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May 16, 2010, 01:21 AM
Innov8tive's Avatar
Thread OP

New and Improved Motor Test Stand

Hello everyone!

I have been working the past few days on finally putting together a new motor test stand that is large enough and strong enough to test just about any electric motor out there. I had built a smaller test stand out of plywood a few years ago, and used it to collect the data for all the Scorpion 22mm and 30mm motors, but this stand had a few limitations. First, I could only run up to around an 18 inch prop on it, and it really was not strong enough to run much more than about 1200 watts of power on. This stand was a typical 90 degree see-saw design that used the motor in a pusher configuration. Here is a photo of the first stand I built being used in a tractor configuration. Later, I flipped the motor around the other way and used it in the pusher configuration so that the prop blast did not hit the frame of the upright arm and change the thrust readings.

The new stand has a few design goals:

1. Be able to handle motors up to 20,000 watts of power.
2. Be able to handle up to a 30 inch prop.
3. Be made from aluminum so it won't warp or twist.
4. Be simple enough that it can be constructed from ordinary hand tools.
5. Not be too expensive.

I think that I have succeeded on all these design goals. For anyone that wants to build a test stand like this, I have included enough information so you should be able to duplicate my efforts.

Before I got started I knew that I would need to get some aluminum extrusion pieces, so I took a trip to my local Home Depot store to see what they had. There was the typical assortment of aluminum extrusion pieces you see at every Home Depot, but nothing that was big enough to suit my needs, so I had to make a run down to San Diego on Saturday and go to Industrial Metal Supply. They have a whole room full of end cuts and left-over pieces of aluminum that sell for $2.49 per pound, so it is a cheap way of getting just about anything you want.

I looked through the racks and found a nice 6-1/2 foot long piece of 1-1/4" square stock, a section of 3" angle stock. a 12" square piece of 1/8" plate and a couple small pieces of 1" angle stock. Here is everything I got set out on a table.

All of these pieces together weighed 13 pounds, so it all cost me about $35.00 with tax. Not too bad! Once I got back to my office, I took a piece of paper and drew up a sketch to get some rough dimensions for the final stand. Here is what I came up with.

The idea here was to have a see-saw type pivoting stand that had multiple points to place the digital scale. The Medusa Thrust Cell that I have can measure up to 11 pounds, but I needed more capacity than that, so I use a thrust multiplier set-up built into the stand. The centerline of the motor is 16" above the pivot point, so if the point where you put the scale is also 16" form the pivot point, each pound of motor thrust will generate 1 pound of force on the scale. If you notice in the darwing above, there are 3 points where you can put the scale, at distances of 8", 16" and 32" from the pivot point. There is a hole drilled in the bottom side of the main cross bar at each of these locations that is threaded for a 1/4-20 machine screw. This is done to provide an exact point of contact for the digital scale to get accurate thrust measurements.

As I said earlier, when the scale is placed at the 16" point 1 pound of thrust equals 1 pound on the scale. If you put the scale under the screw at the 8" point, you have a 2 to 1 mechanical advantage, so each pound of thrust on the scale equals 2 pounds of thrust on the scale. This was done to increase the resolution of the reading when the motor puts out 5 pounds of thrust or less. Then when I read the data files from the motor runs, I simply divide the scale reading by 2 to get the actual thrust.

If I put the scale under the screw at the 32" point, there is a 1 to 2 ratio, so each pound of thrust only reads 1/2 pound on the scale. This allows my 11 pound scale to read up to 22 pounds of thrust. Once I test a motor that puts out more than 22 pounds of thrust, I will have to get a bigger digital scale.

Now that I have the design drawing, the raw materials and theory behind it, now it is time to start building! To be able to cut the aluminum pieces accurately, I got an 80 tooth carbide tipped saw blade for my 10" power miter box saw. With a fine tooth saw like this you can cut through 5052 or 6061 aluminum just like it was wood. Here is a shot of my saw that I used to cut the pieces.

