RIPPY KART

[Hillhater]

Hey Ripper..,
Are you keeping up with the Formula E race series ?
New season with "Gen 2" car spec has just started (ESPN/Fox) with new , bigger 54 kW batt packs so no car swaps mid race. 250 kW limited though but with "Attack" mode and now at 900v from a 209s pack.
Swoopy new car design too !

 

[RIPPERTON]

Are you keeping up with the Formula E race series ?

Sure am, but Im watching it on YouTube instead. May not be live but its free.
I call them the BatMan cars. Love the no stop config as the car swap was ridiculous.
Still dont get the low profile tires / rims. The F1 style wheels / tires are more resilient on ripple strips.
Cant wait till they go AWD as soon as they figure out where to put the drivers feet, they will harvest so much more KE.
https://www.youtube.com/channel/UC-DuRqsBQOEk_5o1q4Ze-Fg

 

[RIPPERTON]

Latest top down shot of new layout. The new battery mounts come from further back outside the frames twist zone.
Seems to steer better but needs to have the rear wheels moved further out as its picking the inside one up mid corner.
Still more work to do with seat backrest support and larger radiator both mounted off the old ctlr mounting brackets.

 

[liveforphysics]

Beautiful kart my friend!

 

[RIPPERTON]

Latest Config with new 300A Kelly Controllers set to 80%. More power but more weight.
Ive done a few ks with the bigger controllers but still havnt floored it, just havnt had enough room.
Ive made some inquiries about practice days at local tracks but this will take some time.
Heres a few laps at a local RC car track which is a bit tight for the kart.
Some helpfull kids video'ed me from trackside.
https://www.youtube.com/watch?v=AZdPenlk5qg

 

[RIPPERTON]

Beautiful kart my friend!

https://www.youtube.com/watch?v=pZujdFY21gA
Thanks LFP
Found some ex race rear tires at the track and they are amazing. Spent a whole day at Marulan Driver Training Center and they only stepped out once. Should have got the fronts as well but will splurge on a full set of new tires.
The recent mods made big improvements especially for the brakes, they are much less dangerous but still need a bit less mechanical advantage in the linkage. This will reduce reaction time, harden the pedal and shorten the pedal stroke.
The top speed is still lacking, it seems that the new lower gearing didnt make any difference but the Marulan track has a much bigger main straight that the Cameron Park kart track.
My best lap was 1m2s, same as the brown MX5 at the end of the video. The Kart record for the is track is 54 seconds and with a 60kg driver, some new tires and taller top speed I think I can beat that.

 

[fechter]

If the gearing didn't change the top speed much, it may be the power output of the motor is equal to the wind resistance so you may not see any real difference over a fairly wide gear range. This happens with my bike, the top 3 gears give the same speed unless I'm going downhill.

What kind of speeds are you getting on the straights? It's kind of hard to judge from the wide angle video. Looks fast as hell though.

 

[RIPPERTON]

If the gearing didn't change the top speed much,

Didnt SEEM to change.
Its a perception thing. The kart is actually going faster but its the scale difference of the 2 main straights thats playing with my acumen.
I dont need to use a GPS speedo, I wouldnt want to be looking anywhere else but the track at thos speeds.
I will do an rpm check in the workshop and calc top speed.
The fact that the ctlrs are set to 80% is the likely culprit.

 

[RIPPERTON]

HURRR Im on Facebook
https://www.facebook.com/PheasantWoodCircuit/

 

[Hillhater]

Simple way to get more top speed on a kart,.. is to recline the seat !
Improves the aero dramatically.

 

[Upperfoot]

Once the gearing is sorted out you should be smashing track records alongside the diff!

Nuxland had a similar problem with speed, essentially after 4200rpm his motor was exchanging torque for rpm because of field weakening.

 

[nuxland]

I suggest you record gps with your phone in pocket. I have cycle analyst but hardly look at it in the race And afterwards add data to you video with racerender (2 minutes is for free).
You can there multiply your speed to calculated constant to get rpm. And when you display rpm in video it makes analyze your driving better. And also others to follow, because it's hard to feel the speed in video
There is app called "Max Speed" in iphone that can record gps and afterwards you can send it to your email.

