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HPI RS4 Evo to Electric Conversion

Old 05-05-2020, 09:53 AM
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caglareric
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Default HPI RS4 Evo to Electric Conversion

Hi Guys,

My first time posting here, I have an old HPI RS4 that I barely use. It has a broken pinion shaft which is proving difficult to get hold of and I thought I could convert it to an electric as I could do with less noise and oil, also, I have a bit of time and could be a fun little project.

I dont want to spend too much on it as I dont have too much time to go out and actually use it. I have found a cheap chinese made brushless motor & ESC comvo that I would like to use.

Specs are as follows:

Features:
4 pole 12 slot high-torque motor design
3.175mm shaft diameter
High purity copper windings maximizes efficiency
Precision engineered for maximum energy conversion
Precision balanced rotor,smoothness for best reliability and maximum RPM
Mutiple protection features: Low voltage cut-off protection, over-heat protection, throttle signal loss protection
Bulit-in 5.5V/3A BEC
Suit for 1/10 scale RC car

Motor Specifications:
Brand name: GoolRC
Watts: 900W
Max voltage: <12V
Max Amps: 75A
KV(RPM/Volt): 4300KV
Max RPM: 50000
Diameter: 36mm
Length: 50mm
Shaft length: 15mm
Shaft diameter: 3.175mm
Plug type: 4mm golden banana plug

ESC Specifications:
Brand name: GoolRC
Item name: waterproof ESC
Continue current: 60A
Burst current: 320A
Battery: 2-3S Li-Po / 4-9S Ni-Mh Ni-Cd
BEC output: 5.5V / 3A
Power supply plugs: T plug male
Motor plugs: 4mm banana plug female
Dimension: 50 * 35 * 34mm / 2.0 * 1.4 * 1.3in (without cables)

It is my first time attempting such a thing so im not sure if the above motor & ESC would be suitable for the convertion. Also what batteries would be suitable to run such a setup? Could I use NiMH batteries as I dont use it much and would want the maintenance of LiPO.

Thanks in advance for your help guys!
Old 05-05-2020, 05:10 PM
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Overvolted
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Default lectric rs4

Im doing the same thing only with an mt2. Is your car a center transmission? Not sure about the motor it may be a little big. Im using a brushed 17t hackmoto with a hobbywing quickrun 60amp esc. The nimh batteries ive tried dont have the stones to push it. I too didnt want to deal with lipo however after looking for a nimh that would work and the price upwards of $80 for a 7 or 8 cell I now have a 2s 5000mah lipo on the charger. It should be done soon so I can hopefully test tonight.
Old 05-06-2020, 12:47 AM
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caglareric
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Originally Posted by Overvolted
Im doing the same thing only with an mt2. Is your car a center transmission? Not sure about the motor it may be a little big. Im using a brushed 17t hackmoto with a hobbywing quickrun 60amp esc. The nimh batteries ive tried dont have the stones to push it. I too didnt want to deal with lipo however after looking for a nimh that would work and the price upwards of $80 for a 7 or 8 cell I now have a 2s 5000mah lipo on the charger. It should be done soon so I can hopefully test tonight.
Looks like I will too be using lipo in the end. How did you manage to get past the one way bearing on your spur to give you reverse & brakes?
Old 05-06-2020, 08:59 AM
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Do you have any pics I would like to keep up with this thread
Old 05-06-2020, 09:25 AM
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Overvolted
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I did not have a one way bearing on my spur. When I removed the engine the spur ran freely both ways. The test run went bad quickly as my steering servo crapped out, stripped I think, as soon as I started running. Im using the brake and reverse function built into the esc. The 2s lipo did the trick though and the light show from the back of the motor can was cool. I will replace the servo today and run again while taking motor temps as I may have too small of a pinion gear in the heavy car with the 17t. Ill post up some pics tonight as well.
Old 05-06-2020, 10:41 AM
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Originally Posted by skurtzicus
Do you have any pics I would like to keep up with this thread
I do have a few, however, I cannot upload as I am new here. Will try again soon..
Old 05-06-2020, 10:51 AM
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Originally Posted by Overvolted
I did not have a one way bearing on my spur. When I removed the engine the spur ran freely both ways. The test run went bad quickly as my steering servo crapped out, stripped I think, as soon as I started running. Im using the brake and reverse function built into the esc. The 2s lipo did the trick though and the light show from the back of the motor can was cool. I will replace the servo today and run again while taking motor temps as I may have too small of a pinion gear in the heavy car with the 17t. Ill post up some pics tonight as well.
I have a one way bearing which lets the 1st gear spur freely spin whilst its in 2nd, so, if I tried to reverse, it would just spin the spur backwards without the actual wheels turning.