As you can see on the table, this process makes a LOT of very fine aluminum shavings, so have a shop vac ready to clean up the mess you make! After a few minutes through the saw, I had all the parts for the thrust stand cut out.

And here is a close-up of those parts.

I think that is enough for now. I will be back a little later to post some more of the build.

See you next time.

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May 16, 2010, 09:06 AM
Registered User
Dr Kiwi's Avatar
Hi Lucien,

What sort of bearings are you going to use for the pivot axle?

Cheers, Phil
May 16, 2010, 03:16 PM
Innov8tive's Avatar
Thread OP

Back to the build!

Dr Kiwi,

I don't want to spoil the story, so read on, and you will see what I ended up using in this test stand!

Since this stand will be handling a large amount of load, the bearing pivot point for main arm had to be able to take a beating, and still provide virtually zero friction for accurate thrust readings. Because of this, the pivot needs to be a ball bearing assembly. I put on my thinking hat and tried to figure out how I was going to implement a pair of bearing holders, and only use common hand tools.

The one thing I miss about my old job is access to the machine shop. Your thought process is a lot different if you have a mill, lathe and drill press at your disposal! I started looking around the shop and came upon what I thought was a brilliant idea. Instead of making a bearing holder, why not just adapt an already existing bearing holder. Over in the corner of the warehouse was a small pile of crash damaged Scorpion motors that customers had sent in for our 50% off crash warranty plan. I looked through the pile and found a couple HK-4025 motors that mechanically were in good shape, but had been burned out due to defective speed controllers that shorted out and fried the motor windings. The Scorpion HK-4025 motors use a nice pair of 19mm x 8mm x 5mm ball bearings, and these would be perfect as main bearings and supports for the test stand!

The plan was to take the motors apart and remove the windings and stator and use the bearing support tube from the core of the motor as the pivot bearings for my test stand. To make it easier to unwind the motor, I took a Dremel tool with a cut-off wheel, and sliced through each of the windings on one end of the motor as shown in the photo below. This way, all the wires would just be one wrap around the stator and this would make it easier remove the wire.

Now that the wires were cut, I just used a small straight screwdriver and a pair of needle nose pliers to pull all the wire off the stator assembly. After about 10 minutes of work, I had pulled all the wire off the stator. Man, there is a lot of wire in one of these motors when you put it all into a pile! Just take a look for yourself.

With that out of the way, the next step was to remove the stator from the bearing tube. The Scorpion motors use stator plates that are 0.2mm thick, so in a 4025 stator there are 125 individual plates pressed together into the stator stack. Since these stators are epoxied onto the bearing tube, and then pinned to prevent rotation, it is kind of tough to pull the stator off in one piece, so I simply split the laminations off one at a time and pulled them off the stack. After about 10 more minutes of work I had managed to pull all the stator laminations off the motor. Here is what things looke like at this point. The bearing tube in front of a pile of wire and stator laminations.

Here is a before and after shot showing the second stator assembly that I still needed to strip next to the one that I had just unwound.

After another 20 minutes or so of work, I completed the same process on the second stator assembly and then I had a pair of bearing mount assemblies for my pivot point.

Now that I had most of the pieces needed for the test stand, it was time to start assembly. I started with the upright tube that the motors would be mounted to. I figured it would be much easier to do all the drilling and tapping on this part before I bolted it to the rest of the frame. I started my making a series of adapter plates that would bolt to the upright tube that I could attach the motor cross mounts to. This would give me a modular way of mounting everything that would allow me to run a wide variety of motors and have them all be centered at the correct point on the arm.

To measure the correct size for the mounting plates, I took a Scorpion 40mm and 55mm motor cross mount, and cut a pair of squares from my piece of 1/8 inch aluminum plate that were just a bit bigger than the mount. Here are the two rough blanks for the two mounting plates.

For the smaller 22mm motors, the cross mount would bolt directly to the upright arm, so no adapter plate wuld be needed. You can see this in the next photo.

