DIY crankshaft balancing with an oscilloscope
DIY crankshaft balancing with an oscilloscope
(OP)
Hi all,
since I cannot find a local place to balance my crank I started to make a balancer stand using ADXL335 accelerometers and a QRD1114 looking at a reflective tape for triggering .
Finding the heavy spot using the acceleration plots is the easy bits .
I can't make the connection between acceleration and gr/cm imbalance .
Could somebody shed some light on that topic ?
Kind regards
Nikolai
since I cannot find a local place to balance my crank I started to make a balancer stand using ADXL335 accelerometers and a QRD1114 looking at a reflective tape for triggering .
Finding the heavy spot using the acceleration plots is the easy bits .
I can't make the connection between acceleration and gr/cm imbalance .
Could somebody shed some light on that topic ?
Kind regards
Nikolai
RE: DIY crankshaft balancing with an oscilloscope
I1=initial vibration at plane 1
I2=initial vibration at plane 2
add a trial oob TB1 at plane 1, vibrations are TM1_1 and TM1_2
take it off and put it on plane 2 at the same angle
vibrations are TM2_1 and TM2_2
so
TM1_1=I1+TB1*IV11
TM1_2=I2+TB1*IV12
TM2_1=I1+TB2*IV21
TM2_2=I2+TB2*IV22
where IV is the influence vector. TB1=TB2=TB in this procedure, and IV21=IV12 by reciprocity. So work out IV11, IV12, and IV22, (eg IV11=(TM1_1-I1)/TB1) and solve for a final balance at each plane to get zero vibration 0=I1+FB1*IV11 etc
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: DIY crankshaft balancing with an oscilloscope
RE: DIY crankshaft balancing with an oscilloscope
I expect to see 5 distinct disbalances, and when the time comes to get it in spec I'll try adding play-dough until everything is balanced .
RE: DIY crankshaft balancing with an oscilloscope
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: DIY crankshaft balancing with an oscilloscope
And to get back on topic .
On a 5 cyl crank I expect number 3 journal to show up equally on both accelerometers. With number4 and 5 having more impact on the rear plane and vice versa .So number 3 should show up as static .
As far as removing the weight I'll aim to find the heavy spot and remove more material from the edges of the counterweights, knife edging the crank .
A big thank you for the productive conversation !
RE: DIY crankshaft balancing with an oscilloscope
RE: DIY crankshaft balancing with an oscilloscope
That's what it looks like . Nothing fancy . For the drive I'll use a 9500 rpm angle grinder with some electronics to limit the rpm .
RE: DIY crankshaft balancing with an oscilloscope
Brian,
RE: DIY crankshaft balancing with an oscilloscope
What you really want is a LOT of stiffness in the vertical and longitudinal planes of the crank - this is why most commercial balancers use solid plate for the idler mounts. This setup may work at some level, but you're likely to lose a lot of sensitivity because your in-plane mount stiffness levels are not going to be very high using extrusions in bending like that.
RE: DIY crankshaft balancing with an oscilloscope
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: DIY crankshaft balancing with an oscilloscope
Very good construction, you put some work into it. Its nice to see some DIY things like this.
RE: DIY crankshaft balancing with an oscilloscope
RE: DIY crankshaft balancing with an oscilloscope
RE: DIY crankshaft balancing with an oscilloscope
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: DIY crankshaft balancing with an oscilloscope
RE: DIY crankshaft balancing with an oscilloscope
Calculating the acceleration of the piston in different angles with this calculator http://www.pats.ch/formulaire/cinematique/cinemati... I don't see 50 % as the ideal balance factor . Something around 64% seems better at equalizing the forces . Any thoughts on that ? How would you guys go about selecting the balance factor ?
RE: DIY crankshaft balancing with an oscilloscope
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: DIY crankshaft balancing with an oscilloscope
je suis charlie
RE: DIY crankshaft balancing with an oscilloscope
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: DIY crankshaft balancing with an oscilloscope
I got the halves to weigh equal (+/-0.2 g ).
I have the correction weights done as well .
The position sensor is a hall effect 0-360 degree 0-5v output sensor, in effect giving me an absolute encoder .
I'll get some play dough and do a dry run, this weekend, figuring out the light spots .
Cheers !
RE: DIY crankshaft balancing with an oscilloscope
RE: DIY crankshaft balancing with an oscilloscope
RE: DIY crankshaft balancing with an oscilloscope
If I'm honest, I'd build it much simpler next time .