View Full Version : Arc EV 2012 race bike

ARC EV Racing
31 July 2012, 1444
We just finished loading our new race bike ready for its first track tests tomorrow. Here are a few pics...


We've developed it from the TTX75 bike we ran last year with the aim of making it more competetive against the ICE machines in the club races we enter. So now we have a 4-speed transmission with a semi-automatic shift and more voltage by going to 30s lipo. The trade-off is less capacity but club races are about half the distance of the 20 mile TTXGP races we're used to and we're well within the pack's discharge rating.

The semi-automatic shift is created by interfacing the Curtis 1238 to an actuator with input from shift buttons on the bars. Up-shifts are programmed to work like a regular quick shifter so you can trigger it at full throttle without using the clutch. Down-shifts will incorporate an auto rev-match. We did all the programming and interfacing in-house.

Thanks to Manzanita and Gene for supplying their excellent BMS boards (also interfaced to the Curtis for a 'get home' mode when the pack is spent).

Updates from the track tests tomorrow via twitter @ARCEVRacing. Thanks for looking!

31 July 2012, 1526
Looks great....can't wait to hear how she rides :)

Keep up the great work guys.
Glad I could help a little

Nuts & Volts
31 July 2012, 1627
Transmissions are stupid...

Really excited to see some data and results :D cool stuff

31 July 2012, 1639
This is really exciting. The transmission use and the auto-rev matching have me really eager to learn more about this bike as it develops. Keep up the solid work!

01 August 2012, 0209
Well done for getting it together so fast since I saw it a few weeks ago.

Blimey, that’s a late night/early morning photo shoot, how many race bikes can be ridden out into the street without waking up the whole neighbourhood?! It looks brilliant even in the gloominess.

I’m looking forward to hearing how your rider compares it to last year’s bike and by how much your lap times have improved. Maybe he will give it a new nickname now :) I’ve haven’t read of any other race bike upgrading to transmission so it will be some useful data.

What ratio’s did you pick? And what are your predictions for 0-60 times and top speed?

Good luck for today for the testing session, I hope the weather behaves and gives you a dry track.

01 August 2012, 1900
Awesome! The bike looks great! :)

Square Wave
02 August 2012, 0917
Good work!...so jealous!

ARC EV Racing
02 August 2012, 1315
couple of better pics


ARC EV Racing
03 August 2012, 0452
Now the dust has settled from the test day I'll add some more detail. So the first thing was that we weren't able to fully test the transmission because the actuator we were using to change gear didn't quite have enough travel to change reliably. We had too many false neutrals/failed shifts so we left the bike in third (about 5.3:1 overall ratio) and ran it like that. A new actuator is on order so that should be fitted next week.

The pack did ok with the higher discharge rate but it was getting warmer than before; about 40 C (110F?) now versus 30C previously. We'll have to keep an eye on that once we're running things harder. How hot do others run their lipos?

As for rider feedback, he felt we were at a similar point now to where we left off with the old bike but with more performance to come. He said he saw over 7600rpm on the motor which is a bit of a worry since it's supposed to be limited to 7500. That equated to just over 110mph with another gear to go, so top speed should be over 120mph with the extra voltage.

We're at Cadwell park in a couple of weeks where we'll be running an acceleration test (drag race!) against some of the petrol bikes we race against. If the result is good then we'll be allowed to start in our qualification position rather than from the back of the grid as we did last season.

03 August 2012, 0743
Sounds like the track test went quite well. It proved your belt driven transmission is strong enough to do a 0-110mph run around. And you have a solution to the shifting problem.

I have been reading on RCGroups forum and most peoples opinions on lipo temperature is they have a 60 degrees celsius limit before degredation but most like to keep them below 50celsius for safety. They might run them for a shorter duration, so a longer time could change their views I guess.

A warm pack can be a good thing for racing as the cells will have a lower internal resistance so you will be able to safely pull higher amps out of it with a much lower voltage drop.

I have bought an IR meter from Wayne Giles and in his for sale thread someone has tested A123 cells from a Dewalt pack arranged 4s. At 25celsius they measure 10 milliohms per cell, at 18celsius it was 13 milliohms per cell, and out of the fridge it was 18 milliohms per cell.

Here is the thread


He has put a mod on my meter so I can also measure single cells for my pack.

Looking forward to hearing how your drag race goes, good luck.

Nuts & Volts
03 August 2012, 0921
LiPo perform best right around 40degC, delivering highest power and lower internal resistance. Above that temp you getter lower Ri but you lose cycle life and power ability because you are closer to over heating the cell with each peak current pulse.

ARC EV Racing
03 August 2012, 1402
Thanks fellas, that's some useful info. I was a little worried by the increase in temp over last year's pack but then with the reduction in capacity they're effectively working twice as hard. We're doing a test day on the Friday before the race weekend so hopefully we can show that the pack temp levels off in the 40s.

04 August 2012, 1129
What a great looking machine! Do you have any details on the transmission you'd be willing to share?

ARC EV Racing
04 August 2012, 1357
a few things you have to keep to yourself! we've spent a lot of time and money so we'll make sure it all works as we've designed and calculated it should before saying anymore on the gearbox. the ratios were calculated based on our motors torque curve.

04 August 2012, 1949
Don't blame ya a bit! Good luck!