Unequal drive trim movement
 

If I use the drive trim switch on the throttle lever, one of the drives changes trim faster than the other (I'm making an assumption that the indicators are accurate). I'm then forced to go to the panel switches to equalize the trim...sort of defeats the purpose of the throttle mounted switch. Is there a way to adjust this to equalize the drive movement?

Re: Unequal drive trim movement
 

Let me know if you find a way!

Re: Unequal drive trim movement
 

I'm not sure about anybody else , but I've never seen two move at the same rate :(

Re: Unequal drive trim movement
 

try it out of the water to make sure they trim differently.
might just be your indicator is hanging up or dirty.

Re: Unequal drive trim movement
 

New boat = fun begins :)

Check the indicators out of water as already said. If ok, then:

Check fluid levels on the drive pumps.
Raise / lower both all of the way several times - sometimes helps
Listen to the pumps - is one running faster (higher pitch) than the other? Maybe bad / corroded electrical connections, check and clean. Also a good time to check the battery / engine block connections as well for corrosion. Those pumps require a fair amount of juice, so it's important that all connections are known to be good.

If none of that works, go out and run it a few times - sometimes this happens when the boat sits for a long time. If you're lucky it may go away. If not, consult the tech q/a forum :) !

Good luck.

Re: Unequal drive trim movement
 

You guys are going to get tired of me asking questions... :p

I've got a bunch more issues rattling around in my head...I'm spacing them out just to keep things interesting....

Re: Unequal drive trim movement
 

I see an invention opportunity...what about a programmable, digitally controlled trim system? It could have a memory setting...push a button and both drives move to 6 in unison (or whatever). Also, a step function...push another button and both drives move by 1 either up or down. Push another button and both drives move all the way down. Just need a little venture capital... :D

Re: Unequal drive trim movement
 

Very doable .....

Re: Unequal drive trim movement
 

That won't come from Merc, then they would be admitting a flaw in their product, which is not possible! :rolleyes: :rolleyes: :rolleyes:

Re: Unequal drive trim movement
 

It's most likely the different pump and pump motor rates. It is extremely hard to get two pumps/pump motors to run at exactly the same rate.

If the rate is off by a bunch, could be one of your pump motors is going south, happened to mine.

Re: Unequal drive trim movement
 

Bennet makes something like that.

The problem is that the likelyhood that both pumps pump at the same preasure is very low. We found with the race boat that when we swapped over to the high performance pumps that they trimmed at the same rate. I think that they probably build them to a much higher tollerance. Another thing to check is that your rams are not bound up at all. The rams tend to chalk up in a part called the scraper and a little behind the scraper and this makes it harder for the rams to move. You can take the ends of your rams off the drives and twist them and see if they all twist with the same effort. You could also put on a throttle that has twin buttons on the handle :D

Jon

Re: Unequal drive trim movement
 

I have been thinking about this actually. I work in prod dev in the auto industry. we supply about 1/3 of all seating systems in the US new cars. we have seat memory. ( and morror, and steering column) i could incorporated this logic box with a linear potentiometer for each drive ram and have up to 3 position presets that you could reasign whenever you want. ( down for planning off, best trim for speed, trailer one touch?) you could even make our keyless remote work and show off your setup from the dock :D

The good thinkg about the solution i have been pondering is that even if the pumps traveled at different speed, they would stop independently once they reached their own setpoint...... so what if one gets there .8 seconds before the other...........

I think I may have a post here about it somewhere.......

but it is on the list behind poor man's digital trim indicator and straight through silent thunder mod (which i am doing presently)


hey... remember how tomcat started with his intercooler idea? ...look at him now... just look at him now !!!!! :woohoo: It just takes the guts to pull the trigger

Ramb

Re: Unequal drive trim movement
 

Ramb .... you do this .... great great idea .... BIG thing is drive and Tab indication by wire !!!! look at less clutter ...less weight (maybe) ...

Re: Unequal drive trim movement
 

Off the....

I assume you mean indicate by electrical wire, not push pull cable. that is my plan for poor mans digital indicators......
I want to find a high caliber rotational potentiometer or encoder( replace the merc puck) then use industry standard 2" digital volt meters in the spots for the merc guages and a solid state voltage regulator/supply . this can be calibrated to read 1 - 10Volt and ta da !!! digital readout to .1 Volt resolution for trim position.

this voltage feed can then also be used for the memory location....

I have not found a small enough package encoder that is water tight... still searching the industry..... the digital volt meters are off the shelf, and the memory logic boxes i can modify from our seat memory modules...........at least for my prototype

Ramb

Re: Unequal drive trim movement
 

Another Similar thread .....

http://www.offshoreonly.com/forums/s...ad.php?t=99410

Dana Marine has indicators .....

http://www.danamarineproducts.com/st...TOKEN=22545117

Re: Unequal drive trim movement
 

Most of the problem lies in the inherent design of the hydraulic trim pump and it's associated check valves, hoses, and pistons. Each pump will have slightly different tolerances of rotating parts, which will allow a certain amount of 'leakage' past the vanes. This leakage results in slightly less volume being pumped per rpm. You also have friction in the piston assemblies that will be slightly different, and possibly slow the travel rate.