Here are the mounting adapter plates shown on the upright arm with the motor cross mounts. The plate I cut for the 40mm motor will also work for the 30mm motors as well as ca be seen in these two photos.

And here is the plate for the 55mm motors being test fit to the upright arm.

The concept here is to have the centerline of the motor be exactly 16 inches from the center of the pivot point when it is mounted on the stand. Since I was using aluminum tubing that is 1-1/4" square, the centerline of the main arm is half this distange or 5/8" from the edge of the main arm. THis means that in order for the motor centerline to be 16 inches from the pivot, I needed to draw a line 15-3/8" from the end of the upright arm tube.

That is quite a few photos for this post, so I will end this one and start another. I will be back soon to continue the build.

Last edited by Innov8tive; May 17, 2016 at 12:13 PM.
May 16, 2010, 03:22 PM
Registered User
Dr Kiwi's Avatar
Great idea, have more patience than Job!

My dinky little stand (400W max) doesn't need anything quite this exotic!
May 16, 2010, 03:52 PM
Innov8tive's Avatar
Thread OP

The Build Continues!

Now it was time to start mounting the adapter plates to the upright arm of the test stand and drill and tap some home to hold everything together. First was the 22mm mount. This was set on the arm with the center of the mount lined up with the line drawn on the upright arm to ensure that the motor would be 16" from the pivot point.

Next I took the plate for the 40mm cross mount and used a Sharpie pen to mark the locations of the mounting holes for the 30mm and 40mm cross mounts as shown in the next photo. Then I took a center punch and marked the center of each of these points to keep the drill bit from dancing on the surface during the drilling process. I also scribed a line on the backside of this piece so it could also be centered on the 16 inch reference line.

This part was then lined up on the centerline and carefully measured to make sure that it was centered in both directons. Then I temporarily attached this plate to the arm with some thin CA glue and a shot of kicker to make sure that it stayed put while I match drilled holes through both parts. I drilled 4 holes through both parts with a drill sized for the minor tap diameter of an M4 metric screw. I just happened to have a box of flat head, countersunk M4 x 8mm screws on hand, so I used these to attach the adapter plates to the upright arm.

After I had drilled all 4 holes, I tapped the plate to break the CA glue jount loose, and then used a larger drill to open the holes in the plate up to a clearance hole for the M4 screws. Once that had been done, I used a countersink bit to open up the holes so the screws would sit flush with the surface of the plate. Once all that was done, the plate was mounted with 4 of the screws, and then looked like this.

At this point I noticed a slight problem. The 4 holes for mounting the 30mm cross mount were a bit too close to the screwheads used to hole the plate in plave, so I made a slight change in plans. I rotated the 30mm mount 45 degrees, and marked a new set of holes to attach this part. This actually worked better, and when done, the plate looked like this.

In this photo you can see that the holes for the 40mm mount were drilled and tapped for a set of 8-32 screws, and the holes for the 30mm mount were drilled for 6-32 screws. This process was repeated for the larger mounting plate for the 55mm motors, and when it was done and mounted to the arm, it looked like this.

This left quite a few holes in the upright arm, and with all of the plates removed, it looks like this.

Now that I had the holes drilled in the upright arm, it was time to mount it to the main arm. Since I do not have access to an aluminum TIG welder, I decided to bolt the parts together with some gusset plates to support the joint. As you saw earlier in the parts photo, I had cut a pair of 5 inch square pieces from the 1/8" aluminum plate, and then cut a couple traingle shaped pieces from these to make the support gussest for the joint between the main arm and the upright arm. To make the drilling job a bit easier, I taped the two parts together and drew in the locations of the two arms so I coulld lay out the locations of the screw holes in the gussets.

I marked the holed locations on the gusset using my digital calipers as a scribe to keep the spacing consistant, and then used the center punch to mark all the hole locations. Here is the assembly about half-way through the drilling process. I once again used the drill bit for the minor diameter of the threaded hole for the M4 screws. By doing this, each of these gusset plates could be used as a template to match drill the holes into the square aluminum tubes.

