Jim Robinson says less than $500 for a roller in his excellent step by step description of how to build a chassis http://electrathonfl.homestead.com/Jimsbuildseries.html. I would say the actual tubing, sheet metal and bolts might be even less, so $300 in materials to build the raw chassis.
Batteries: Optimas are $200 each, so $800 for two packs. There are cheaper lead acids but I do not know which ones offer quality. The cheapest option long term is lithium. $600 will get two packs with BMS and slow chargers included. They seem pretty child proof with over discharge protection and automatic charging. They are not perfect but they will provide 800+ Whrs repeatly. Here is my test report: https://electrathonamerica.activeboard.com/t66140971/proev-tests-an-18650-lithium-pack/
Controller: I would consider a Kelly Controller 72 volt 80 amp for $180 a good choice but would be very tempted to spend the extra $120 and get a Phaserunner.
To properly research motors, I would use the handy dandy motor simulator page that ebikes.ca offers. Use the full recumbent bicycle choice and look at efficiency as well as speed.
Tires and tubes at $25 per wheel (though I would run them tubeless).
So $300+$600+$180+$350+$150+$75
So $1,655 will give a quite competitive vehicle with two packs and chargers.
I would also highly suggest some sort of data collection. The cycle analyst give Whrs and time for slightly over $100. Or build a Arduino system with GPS and a WiFi display to allow a phone browser to show energy used per lap. This can cost under $75.
I think this could be a winning car, not just one that would finish races.
To answer to my own earlier question, I decided to undertake a "budget-beater" electrathon car project. Something where I can see just how cheaply a car can be built from scratch and put on the track. The idea is to get a sense of the bare minimum to come up with something passable so that it can be emulated by teams just starting out or those facing very tight budgetary constraints.
I figure it may be less daunting to raise funds for improvements to an existing car than to try to come up with $5k or so for a kit car.
To make matters worse I decided on a no-weld type of construction because I figured these fictitious people I was simulating didn't have a welder either. I settled on an unconventional, but cheap approach to frame construction utilizing conduit with flattened and rolled ends.
You'll see it in the pictures. What you might not be able to see is the rivets that keep the tube from sliding down the frame rails.
I used a 2x6 ripped to a 15 degree angle to set the caster for the front axle. It's got three 5/16" carriage bolts passing up through the bottom of the car, through the 2x6, and through the axle too. The lumber is also cross bolted (screwed) through the adjacent uprights as well as up through the lower frame tubing.
The motor is from a 40v Ryobi cordless pushmower motor with a modified shaft. I showed how that was accomplished in a YouTube video titled "Turning down a motor shaft the wrong way." The motor is driven by a $37 eBay ebike controller.
Steering is repurposed Razor scooter (I'm almost proud of that part)
Keep in mind this wasn't ever meant to be a wonderful piece of race car engineering. This is more of a feasibility study to show prospective teams how cheaply they can get on the track. Hopefully once they did, they would find it easier to raise funds to build something better and put this travesty behind them.
-- Edited by Archer321 on Sunday 8th of August 2021 03:17:24 PM
-- Edited by Archer321 on Sunday 8th of August 2021 03:25:07 PM
Here's the no-weld spindle solution I came up with for my "Budget-Beater" Electrathon car. It started as a section of 2" square tube with a 1/4" wall. I used a 1/2" fine thread grade 8 bolt as the axle. 3/8" shoulder bolt for the kingpin. Oilite bushings in the axle tube which is a 1.25" mild steel square tube with .0625 wall from Home Depot.
-- Edited by Archer321 on Sunday 8th of August 2021 03:27:36 PM
The three day Lee County Electrathon event put on by Electrathon Of Tampa Bay went off without a hitch. It was certainly hot on that runway in South Florida (at least 100 degrees F in the sun) but it was the perfect opportunity to put the Budget-Beater, a.k.a. Lemon Shark, a.k.a. Angry Banana through its paces and see how it held up under race conditions.