IMHO the way to solve this issue is to have a single pump pressure and capacity that significantly exceeds what the pistons basic requirements are. Then the pump's excess capacity can be throttled back slightly to have the exact flowrate under ALL loading conditions (fluid viscosity, friction, propload, etc.) without blowing out the piston seals. This pump would be used for BOTH drives and just controlled using two directional solenoid control valves.

Just my $.02

-Larry

Re: Unequal drive trim movement
 

Larry, incorporating some type of accumulator would also help keep a consistent pressure but you continue to add weight and complexity to the package the more you "engineer" it. :D

Re: Unequal drive trim movement
 

Yes it would, but as you indicated it will add weight. The accumulator will not add pressure (that is a factor of the pump and relief valve setting), but it will help keep it stable and keep the volume fairly consistent. I think, with the right pump and motor combo, there would not be a need for an accumulator in the system.

When in doubt, just add more power! :D :D :rolleyes:

-Larry

Re: Unequal drive trim movement
 

well ...... he elminated one pump .....why not bump it up some more and use one pump for drives .....AND tabs

Re: Unequal drive trim movement
 

EXCELLENT SUGGESTION!!

Just add another few solenoids and check valves and BINGO....A kickass hydraulic system! :D :D

Re: Unequal drive trim movement
 

The slow one might have air in its trim system.
Happened to me, after I bled the air out of my slow one, the speeds were close to the same.

Re: Unequal drive trim movement
 

The problem with that is I often run my tab and drives at the same time......

Re: Unequal drive trim movement
 

Another way to control cylinder speed is with a in-line hyd. flow control to slow down the faster drive to match the slower one. It's done all the time on hyd. systems. Just make sure it's installed correctly to work properly for you. Propwash.

Re: Unequal drive trim movement
 

With the right volume/pressure pump, and the proper solenoid control valve system, it would be possible to run tabs and trim at the same time. A flow control/check valve system would dump excess pressure/volume if only tabs or one drive is used.

Yep...the more I think about it, a single pump would work very well.

-Larry

Re: Unequal drive trim movement
 

It would work but you would probably want a pressure accumulator, seperate up and down electric valves for each item, and of course a larger reservoir. Probably more expensive than the current stuff. But I think it would be pretty nice. Any slight differences in restriction and load could still cause differences in speed of trim. An automatic system, combination supply pump or not, would be a big improvement.

Re: Unequal drive trim movement
 

All that would be needed is a bank of 4 double-acting solenoid control valves, a pump and motor combination, a flow control regulator, a few check valves, and a reservior. Not too expensive or complicated. The pump sizing is key as well as the system pressure control. The flow would be limited by piping size and system pressure. If you had a pump running at say, at a 300psi constant, and your drives and tabs only took 200psi to work smoothly and uniformly, the flow control regulator would dump the excess flow (100psi) back into the reservoir. If the loads (flow requirements) change, this valve would automatically dump more or less to keep the system pressure constant - no matter how many solenoids were calling. The pump would have more than enough capacity to handle all loads at once (drives + tabs).

I have seen injection molding machines with multi-actuating cylinders driven off of one HPU (hydraulic power unit). The cylinder stroke speed does not change if one or more cylinders are being actuated at any given time.

Ain't hydraulics and pneumatics FUN!? :rolleyes: :cool:

-Larry

Re: Unequal drive trim movement
 

Part of the problem is the pressure needed to trim out against the thrust of the prop. That's why the drive pump trim out pressures are set higher than 2000 psi. That's another reason why there can be different trim rates, the pumps are working at near max pressure. I'm not sure if the tabs would usually need high trim down pressure. With a common pump/supply you would need enough pressure for the highest need.

Re: Unequal drive trim movement
 

ljsmith's idea is good, but I would add a second pump to generate more pressure under high demand and also to build in some fault tolerance. If one pump fails, everything still works....

Re: Unequal drive trim movement
 

With a common pump, the drive that moves the easiest will get the most fluid, thus move the most.
Two independant pumps would be cheaper than the flow control devices needed to utilize a single pump. Not to mention the constant adjustment of the flow controls that would be needed to keep the movement speeds the same with a single pump.
My Formula uses four pumps, one each for each drive and K-plane. I would hate to try running at speed in rough water while constantly trimming drives and tabs with a smaller number of pumps.

Re: Unequal drive trim movement
 

The pressures generated by a single pump are not the issue, nor are the costs for standard hydraulic control valves. If the setup could be packaged properly (i.e. USCG approved, marinized, etc.). I would bet it would cost less than 2 drive pumps and a trim tab pump setup. Actuator friction will always be an issue no matter if you have one or two pumps. As long as the friction is normal (i.e. no binding or corrosion issues with movement), there will be no appreciable difference in speed. The cylinder speed is controlled by pressure and volume. If the pressure is kept constant via the automatic pressure compensating valve, the volume will be a constant because of the finite pump output and the size of the hydraulic lines going to the cylinders. If two drives are actuated at the same time, less excess pressure is dumped to the reservior and directed to the drive movement. The drive should move at the same speed as if only one is being actuated at a time.

We are not talking about large volumes of fluid here, or extremely high system pressures....

-Larry

Re: Unequal drive trim movement
 

The drives require quite high pressure to trim while accelerating to counteract the thrust. Could be 2000psi or more depending on the type of drive, spacer length, prop pitch, torque at the prop, etc. Tabs would be more reasonable, they can reach high cylinder loads under certain circumstances, but not usually while you are trying to move them.