I have an idea in theory but not sure how well it would do if I actually did them.

On my transmission, I have a clutch bell with an already threaded hole to mount the inner parts to the shaft, it currently has a grub screw in there which allows the outer casing of the clutch to spin freely until the clutch catches onto it which in turn spins the spur. My idea is to put a longer screw in there so that the out and inner parts of the clutch are locked, therefore, it will turn the wheels both ways. The only issue i may face with this is that the torque may bend/brake the screw or clutch casing.

If that fails, apparently there is a traxxas spur gear which would mount straight on, however its only a 34 teeth spur where as mine is a 47 teeth.

I have bought a set of pinions that range from 15t to 20t so hopefully one of them should do the trick.
Old 05-06-2020, 12:48 PM
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Overvolted
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Originally Posted by caglareric
I have a one way bearing which lets the 1st gear spur freely spin whilst its in 2nd, so, if I tried to reverse, it would just spin the spur backwards without the actual wheels turning.

I have an idea in theory but not sure how well it would do if I actually did them.

On my transmission, I have a clutch bell with an already threaded hole to mount the inner parts to the shaft, it currently has a grub screw in there which allows the outer casing of the clutch to spin freely until the clutch catches onto it which in turn spins the spur. My idea is to put a longer screw in there so that the out and inner parts of the clutch are locked, therefore, it will turn the wheels both ways. The only issue i may face with this is that the torque may bend/brake the screw or clutch casing.

If that fails, apparently there is a traxxas spur gear which would mount straight on, however its only a 34 teeth spur where as mine is a 47 teeth.

I have bought a set of pinions that range from 15t to 20t so hopefully one of them should do the trick.
Both my rs4(evo 3 ?) and mt2 are single speed so I dont know much about the two speed tranny. Can you replace the one way bearing with a conventional bearing?
Old 05-06-2020, 01:04 PM
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Originally Posted by Overvolted
Both my rs4(evo 3 ?) and mt2 are single speed so I dont know much about the two speed tranny. Can you replace the one way bearing with a conventional bearing?
I guess the shaft sizes are different or the spur may be a different fit otherwise others would have done it. Need to look into it, maybe it will
Old 05-06-2020, 03:33 PM
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Hi Guys, quick update, so the only way I could lock the spur to the shaft was by locking up the clutch bell on the transmission. I used an M4 screw as there was already a thread for the grub screw holding the clutc onto the shaft. I cut the screw head off to minimize the weight as I may have a balance issue once I get it to run. It looks promissing for now, so I would get ESC brakes & reverse. The only issue I may have is the balance which then I will need to find another way of doing it.

Unfortunately I cannot post any photos until I have 10 posts so I am photo bound for now
Old 05-06-2020, 04:52 PM
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Default Flu Bug




Good deal. You may be able to use some small stick on weights if you have balance issues. That screw cant weigh more than a gram or two. Here are a couple of pics of mine so far. Have to work on my full size cars later and hope to change out the steering servo tonight and make another test run.
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Old 05-07-2020, 03:05 AM
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Originally Posted by Overvolted
Good deal. You may be able to use some small stick on weights if you have balance issues. That screw cant weigh more than a gram or two. Here are a couple of pics of mine so far. Have to work on my full size cars later and hope to change out the steering servo tonight and make another test run.
Looks cool!! Wheres the battery pack going?
Old 05-07-2020, 06:43 AM
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Originally Posted by caglareric
Looks cool!! Wheres the battery pack going?
The nimh batteries I was going to use slipped in through the roll bar and one end rested on the front bulkhead. The lipo is a little bigger so I may try to clearence the roll bar and fit the battery there strapped in securely of course. If that doesnt work out I will lose the roll bar and build a tray from aluminium that will sit just above the spur gear. The goal is to keep the battery weight in the center and as low as possible.

I did another test run last night. This thing is a lot faster than the G3.0 nitro engine. Motor temps were a little over 170° after only three high speed runs with the 18 tooth pinion so im going to try the 19 tooth pinion tonight. Also have to check my battery as after the three runs power dropped quite a bit. I dont think the esc folded the power back due to temp as it was just under 100°. I would like to see motor temps at or under 160° or so.
Old 05-10-2020, 04:41 AM
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Originally Posted by Overvolted
The nimh batteries I was going to use slipped in through the roll bar and one end rested on the front bulkhead. The lipo is a little bigger so I may try to clearence the roll bar and fit the battery there strapped in securely of course. If that doesnt work out I will lose the roll bar and build a tray from aluminium that will sit just above the spur gear. The goal is to keep the battery weight in the center and as low as possible.

