RJ Speed Speedway Sprinter

[Iowa crawler]

Hey Iowa crawler, your build has my sprint car juices flowing again. Gotta get me a kit, if only for a shelf queen.

On a personal note, at image is the sprinter I crewed on in the '70s. Pits at the 'Flying Mile', Springfield, Illinois. Track was w-a-y too big for our little 327. We ran back of the pack in the B-main. After the event our driver climbed out shaking his head, "Never went that fast in my life, and never again here."
We got a good laugh out of that and could brag we did a big-deal USAC event. Once. Cheers. 'AC'

View attachment 154575

I crewed for a sprint car team once. It was a ton of work. I loved the sound and smell. I was like 15 at the time and just getting into real racing.

 

[Iowa crawler]

Just finished my first heat. Fifty laps I have no idea how it went.
What a rush.

 

[Iowa crawler]

Second place in the first heat and second heat. Now I got a 75 lap main event.

 

[Iowa crawler]

Super fun night. I made the A main in second place. And the main is a seventy five lap race. So I started in second place and was just gliding along. I held second place for 66 laps and side smacked the wall. That shattered the rear wheel bearing and caused the axle and spur gear to go out of alignment ending my night. So forth place with a fast lap of 4.41 seconds. I hope I can get some 3 second laps someday.

 

[Greywolf74]

Super fun night. I made the A main in second place. And the main is a seventy five lap race. So I started in second place and was just gliding along. I held second place for 66 laps and side smacked the wall. That shattered the rear wheel bearing and caused the axle and spur gear to go out of alignment ending my night. So forth place with a fast lap of 4.41 seconds. I hope I can get some 3 second laps someday.

Gratz bro! sounds like a good time!

 

[Iowa crawler]

It’s a blast, and a good first time out. The bearing was damaged earlier. I know this because I had to adjust my pinion mesh. And when it hit the wall the bearing came apart. These cars also have a problem with the chassis kinda snapping apart and causing steering problems. It snaps back no problem but hurts the race.
I added a brace to see it that helps but not crashing is the key. Fifty laps sounded like a lot when they announced it. I was kinda freaked out. I was expecting ten laps. But the fifty laps took four minutes and there is no time for recovery if you crash.
Tire dope is super important. You have to clean off you tires when you come off the track and then coat them with tire dope. I also put a piece of tape on the outer edge of the front tire. I started out with just dope on my three tires and left the right front without. This reduced traction and I felt good about it. After two races I used tire wash and cleaned that tire. When I drove back out on the track it picked up dope from the track. I went into the first turn and flipped violently off the track and hit the wall. The track marshal told me to tape my tire and it works great.
I am looking forward to racing it again in two weeks.

 

[ahr43]

Great first time out with the sprinter, IC. She done good.

Doing the math and averaging your 4.41sec laps works out to ~5min 30sec run time for 75laps. That about how it worked out? Lots of battery left?

Yeah, live axle cars want a lot of spur gears in the spares box. Slapped the wall, up did. O.K., you're initiated into the circle track club. Paid your dues.
Tire wear or just went wide? 4.41sec lap can be dizzying. At 66 laps maybe coming up on lap traffic?

Good show and thanks for posting up results. Cheers and two thumbs up. 'AC'

 

[Iowa crawler]

I always take a photo of the results to analyze the math. I am big old number two.

 

[Doom!]

Glad you had a good time and a good showing. 55 laps did sound like a lot, but your right, if it went by that fast, not as bad as it sounds.

 

[Iowa crawler]

I am getting ready for the next race on the following Friday and maybe a couple practice days before then. I am now working on the car.
First thing was the rear axle. It’s fine after the race and broken bearing. The tire took a hit. The crash was a freak thing, I clipped the edge of the panel that makes the guardrail. I have a replacement bearing and the kit comes with a bushing. Having both on hand is good insurance.

One problem I found is the chassis has a habit of popping apart when you crash. It pops back together but the steering is messed up for the remainder of the race. I added a brace across the servo to hold it together. Another thing I did was put Velcro on the top brace under the fairing. It holds tight now. The chassis is assembled with cross bracing and Mortise and tenon joints. but the cross bracing is not tight. So that the chassis is allowed to flex.

I made some adjustments to the ESC and radios. I have to reduce the steering travel to 65% and -50% speed and -50% exponential. That keeps it from turning to sharp.

Three bad thing happed when you turn to sharp. First you scrub speed. Second you spin out. Third the front tire grabs and you fly off the track. To prevent the tire from grabbing I tape the outside edge of the right tire. This is super effective at preventing flipping.