After all the holes were drilled, the tape was torn off, and each gussett positioned carefully at the intersection of the two arms of the test stand.

To make sure that the gusset plate did not shift during the drilling process, I started with one corner hole on the main tube. After I drilled the first hole, I removed the gusset and threaded the hole in the main tube. Then I drilled out the hole in the gusset just a hair bigger that the outer diameter of an M4 screw, and then temporarily used a socket head M4 screw to hold the gusset in place. Then I drilled the opposite corner hole and repeated the process to install a second temporary screw to lock the gusset in place. Here is what the parts looked like at this point.

I then carefully lined up the upright arm so it was centered in the gusset and drilled the two opposite corner holes into the upright arm. This was then drilled and tapped like before and two more temporary socket head M4 screws were used to lok that arm into place. Once that was done, the remaining screw holes were match drilled, then the gusset was removed and all the holes in the tubed were tapped with a metric M4 x 0.7mm tap. To complete the operation, all the holes in the gusset were enlarged to clearance holes for the M4 screws and then they were all countersunk so the screws would sit flus with the surface of the gusset. Finally, the gusset was attached to the two tubes with 14 M4 countersunk screws, and the completed assembly looked like this. I think that this joint should be strong enough to handle any motor that would be bolted to the stand!

At this point, I was exactly half way done with this step, because I need to put another plate on the other side, so I flopped the assembly over, and repeated the last process to install the gusset plate on the opposite side of the arms.

This looks like a good stopping point. Next time we will build the pivot points for the arm and start putting things together.

See you later!

Last edited by Innov8tive; May 16, 2010 at 04:31 PM.
May 16, 2010, 04:31 PM
Innov8tive's Avatar
Thread OP

Now we focus on the pivot axle!

Once I got both of the gusset plates installed, it was time to install the pivot axle intothe stand. As you saw earlier, I had taken apart a couple HK-4025 motors for the bearing mount assembly to use in this stand. These would be mounted into the two pieces of 3 x 3 inch angle aluminum that I had cut earlier. The diameter of the bearing mounts is just a little under 2 inches, so I measured down 1 inch from the top of each of these pieces of angle stock and drilled a 1/4" starter hole. Then I used a Step drill to accurately open this hole up to a diameter of 11/16" to be able to fit the diameter of the bearing tube on the part from the Scorpion HK-4025 motor that I was using as a bering support. I used a set of Step drills that I got at Harbor freight that look like those in the next photo. I used the one on the right to get the hole up to 11/16". These drills are nice, because they use the previously drilled hole as a pilot for the next step on the bit so each successive hole stays centered on the last one.

Once the holes were drilled in the angle brackets they both looked like this.

Here is the bearing holder being test fit into the hole to check the alignment.

I decided to rotate the bearing holder so the holes would be at the 12:00, 3:00, 6:00 and 9:00 positions. The threaded holes in the bearing mounts ae normally a metric M3 thread, but I wanted to use a slightly larger screw, so these holes were drilled out and tapped for an 8-32 thread, since I had a bunch of 3/4" long 8-32 stainless steel screws that would be perfect for this application. I dirlled 4 holes in the angle bracket for the mounting screws and when finished, they looked like this.

The center tube on the bearing supports are about 1" long, but I wanted them to fit flus with the outer surface of the angle stock, so I set the bearing tube into the hole I just drilled and spun the part while I held a Sharpie pen against it to mark a cut line to saw off the excess. I did this to both tubes and then mounted them in my bench vide and used a hacksaw to cut off the excess material as shown below.

After both parts were cut, they were mounted into the angle stock with four 8-32 x 3/4" phillips head screws as shown in this next photo.

An from the other side, the completed assembly looked like this.

You will probably notice that there are no bearings installed in the holders yet. I took them out before I started doing all the work so I would not get metal dust and grinder shavings in the bearings while all the machining work was being done. Now that everything was done, I pressed the ball bearings back into the completed bearing holder assemblies.