I did another test run last night. This thing is a lot faster than the G3.0 nitro engine. Motor temps were a little over 170° after only three high speed runs with the 18 tooth pinion so im going to try the 19 tooth pinion tonight. Also have to check my battery as after the three runs power dropped quite a bit. I dont think the esc folded the power back due to temp as it was just under 100°. I would like to see motor temps at or under 160° or so.
I may need some assistance once I get to electricals as I have never touched an electric RC. Not too sure about temperatures etc.

As the car had been sitting for a while, it was completely covered in rust. I used some rust remover which got most of it off, however, it also took some annodizing off the suspension & chassis so I have now de-annodized those parts to get to the bare metal. I have also polished them to get a nice crome finish.

I cannot post photos until I have 10 posts so once I get to it I will upload all the photos. )
Old 05-10-2020, 03:56 PM
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Originally Posted by caglareric
I may need some assistance once I get to electricals as I have never touched an electric RC. Not too sure about temperatures etc.

As the car had been sitting for a while, it was completely covered in rust. I used some rust remover which got most of it off, however, it also took some annodizing off the suspension & chassis so I have now de-annodized those parts to get to the bare metal. I have also polished them to get a nice crome finish.

I cannot post photos until I have 10 posts so once I get to it I will upload all the photos. )
What is this rust you speak of,lol. Im in the middle of the mojave desert so no rust here. Im still learning the electricals and will help any way I can. Ive made the magic smoke come out of a couple of components and have learned quite a bit.

Im waiting on some more pinion gears to put on and try as the one I was using was the biggest one I had. I have a fan/heat sink combo coming as well. Hopefully get to test pinions by midweek.
Old 05-12-2020, 10:16 PM
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I think I went the wrong way with the pinion gear. Put a 23t pinion on and one shot up the street and back made the magic smoke come out. Hoping I can put some new brushes in and be ok. Ive got a 23t and a 35t motor I could try next and see if I can melt those down too. Gonna need more pinions to dial it in I suppose.
Old 05-17-2020, 02:01 PM
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That’s cool!
Old 05-29-2020, 07:22 AM
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Default conversion

Any updates on your conversion? Ive melted two motors trying to get the right pinoin. Cobbled the two smoked ones together for one running one and more pinions on the way.
Old 05-29-2020, 08:03 AM
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Originally Posted by Overvolted
Any updates on your conversion? Ive melted two motors trying to get the right pinoin. Cobbled the two smoked ones together for one running one and more pinions on the way.
Hi Mate, not yet. The car is ready with batteries & esc almost in place, just waiting for the motor, mount & pinions to arrive.

They are taking really long to arrive as its coming from China.

Is it normal for yours to do that? Maybe theres an underlying issue?
Old 05-29-2020, 10:41 AM
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Yeah the slow boat from china just got slower. Burning up motors is deffinetely not normal at least with what im doing. I think its due to the trucks weight, 4wd and nitro engine sized spur gear. I started with an 18 tooth that cooked an armature, then tried a 23 tooth that melted the brush holder, then a 15 tooth that ran awesome but melted another brush holder so im going to try a 10 tooth pinion next. The original nitro engine had a 10 tooth on it. The truck with the 15t pinion was really fast and handled the best the truck ever has.
Old 05-29-2020, 10:44 AM
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Default battery holder


I used a Radcat Racing battery holder and made two aluminium mounts. Works great and the truck handled the best it ever did.
Old 05-29-2020, 10:45 AM
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Originally Posted by Overvolted
Yeah the slow boat from china just got slower. Burning up motors is deffinetely not normal at least with what im doing. I think its due to the trucks weight, 4wd and nitro engine sized spur gear. I started with an 18 tooth that cooked an armature, then tried a 23 tooth that melted the brush holder, then a 15 tooth that ran awesome but melted another brush holder so im going to try a 10 tooth pinion next. The original nitro engine had a 10 tooth on it. The truck with the 15t pinion was really fast and handled the best the truck ever has.
i hope I dont have such issues 😅 I bought a set of pinions ranging from 15-20T so I will experiment with all
Old 05-29-2020, 10:46 AM
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Originally Posted by Overvolted

I used a Radcat Racing battery holder and made two aluminium mounts. Works great and the truck handled the best it ever did.
I bought a carbon fibre mount for another model and modified it to fit. Its a shame I cant post photos
Old 05-29-2020, 10:50 AM
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infact I may be able to post as I have hit the 10 posts mark.


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Old 05-29-2020, 10:53 AM
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Originally Posted by caglareric
infact I may be able to post as I have hit the 10 posts mark.



Heres another one

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