Topic: Help please! 2 step rpm limiter on road race bike

[stephenpettinger]

Hi all,
I am working on a dyna drl400. Seeking advice on how to de activate the launch rpm circuit after the beginning of a sprint road race. I’m toying with the idea of an abs ring and sensor connected to my rear brake rotor carrier, communicating to an arduino that can turn off the launch circuit automatically.  Anyone have experience with this or another effective launch control method?

Thanks a bunch
Steve

[scottly]

How are you planning on using it? At the start, are you going to peg the throttle, letting the engine "bounce" off the rev limiter, until you launch by letting the clutch out? If so, maybe a clutch switch would work?

[MRieck]

How are you planning on using it? At the start, are you going to peg the throttle, letting the engine "bounce" off the rev limiter, until you launch by letting the clutch out? If so, maybe a clutch switch would work?

I know Rick Stetson used that many years ago before actual 2 steps existed. I think Byron did too right about the same time.

[dragracer]

The low side limiter on a DRL 400 is only activated when 12 volts is applied. Once the 12 volt signal goes away, the Dyna will only recognize the high side limiter. If at any time you apply 12 volts to the low side again, the limiter will activate. We run the 12 volt signal for the low side through the clutch switch. In most drag race applications,  i use an adjustable clutch switch so i can fine tune exactly where the 12 volts drops out to the limiter. The idea is for the 2 step to deactivate just before the bike begins to engage the clutch. Otherwise you'll be launching off the low side limiter, causing the bike to bog. You absolutely have to synchronize the off signal with clutch engagement(forward movement). So people mistakenly continue to bump up the low limit to compensate for the bog, no realizing the two points are crossing over. Movement must occur only after the low limit is released so the bike launches at full throttle. I don't know what your intentions are in a road race application but a stock clutch switch might be fine. MPS sells the adjustable switch assemly with lever and perch.

[stephenpettinger]

Thanks guys!
Drag racer, my intention is to set a consistent launch rpm. At our races, we can have 10-15 sportsman bikes starting on the grid, with all the different engine and exhaust sounds, this would remove one variable at the start, to be able to just pin it and watch for the green flag. The clutch switch is interesting, I would need to have another thumb switch to turn it off after the launch to prevent the 2 step activating during high rpm downshifts into corners. Thanks for the tip. I’ll check out mps

[stephenpettinger]

MPs lever is ordered and will meet me at Blackhawk!
Drag racer, my surface conditions are different than a prepped drag strip. I run a Continental cr3 tire at 30 psi @150F from a tire warmer. Road race settings on race tech shocks, seat bottom is about 3” above the frame rails. I’m thinking my usual non assisted launch is a slow clutch release from about 7000 rpm.
Think I’ll baby step way into using this adjustable clutch switch controlling the dyna 400. Would it make sense to practice full throttle launches from low rpm’s, or high rpm’s with gradually increasing partial throttle opening?

Thanks all. I’m tickled pink to surprise the hell out of my fellow racers with some fast starts this weekend

[stephenpettinger]

MPS clutch lever is awesome!
Worked my way up to 5750 rpm full throttle launches. Hooked and booked, as the kids say. Next race is Pittsburgh, will try 6000 and higher. Just barely picked up the front wheel at the top of first gear. My dad and I are now cooking up a latching relay to auto disconnect the power to the clutch switch using the neutral switch on the bottom of the engine.