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View Full Version : Question about kart frame construction....3Phase??



winchman
10-30-2005, 12:51 AM
I ran across this while looking for something else:
http://cgi.ebay.com/ebaymotors/05-T-Kart-T1-New-Worlds-Only-Backyard-Racing-Kart-NR_W0QQcmdZViewItemQQcategoryZ46105QQitemZ45857553 67QQrdZ1QQsspagenameZWDVW

What caught my eye was the frame construction at the rear. You can see it best in this photo:
http://www.tkartsusa.com/images/karts/IMG_9857.JPG

Seems like by leaving out the piece between the ends of the inverted U-shaped seat support he made the frame much less rigid. The weight of the seat will try to spread the rear of the frame, and that will put a lot of thrust load on the axle bearings. The rear bumper provides a little support, but it has that raised section on the lower bar that makes it less rigid, too.

Is there a reason for designing the frame to be less rigid? It looks like a nicely done kart in most other aspects, but this part made me curious.

Roger

TTODD
10-30-2005, 04:20 AM
You need the frame to flex for cornering also if yiu are running a high horse power motor you need flex to get the rear to hook up off corners. If the frame is to rigid th e kart will push going in and be way loose coming off the turn.

torker
10-30-2005, 05:49 AM
<font face="Verdana, Arial" size="2">Originally posted by TTODD:
You need the frame to flex for cornering also if yiu are running a high horse power motor you need flex to get the rear to hook up off corners. If the frame is to rigid th e kart will push going in and be way loose coming off the turn.</font>

That would be my guess also.
The guy who built this knew what he was doing by the look of it.
Very nice bending he did there.
I'm assuming this would be made out of 4130 cromoly so it'd be stronger than it looks.

Your Old Dog
10-30-2005, 06:37 AM
torker, would you believe....


<font face="Verdana, Arial" size="2">Paul bought T Kart Chassis #12 with a chrome powdercoat finish, dry clutch Honda and 6" Burriss tires.</font>

as taken from the ad. Pretty neat stuff!

3 Phase Lightbulb
10-30-2005, 09:30 AM
My guess is that bracket is only for supporting the seat and probably not a needed structual part of the frame. It appears by designing it like that it might offer a tiny bit of spring to the driver's seat (Something I really wish the PsychoKart had). I'm only guessing.

If the kart doesn't have a very strong engine, then you really need to get the inside rear wheel off the ground when making turns otherwise the rear tire scrubbing will slow you down with a live axle.

-Adrian

Fasttrack
10-30-2005, 08:43 PM
yeah, you want them just a little springy. Racing karts run a really steep caster angle so when you steer it actually picks the rear wheel up off the ground a little bit, but if you run a big engine in a rigid cart with steep caster it gets really squirrely coming out of turn.

tkarttrev
11-10-2005, 03:33 PM
Hello,
I found you discussion to be very insightful and appreciate the positive comments about the craftsmanship of the T1. I would like to add some background to the discussion.

The T1 was designed for use on backyard dirt kart tracks, both road courses and ovals. The creation of the T1 came as the result of a blossoming network of backyard private kart tracks. Starting in Essex, CT and spreading to NH, NY, and Ohio so far, the concept is that kart racing can be safe and fun and inexpensive, thus the stock 6.5 hp Honda motor. There is much more about backyard kart racing at www.grasspass.org (http://www.grasspass.org)

As for the design of the rear crossmember on the T Kart, it is the result of 5 years of backyard karting and the study of what frame designs and component selections worked best on dirt road courses with low horsepower. Inspiration was taken from an early 80s era Margay design that was almost unbeatable in the backyard.

I worked with a local chassis builder, T&M Chassis, to create a prototype incorporating what we had learned. The rear hoop is the only crossmember behind the steering column crossmember, and serves several purposes. First, it greatly softens the back of the kart and helps to direct the weight transfer. The bar also allows for easy seat adjustment and has the option of a clamp in aluminum blade type torsion bar. We have tested the bar recently with much success. We also use a 1/4" thick 1-1/4" dia aluminum axle to soften the rear of the kart.

Mention was made of the frame material. We specifically chose a high quality DOM mild steal rather than 4130 to allow more flex with less fatigue and cracking. As we run on very low grip surfaces, often with a moderate amount of surface irregularities and bumps, dust and sometimes mud, we have found that the softer we can make the kart, the easier it is to drive quickly and consistantly. Almost any slide can be recovered, and the kart is very compliant under braking.

We are, never the less, working on a T2 which will incorporate more adjustability, better weight transfer and less rolling resistance.

As you also noticed, we use different rear bumper designs to controll the stiffnes of the rear of the kart.

I would greatly appreciate any more feedback you may have on the design and construction. The whole concept is somewhat "outside the box" so no suggestion will be dismissed, as we currently have about 14 T1's racing in our group, and I would like very much to be able to improove my own karts performance as well as improove the performance of future designs.

