| Here is a typical go kart building scenario: | | | | a 1.5 inch sprocket for the engine the following will |
| "The anxious go kart builder was putting the finishing | | | | occur: |
| touches on his go kart. He just applied the giant decal | | | | Tengine = 300*.17*(6 inches* .75 inches)/(4 inches) |
| that said "monster" on the ground effects graphics on | | | | Tengine = 57.3 in-lbs |
| the side of his gocart. He then fired up the engine on | | | | Hp = 3.27 hp |
| the go kart and proceeded to smoke the clutch." | | | | A word of caution: we might be all ecstatic about the |
| Notice, the scenario here: "smoking the clutch" versus | | | | information just calculated, but remember that the 3.27 |
| "smoking the tires." | | | | hp is probably going to be the amount of HP required |
| In fact the go kart did not go anywhere and it was | | | | at 1800 rpm and typically a 5 hp engine for example |
| very frustrating. The question should be: "Why in the | | | | will be giving off that much power at 1800 rpms. |
| world was the clutch smoking?" | | | | The thing to keep in mind is that the go kart, even |
| More specifically, when the go kart was being | | | | though it has a 5 hp engine may stall at the top of the |
| developed and designed, why was this clutch problem | | | | hill. |
| not addressed? | | | | So the question is what do we do? |
| The answer lies in the fact that the assumption was | | | | -If you want the go kart to climb hills but cannot afford |
| made that the drive system was fine, that the clutch | | | | to change out engines, then make the rear drive |
| size, the chain size, the sprocket sizes were simple | | | | sprocket larger. |
| things that really didn't need that much attention. After | | | | -If you want the go kart to climb hills and can afford to |
| all, a go kart is simple right? | | | | up HP then increase the hp, but beware, make sure |
| Yes, the concept of a go kart is simple in its | | | | the clutch is rated for the higher hp. |
| conception, but really does require some thought when | | | | -If you want to climb hills, but not change the ratio, then |
| the weight of the go kart starts to exceed 100 pounds. | | | | you need to consider a more complex solution which |
| The standard off the shelf components may not apply | | | | amounts to a variable speed clutch. |
| to the go kart that is being designed. | | | | When you start increasing the ratios, you automatically |
| The next most common question is "How do I | | | | start increasing the chain tension. You will run into |
| calculate the drive system so that the clutch won't | | | | issues with that, in that the chain tension may be too |
| smoke?" | | | | high and cause it to fail prematurely. |
| The answer lies in the following variables: | | | | So the next problem that a go kart will run into is the |
| -Weight of the Go Kart (with occupant) | | | | chain tension is too high for the chain rating. |
| -Engine Drive Gear Size | | | | Using the following equation you can calculate the |
| -Rear Axel Drive Gear Size | | | | chain tension and then apply it to the chain ratings |
| -Rear Tire Size | | | | charts that chain manufacturers put together. |
| -Angle of Hills Being Climbed | | | | Chain Tension = Engine Torque/Radius Engine |
| What you will be looking to define from these variables | | | | Sprocket. |
| is the chain tension and the clutch loading. | | | | Visit chain manufacturer sights for chain loading charts |
| First the clutch loading is figured by determining the | | | | and acceptable load data. If you look hard enough |
| rating of the clutch and the expected torque that is | | | | there are chain programs available for download. One |
| required by the go kart, especially when climbing a hill. | | | | thing to keep in mind though is that chains are typically |
| A rule of thumb when climbing a 10 degree hill (which is | | | | rated very high in hours because they are designed to |
| a typical hill) is that you multiply 0.17 times the go kart | | | | run for years not weeks. |
| weight (including the person) and that is the amount of | | | | A go kart will only run for weeks at the most. It is not |
| force that is required to get the go kart to go up the hill. | | | | uncommon to replace your chain at least 4 times over |
| Plug the Force into the following equation and you get | | | | the life of the go kart. |
| the torque required to make the go kart climb the hill. If | | | | So be aware that chain program pro-rate their chains |
| the engine torque equals this value, then the clutch will | | | | for 15000 hours. Lubrication is a big factor as well to |
| slip and you will not be able to climb the hill, but the | | | | chain life. |
| clutch will smoke. | | | | So in conclusion:calculate your theoretical chain tension |
| Tengine = Fg* (Rt*Re)/Rg | | | | that is required to get your go kart to go up a hill. |
| Hp = Tengine*.057 | | | | Second: Match the horsepower on your go kart engine |
| Tengine = Torque Engine | | | | with the theoretical value: If the Horsepower required is |
| Fg = Force Go Kart to Go Up Hill | | | | more than the engine can dish out, you will have |
| Rt = Radius Tire | | | | trouble |
| Re = Radius Engine Sprocket | | | | Third: Calculate chain tension and evaluate if the chain |
| Rg = Radius Rear Drive Sprocket | | | | will hold up. Use programs, and charts supplied by chain |
| So if you have a 300 pound go kart, a 10 degree hill, a | | | | manufacturers for the final decision. Remember chains |
| 12 inch diameter tire, 8 inch diameter rear sprocket and | | | | are pro-rated. |