Hi All,

Been digging through this forum for a couple of weeks and trying to get up to speed on DIY dynos.  Interesting that I see few people here from the states.  I would have thought there would be more activity here. 

This interest came about when I had the chance to purchase a "tow dyno".  I had never heard of one, but it came available and it had a Telma CC135 retarder, and SCR driver, so I grabbed it.  Maybe they are familiar to some of you here, but if not, the dyno is actually built as a trailer.  Not in the sense of having it built "on" a trailer, but as a trailer you tow and control the load dragging down on the vehicle.  It's a small, but heavy unit, and it uses a automotive differential as the axle.  That is coupled to the retarder and has a 24v alternator driven off the shaft.  The alternator feeds a pair of batteries that supply the power to the retarder.  The retarder is fixed in the frame, and the load is measured by a load cell integrated into the tongue.   It was manufactured by Mustang, and I suspect it had a model number something like MTD 1100.  I called Mustang and they have given me some information. but not complete, by any means.  Can't blame them, they are not selling me $50,000 worth of new machine.  He did offer to trade it for a used MD 1000 frame/ rollers/ brake, for more money than I'm willing to part with.  In the long run, it would probably be smarter, but what's the fun in that. Why buy something that is all sorted, when you can spend twice the money and three times the effort to build it yourself? 

Either way, I will have to supply control and monitoring, so that's why I have taken an interest in YourDyno.  I like the way it is accessible, and evolving. 

I have a background in control electronics, so that doesn't worry me, I just need to learn from the experience of others that have already learned the lessons.  

I rally race a car, but realistically, this would be a play toy for me. Probably never going to have more than 400hp on it, and my car is in the sub 200hp range.   Sure, I will learn stuff, and possibly improve my car, but I don't plan on opening a shop and do tuning for others all day.  In that regard, there's no way this is going to be justified if I spend too much on it.  That being said, this control system seems wonderfully powerful for the price. 

I have a couple of hurdles to figure out.  The first is finding, or building rollers, or, buying an existing roller assembly.  I have been warned that used emission rollers are designed for 60 mph, and might not be suitable for heavier use. I have found one of those for ~$2000.  The other option is to just trade for the used Mustang for $8000.  I'm thinking with some careful material choices, some creative machining, and a little bit of innovating as far as balancing, I should be able to build a roller bed for under $3k.    I have seen it said here that the DIYdyno group on FB has some good mechanical stuff.  I have found a few nuggets of wisdom, but not as much as I expected.  One was the use of hydraulic cylinder bodies as a good choice to build rollers from.  That seems like a good start. Heavy and consistent wall thickness.  I'll have to visit the local hydraulic repair shop and see if I can learn more.   It seems like a diameter in the range of 9" to 12" is the range to look for.  To my thinking, if it were built as 4 separate rollers (two pairs), and the shafts were coupled, they could be balanced individually as a manageable size. 

The second is that I'm going to have to add stub shafts to the retarder to change it from fixed mount to floating so I can add a torque arm and relocate the load cell.  That looks like pretty straight forward lathe work unless I'm missing something.  

Bearings seem to be something that have been mentioned.  I haven't yet looked, but it seems like standard pillow blocks in the 2"3" range should be able to run as high as the 4000 rpm limit of the retarder.  I'm sure some high quality grease is needed, but is there an issue here?  

Sorry for the long winded post, but I was just thinking out loud as to the steps that I need to consider before jumping in.  

Comments, suggestions, and critiques are welcome.  I definitely have a lot to learn on this subject. 

Thanks

bo

Michigan, USA