how do i make a sled?

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Location: Holland

Post by Micropuller » Sat Apr 10, 2004 11:44 am

Here you can find some pics taken during the construction of the sled we currently use for our competitions: ... woerd.html

A short run through:

The rear wheels drive a gear reduction unit, which drives the chain. The weight-box has a pin in the back which can be put through the chain, so when the chain moves. the box (which runs on bearings) gets pulled foreward.
Just before the box reaches the front of the sled, the chain makes a 180 degree turn and the box runs off the chain. This way the drive doesn't seize up when the box tops out.
Our sleds are built using the "downhill" principle. This keeps the centre of gravity low, so there's less chance of the sled toppling over during course corrections at high speed.
The pan is mounted "hinged" for two reasons. First is to enable it to run over uneaven parts of the track more easily. Secondly, our sleds have a mechanism which lifts the rear of the pan off the track, so less resistance is created at the start. During the pull, the weight-box gradually pushes down two leavers, lowering the pan. In the part of the pan which can be raised / lowered, there are also some metal strips, which can be adjusted to protrude from the underside of it. These create even more resistance.
One very important thing is having the correct balance in your sled, so there's not too much weight on the pan at the start (the truck or tractor won't be able to get up to speed if this is the case) But if it's too light, the puller won't have enough grip and just spin the tires. To achieve this, our sleds have an aluminum pan, with a thin stainless steel sheet attached to the bottom (if the stainless wasnt there, we'd need a new pan every four or five times whe have a competition, because of the wear)
The last very important thing is the chain which connects the puller to the sled. If it's too long, the truck / tractor won't get any grip. If it's too short the front of the truck / tractor will climb way too high and the driver can't control it. Another bad thing about a chain that's too short is, that the rear tires of the puller can touch the pan when doing a major correction, ripping the rear tires to shreads.

One important thing to remember is that there's two way's of pulling; just using grip, which requires a heavvy puller with lots of torque (high gear reduction). The other way to do it is using "friction pulling" This requires the rear wheels of the puller to rotate at high speeds, thus creating friction between the tires and the track, which in turn provides foreward motion. This method enables a relatively light truck / tractor to pull a lot more weight.
All the pullers in our club are set up for friction pulling, which means that our sled have to be relatively light weight at the start of a pull and brake very hard at the end (that's why we have the strips)

We noticed the difference very clearly when we had some German micropullers over for a demo. Their tractors, although being the same size and weight, are built to have a lot more grip and less wheelspin. Also (or because of this), their sled is a lot heavier at the start. As a result, when we used one of their sleds, our tractors could not get up to speed and showed some very poor results. But when our sled was used, the German tractors didn't have the speed to keep the sled moving when it really started to brake (or "throw out the anchor" as we describe it)
Real tractorpullers do it in the dirt

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Post by fantomracer » Sun Apr 11, 2004 12:35 am

what tires dyou use what gear ratio? and what do you use to make the box heavy? and what do you use for tracks? how long should it be?

Clodosaurus Rex
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Re: how do i make a sled?

Post by Clodosaurus Rex » Thu Jan 19, 2017 11:18 am

I'd apologize for epic necro... but nah, sleds and pulling are just too cool to leave sitting back on the last page.

I've always got the idea to eventually try and build one in the back of my head, I understand the general principles and how it all works together, but working out that gear reduction for 30ft seems like a good way to wind up in a rubber room or something lol. Would love to see pics from anybody who has put one together and hear how you managed it all.

Just gonna leave this here for anybody who has too many spare gear sets in their parts box that need stripping and waaaaay too much time on their hands!

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