Hi, guys. I have been desperately scouring the internet for resources on these fine, sometimes overlooked, electrathon details to help guide me and my team. We really want to not only know what is best, but understand the concepts on why it is best. Most of us are engineering/physics nerds. We haven't found too much.
So far, this is what I have collected on tires:
Apparently, I want skinny bicycle tires. One resource said never go any more than 2 inches, 1 inch being preferred. This confused me a little, to be honest. Wouldn't you want more surface area for better traction and a better transfer of energy? It just sounds like it would not be enough surface area to be efficient. However, on the other hand, do they mean that by there being less surface area there is less of a waste in energy? It also could be maybe considered more aerodynamic...?
Could someone give me something on tires? More specifically, where does the balance between traction and aerodynamics lie? What is the concept I should be applying here? One resource said you don't want treads?
Braking
Everything I have found has just simply said "bike brake" and nothing more. What are the options? Wouldn't the biggest concerns be: 1. Weight 2. Interference with the efficiency of other systems ?
More importantly, any resources here on braking? There has to be a better option than a bike break?
Anyways...
Any help or knowledge passed on would be GREATLY appreciated!!! Also, if you have any resources you have collected, if you could send me a link, I would be extremely grateful. We are a pitiful, high school team with a horrible track record in electrathon. I really want to turn it around for us
Tires do depend on tracks, down here in the south we run wider tires since we run very tight courses, so with a fatter tire we get better handing but we have more aerodynamic drag. If you plan on racing on much faster straight courses thin tires would be best. Think of it like on mountain bikes and road bikes, mountain bikes have wide tires for slow speed and good traction, road bikes traction isn't as important, only speed is. But if you notice race cars have fat wheels but they are smooth, smooth = less drag but when it rains they get treads. On my car I use 2x1.5x16 in the front and 2x1.5x24 in the back but we have run tires that are smooth and ones that are for off road, while both give good traction on rough road surfaces the off road wheels seem to last longer but they have more drag. Talk to your local bike shops, tell them how you'll be racing and they could help you find a good wheel, and probably for a really good cost.
When you say a brake better then bike brakes why would you need one better? With Electrathons you don't travel at crazy fast speeds and weight difference isn't far off? Did you have any things in mind by this?
As for brakes both the cars at my school use disk brakes, easy to install, work very wheel, and are light. These work very well, especially with our car that has them in the front. Another option that I would use on my own school's car are U-brakes, these are the ones like on a normal bike. With these they are easy to find and install but they don't have a mechanical advantage like disk brakes. Disk brakes get so much power because they work like a vise, converting a rotational force into a lateral force. U-brakes (caliper rim brakes) only have the power of the driver. One thing I found helps a ton with brakes isn't what they are but HOW.
Brake handles are very important, on my #80 car we have a single lever to pull both brakes, while this does allow for equal pressure on each side of the car at all times it doesn't pull as far. But on the other we have 2 single levers, one for each side, and those can be pulled about 30% farther. So with individual ones that can be pulled farther you get much more power. I believe Mr. Hogart in the NW made a post or comment about using motorcycle lever because they have a bigger open and smaller close so you can get much more power.
On page 23 of the handbook there is a lot more info about brakes, any should give sufficient power needed to stop/not move. But don't be afraid to ask bike shops, I know they few we use love to help us and always have something to say to help us.
I also found this website that has all types of brakes (all for bikes) but it has more info on each then I could ever tell you. http://sheldonbrown.com/brake-choices.html
And what area do you race in?