Now that this part is complete, it is time to put everything together. I will do that in the next installment of this build thread.

See you all a bit later!

May 16, 2010, 07:17 PM
Innov8tive's Avatar
Thread OP

Putting all the pieces together.

Now that the bearing supports are completed, it was time to make the shaft to tie everything together. For the shaft, I used a solid 8mm main shaft from a Scorpion HK-4035 motor that I had left over in my scrap box. I needed to cut a bit of the shaft off, so first I needed to get a measurement of the total length required. The plan was to drill a hole through the main arm and gussets that was exactly the same diameter as the shaft, so I would have a slop free fit. Actually, the hole was drilled just about 1/2 a thousandth under-size so the shaft needed to be lightly hammered into place. Using my digital clipers, I measured the thickness ot the completed arm assembly, plus two retaining collars, plus the two bearing supports and added these all together. This total was marked onto an 8mm shaft and the excess was cut off. This is easily done by chucking the shaft up in a drill, and then spinning it while you hold a cutting wheel from a Dremel tool up against it. This makes a rotary grinding lathe that provides a nice clean cut. Here is a photo of a full shaft next to the one that was cut so you can see how much was cut off.

Normally, I would use a drill press to drill the hole through the main arms and gussets to ensue that it was drilled straight through from one side to the other. Unfortunately, I do not have a drill press available, so I did the next best thing. I very carefully measured up exactly 0.625" from the bottom edge of the arm and scribed a line on both sides. Then I carefully measured back from the end of the main arm to the exact center of the upright arm and scribed another line on both sides. Then I used a center punch and marked the exact spot to drill on each side. Once the marks were in place, the holes were drilled one drill bit size smaller than required from each side, the the correct size drill was used to drill from one side, out through the hole on the opposite side to make sure that the holes were in line with one another. Apparently my measuring was accurate, because when I was done, I had a perfect hole through both sides as seen here.

Now all that was left to do was to install the axle shaft. I tapped the shaft into place, making sure that an equal amount was sticking out each side. Then I put on a pair of shaft retaining collars from Scorpion S-4035 motors. These collars have a narrow ridge on one side that makes contact with just the inner race of the bearing, to make sure that nothing rubs the face of the bearings. It also widens up the stance of the bearing supports for better support of the arm assembly. Here is what the shaft looked like after it was installed and the retaining collars were put into place.

With the axle installed, I couls add the bearing supports and see how everything fit together. Here are a couple photos that show how all the pieces fit together.

The arm pivoted nicely, but it was not far enough off the table surface to allow the scale to be placed underneath the main arm. To make room, the angle brackets need to raised 1-1/2 inches above the table top. What I did to make this happen was to start with a 24" x 48" piece of 3/4" plywood. I used my hand circular saw to cut the plywood piece to a finished size of 24" x 42", which left a piece 24" x 5-7/8" due to the material that was lost from the thickness of the saw blade cut. I set this piece under the angle bracket supports and found that I had about a 1/2" clearance on each edge, so I measured the length of the assembly and added an inch to this number and cut two pieces this length from the left-over piece of plywood. These ended up being 5-7/8" x 9-1/4" each. SInce I needed a spacr 1-1/2" thick, I took the two pieces of 3/4" plywood and glued them together to make a spacer 1-1/2" thick. Here are the two pieces just before I stuck them together.

After about 10 minutes, the glue was dry enough to handle the parts, so I marked the location of this piece onto the 24" x 42" plywood base plate. Here is that part.

After the outline of the spacer was marked, I measured in 1 inch from each edge and drilled 4 holes thorugh the base board for the screws that would hold the spacer in place. I also drilled one hole right in the middle. After these holes were drilled through, I flipped the board over and countersunk the 5 holes so the wood screws would set flush with the surface.

