Q&A Forum
I had an issue yesterday with my hydraulic chassis dyno. When I slow the run down to the point where I can get good AFR samples, I'm getting a funny reaction with the load cell/information calculated. My readings on the load cell are actually going negative. I do not have this issue when I keep the hydraulic braking to a minimum and let the bikes accelerate fairly quickly. You can see on the logs, it's a good consistent acceleration and hydraulic pressure, but my HP and TQ readings are way off. My pump is mounted on a bearing, so it free floats with a transducer and torque arm. Any suggestions? Runs attached.
Tables, showing all the parameters. Hydraulic pressure remains stable, but the acceleration. Load cell issue?
Looks like your load cell too small. This causes the analog to digital converter to over scale, which results in negative values. Use a larger load cell or increase the load arm length.
I believe you are correct Jostein, I have a 100KG (220 lbs) with a 14" arm, so it would be about maxed out. I noticed when I was doing steady state tuning, holding RPM, my torque readings were negative then also. I will try a bigger load cell.
I tried the new software, and love some of the added features, but it still doesn't work with my setup. I need to start the run at 2000 RPM, at a high brake pressure, then reduce the braking 1% every second as it accelerates until the run ends at 6000 RPM. Just like shown on the logs attached. With the newer software version it increases the brake pressure by the setting, so it stalls out the bike/prevents acceleration. I used to be able to put in a negative (-) number in the "brake % sweep rate", but can't after version around 3.2.154.0
how do you control the pressure on the pump? With my setup its hard to make a upward rpm sweep without getting pig tails in the curve. If I sweep down it works better. I use the rpm sweep function and have PID control the brake %
@rub87 have you tried the sweep without PID control? Which kind of valve are you using?
without PID I cannot do an rpm sweep. I use a pressure regulating valve, like a relief in which I replace the setsrew by a wastegate actuator thats controlled with PWM. I works really good to measure steady state tho.
@rub87 Im currently using sweep without PID and in my setup (100cc direct drive kart engine ) works fine in upward, from 6000rpm to 19000rpm. I only set the brake % per second
Ok so I assume your valve just controls the cross section on the pumps outlet. Which is makes that a certain brake % mainly governs a certain HP. In my setup the % brake governs more like a torque. Like 30% brake is for example 10 Nm at 3000 rpm and 13 Nm at 10k rpm.
I think for doing a rpm sweep your method is better
I tried the new software, and love some of the added features, but it still doesn't work with my setup. I need to start the run at 2000 RPM, at a high brake pressure, then reduce the braking 1% every second as it accelerates until the run ends at 6000 RPM. Just like shown on the logs attached. With the newer software version it increases the brake pressure by the setting, so it stalls out the bike/prevents acceleration. I used to be able to put in a negative (-) number in the "brake % sweep rate", but can't after version around 3.2.154.0
You just set the sweep rate, no + or -. The dyno software understands whether to increase or decrease the brake based on the start and end RPM. So you can ramp up and down like before.
I can confirm the brake sweep is working to decrease the brake amount.
I'm seeing another issue though. If I'm shifting up through the gears to get to the pull gear, if I take the RPM's up, say 500 or 1000 rpm past the "start rpm", it will turn the brake on 100%. It does not show the brake is on, on my screen/gauge, but if definitely is on, and it will not shut off until I go into the options and test the brakes or change modes and check/uncheck the brake on box. I can see the output to my brake control is at 100%, but the software shows 0% brake. Has anyone seen this? When that brake comes one, it's not good for the motorcycle, that's for sure.
@hansl can you send me your config file? I will take a look. Send to jostein@yourdyno.com