But I hope this helps
-- Edited by Nitoragro on Tuesday 24th of March 2015 08:33:17 PM
-- Edited by Nitoragro on Tuesday 24th of March 2015 08:38:08 PM
Out here in the N.W.Division we have had no problems with traction in general with most teams using 20" bicycle tires (I use maxis "hookworms" inflated to 100psi)
I have NEVER slid out of a corner (except in rain conditions) and we have VERY tight tracks with lots of corners... I (and others) are completely capable of 20mph to 40mph in corners... and once (in practice) I geared my car up to 70mph (at Portland international raceway) and was able to do the whole track (corners and all ) without lifting off.. so that was 60 to 70mph+ in corners & straights... (batteries dead in 9 miles) so obviously standard 20" bike tires have plenty of traction... (I did however gear down to 42mph for the race.. went 38 miles)
as to brakes... Out here I have seen everything from the old "pinch" style (rubber pads that pinch the rim) bicycle & gokart style disc brakes, and moped style rims with "drum brakes".. all work well except for Pinch brakes in the rain...I advise STRONGLY against them.. and recommend that they be changed for better brakes when I see them when inspecting cars (as a tech inspector)
as to the weight of brakes... there isn't enough to matter... I weigh 270lb and my car weighs over 200lb (with batteries) and I am still able to post more laps than some of the "lightweight" cars in my area ( car/driver combos that weigh over 200lb less than I do )
just remember: once you get it moving weight really doesn't matter remember Newton's law "an object in motion tends to stay in motion"
of course hills are BAD if you're heavy... and braking more than needed is a DEFINATE "no-no" ... but as long as the brakes don't "drag" then you're OK
the BIGGEST and I DO mean MOST IMPORTANT part of making a competitive car is to get the steering geometry correct (toe in/out, & ackerman angles) this will cause more excessive power use more than anything except dragging brakes (or over tightened bearings)
On cars that I have had & on the Willamette High team if you lightly "spin" the tire (supported off the ground) we will see times between 1 & 3 minutes before the tire stops spinning... if you can do the same, start checking steering geometry for problems... (or over tightened bearings)
and last but not least (sorry for writing a novel here folks)
Drivers MUST have patience... DO NOT BRAKE any more than ABSOLOUTLY NECCESARY to make a corner and then accelerate as LIGHTLY and smoothly as possible... do not "hammer the throttle" to pass... wait for a place that you can pass with MINIMAL throttle increase...
just remember that someone that does 30mph in the straights and 23mph in the turns will go fartherthan a person going 45-50 in the straights and 15-20 in the corners..... REMEMBER "slow and steady wins the race"
OR at least A constant and sustainable speed (without prematurely draining battery) will get you close to the winners circle...
Hope this helps
Ron Jacobson cars 13 & 14 NW Division
if you think it would help (shorter question to answer time) give me a call... (after 10am pacific standard time please... I work nights)
so you can call from 10 in the morning til midnight or 1am... I'll be available 541-520-3576 (cell)
-- Edited by Ron on Friday 27th of March 2015 11:47:40 PM
Newbie - Good advice from Ron (above). Let me add my two-cents worth:
Tires - I have been building and driving Electrathon cars here in Florida since 2003. I have tried several different brands and styles of tires. By far, the best tire I have found is the Maxxis Hookworm. It is a fairly hard durable tire that still provides good traction and has a minimal tread. We run mostly tight, twisty courses here, usually set up in parking lots, so I run 70 psi in the tires. If I go to a large course I can inflate them up to 90 - 100 psi to reduce rolling friction. The Kenda Kontact is a decent substitute if you can't get the Hookworms. Any knobby treaded (dirt) tire is unacceptable; they will shred and pop within about 40 - 45 minutes on asphalt.
Wheels - I assemble my own hybrid wheels using 20-inch 36 hole double-wall alloy rims (Weinmann DM-30), mountain bike 36 hole hubs with either 15mm or 20mm thru axle, and 12-gauge spokes. The alloy rim resists flexing, the mountain bike hub accepts standard 6-bolt brake disc, and the 12-gauge spokes hold up better than standard 14-gauge. You have to drill all the spoke holes (in the rim and hub) out to 1/8 inch to accept the big spokes. I get the 12-gauge x 184mm spokes from Bikeworld USA on Amazon. Avoid using 24 or 26-inch rims; they flex too much and the long spokes stretch and break too easily. Also, the larger diameter wheels are less aerodynamic than the 20 inch. I have a pair of 16 inch rims that I am going to experiment with, but I am skeptical of them because they have fewer spokes and 14-gauge spokes are all that's available for them. For now I recommend sticking with the 20-inch rims.
Brakes - Hub mounted disc brakes are the most effective. By that I mean they work with the least pressure from the driver. There are many different brands available in all price ranges. I like Bengal brand mechanical disc brakes. They are reasonably inexpensive and work really well. I buy them on Ebay. I have also used MTB brand. They are also reasonably priced and very durable, but they are really ticklish to adjust properly.
I don't know what you are considering for a motor and that's a topic that can be discussed for hours. Whatever you choose, I recommend that you stick to some kind of conventional motor with sprockets and chain drive. A few teams here have experimented with hub motors. I am yet to see them do well. The problem with them is it's not possible to change gear ratios to get the motor into its efficiency rpm range on all courses.