After the holes were drilled, I flipped the board back over and set the spacer block onto its marks. Then while I held it in place, I used my hand drill to spot drill the locations of these 5 holes onto the bottom side of the spacer. Then I flipped over the spacer block and drilled pilot holes about 1" deep into the spacer block for the screws. Once that was done, the 5 screws were installed and everything was tightened down. Here is what the installed spacer block looked like with the bearing supports in place.

Finally I fit all the pieces together on top of the spacer block and marked the 4 holes in each piece of angle stock. These holes were pilot drilled and #10 sheet metal screws were used to attach the angle brackets to the spacer block. Once everything was screwed down, it looked like this.

Here is a shot of the basically completed test stand with the scale in place at the 32" mesuring point.

As I said earlier, there are screws drilled and tapped into the bottom of the main arm that provides 3 different positions for the digital scale. Here is a shot of the bottom of the main arm that shows these 3 different locations.

Now the stand is done, but there is one last thing left to do. Can you think of what that is? We will find out in the next installment of the build.

See you later!

May 16, 2010, 07:42 PM
Innov8tive's Avatar
Thread OP

Putting things into balance!

As I said in the last post, there was one last step needed to complete the test stand, and that step is to balance the stand. If you look at the photo of the entire stand from the last post, you will see that the long end of the main arm that rests on the scale sticks out quite a way. The way it sits not, the arm puts a little over half a pound of weight on the scale. I want to be able to balance the stand so that there is no weight on the scale at the beginning of the test, or at the most a gram or two just to keep the arm in contact with the scale at the beginning of each test. To do this, we need to add a counterbalance out the front end of the stand. Some of you may have been wondering what the extra 8" of tube was doing sticking out past the front end of the pivot point, so now you know.

I did a little bit of balancing, and figured that I needed about 3 pounds of weight at the front end of the stand to balance out the long tube that goes back to the digital scale. I wanted to have a weight that could be easily adjusted for varying weights of motors installed on the stand so the balance point can be zeroed out for each setup.

I went to the local Home Depot store looking for something that could be used as a counter weight and after a trip around the store, I came up with the following solution. I picked up a pair of 2" galvanized pipe caps and a 2" coupler pipe. I drilled holes in the center of each cap as shown below.

Once these 3 parts were screwed together, I enlarged the holes to 1/2 inch, and bolted in a piece of 12" long 1/2"-13 threaded rod to make my counter weight. Here is what the finished part looked like.

The plan is to thread this assembly into the end of the motor stand, and screw it in or out as needed to balance the colpleted test stand assembly. I was trying to come up with a novel way of getting a 1/2"-13 thread into the end of a piece of 1-1/4" aluminum tube. After a bit of head scratching I came up with the following solution. I picked up a 2" long threaded rod coupled and epoxied it into the end of the tube. The coupler measues 3/4" from flat to flat, and the pipe has an inside size of 1" square, so I needed to have a 1/8" spacer on each side to get it to fit in the tube. If I measured the coupler from point to point, it was 0.84", meaning I needed two spacers that were 0.080" thick for the sides.

I went through my scrap box and found some 1/8" plywood and some 0.080" plastic sheet, so I used these to cut the necessary spacers to put the threaded coupler into the end of the tube. Here are all the parts cut out and ready to use.

Here are all 5 pieces being dry fit into the end of the tube so you can get an idea of how all this fits together.

Now that I was sure that everything fit together nicely, I pulled all the pieces out and sanded the spacers on both sides to make sure the glue would stick well. I also scuffed up the inside of the end of the aluminum tube and cleaned it out with some alcohol on a paper towel to make sure that no oil was left over from all the drilling and tapping operations that were done on the tube. Then I took a Dremel tool with a cutoff wheel and used it to scratch up the surface of the threaded coupler as seen here.

Now that everything was nicely roughed up, I mixed up a batch of 15-minute epoxy and coated all the parts and put the all back into the end of the tube. After the eboxy had cured up well, I screwed the completd counter weight into the end of the of the test stand as seen here.

That pretty much completes the mechanical assembly of the test stand. Now I have to hook up the sensors, speed controller and the rest of the wiring to make it functional. I will be doing that later this week, and after I get it done, I will post an update here.