 

[Iowa crawler]

I raced my sprinter last night and the car is dialed in really well. I won both qualifiers with the second fastest lap time. But at the end of the second qualifier I hit the wall pretty hard and it removed the wheel.
The wheel is held to an axle. The axle is just a shaft with an e clip. And a bolt to hold on the wheel. There are some serration on the axle and that, along with a drop of CA hold the front axle into the steering block. A good hit will pull the axle through the steering block and the clip pops off. It should be a nail rather that a clip, but it is what it is and can’t be modded. I did a quick repair between rounds but I under estimated the damage. So while fighting for first place in the main I taped the wall and off went the wheel and my dreams of glory.
The proper fix is to replace the whole steering arm. Cost $7.00 for enough parts to fix it twice and about a dozen clips. So now I know. I’m gonna use some JB weld to fix the broken parts and have them as spares.

Racing the RJ speed products is a lot of fun. They are inexpensive kits. Like 150 dollars and when you smash into the wall it will not be ruined. It’s just that stuff will come apart. You can’t wreck a real car and just keep racing so it is kinda realistic in that sense. They are pretty fast. Just about four second laps and fifty lap races is good.

So I decided to add a modified car to the stable. It’s called an RJ modified and is a little different. No Exocage like the sprinter and slightly different construction. The big difference is the rear suspension is floating. It has a crude suspension and per the rules is five cell nicad with a 20 turn motor. 300 bucks complete and I can run both of these on Sunday morning.

 

[Iowa crawler]

I got most of this together. Need to exchange the motor and get a servo mount. Racing is tomorrow morning if I get it finished.

 

[Greywolf74]

you're a fiend! GO RICKY BOBBY!

 

[Iowa crawler]

Looks like I am going to make the race. Box stock and ready to go.

 

[Iowa crawler]

I put the two cars on the scale. I have never driven the blue one as I just finished it this morning. But the white sprint car I raced last night and it felt really good.
The difference between to two cars is major and I can’t wait to see it n the track. The blue car has a lower CG but 20 grams heavier. Sprint car is 25.5 brushless 2S lipo. The modified is brushed 20T with 5S metal battery.
The modified has a rear suspension. Last night both class had about the same time of 50 laps in four minutes.

 

[Iowa crawler]

Haha did it again. Race tomorrow is pan car. But this gives me a chance to drive it this week.

 

[Iowa crawler]

No race today and it’s cold and raining. So I decided to see if I could build what I want from stuff I have.

The RJ kits come with a somewhat crude steering linkage. It’s two rods held together with wheel collars. I doubled up on the collars but still it seems like crap.
If you hit the wall that’s going to give. Yes you can fix it but your race is done. According to the rules I can add the eight dollar steering kit that RJ sells. But it’s early Sunday morning and I can make it myself. Took me a while to find the parts but I have a bunch of model airplane stuff and after a long parts hunt I realized I pulled the locking diffs out of my TRX6 and it used pivot balls on micro servos. Bingo. A quick Z bend with my fancy Z bend pliers. Then some solder work and presto. Solid adjustable steering links. If I slam the wall the link will pop off. A marshal can pop it back together and I might only loose a lap, not the whole race.

 

[Iowa crawler]

I have tools. I mean a lot of tools. I have worked in a number of jobs and have collected tools for fifty years. I actually want to sell a large percentage of them but no one wants them.
Anyhow one old tool I bought to measure speed of belts and pulleys when building custom cars was a digital photo tachometer. Not something you need like ever. Until you start racing in a spec class using a brushed motor. I can put a piece of tape on the back tire and measure the wheel speed. Then I can change motor or polish a bushing and see if it improves or hurts the wheel speed. I have had this thing for decades and now I get to use it.
Same gearing and same tire diameter on both cars. The RJ Sprinter with a 25.5 brushless motor on 2s lipo turned 3290 rpm. The RJ Modified with a 20T brushed motor on 5S nickel turns 5390. Now I have a base line.

 

[WickedFog]

That is a pretty wicked tool to have.

 

[Iowa crawler]

My regular airplane tach reads through the blades and has a setting of 2 or 3 blades and it measures the brake in the light as the blade passes the sensor. This actually has a light bulb inside and reads off a shiny sticker.
I just peaked the batteries so I have a better base line. Both rigs picked up about 400 rpm.
The reality is the cars drive better as the battery goes down a little. It will be interesting to see the RPM at the start and at the finish of the race.