I recruited two friends with Electrathon experience to drive it for me as I was busy driving my 321 car. The event featured two different track layouts and two different race formats. Friday was two dash races of 20 minutes each around a 1.1 mile roughly rectangular course with a slight dogleg on one end. As it was the first race of six of the weekend, we started off taking it pretty easy on the untested car and my friend Todd Thuma racked up 9 laps in it during the 20 minutes averaging 28.6 mph. It finished 4th overall out of the six cars on the track. He did not deplete the 48v 20ah lifepo4 pack and it recharged in the two or so hours between races without a problem. The only instrumentation on the car is a combination volt/amp meter so in the absence of a watt/hr meter I don't know how much energy was used.
We decided to push it a little harder for the second race and Todd knocked down 10 laps with an average speed of 31.2 mph and again finished 4th overall. Everything held up fine, no problems. The little Ryobi motor was definitely hot after the race, probably in the neighborhood of 200 degrees F, but the poor little thing had zero airflow as I had entirely closed up the tail section.
Saturday's races were around the same 1.1 mile course but this time were the standard 60 minute length. Another friend of mine, Ryan Norden stepped in to take the controls and turned out 25 laps in the first race with an average speed of 27.4 mph. This was good enough for 2nd place overall. No problems, no drama.
Since nothing broke, he pushed it a little harder in the second race with 26 laps and an average of 28.5 mph and again placed 2nd overall.
Sunday's course used the same perimeter as the previous one but doubled back on itself with three 180 degree turns including a very tight hairpin in the middle. (I took that one a little to fast in the 321 car on one lap and had it up on two wheels as I ran off the track) The overall length in this configuration was 1.4 miles. We also had one competitor drop out that day, but another car joined in so the total number of cars remained at 6. The newcomer brought a VERY fast lithium powered car and dominated both races.
In the first race, the Budget-Beater-Banana-Shark once again piloted by Ryan Norden racked up 19 laps with an average speed of 26.8 mph and placed third overall. Still no problems, didn't run out of battery during the race.
For the last race of the event, since nothing had failed, I told Ryan to go out and try to blow it up. Give it everything it has and let's see what happens. I think he took that as a personal challenge and went out and started averaging 31.5 mph for multiple laps before the motor sprocket loosened up and came off losing the key insert in the process. He pushed it back to the pits, made a new key insert by grinding down a spare Allen wrench from my toolbox and got back out on the track all in about 12 minutes. He put the hammer back down and was passing other cars on the straights at 40 mph. The time in the pits couldn't be completely made up though and he finished 4th overall.
The $1350, bolted together, ridiculous, Ryobi powered, yellow, googly eyed Electrathon car went a total of 126 miles in competition last weekend at an average speed of 27.4 mph. It never ran out of battery during competition, suffered no notable failures, and did it all on one set of tires. My only regret is that we didn't push it harder earlier. I feel like we never really saw what it is truly capable of. My thanks go out to both Todd and Ryan for their help in this little experiment. In the next few weeks I hope to shoot some videos doing a thorough walk-through of this car discussing it's construction, the components used, how it worked out, and what should have done differently.
Wow! I did not realize the extent you went to keep the price down. These are really clever engineering solutions to make the car easy to build and inexpensive.
Been a while since I visited, and there's been a lot of action on here since then.
Just following up the 'no welding' construction method. Over here I've been having kids build non-welded chassis using aluminium tube and sheet with thicker aluminium gussets riveted together. I've attached a few pics.
Our latest cars also use aluminium honeycomb panel for the floor, 1" x 2" RHS aluminium tube 'rails' that are both riveted and glued (using marine grade sikaflex) to the floor panel to add strength in bending. I've had kids aged 12-18 use these methods with a reasonable degree of success. The cars are strong and light - with battery, motor and safety gear (and on the proviso we use smaller LiPO batteries) our cars weigh only 90-95lbs without a driver. I'd suggest they'd work in EA as well.