Hopefully this has been informative and given you a few hints on how to build a test stand for yourself if you desire.

See you next time!

May 16, 2010, 08:40 PM
Registered User
Dr Kiwi's Avatar
Nice counterweight, but, as you well know, your scale has a tare function for precise "balance" once you've added a motor.
May 16, 2010, 08:56 PM
Innov8tive's Avatar
Thread OP
Dr. Kiwi,

That is true, but any starting weight takes away from the total capacity of the scale. Also, if you are using a scale that you are taking a raw reading from, other than the Medusa Thrust cell used in conjunction with the Medusa Power Analyzer, when you Tare the scale, it only zeros out the digital display, not the output of the load cell inside the scale.

I also have the new Hyperion E-Meter, and I am going to experiment with that to see if I can feed a raw analog input into the auxillary channel on the interface module and use a larger digital scale if needed later on.

Thanks for the input!

May 25, 2010, 05:27 PM
Innov8tive's Avatar
Thread OP

Quick update!

I have been getting the space cleared in the warehouse to set up the new test station. I still need to wire up my new 45 volt 110 amp power supply. Thankfully the new shop has 3-phase 208 volt power, so I can run the larger power supplys now.

More info to come!

May 25, 2010, 07:08 PM
Registered User
Dr Kiwi's Avatar

We amateurs are green with envy... oh for 45v/110A and a 3-phase supply!

Cheers, Phil
May 25, 2010, 10:26 PM
Suspended Account
the process and pic are very details ,we can see the whole procedure
Jun 04, 2010, 09:49 PM
Innov8tive's Avatar
Thread OP

Power Supply Update

I just about have everything hooked up and ready to go now. To power the test station, I have a pair of nice EMS power supplies as seen in the photo below.

The one on top is a 20 volt, 100 amp model that I have had for a while. When I bought it of of eBay, I was hoping that I could get it to go up to 22 volts somehow to be able to simulate a 6-cell Li-Po pack under load. When I hooked it up, it would go up to exactly 20.0 volts on the digital display, and not a bit higher. Bummer!

Well, a couple days ago I made a call to the company that makes the supplies and spoke with one of their senior repair technicians. He was kind enough to send me a PDF copy of the power supply schematic, and even told me which resistors on the control board control the maximum voltage output of the power supply. With that information in hand, I popped open the power supply and removed the controller board from inside and changed the replaced two resistors with new ones with different values and then put everything back together. I was shooting for 24 volts max, and when I powered it up, I was able to get the power supply up to 23.2 volts at full voltage. Since I only need 22 volts for the 6-cell pack, it is good enough, and now I can use the smaller supply to test all the motors up to 6-cell power and up to 100 amps of current!

The bottom one is the new 45 volt 110 amp model that runs off of 3-phase 208 volt power. I actually have 2 identical power supplies like this that I also found on eBay, and I still need to do some re-wiring on them to bypass the GPIB controller board on the back and convert it back to a straight stand-alone manually operated power supply. When I get them both working, I will be able to run them independantly, or gang the two together to make either a 90 volt 110 amp supply by placing them in series, or into a 45 volt 220 amp supply by putting them in parallel. I think that should get me enough power to run even the biggest motors that I may need to test!

I am currently wiring up the power analyzer and the digital scale for the thrust measurements. I have the Medusa Power Analyzer set up in conjunction with their 11 pound thrust cell. If you remember, I have 3 different positions on the test stand to put the scale. In position 1 the scale will have a 2 to 1 advantage, so 0 to 11 pounds will actually be 0 to 5-1/2 pounds, and I will just divide the scale reading by 2 to get the actual thrust. In the middle position, the stand has a 1 to 1 ratio, so the 0 to 11 pounds will be the actual reading. In position 3, the stand has a 1 to 2 ratio, so the 0 to 11 pounds will actually be 0 to 22 pounds of thrust, and I just multiply the scale reading by 2 to get the actual thrust. By going this route, I get maximum resolution on the smaller motors of 5 pounds of thrust or less, and also have the scale be able to read twice as much thrust as it was designed to.

