This is the build pics of my newest car. It was designed specifically for my local race which is held on a 1/2 mile banked oval. It is mostly constructed of 1/2" conduit and has sliding pillar front suspension and a swingarm rear suspension. It has 12.5" front tires and a 20" rear. It is 31" wide, 22" tall, and just over 9 feet long. I initially tried to power it with a Heinzmann PMS080 brushless motor but couldn't get the new controller settings sorted out in time for the race so I switched to my old, faithful, Heinzmann PMS126 a week before the event. Three Interstate dcm0035 batteries for a 36v lead acid pack. It has a Coroplast body and a lexan windshield.
-- Edited by Archer321 on Wednesday 18th of May 2022 08:56:11 PM
-- Edited by Archer321 on Wednesday 18th of May 2022 09:40:15 PM
The end result was that the car set a new track record for Electrathon vehicles with 81 laps in the first race and 82 laps in the second. I lost about 3 minutes in the second race when it rained for a couple minutes and the windshield fogged up so I had to pit to get it cleaned off. It finished more than 50 laps ahead of the 2nd place car after both 1 hour races.
The controller wasn't set quite as optimally as it should have been so I think there are more improvements to be made. I'm pretty sure it is capable of 90 laps on this half mile track. Here is the graph of the speed and wattage from the first race.
-- Edited by Archer321 on Wednesday 18th of May 2022 09:53:06 PM
This looks great. You say Speedway only, why? Do you feel the car is too long to turn easily?
What steering set up are you using?
What brand tires on the front? I like their width. They make the 20 inch rear tire look huge.
Was there a reason you did not run the smaller wheel in the rear as well?
Looking on the graph you posted, where you lifting off the throttle at a particular point (because the car needed to slow for the corner?) or to save energy?
Finally, were the large pair of nuts in the 6th picture you posted required to drive the car?
I say speedway only because the front wheel track is only 24.5" wide which would probably make it pretty sketchy on tight turns. Also the steering is pretty unwieldy so it's best kept on a track like 5 Flags. It's a modified version of the push/pull steering like on the Blue Sky cars only this one is more like raise/lower.
I actually never lifted off the throttle in that entire race. It has a dial potentiometer with a Deadman switch on the handlebars. Once I got it set where I wanted, I just left it there and kept cruising. You can see how I stepped up the speed twice during the race. The variation in speed is just a side effect of the current limit I had in place and the fact that the track is sloped one way. The extra interesting thing is that when I was set to the slower speed of 40mph, it would actually regen frequently coming out of turn 2 WITHOUT me letting off the throttle. I take this to mean that it was coasting faster than 40mph coming down the bank of turn 2. (Note all the downward spikes that dip below zero on the wattage graph) Kinda crazy.
The driving experience was pretty crazy. I hit a top speed of 48mph I think.
Good times. I wish you would have been there!
The front tires are 12.5" Cult Dehart Juvenile and they seemed to do fine on the relatively easy track.
I stayed with the 20" on the rear because that's about the same height as the top of my helmet so going smaller didn't seem to offer any advantages as far as frontal area is concerned.
-- Edited by Archer321 on Tuesday 24th of May 2022 08:38:55 PM
<The front tires are 12.5" Cult Dehart Juvenile and they seemed to do fine on the relatively easy track.>
I liked the 16" Cult Dehart Juvenile because their max pressure was 110 psi. They stopped making them as soon as I tried a set. What pressure are you running the 12.5" at?
I am running Chaoyang 16" 2.5" at 120 psi tubeless. Their max pressure is 60 psi. The rubber is pretty thick which means high rolling resistance until they wear down but they make it to the end of a race on a rough course which is my limitation at the moment.
Does your potentiometer control speed, and you also had a current limit set?
In back to back races on a running oval, I tried setting a fixed speed and then a fixed current using a potentiometer. In my case, both forced the motor/controller to run at an inefficent combination of current and RPM. After testing for 10 laps each time, I switched to accelerating at an higher and more efficient combination of current and RPM and then lifting and coasting at the end of the straight and went faster while using less energy.
Since nothing changed but speed and current when you upped the speed, you might be able to factor out aero drag and calculate whether your motor efficiency was better or worse with the change in RPM, which in turn might suggest whether you can improve gearing.
I've been running about 80 psi in all my tires lately.
My controller has a programmable performance curve where I can set how much current it can allow at given speed points. So presumably the throttle controls speed to the extent it is allowed by the current limits.
I'm sure there's a lot more fine tuning that could be done to this car, but I might just move on to the next design instead.
Haven't decided.
My controller has a programmable performance curve where I can set how much current it can allow at given speed points. So presumably the throttle controls speed to the extent it is allowed by the current limits. I'm sure there's a lot more fine tuning that could be done to this car, but I might just move on to the next design instead. Haven't decided.
Did you program in the curve (and if so, how did you design the curve) or was there one already set for your motor?
And inquiring minds want to know-What is the next design?
I'll attach a pic of my throttle curve. Keep in mind the current is in "deci-amps". I guess it's a German thing. Mostly I just set a curve that gave me enough current on the bottom to accelerate decently and had it taper off to what I could afford to maintain at the top.
I think I can make the next car a little narrower and still meet the required 24" minimum track width. Also I'll likely do more of a forward windshield design like some velomobiles.
-- Edited by Archer321 on Thursday 2nd of June 2022 12:13:10 AM
