Electrathon America Forum

Kyle Keenan · Veteran Member

Gearing for Briggs Etek

electrathon · administrator

Basic rule is the front pulley needs to double in size from what you were running with the Scotts motor. Hodgert has a gear ratio chart that shows simple gearing for the top speed of the track.

Kyle Keenan · Veteran Member

Double the size? We are using a Pern currently and the smallest gear we are running is an 18 up front. If I remember, our motor turns out only 1400 RPM's at 24 volts.

electrathon · administrator

Sorry, I was thinking you were running a Scotts.

If I am remembering correctly the Etek turns 1800 at 24 volts.

bd64 · Senior Member

I think the Etek is rated at 72RPM per volt or 1728 at 24v no load. A good starting point is 1600 RPM loaded and you will need to make adjustments from there depending on the car's effieciecy, battery pack, track and most of all the driver's ability to conserve energy.

radigan · Member

I have a spreadsheet set up to play with different gear ratios and rpm and speed. I will email it to you.

Kyle Keenan · Veteran Member

Ron, that would be awesome! Thank you very much!

Chenega · Team Advisor

Best bet is to go out and test... Then test some more as there are a lot of variables to consider

Kyle Keenan · Veteran Member

@ Chenega, the reason I ask is so I can find a decent median to start testing at. We don't have a budget to just freely test any gear avalible to us.

electrathon · administrator

The spreadsheet Hodgert has should really help you. There are SO many variables here. The track can make all the difference in the world.

As a starting point, a 20 on the front and a 65 on the rear and go from there.

Vic · teacher

We are using the E-Teck R
I found a site on line that has a gear ratio calculator.
It is infinately variable.
Plug in:
Wheel circumference, # of teeth on sprocket gear, # of teeth on wheel gear and motor rpm and it will give you fairly accrate speed.
We have a 14, 16, 19, 21 and 24 teeth sprocket gear (for the motor)
We have one front wheel set up with a 60t and another set up with a 40t gear.

gokartracing.org/calculate.htm.

Vic

drewjet · driver

I geared mine with a 16 on the etek and a 53 on the wheel. Gives me 28 MPH wide open and slightly less than 40 amps. I am hoping that will do about right for a road course. My first race is in 2 weeks. I think for a oval I could gear for a little more speed.

electrathon · administrator

We are on oposite sides of the country so I have notseen the course you areon, but 28 top speed is about correct for many of our parking lot tracks around here.

When first starting out, it is best to learn how to drive for the complete hour and then learning how to go faster than it is to go fast for 50 minutes and go dead, then learn how to go longer.

bd64 · Senior Member

It seems as if the story is the same everywhere in the country and the moral is " Slow down so you can go faster ".

stan r · Veteran Member

etek motors turn 72 rpm per volt therefore 24 volts equal 1728 rpm. However some motors vary slightly. Mine is 1680 thru the controller & 1700 eliminating the controller. If you know motor rpm, no. of teeth on motor sprocket, no. of teeth on drive sprocket, circumference of driven wheel, you can figure speed. There charts on the internet or ask any math student/teacher

mhodgertt · EA President

In looking this over I see that there is a reference or two to a gear ratio spreadsheet that I put together which is nothing special by any means but if anyone wants it, email me--listed on EA website under board members- and I will gladly send it as an attachment.

At the start of the race with charged batteries, the eTek holds a good 1600 rpm but in the NW on our tight hilly road courses, many of our drivers are taking the batteries down well below 20 volts under load by the end of the race. I started using 1550 as the average RPM but then to help my kids conserve and finish the race I set up my spread sheet at 1500 RPM. I look at the winning distance for the race the last couple of years (hopefully in the same weather conditions) and then tell the kids that if they want to end up in the top 25% to gear as the spread sheet shows but if they think their car and driver is light enough and good enough to take first place they will need to gear a couple of miles an hour faster. This seems to work as I don't have time to check the gearing on all 20 of our cars each week before that weekend's race.

Mike Hodgert

stan r · Veteran Member

We know the old etek turns about 1728 rpm. That's where it will use the least amount of electricity. If a car can't attain that full rpm it is geared incorrectly.If you can only attain 1500 rpm you will consume more electricity, (amps). This is not something I dreamed up, ask someone with electric motor experience

electrathon · administrator

Stan,

Out here on the West Coast we run rally tracks. It is rare to be able to just pull the throttle and sit still for an hour. We are constantly speeding up, slowing down, rounding a corner and doing it all over again. We have to gear acordingly and rarely get to run at top speed for more than a few seconds at a time. Many of our tracks have elevation changes too. Mikes rounding off of the numbers reflects this averaging we end up doing to figure gearing.

Aaron

mhodgertt · EA President

Stan,
The 1550 RPM is not something I dreamed up either. It came about by figuring the winning distance at many races and then working back to find the 'average' RPM of the eTek motors. At the beginning of the race I will be going faster than my 1550 gear chart says I will but by the end I will be traveling a little slower.

I agree that at a full 24 volts an eTek will turn 1728 RPM at it peak efficiency. But at the end of the race when the batteries are down to 20 volts it turns 1440 RPM (1584 average). If you take it down to 19 volts under load (where speed just starts to drop significantly) it is now at 1368 RPM. As Aaron stated in our tight and hilly road courses we can not run at full speed on most of the course, we often have to slow for corners, hills, or traffic as we have 30+ cars on the track at a time at some races. Also many students run their batteries down to below 20 volts measured under load by the end of the race so the 1500 to 1550 is a fairly good average for the RPM range. For these reason it works out best for us to gear a little slower so we can stay in the 'sweet spot' of the motors RPM--efficiency curve over the whole track and the whole race.

Often there are cars geared higher than I do, and at the beginning of the race they may be ahead of me. But outside of the Pac-lite and Dave Cloud cars very few cars ever beat me in a tight road race and I weigh 220 pounds and my car is about 30 pounds heavier than most of my student's as it is made to fit very large (6'6"-300#) to small drivers (5'-110#) and hold up for several years of hard racing. So I am spotting about 70 pounds to most of my competition. I use my car as a promotion and trainer car for donators, our superintendent (first at this fall's Eugene race), school board members, people thinking of constructing a car, my students, etc. so I made it fairly adaptable to drivers of all sizes.

As I stated this system seems to work fairly well for my students as well. Last year we had 8 of the top 14 spots in the NW short track series out of the 52 cars from 13 school that competed. Yes we raced 17 student cars but 6 of those missed at least 2 of the 7 races so did not have a chance to score in the top 25% of the 7 race series. Many cars/teams gear for a higher RPM but die early. As 'BD 64' stated above--'slow down so you can go farther'-seems to work for us.
Mike