I was originally going to use the new Hyperion E-Meter that I got with the RDU module in circuit for measuring the motor parameters. Unfortunately, the RDU does not have an input for a digital scale, so thrust measurements cannot be taken. If anyone out there knows how to interface a digital scale into the RDU, please let me know, and I will give that try.

In the past, I have used the optical tach module from the Medusa Power Analyzer to measure motor RPM. Unfortunately, this unit does not work well with indoor lighting, because you get a false 3600 RPM reading from the pulsations of the 60Hz lights indoors. To get around this, I was using a 25 watt quartz halogen spot-light that was driven by a 5 volt power supply to get a good solid DC light source that I could focus on the sensor. This was a bit of a pain to use, and the optical tach would give false readings sometimes.

The new Hyperion E-Meter that I got came with a phase tach, that plugs into one of the motor leads to read the pulses going to the motor from the ESC. You program into the E-Meter the number of magnets the motor has, and it divides the pulses it counts by the magnets and gives you RPM directly. I got to thinking, the Medusa analyzer also has an input for a phase tach, so I wondered if the Hyperion Phase Tach would work with the Medusa Analyzer. I hooked it up, and told the Power Analyzer that the motor I was testing had 14 magnets and fired it up. I had a motor with a Kv of 1000 on the stand and set the power supply to 10 volts. When I ran it up to full throttle, the phase tach registered 10,000 RPM, so it was reading exactly what it should have! I love it when a plan comes together!

Now I just have to instal my ESC on the test stand and wire up a few sensors and I am good to go. It will be good to have the new station up and running so I can complete some much overdue prop tests on the SII-3026 and SII-3032 motors, as well as all of the S-4020, S-4025 and S-4035 motors!

One thing that I have planned to do is to re-run all of the prop charts on all of the scorpion motors. When I first did them, it was almost 2 years ago, and back then, the average working voltage of Li-Po batteries was about 3.5 volts per cell under load. Back then, 10C and 15C batteries were the norm, and 20C batteries were just starting to come out. Today, 35C and 40C batteries are common, and they are typically holding about 3.7 volts per cell under load. Because of this, instead of testing at 10.5 volts for a 3-cell pack, I will now be testing at 11.1 volts. That extra 0.6 volts may not seem like much, but the power output of a motor goes up roughly as the square of the input voltage, so a 5% increase in voltage gives almost an 11% increase in power output, so it does make a big difference. Also, people have been using the old prop charts and finding a prop that put the motors right at 100% of their rated power, and in actuallity, with the newer batteries, this would put the motor 10 to 11% over it's power rating.

I will also be testing more props this time, including GWS 2-blade and 3-blade, APC E-series and SF series, Xoar wood props and Master Airscrew Electric Series and the 3-blade series, so there should be plenty of data to pick from. It will take months to complete all of the testing, but in the end, I think that it will be worth it to get some real world data on all the motors with all the different props so people know exactly what to expect when they strap a prop on a Scorpion motor.

More stuff to come, so stay tuned!

Jun 06, 2010, 12:20 PM
Registered User
Fourdan's Avatar
Originally Posted by Innov8tive
Instead of making a bearing holder, why not just adapt an already existing bearing holder. Over in the corner of the warehouse was a small pile of crash damaged Scorpion motors that customers had sent in for our 50% off crash warranty plan. I looked through the pile and found a couple HK-4025 motors that mechanically were in good shape, but had been burned out due to defective speed controllers that shorted out and fried the motor windings. The Scorpion HK-4025 motors use a nice pair of 19mm x 8mm x 5mm ball bearings, and these would be perfect as main bearings and supports for the test stand!
Hi Lucien
For me I would prefer to rewind your crashed motors.

Good stand design anyway ...
Maybe a little risky for a 20 kW motor

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