.3 tungsten is good. BTW- what is your wheel spacing and what is car front end weight? The reason I ask is you reference- is there anything else ie MOI that I should be concerned about... This track as you know can produce the shimmies very easily when you start to press it. I just want you and your son to build a smoking fast car, BUT stay on the Track! Extended WBase will help and CM isnt over the top and Tungsten isnt overweighted, so it would be helpful to know wheel to body spacing and front end weight. We have pushed front end weight to the limit, however what I would recommend on your car is for front end weight to be at least .75 oz! Do you have pic? TKP
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Post by dnd720 on Feb 1, 2012 22:00:34 GMT -6
Thanks for the additional info TKP.
When checking the rear wheel alignment per your method, if the car doesn't track straight, how do you determine which wheel/axle needs adjustment since they are both essentially dominant?
To answer your questions about spacing and front end weight. I was planning on using 0.035" wheel to body spacing. The car isn't totally finished yet, but front end weight looks to be very close to 0.75 oz.
Sorry, I don't have pic, camera is not cooperating tonight. Will try and get one.
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tkp
Pine Head
Posts: 65
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Post by tkp on Feb 1, 2012 22:47:23 GMT -6
This post is really turning into quite a good set of topics! Not sure I even want to bring up camber and RR yet and this topic falls under Plastic track and ride height...so....Trying to keep it straight and simple as possible.... To start- if the car drifts to the right then you most likely have some "toe out" going on with the right rear. If you drift going left, then you most likely have "toe out" on the rear left wheel. Toe out is front side of wheel slightly opened from being flush/exactly parallel to car body, toe in is front side of wheel slightly angled toward car body- make sense? Meaning if it drifts right you have the rt rear tire with a slight angle going to the right. (I suppose it could also mean some Serious Toe in on the left tire- but most likely toe out on rears) If you used axles slots and no drilling (like we have to) you can use shim method to adjust the steer/toe or use needle nose pliers carefully to tweek the axle toe in/out. Hopefully this at least gets you to align rears and tune it a bit, (assuming no RR and no camber) Again, at the end of the day, needs to run straight on rears and ride on axle head frontwards and backwards- these are the keys. Then you can have some fun with your son on the fronts! For me and my son, this is the most tedious part of his cars every year. Like Murph states- we take breaks and come back to it if necessary. Lastly, there are other folks on this Forum that are way more anal then us or have better processes, so hopefully they can chime in. Oh- on wheel to body spacing- we use a gauge for that, but generally a credit card width will do nicely. TKP
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