John82601
Rock Crawler
The LHS has purchased a sled and has announced that we'll start pulling outdoors this spring and will be using the 5280 Pulling Club rule set. I've always enjoyed pulling at our gatherings but it's always been very informal with no real rules. So I decided to try to build a truck, on a budget, that would be competitive. Unfortunately, my patience and fab skills are both, um, lacking. So here we go.
I purchased a used chassis set from another member here. Soaked in Simple Green and attacked with a toothbrush and it came pretty clean.
The rules call for a max wheelbase of 11.75" which just happened to match up pretty well with a body I had laying around. My friend Ryan painted this some time ago but I'd just never found the right use for it.
Once I'd mounted the body where I wanted it, it was time to figure out where to set the wheelbase. I'll be competing in two classes with the truck, 4WD Super Stock requires a scale looking tire, 1.9" wheel or smaller. 4WD Mod calls out two spec tires and one of them is the TLT-1. The body resting on the tires.
The toughest part of this project has been the challenge presented by the small amount of underhood area the body provides. I wanted to keep the ride height as low as possible but have enough front suspension to tame a track that might not be perfectly groomed. I tried front steer, rear steer, attempted a Wheely King style pivot mount and ended up at a front steer setup. LOTS of experimenting went on.
Ultimately, I ended up limiting the stock SCX shocks inside and out to get a reasonable height and 8mm of travel (no scientific reason, 8mm just looked right). I gained some clearance for the upper Y link by removing the crossmember that ties the shock towers together. I put some strength back into the structure by tying the upper shock mounts together.
In the rear I started out with a simple L bracket to tie the axle housing to the chassis. I went with shorter lower links to put them at a greater angle so the moment about the axle will be trying to lift the front of the truck vs pushing straight forward. This can be played with later once I find out if this works or not. Later, I added a 3rd link from the alum plate above the axle to the skid. This way the axle is locked from rotation in both directions in 2 axis.
I thought about fabbing a hitch but the one offered by 3Racing for the SCX is just a pretty unit. Time will tell if it's strong enough. Drawbar height came out about 2.3", just below the 2.5" limit. I used 1/2"x1/8" flat strap for the structures to hang the weights on. The rear is a really simple L mounted to the top of the axle and the front is a U shaped piece with an additional front piece bolted on. I'm somewhat skeptical about the front piece being attached to the frame with M3 hardware. I'm thinking an alum front crossmember and some M4 hardware will be added soon.
I found weights on line, a little over $1 ea, weigh in at .25lb each. A pair of Baja 5b body clips seemed like a simple enough solution to keep them in place. Looks like I can add 3lb on the front and 1.5lb over the rear axle. Both classes I'm planning to run are 10lb max. W/O tranny, electronics, etc but full of weights the truck is currently at 7.3lb. Might be a little light when all is said and done. (warning - blurry picture)
So here's where we sit today. I'm waiting for my last Robinson Racing steel trans gear to come in so that I can finish the drivetrain. MIP driveshafts are on order. For power I'm planning to run a Castle 3800kv on 2s in the lower class and switch to 3s for Mod. It will present quite an amp load but I think a MMP will be sufficient as the runs are only 7-10 seconds in duration.
The last real "modification" I have planned before doing some testing is to narrow the rear axle. I've read that it's pretty straightforward by using some C's off of the front axle and trimming the ears off. I've ordered a pair of 13x5x4 bearings to do the job and will be trying it out once they get here.
Any questions, comments or suggestions please post up!
I purchased a used chassis set from another member here. Soaked in Simple Green and attacked with a toothbrush and it came pretty clean.
The rules call for a max wheelbase of 11.75" which just happened to match up pretty well with a body I had laying around. My friend Ryan painted this some time ago but I'd just never found the right use for it.
Once I'd mounted the body where I wanted it, it was time to figure out where to set the wheelbase. I'll be competing in two classes with the truck, 4WD Super Stock requires a scale looking tire, 1.9" wheel or smaller. 4WD Mod calls out two spec tires and one of them is the TLT-1. The body resting on the tires.
The toughest part of this project has been the challenge presented by the small amount of underhood area the body provides. I wanted to keep the ride height as low as possible but have enough front suspension to tame a track that might not be perfectly groomed. I tried front steer, rear steer, attempted a Wheely King style pivot mount and ended up at a front steer setup. LOTS of experimenting went on.
Ultimately, I ended up limiting the stock SCX shocks inside and out to get a reasonable height and 8mm of travel (no scientific reason, 8mm just looked right). I gained some clearance for the upper Y link by removing the crossmember that ties the shock towers together. I put some strength back into the structure by tying the upper shock mounts together.
In the rear I started out with a simple L bracket to tie the axle housing to the chassis. I went with shorter lower links to put them at a greater angle so the moment about the axle will be trying to lift the front of the truck vs pushing straight forward. This can be played with later once I find out if this works or not. Later, I added a 3rd link from the alum plate above the axle to the skid. This way the axle is locked from rotation in both directions in 2 axis.
I thought about fabbing a hitch but the one offered by 3Racing for the SCX is just a pretty unit. Time will tell if it's strong enough. Drawbar height came out about 2.3", just below the 2.5" limit. I used 1/2"x1/8" flat strap for the structures to hang the weights on. The rear is a really simple L mounted to the top of the axle and the front is a U shaped piece with an additional front piece bolted on. I'm somewhat skeptical about the front piece being attached to the frame with M3 hardware. I'm thinking an alum front crossmember and some M4 hardware will be added soon.
I found weights on line, a little over $1 ea, weigh in at .25lb each. A pair of Baja 5b body clips seemed like a simple enough solution to keep them in place. Looks like I can add 3lb on the front and 1.5lb over the rear axle. Both classes I'm planning to run are 10lb max. W/O tranny, electronics, etc but full of weights the truck is currently at 7.3lb. Might be a little light when all is said and done. (warning - blurry picture)
So here's where we sit today. I'm waiting for my last Robinson Racing steel trans gear to come in so that I can finish the drivetrain. MIP driveshafts are on order. For power I'm planning to run a Castle 3800kv on 2s in the lower class and switch to 3s for Mod. It will present quite an amp load but I think a MMP will be sufficient as the runs are only 7-10 seconds in duration.
The last real "modification" I have planned before doing some testing is to narrow the rear axle. I've read that it's pretty straightforward by using some C's off of the front axle and trimming the ears off. I've ordered a pair of 13x5x4 bearings to do the job and will be trying it out once they get here.
Any questions, comments or suggestions please post up!
