Electrathon America Forum

4TRIDENT4 · Veteran Member

USF Engineering expo 2018 race

ProEV · Senior Member

Fun race. Look at Slam lift the inside wheel (red #90).

This was the 10th anniversary race for Electrathon of Tampa Bay. We had a big field including 6 advanced battery cars. A new record!

It was not a good day for rear tires. I was leading the first race at the 45 minute mark when my rear tire went down and USF was in the lead even closer to the end of the second race when they lost their rear tire. The Electocutioner`s #90 took both wins.

Here is the restart from race 1. 360 view.

https://www.youtube.com/watch?v=ov8AGUNpbPk&feature=YouTube.be

4TRIDENT4 · Veteran Member

somehow our valve stem got ripped clean off, moreover it was a good test with our new battery setup and new motor/controller, things are alot different when your car is 30 pounds lighter!

Archer321 · Senior Member

Usually when a valve stem tears off it's due to tire pressure low enough that it allows the tire and tube to rotate on the wheel. Since the stem is stuck through the hole of the wheel, it's not very forgiving of any slippage of the tire to the rim. The same thing happened to me when I lowered the pressure to soften the ride on a rough track. What new battery, motor, controller, setup? What 30lbs lighter? Seems you have more to tell...

Nitoragro · Senior Member

Is there no more 30hp massive motor?

4TRIDENT4 · Veteran Member

we had a ME 1003 30hp peak motor ( for those sick burnouts ) + the alltrax AXE 7245 controller + the wires to support up to 350A, we swapped to the Crystalline MTC30100R 2kw motor with a grintech 72v controller, with thinner wire is about 30 pounds lighter. This also gives us much better weight distribution, for our batteries we just added a BMS.

In terms of the tire i was running 65PSI on a maxxis tire, ive run full races with the 30hp motor doing those aforementioned sick burnouts, with 55psi with no problems, so im not sure whats up with that.

-- Edited by 4TRIDENT4 on Friday 23rd of February 2018 03:05:23 PM

Archer321 · Senior Member

What changes have you noticed with your new setup? Are you using the same voltage as before? Has your wattage usage decreased?

4TRIDENT4 · Veteran Member

previously my amp draw under acceleration was about 67A and i was quite regularly using 15-16ah per race, with the new controller the highest ive been able to push it to is 37.5A and i would say running at a similar pace to the other motor albeit quite alot less acceleration i only drew 11ah. our old motor we got a 0-60mph of about 3.2 seconds, the new one goes from 0-37mph in about 3.4 seconds and it takes quite a run up to get to its top speed of somewhere between 40-42 mph

-- Edited by 4TRIDENT4 on Friday 23rd of February 2018 05:54:17 PM

Archer321 · Senior Member

And what is the voltage of your battery pack?

4TRIDENT4 · Veteran Member

72v 16ah lithium ion pack

ProEV · Senior Member

Are you running more aggressive regen then before or using a different rim? When we were running 20 inch wheels, we had tire rotation even at high pressures. The rear tire was being torqued both accelerating and regenning. This took off the valve stem more then once. You can check by making a mark on the tire and rim and seeing if the marks stop lining up after a session.

We used a messy black gunk called tire bead sealer to increase the friction between rim and tire. The trick was to glue the tire, at least 8 hours before using the wheel or the gunk only acted as a lubricant.

We have been running DIY tubeless with good results but it let us down this race. The plastic 16 inch wheels have nice smooth flat sides which helped give a good seal between tube and tire bead. The rims on the spokes wheels we are running now have a folded lip which might be part of the problem. We also have not fiquired out the torque specs and our spokes are coming loose during the race. We think the shifting rim might also have contributed to the rear flat. Our rear tire lost pressure gradually. Even stranger, our right front tire was fine when we pulled in to change the rear but went flat while sitting in the pits.

4TRIDENT4 · Veteran Member

we are using a different rim since we are running a hub motor now, but we are currently not running any regen, im thinking i might try to clean up the valve stem hole or something, we are going to switch to the 20x 2.25 tires which mike make a diffidence. its probably a factor of new rim + the tube we used was over a year old, it came on and off the rim probably 10-15 times, so it might have been long term stress.

Archer321 · Senior Member

72v x 16ah= 1152wh > 1kwh

(Page 12, section 28, point2)

-- Edited by Archer321 on Sunday 25th of February 2018 07:03:42 PM

4TRIDENT4 · Veteran Member

controller and cycle analyst, we limit our usage, we use multiple prebuilt RC car packs since they are already wired and are in battery bags to be as safe as we can, its next to impossible to find a prebuilt pack ( unless custom ordered ) that ticks all the right boxes. on our old system we used to run 60V (16cell pack) to get around this. Also we wanted something that is bigger so that that way we wouldn't hit any issues when heavily discharging our packs.

how we limit our packs:

Controller - ah limit though programming

cycle analyst v3.1 - Watthour limit at 1000wh, we have an external sensor connected to the battery that reads the watt hours, and an Ah limit ( if any one of these goes over the car shuts off )

Not sure if im explaining this right as im not the person that does the electrics in the car, im more of a mechanical guy, but i feel as though with all the limits we put it keeps me within the rules, but id refer to @proev if he tells me that its not enough

-- Edited by 4TRIDENT4 on Sunday 25th of February 2018 11:44:04 PM

Brendan_Smith · Veteran Member

Hmmm... The rules are pretty clear on this, but oh well.
For a 15Ah LiFePO4 battery (1080 nominal Wh, still over but at least it's closer) -> bmsbattery.com/ebike-battery/531-72v15ah-40152-lifepo4-battery-24-cells-ebike-battery-pack-battery.html
For a 12Ah LiFePO4 battery (864 nominal Wh) -> bmsbattery.com/ebike-battery/536-72v12ah-38140-lifepo4-battery-24-cells-ebike-battery-pack-battery.html

It certainly is difficult to get as close as possible to the 1kWh limit particularly as you go to greater voltages, but being 15% over the specified mark is quite a bit, even if a self-imposed consumption limit is used.

I'm working on set-and-forget brass valve stems to insert to a Schraeder-holed rim, to enable Presta valve use (to mitigate air loss through inertia pressing of the Schraeder stem) but they're a little way off being available. Presta thumb nuts likely also lessen the tube torque effects you've found too, so that might be worth investigating.

EDIT: Awesome vids by the way!

-- Edited by Brendan_Smith on Monday 26th of February 2018 04:54:58 AM

4TRIDENT4 · Veteran Member

well that is how we did it last race which is the first time we had the car set up like this while still using our old prebuilt battery packs previously we had the 60v16ah with the other motor, good thing is that we have a new battery set that is being custom made from one of our sponsors ( hopefully delivered on the first week of march ) that set i know is directly rated and tested under 1kw (960wh) so it should get here for our next race, and lithium iron phosphate is easier to find, we use lithium lon.

new pack should be 48v rated at 20ah using (samsung/LG?) deep cycle cells, this would solve all that of that anyways. our old batteries were already over 3 years old and not really treated the best since it was our first lithium pack.

-- Edited by 4TRIDENT4 on Tuesday 27th of February 2018 02:44:54 AM

Brendan_Smith · Veteran Member

Sounds pretty ideal! Your sponsor might have a market for them if they want to produce more...

4TRIDENT4 · Veteran Member

www.rosebatteries.com if anyone is interested, currently they dont sell unless its for industrial use, but hopefully they will warm up to us!

-- Edited by 4TRIDENT4 on Monday 26th of February 2018 05:44:28 AM