 

[RIPPERTON]

Thats all pretty easy Nux but how do I get off facebook

After 6 laps (9.6km) Ive charged for 2 hours and 20 minutes with a 500W charger, thats 1.15kWh or 120Wh/km.
http://www.batterysupports.com/72v-74v-84v-10a-lithium-ion-lipo-battery-charger-20s-20x-36v-p-445.html
Just bought 4 of these for $560AUD which makes for 3.3kW of charging grunt should have the packs recharged in 20 minutes.
Also ordered a set of MG red (medium hard) tires for $260.
Did the rpm check and the wheels are spinning at 120kmh at 6200 motor rpm.
Could go to a 17t motor sprocket for 160kmh.
Will have to add a battery pack cooling fan.

 

[RIPPERTON]

Whinging all this time about understeering being caused by weight bias or steering geometry was probably the simplest thing all along. Tires are old and shagged. Can relax though, got the new MG reds to go on for the next track day.
One observation I have made about standard "kart engineering" (sic) is the fact that the brake pedal and master cylinder are on opposite sides of a major flex zone in the chassis. So you are supposed to think that the force input to the MC is smooth and linear when you are lolloping into a turn and the chassis is tweaking around underneath you.... lol
Towards the end of the track day I noticed my battery boxes were getting warm so I settled on a ram air cooling system.
The bakalite busbar frames are grooved where they face the busbars to allow air to flow along them.
So here are some ram air ducts in 2mm alloy and atrocious welding

 

[liveforphysics]

If you throw some fine-ish mesh on the face of that scoop, you won't have those holes get filled up with tire rubber and pebbles and grit.

The aero nerd in me is also thinking you could use approximately the same cross sectional area of the inlet port area to the battery, and it would maintain roughly identical pressure at the port unlet and hence mass air flow/cooling. Or you could use that nice sloping volume as a plenum chamber, and then restrict maybe 70-80% of that inlet area, you could get a pressure boost that makes a net mass airflow/cooling increase.

 

[RIPPERTON]

Yeah the screen is obvious but the scoop was quasi a style thing. I was going for the Hypercar bump and swoosh (photo).
Almost every supercar / hypercar and Lemans endurance racer has this bodywork design feature where the front wheel guard drops down behind the front wheel then races up a slope to the rear wheel. Of course the Rippy Kart will need a spoiler now.
The large inlet (110mm) can be fitted with a temporary 120mm "pit" fan with an acetal collar.
The large holes visible at the base of the duct will be replaced with a bigger rectangular opening.

 

[RIPPERTON]

https://www.youtube.com/watch?v=6jnqbhrqe8E
Brake bumps

 

[RIPPERTON]

Heres the 3.3kW charger for the kart. Cost $558 AUD for 4x 84v 10A units.
The kart is the same voltage as the R1 but Im charging each pack separatly as its easier to find 84v chargers than 174v ones.
Have removed the 8kWh pack out of the R1 and cannabalised some cells out of it to fill that space in the kart pack that has the busbar in it.
I can make some more kart packs in aluminium for the R1.

 

[RIPPERTON]

Improving driver comfort, Ive grafted on a shoulder restraint in 4mm alloy and more atrocious welding. Wont have to use the steering wheel to stop myself from being flung out in fast turns. Now should be ready for the New MG tires and some real grip.
Got some stick on flyscreen repair to go over the air scoops but when I took it out of the packet found that it was fake fly screen like a big sticker and doesnt let air flow through... :x

 

[RIPPERTON]

Rippy Kart has been decommissioned cause I just dont have time to drive it.
Ive taken the LiPo cells out of it for another project.
The kart still drives fine but should have new batteries.
Some of the Chinese manufacturers should have a 4 or 5 Ah double ended cell that would fit the existing battery boxes.
Its for sale for about $2k AUD.

 

[Hillhater]

Good to hear from you again Ripperton.
Have you been working up some new project , or just been “locked down” ?