I had not seen this forum before, but from the looks of the threads, there are some knowledgable and creative minds here.

Thank you again for the discussion.
There are more pictures of the kart at www.tkartsusa.com (http://www.tkartsusa.com)

Trevor Hilliar
T Karts

3 Phase Lightbulb
11-10-2005, 05:30 PM
<font face="Verdana, Arial" size="2">Originally posted by tkarttrev:
The T1 was designed for use on backyard dirt kart tracks, both road courses and ovals.</font>

I'm not sure if my design is more suited for a backyard track, or a grave yard track http://bbs.homeshopmachinist.net//smile.gif

PsychoKart Video High Quality (720x480) (23MB .wmv) (http://www.psychokart.com/videos/psychokart_video_high.wmv)

PsychoKart Video Med Quality (320x240) (2.4MB .wmv) (http://www.psychokart.com/videos/psychokart_video_low.wmv)

http://www.psychokart.com

http://www.psychokart.com/photos/photo2.jpg

-Adrian

torker
11-10-2005, 06:31 PM
Trevor, I didn't realize you used these on dirt.
I therefore agree with your choice of DOM tubing.
I've raced tube chassis blown alky powered mudrails for years and we eventually found the same thing.
The rough pounding our machines take and the high horsepower(some around 3000hp) causes chromoly to fatigue over a short time.
Some (mine included)of these DOM chassis are quite old now and still stand up to the abuse.
Russ

CCWKen
11-10-2005, 06:55 PM
I used to race karts in the super stock and modified classes with Briggs engines. The chassis made from chrome molly tubing would last about a year then develope cracks. The cracks weren't near welds so it wasn't bad welding techniques just high stresses and flexing.

A tight chassis wouldn't turn worth a hoot. A wet track (pavement) made a tight chassis worse. You learned quickly that full power into a turn got you through a hairpin even on a wet track with slicks. Frame flex and weight transfer was key.

The pic of the T1 brings back a lot of fond memories. My SS was clocked at 60 on a 200' straight. The modified would do over 100. All with your ass 1/2" off the ground. http://bbs.homeshopmachinist.net//biggrin.gif

BillH
11-10-2005, 09:43 PM
I had a go-cart once. One time the brake cable snapped and I rolled off my driveway into a street, thankfully no cars. Another time I didnt quite make it up a hill and I started to roll backwards. The band brake only worked going forward. My head missed the boat trailer by inches. Thought I would sell the thing before I killed myself on it.

jburstein
11-11-2005, 09:50 AM
So you essentially create suspension for the cart by making the frame floppy? That's kinda weird. I guess that's one way to skin that cat, but it seems like it would be better to add in some actual tunable suspension. Is it just a cost issue, or is there another reason?

-Justin

tkarttrev
11-11-2005, 10:38 AM
Regarding the use of suspension, the T Kart is based on a racing kart design, which specifically prohibit any suspension. The kart is not only able to race in the back yard, but can be taken to one of many paved kart race tracks and raced competitively with groups like the WKA, IKF and SKUSA.

If you look at racing kart designs, there is very little variety among designs mostly due to rules.

Trevor

3 Phase....Nice rocket you have there. I would like to try that in my back yard http://bbs.homeshopmachinist.net//smile.gif

Farmer Joe
11-11-2005, 11:05 AM
tkarttrev,

Thank you for the information you provided! I have a 5 acre field that I thought would be a fun track for my son to run on ( he is 2 1/2). I was discussing with my friends making a track for him when he is older. Now I'm really motovated!

Ron LaDow
11-11-2005, 12:52 PM
<font face="Verdana, Arial" size="2">Originally posted by tkarttrev:
[B]Regarding the use of suspension, the T Kart is based on a racing kart design, which specifically prohibit any suspension.</font>
Sports car racers used to joke about the '5th spring' on Brit cars; one on each corner and the flexi bits connecting them.
But there was also a guy who ran the 750 Club races where they mandated a suspension. He mounted the axels in Lord mounts and probably got close to what you have. He also got banned...
Thanks,
Ron LaDow

CCWKen
11-11-2005, 08:17 PM
Oh, but the kart frames WERE able to be tuned! You don't need "suspension" to tune a frame. The tuning was done at the front, rear and bearing hangers. The frames weren't "floppy" and you could feel every bump.

Dang! I'm gonna have to build a kart and track now. That is if I can find a couple of acres without cactus. http://bbs.homeshopmachinist.net//biggrin.gif

tkarttrev
11-14-2005, 07:54 AM
Great to hear the interest, we have a great time with it. We just started running on grass, it turned to dirt and now we have a surface which is incredibly hard. A donut in a kart will leave black circles on the dirt.

Trev

mattc
11-14-2005, 08:12 AM
maby I should put a track in when I get done clearing I think I will have enough room to make about a 1/4 mile circle track for now I would need some realy big tires
http://img.photobucket.com/albums/v639/mattcatledge/4-7-05006.jpg

Matt in AK